port assignments iana

IANA Procedures for the Transport Protocol Port Number Space draft-ietf-tsvwg-iana-ports-00

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This document defines the IANA procedures for registering port number values for use with the various IETF transport protocols, including TCP, UDP, DCCP, and SCTP. It provides clear procedures for the management of the port number registry, which is important for its long-term management. It updates RFC2780 by obsoleting Sections 8 and 9.1 of that RFC, and it updates the IANA allocation procedures for DCCP as defined in RFC4340.

Table of Contents

1.   Introduction 2.   Terminology 3.   Port Number Types      3.1.   Assigned Port Numbers for Experimentation 4.   Principles for Port Number Space Management      4.1.   Basic Principles of Port Conservation      4.2.   Principles Specific to Individual Port Number Ranges      4.3.   New Principles 5.   IANA Procedures for Managing the Port Number Space      5.1.   Port Number Registration      5.2.   Port Number De-Registration      5.3.   Port Number Re-Use      5.4.   Port Number Revocation      5.5.   Port Number Transfer      5.6.   Maintenance Issues 6.   Port Number Space Requests      6.1.   Request Procedure 7.   Security Considerations 8.   IANA Considerations 9.   Acknowledgments 10.   References      10.1.   Normative References      10.2.   Informative References Appendix A.   Updates to DCCP Registries      A.1.   DCCP Service Code Registry      A.2.   DCCP Port Numbers Registry §   Authors' Addresses §   Intellectual Property and Copyright Statements

1.  Introduction

The Transmission Control Protocol (TCP) [RFC0793] ( Postel, J., “Transmission Control Protocol,” September 1981. ) and the User Datagram Protocol (UDP) [RFC0768] ( Postel, J., “User Datagram Protocol,” August 1980. ) have enjoyed a remarkable success over the decades as the two most widely used transport protocols on the Internet. They have introduced the concept of "ports" as logical entities for Internet communication. Ports serve two purposes: first, they provide a demultiplexing identifier to differentiate transport sessions between the same pair of endpoints, and second, they also identify the application protocol and associated service to which processes bind [I‑D.touch‑tsvwg‑port‑guidelines] ( Touch, J., “Guidelines for Transport Port Use,” July 2008. ) . Newer transport protocols, such as the Stream Control Transmission Protocol (SCTP) [RFC4960] ( Stewart, R., “Stream Control Transmission Protocol,” September 2007. ) and the Datagram Congestion Control Protocol (DCCP) [RFC4342] ( Floyd, S., Kohler, E., and J. Padhye, “Profile for Datagram Congestion Control Protocol (DCCP) Congestion Control ID 3: TCP-Friendly Rate Control (TFRC),” March 2006. ) have adopted the concept of ports for their communication sessions and use port numbers in the same way as TCP and UDP.

Port numbers are the original and most widely used means for application and service identification on the Internet. Ports are 16-bit numbers, and the combination of source and destination port numbers together with the IP addresses of the communicating end systems uniquely identifies a session of a given transport protocol. Port numbers are also known by their corresponding service names, such as "telnet" for port number 23 and "http" for port number 80.

Hosts running services, hosts accessing services on other hosts, and intermediate devices (such as firewalls and NATs) that restrict services need to agree on which service corresponds to a particular destination port. Although this can be a local decision between the endpoints of a connection, most Internet components use a single, shared view of this association, provided by the Internet Assigned Numbers Authority (IANA) through the port number registry [REGISTRY] ( Internet Assigned Numbers Authority (IANA), “Port Numbers,” . ) .

Designers of applications and application-level protocols may apply to IANA for a registered port number for a specific application, and may - after successful registration - assume that no other application will use that port number for its communication sessions. It is important to note that ownership of registered port numbers remains with IANA. For many years, the allocation and registration of new port number values for use with TCP and UDP have had less than clear guidelines. Information about the registration procedures for the port namespace existed in three locations: the forms for requesting port number registrations on the IANA web site [SYSFORM] ( Internet Assigned Numbers Authority (IANA), “Application for System (Well Known) Port Number,” . ) [USRFORM] ( Internet Assigned Numbers Authority (IANA), “Application for User (Registered) Port Number,” . ) , an introductory text section in the file listing the port number registrations themselves [REGISTRY] ( Internet Assigned Numbers Authority (IANA), “Port Numbers,” . ) , and two brief sections of [RFC2780] ( Bradner, S. and V. Paxson, “IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers,” March 2000. ) .

This document aggregates this scattered information into a single reference and at the same time clarifies the guidelines for the management of the port number space. It gives more detailed guidance to prospective requesters of ports than the existing documentation, and it streamlines the IANA procedures for the management of the port number space, so that management requests can complete in a timely manner. A key factor of this streamlining is to establish identical registration procedures for transport protocol ports, independent of a specific transport protocol. This document brings the IANA procedures for TCP and UDP in line with those already in effect for SCTP and DCCP, resulting in a single process that requesters and IANA follow for all port number requests for all transport protocols, including those not yet defined.

A second purpose of this document is to describe the principles that guide the IETF and IANA in their role as the long-term joint stewards of the port number space. TCP and UDP have been a remarkable success over the last decades. Thousands of applications and application-level protocols have registered ports for their use, and there is every reason to believe that this trend will continue into the future. It is hence extremely important that management of the port number space follow principles that ensure its long-term usefulness as a shared resource. Section 4 ( Principles for Port Number Space Management ) discusses these principles in detail. Guidelines for users seeking port numbers, as well as a detailed history of the port number registry and alternate means for coordinating host agreement on service-to-port-number mappings, is provided in a companion document ( Touch, J., “Guidelines for Transport Port Use,” July 2008. ) [I‑D.touch‑tsvwg‑port‑guidelines].

In addition to detailing the IANA procedures for the initial assignment of port numbers, this document also specifies post-assignment procedures that until now have been handled in an ad hoc manner. These include procedures to de-register a port number that is no longer in use, to re-use a port number allocated for one application that is no longer in use for another application, and procedure by which IANA can unilaterally revoke a prior port number registration. Section 5 ( IANA Procedures for Managing the Port Number Space ) discusses the specifics of these procedures.

This document also addresses two technical issues related to the ports registry that are tangential to long-term stewardship. First, it clarifies that a method for the early allocation of port numbers is available for IETF working groups, in line with [RFC4020] ( Kompella, K. and A. Zinin, “Early IANA Allocation of Standards Track Code Points,” February 2005. ) . Second, it discusses how the use of symbolic names for assigned ports (the "keyword" field in [REGISTRY] ( Internet Assigned Numbers Authority (IANA), “Port Numbers,” . ) ) for Service Resource Records (SRV RRs) in the Domain Name System (DNS) [RFC2782] ( Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000. ) relates to the use of SRV RRs for applications without an assigned port.

This document updates [RFC2780] ( Bradner, S. and V. Paxson, “IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers,” March 2000. ) by obsoleting Sections 8 and 9.1 of that RFC. Note that [RFC5237] ( Arkko, J. and S. Bradner, “IANA Allocation Guidelines for the Protocol Field,” February 2008. ) updates a different subset of the IANA allocation guidelines originally given in [RFC2780] ( Bradner, S. and V. Paxson, “IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers,” March 2000. ) (specifically, the policies on the namespace of the IP protocol number and IPv6 next header).

2.  Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14, RFC 2119 [RFC2119] ( Bradner, S., “Key words for use in RFCs to Indicate Requirement Levels,” March 1997. ) .

3.  Port Number Types

TCP, UDP, SCTP and DCCP use 16-bit namespaces for their port number registries. The port registries for all these transport protocols are subdivided into three ranges of numbers, and Section 6 ( Port Number Space Requests ) describes the IANA procedures for each range in detail:

• the Well Known Ports, i.e., the System Ports, from 0-1023 (assigned by IANA)
• the Registered Ports, i.e., the User Ports, from 1024-49151 (assigned by IANA)
• the Dynamic Ports, i.e., the Private Ports, from 49152-65535 (never assigned)

Of the assignable port ranges (Well Known and Registered, i.e., port numbers 0-49151), individual port numbers are in one of three states at any given time:

• Assigned: Assigned port numbers are currently allocated to the service indicated in the registry.
• Unassigned: Unassigned port numbers are currently available for assignment upon request, as per the procedures outlined in this document.
• Reserved: Reserved port numbers are not available for regular assignment; they are "assigned to IANA" for special purposes. Reserved port numbers include values at the edges of each range, e.g., 0, 1023, 1024, etc., which may be used to extend these ranges or the overall port number space in the future.

When this document was written, approximately 76% of the TCP and UDP Well Known Ports were assigned, as were a significant fraction of the Registered Ports. (As noted, Dynamic Ports are never assigned.)

3.1.  Assigned Port Numbers for Experimentation

Of the Registered Ports, two TCP and UDP port numbers (1021 and 1022) have been assigned for experimentation with new applications and application-layer protocols that require a port number in the Registered Ports range [RFC4727] ( Fenner, B., “Experimental Values In IPv4, IPv6, ICMPv4, ICMPv6, UDP, and TCP Headers,” November 2006. ) . [sctp-dccp-exp] ( Lars: This document should register ports 1021 and 1022 for DCCP and SCTP. )

The experimental ports 1021 and 1022 SHOULD be used for local experiments only in controlled environments, and they SHOULD NOT be used on the global Internet. Many new applications and application-layer protocols can be experimented with without requiring a port in the Registered Ports range, and port numbers in the Dynamic Ports range can be also used.

Unfortunately, it can be difficult to limit access to these ports. Users SHOULD take measures to ensure that experimental ports are connecting to the intended process. For example, users of these experimental ports might include a 64-bit nonce, once on each segment of a message-oriented channel (e.g., UDP), or once at the beginning of a byte-stream (e.g., TCP), which is used to confirm that the port is being used as intended. Such confirmation of intended use is especially important when these ports are associated with privileged (e.g., system or administrator) processes.

4.  Principles for Port Number Space Management

Management procedures for the port number space include allocation of port numbers upon request, as well as coordination of information about existing allocations. The latter includes maintaining contact and description information about assigned ports, revoking abandoned ports, and redefining port allocations when needed. Of these procedures, port number allocation is most critical, because of the limited number of remaining port numbers.

Before the publication of this document, the principles of port number space allocation followed some simple, undocumented guidelines:

• TCP and UDP ports were simultaneously allocated when either was requested
• Port numbers were the primary allocation; service names were informative only, and did not need to be unique
• Port numbers were conserved informally, and sometimes inconsistently (e.g., some services were allocated ranges of many port numbers even where not strictly necessary)
• SCTP and DCCP port number and service name spaces were managed separately from the TCP/UDP spaces

This document attempts to update these guidelines to more conservatively manage the limited remaining TCP and UDP port number spaces, recognizes the potential use of service names in the absence of corresponding port number allocations, such as in SCTP and DCCP.

The basic principle of port number registry management is to conserve the space where possible. Extensions to support larger port number spaces would require changing many core protocols of the current Internet in a way that would not be backward compatible and interfere with both current and legacy applications.

Port numbers are intended to indicate a service and enable process demultiplexing at an endpoint; uses beyond those basic requirements should be avoided [I‑D.touch‑tsvwg‑port‑guidelines] ( Touch, J., “Guidelines for Transport Port Use,” July 2008. ) . This document also focuses on service names as a unique identifier, to increase the space available (from 4 bytes to 14), and to enable their use in the absence of corresponding port number assignments.

4.1.  Basic Principles of Port Conservation

This section summarizes the basic principles by which IANA attempts to conserve the port number space. This description is intended to inform applicants requesting port numbers. IANA decisions are not required to be bound to these principles, however; other factors may come into play, and exceptions may occur where deemed in the best interest of the Internet.

Conservation of the port number space recognizes that because this space is a limited resource, applications are expected to participate in the demultiplexing process where feasible. The port numbers are expected to encode as little information as possible that will enable an application to perform further demultiplexing by itself. In particular, there should be:

• only one port per service
• one port for all versions of a service
• the same port for different types of devices using the same service

A given service is expected to further demultiplex messages where possible. For example, applications and protocols are expected to include in-band version information, so that future versions of the application or protocol can share the same allocated port. Applications and protocols are also expected to be able to efficiently use a single allocated port, either by demultiplexing multiple streams within one port, or using the allocated port to coordinate using dynamic ports for subsequent exchanges (e.g., in the spirit of FTP [RFC0959] ( Postel, J. and J. Reynolds, “File Transfer Protocol,” October 1985. ) ).

These principles of port conservation are explained in [I‑D.touch‑tsvwg‑port‑guidelines] ( Touch, J., “Guidelines for Transport Port Use,” July 2008. ) . That document explains in further detail how ports are used in various ways, notably:

• Endpoint process identifier
• Application protocol identifier
• Firewall filtering

The process and protocol identifier use suggests that anything a single process can demultiplex, or that can be encoded into a single protocol, should be. The firewall filtering use suggests that some uses that could be de-multiplexed or encoded must be separated to allow for firewall management. Note that this latter use is much less sound, because port numbers have meaning only for the two endpoints of a connection (again, as discussed in detail in [I‑D.touch‑tsvwg‑port‑guidelines] ( Touch, J., “Guidelines for Transport Port Use,” July 2008. ) ).

4.2.  Principles Specific to Individual Port Number Ranges

It is important to note that different IANA procedures apply to different ranges of the port number registry. Section 6 ( Port Number Space Requests ) discusses the details of these procedures; this section outlines the rationale for these differences:

• Ports in the Dynamic Ports range (49152-65535) have been specifically set aside for local and dynamic use and cannot be registered through IANA. Applications may simply use them for communication without any sort of registration. On the other hand, applications MUST NOT assume that a specific port number in the Dynamic Ports range will always be available for communication at all times, and a port number in that range hence MUST NOT be used as a service identifier.
• Ports in the Registered Ports range (1024-49151) are available for registration through IANA, and MAY be used as service identifiers upon successful registration. Because registering a port number for a specific application consumes a fraction of the shared resource that is the port number registry, IANA will require the requester to document the intended use of the port number, and have a technical expert review this documentation to determine whether to grant the registration request. This documentation MUST explain why a port number in the Dynamic Ports range is unsuitable for the given application.
• Ports in the Well Known Ports range (0-1023) are also available for registration through IANA. Because the Well Known Ports range is both the smallest and the most densely allocated one, the bar for new allocations is higher than that for the Registered Ports range (1024-49551). A request for a Well Known port number MUST document why a port number in the Registered Ports or Dynamic Ports ranges is unsuitable.

4.3.  New Principles

Several new practices stem from the conservation principle that guides management of the port numbers registry, and will take effect with the approval of this document:

• IANA will allocate port numbers only to the transport protocols requested
• IANA will recover unused port numbers, via the new procedures of de-registration, revocation, and transfer

IANA will begin assigning protocol numbers only for those transport protocols explicitly included in a registration request. This ends the long-standing practice of automatically assigning a port number to an application for both TCP and a UDP, even if the request is only for one of these transport protocols. The new allocation procedure conserves resources by only allocating a port number to an application for those transport protocols (TCP, UDP, SCTP and/or DCCP) it actually uses. The port number will be marked as reserved - instead of assigned - in the port number registries of the other transport protocols. When applications start supporting the use of some of those additional transport protocols, they must request IANA to convert the reservation into an assignment. An application MUST NOT assume that it can use a port number assigned to it for use with one transport protocol with another transport protocol without another registration with IANA. The reason for this procedure is to allow allocation of reserved port numbers on the day the range has no more unassigend values. [port-reserv] ( Magnus: The usage of for the above reason reserved port numbers should probably not have the same rules as the other reserved ports. Needs discussion if we should separate this properly. I think the IETF consultation part will make it difficult the day one registry runs out of unassigned ones. )

Conservation for the port numbers registry is improved by procedures that allow previously allocated port numbers to become unassigned, either through de-registration or through revocation, and by a procedure that lets application designers transfer an allocated but unused port number to a new application. Section 5 ( IANA Procedures for Managing the Port Number Space ) describes these procedures, which so far were undocumented.

5.  IANA Procedures for Managing the Port Number Space

IANA supports various procedures to manage the port number space that enable ports to be registered, de-registered, reused, and revoked. This section explains these procedures, as well as other related issues.

5.1.  Port Number Registration

Registration refers to the allocation of port numbers to applicants. All such registrations are made from port numbers that are Unassigned or Reserved at the tine of the allocation. Unassigned numbers are allocated as needed, and without further explanation. Reserved numbers are assigned only after review by IANA and the IETF, and are accompanied by a statement explaining the reason a reserved number is appropriate for this action.

When a registration for one or more (but not all) transport protocols is approved, the port number for the non-requested transport protocol(s) will remain unassigned but is marked as reserved. However, IANA SHOULD NOT assign that port number to any other application or service until no port numbers remain unassigned in the request range. The current registration owner of a port number MAY register the same port number for other transport protocols when needed.

A port number registration consists of the following tuple:

Registration Contact: Name and email address of the contact person for the registration. This is REQUIRED. Additional address information MAY be provided. For registrations done through IETF-published RFCs, one or more technical contact persons SHALL be provided. In addition, in this case the registration ownership will belong to the IETF and not the technical contact persons. Transport Protocol: The transport protocol(s) for which the port allocation is requested, currently limited to one or more of TCP, UDP, SCTP, and DCCP Port Number: The currently unassigned port number(s) the requester suggests for allocation. If specified and when possible, IANA is encouraged to allocate the suggested number. If not specified, IANA will choose a suitable number from the Registered Ports range. Broadcast, Multicast or Anycast: Indicates whether the protocol supports either broadcast, multicast or anycast network layer addresses. Port Name: The long name (description) of the port. It should avoid all but the most well known acronyms. Service Name: This short name for the port number, used in various service selection and discovery mechanisms, currently including TCPMUX [RFC1078] ( Lottor, M., “TCP port service Multiplexer (TCPMUX),” November 1988. ) and DNS SRV resource records [RFC2782] ( Gulbrandsen, A., Vixie, P., and L. Esibov, “A DNS RR for specifying the location of services (DNS SRV),” February 2000. ) . This name is limited to 14 bytes, case-insensitive US-ASCII letters, digits, and dashes. It MUST NOT conflict with already allocated names in the service name registry [serv-nam-reg] ( Lars: Add citation to the service name registry draft, when it exists ) . Reference: A reference document describing the protocol or application using this port. For registration requests for Registered Ports, this documentation MUST explain why a port number in the Dynamic Ports range is unsuitable for the given application. For registration requests for Well Known Ports, this documentation MUST explain why a port number in the Registered Ports or Dynamic Ports ranges is unsuitable.

The following rules apply to the port number registry database maintained by IANA: [database-rules] ( Lars: Some of these rules below allow entries that aren't in full alignment with the procedures in this document. I assume that is, because the rules attempt to describe the state of the IANA database including all existing entries? If so, we should make that clearer. )

• Service Names MUST be unique
• Service Name MUST exist for all transport protocols
• Port Number MUST exist for TCP and UDP; it MAY exist for SCTP and DCCP
• Transport Protocol MUST exist for all entries
• Service Code MUST NOT occur for TCP, UDP or SCTP, and MUST occur for DCCP
• Port Name MUST exist for all entries
• Currently valid Registration Contact SHOULD exist for all entries; it MUST exist for all new entries
• Reference SHOULD exist for all entries

5.2.  Port Number De-Registration

The original requesters of a granted port number assignment can return the port number to IANA at any time if they no longer have a need for it. The port number will be de-registered and will be marked as reserved [res-vs-unass] ( Lars: This used to say "unassigned" instead of "reserved". I suggest "reserved", so that IANA has an indication in their list that they need to be careful when re-assigning a previously de-registered port. ) IANA should not re-assign port numbers that have been de-registered until all other available port numbers in the specific range have been assigned.

Before proceeding with a de-registration, IANA needs to confirm that the port number is actually no longer in use.

5.3.  Port Number Re-Use

If the original requesters of a granted port number assignment no longer have a need for the registered number, but would like to re-use it for a different application, they can submit a request to IANA to do so.

Logically, port number re-use is to be thought of as a de-registration followed by an immediate re-registration of the same port number for a new application. Consequently, the information that needs to be provided about the proposed new use of the port number is identical to what would need to be provided for a new port number allocation for the specific ports range.

IANA needs to carefully review such requests before approving them. In some instances, the Expert Reviewer will determine that the application that the port number was assigned to has found usage beyond the original requester, or that there is a concern that it may have such users. This determination MUST be made quickly. A community call concerning revocation of a port number (see below) MAY be considered, if a broader use of the port number is suspected.

5.4.  Port Number Revocation

Sometimes, it will be clear that a specific port number is no longer in use and that IANA can de-register it and mark it as reserved [res-vs-unass2] ( Lars: See [res-vs-unass]. ) But at other times, it may be unclear whether a given assigned port number is still in use somewhere in the Internet. In those cases, despite the requester's wish to de-register, IANA must consider the consequences that de-registering the port number.

With the help of their IESG-appointed Expert Reviewer, IANA SHALL formulate a request to the IESG to issue a four-week community call concerning the pending port number revocation. The IESG and IANA, with the Expert Reviewer's support, SHALL determine promptly after the end of the community call whether revocation should proceed and then communicate their decision to the community. This procedure typically involves similar steps to de-registration except that it is initiated by IANA.

5.5.  Port Number Transfer

The value of port numbers is defined by their careful management as a shared Internet resource, whereas enabling transfer allows the potential for associated monetary exchanges to motivate this management. As a result, current IANA procedures do not permit port number assignments to be transferred between parties, even when they are mutually consenting. The appropriate alternate procedure is for the new party to request its own port number registration and for the previous party to release its registration via the de-registration procedure outlined above.

5.6.  Maintenance Issues

The previous procedures help IANA manage defining properties of the port name space. There are additional procedures which are administrative, and help IANA maintain non-defining information in a registration. This includes changes to the Port Name (i.e., description), and changes to contact information. These changes are coordinated by IANA in an informal manner, and may be initiated by either the registrant or by IANA, e.g., the latter when requesting an update to current contact information.

6.  Port Number Space Requests

This section describes the process for requests associated with IANA's management of the the port number space. Such requests include initial registration, de-registration, re-use, changes to the service name, as well as updates to the contact information or port name (description). Revocation is initiated by IANA.

6.1.  Request Procedure

All registration requests for a TCP, SCTP, DCCP and/or UDP ports must contain the following pieces of information:

Port number tuple: A port number tuple, as described in Section 5.1 ( Port Number Registration ) . The port number would typically be omitted; when provided, it indicates a preference for requesting a currently unassigned value. Port Range: Indicates the port range desired (i.e., Well Known Ports or Registered Ports). Requested Action: One of REGISTER, DEREGISTER, REUSE, SVC_NAME_CHANGE, or UPDATE_INFO (port name, registration contact).

The Well Known Ports are assigned by IANA and cover the range 0-1023. On many systems, they can only be used by system (or root) processes or by programs executed by privileged users. Registration requests for a Well Known port number MUST follow the "IETF Review" policy of [RFC5226] ( Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008. ) . Registrations for a port number in this range MUST document why a port number in the Registered Ports range will not fulfill the application needs.

The Registered Ports are assigned by IANA and on most systems can be used by ordinary user processes or programs executed by ordinary users. The Registered Ports are in the range 1024-49151. Registration requests for a Registered Port number MUST follow the "Expert Review" policy of [RFC5226] ( Narten, T. and H. Alvestrand, “Guidelines for Writing an IANA Considerations Section in RFCs,” May 2008. ) .

7.  Security Considerations

The IANA guidelines described in this document do not change the security properties of either TCP, SCTP, DCCP or UDP.

Assignment of a port number does not in any way imply an endorsement of an application or product, and the fact that network traffic is flowing to or from a registered port number does not mean that it is "good" traffic, or even that the it is used by the assigned service. Firewall and system administrators should choose how to configure their systems based on their knowledge of the traffic in question, not whether there is a port number registered or not.

8.  IANA Considerations

This document obsoletes Sections 8 and 9.1 of [RFC2780] ( Bradner, S. and V. Paxson, “IANA Allocation Guidelines For Values In the Internet Protocol and Related Headers,” March 2000. ) . Upon approval of this document, IANA is requested to adopt the procedures described herein.

IANA should take immediate actions to resolve inconsistencies raised by requirements of this document.

9.  Acknowledgments

The text in Appendix A ( Updates to DCCP Registries ) is based on a suggestion by Tom Phelan.

Lars Eggert is partly funded by [TRILOGY] ( , “Trilogy Project,” . ) , a research project supported by the European Commission under its Seventh Framework Program.

10.  References

10.1. normative references.

10.2. Informative References

Editorial Comments

Appendix A.  Updates to DCCP Registries

This document updates the IANA allocation procedures for the DCCP Port Number and DCCP Service Codes Registries as defined in [RFC4340] ( Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006. ) .

A.1.  DCCP Service Code Registry

Service Codes are allocated first-come-first-served according to Section 19.8 of [RFC4340] ( Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006. ) . This document updates Section 19.8 of [RFC4340] ( Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006. ) by extending the guidelines given there in the following ways:

• IANA MAY assign new Service Codes without seeking Expert Review using their discretion, but SHOULD seek expert review when a request seeks an appreciable number of Service Codes (e.g., more than five).
• IANA should feel free to contact the DCCP Expert Reviewer with questions on any registry, regardless of the registry policy, for clarification or if there is a problem with a request [RFC4340] ( Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006. ) .

A.2.  DCCP Port Numbers Registry

The DCCP ports registry is defined by [RFC4340] ( Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006. ) in Section 19.9. Allocations in this registry require prior allocation of a Service Code. Not all Service Codes require IANA-registered ports. This document updates Section 19.9 of [RFC4340] ( Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006. ) by extending the guidelines given there in the following way:

• IANA should normally assign a value in the range 1024-49151 to a DCCP server port. IANA allocation requests to allocate port numbers in the Well Known Ports range (0 through 1023), require IETF Action prior to allocation by IANA [RFC4340] ( Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006. ) .

Section 19.9 of [RFC4340] ( Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006. ) requires each DCCP server port assignment to be associated with at least one Service Code value. This document updates [RFC4340] ( Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006. ) in the following way:

• IANA MUST NOT allocate a single Service Code value to more than one DCCP server port.
• The set of Service Code values associated with a DCCP server port should be recorded in the ports registry.
• A request for additional Service Codes to be associated with an already allocated Port Number requires Expert Review. These requests will normally be accepted when they originate from the contact associated with the port registration. In other cases, these applications will be expected to use an unallocated port, when this is available.

[RFC4340] ( Kohler, E., Handley, M., and S. Floyd, “Datagram Congestion Control Protocol (DCCP),” March 2006. ) notes that a short port name MUST be associated with each DCCP server port that has been registered. This document requires that this name MUST be unique.

Authors' Addresses

Full Copyright Statement

Copyright © The IETF Trust (2008).

This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights.

This document and the information contained herein are provided on an “AS IS” basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr .

The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at [email protected] .

How to Choose a Default Port Number for a New Network Service?

Last updated: March 18, 2024

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1. Introduction

In the context of computer networks, a port is an endpoint for communication between applications (or network services). Each port has a port number for identification. Thus, a network service can use one or more ports by specifying their numbers.

By definition, there are 65,536 possible ports for use. However, many of them have a specific purpose or have already been assigned to some service. In this article, we’ll study how to choose a default port number for a new network service.

The main issue we have to deal with is choosing a port that’s not being used by any other service. Otherwise, there’s a good chance that our new service will eventually be executed on a machine with another service running on the same port. This would prevent both services from working.

To have a full view of the problem, we’ll first understand the subdivision of the port range. Next, let’s learn how to choose ports other than those used by well-known services. Then, we’ll see how to avoid conflicts with services running on our machine or the local network. Finally, we’ll briefly look at how to request an official assignment of the chosen port for our service if desired.

2. Understanding the Subdivision of Port Ranges

The full range of possible port numbers extends from 0 to 65535. However, properly using this large but limited port range requires global coordination. In this sense, RFC6335 designates the Internet Assigned Numbers Authority ( IANA ) as responsible for the assignment of these ports.

IANA handles port number assignments through procedures also specified in RFC6335. In short, the specification subdivides the full range of port numbers into three smaller ones. Each one of them is intended for different uses, as described in the table below:

System Ports and User Ports are available for assignment through IANA, which requires the IETF review or the IESG approval. However, the Dynamic Ports range has been specifically set aside for local and dynamic use, so it can’t be assigned through IANA.

The possible states for each port are Assigned, Unassigned, or Reserved. So, the only ports free to use are those with Unassigned state.

2.1. From Which Sub-range Should We Choose a Port?

The System Ports range (also known as the Well-Known Ports) is both the smallest and the most densely assigned. So, the requirements for new port assignments in this range are much more strict than those for the User Ports range (also called Registered Ports). Therefore, ports in the System Ports range are only used by very well-known services and protocols.

Ports in the Dynamic Ports range are considered ephemeral ports, i.e., they’re only for temporary and dynamic use. Therefore, we should never use a port in this range as a service identifier since there’s no guarantee that ports will be available for the service.

Thus, in most cases, we should look for a free port in the User Ports range when choosing a default port for a new service.

3. How to Avoid Conflicts With Well-Known Services?

Nowadays, there’s a wide range of network services (and protocols) used worldwide. Most of them are well-known services that have assigned ports in the IANA. Other services, although well-known, don’t have IANA-assigned ports for some reason.

Next, let’s see how to avoid selecting a port that services in both cases are already using.

3.1. Check Allocated Ports in IANA

For not choosing a port assigned by IANA, we need to check the IANA port number registry . It lists all port assignments and their respective services. In this case, the ports available are the ones that aren’t listed in the registry or have the Description field marked as Unassigned .

Given the large number of port assignments, it can be challenging to find available port numbers in the desired range. For convenience, we can download the IANA port number registry in CSV format and use the Python script list_iana_available_ports.py below to list the available ports in any given range.

To use the script above, we just need to run the command below, replacing <port-start> and <port-end> according to any range of our choice and <csv-file-name> with the actual name of the downloaded file.

It may be a good idea to select one or more of the available ports according to IANA. For example, we may use the provided script to find available ports ranging from 2000 to 3000 (which is a subrange of User Ports) and then select one or more ports.

After that, we can follow the next steps just to make sure that no other service is unofficially using the chosen port.

3.2. Check Ports Listed by NMAP

Some widely used services utilize ports that haven’t been officially assigned to them in the IANA registry. So, to avoid choosing a port used by one of these services too, we need to refer to an alternative (unofficial) but comprehensive listing.

An example of such a list is provided by NMAP.org . The NMAP list includes port assignments registered in IANA and others that have been detected by NMAP itself.

Thus, by accessing this list, we can check whether the port (or range) we selected in the previous step has also been identified by NMAP as frequently used by services. Since the port we’ve selected so far isn’t present in the NMAP list, we can follow the steps below to check further.

4. How to Avoid Local Conflicts?

Besides avoiding conflicts with widely used services, we also need to ensure that the chosen port doesn’t create conflicts with our organization’s own services. Next, we’ll see how to avoid conflicts with other services on our local machine or local network.

4.1. Check the Local System

Usually, Operating Systems (OS) have a file that maps services and their respective ports. Applications use it to convert human-readable service names into port numbers. Specifically, in Linux and MacOS, we can find this file at /etc/services , whereas, in Windows, its location is %windir%\System32\drivers\etc\services .

The services file includes the assignments made by IANA but also maps services related to the OS and others running on the local machine. For example, in a Debian-based distribution, the file includes a section named “Services added for the Debian GNU/Linux distribution” and another named “Local services”.

Hence, we can just open the file and search for the chosen port. So, if we don’t find the port in the file, we know that there are no local conflicts.

4.2. Check the Local Network

To check if another service on our local network is using the port we’ve chosen so far, we can use a network scanning tool. An example of such a tool is NMAP, which is widely used and available for various OSes , including Linux, Windows, and MacOS.

In short, NMAP has a command-line interface that expects some parameter (or command option) and a target host. The target host refers to the host that will be scanned. So, it can be a hostname or an IP address.

However, in our case, we don’t want to scan a specific target host but the whole network for open ports (ports being used by some service). Fortunately, the NMAP command line also supports multiple target hosts. There are many ways to do this , but one of the easiest is by using the CIDR notation.

This way, we can scan the entire network at once, specifying the target host in the format <network-ip-address>/<netmask> . For example, we can search for all open ports on the network 192.168.1.0/24 by typing the following command.

In addition, we can also scan only the port we’ve chosen later. The command below exemplifies a search for hosts using port 3000 on the network 192.168.1.0/24 .

5. How Can We Request a Port Assignment for Our Service?

Once we’ve chosen a port that’s currently available, we can request that the port be assigned to our service if we so desire. However, we should do this only if the service is genuinely distinct. Otherwise, IANA will probably not approve the port assignment.

For example, if the service is a new web application, instead of requesting a new port assignment, we should use the ports already assigned for this kind of service (such as 80 for HTTP and 443 for HTTPS).

Nevertheless, to make the request, we can submit an application for port assignment through the official IANA form .

6. Conclusion

In this article, we learn how to choose a port for a new network service. A good choice requires in-depth investigation to avoid choosing a port that’s already in use by another service.

The first step is to check the IANA port assignment registries. After that, we can consult unofficial registries and local port mappings and scan the network for ports in use.

In conclusion, these are the key steps to selecting a port number for a new network service, ensuring effective communication.

Ports Master – Information on Network Ports

Ports Master is an extensive online database that provides detailed information about network ports. It serves as a centralized repository of port numbers, their associated protocols, and the services they commonly support. Ports Master aims to be a go-to resource for anyone working with network ports, offering a user-friendly interface and a wealth of technical information.

The database is regularly updated to include the latest port assignments and any changes in port usage. Ports Master covers a wide range of port numbers, from well-known ports (0-1023) to registered ports (1024-49151) and dynamic or private ports (49152-65535). It provides a brief description of each port, along with the associated protocol (TCP, UDP, or both) and the typical services that utilize the port.

Ports Master’s comprehensive coverage and up-to-date information make it an essential tool for network administrators, security professionals, and developers who need to understand and manage network ports effectively.

Common Network Ports and Their Uses

Ports Master provides a comprehensive list of commonly used network ports and their associated services. Here are a few examples:

These are just a few examples from the extensive list of ports available on Ports Master. The database provides detailed information about each port, including a description of its purpose, the associated protocol, and any known security vulnerabilities or considerations.

Port Numbers and Their Significance

Port numbers are divided into three ranges: well-known ports (0-1023), registered ports (1024-49151), and dynamic or private ports (49152-65535). Well-known ports are reserved for common services and are typically assigned by the Internet Assigned Numbers Authority (IANA). For example, port 80 is reserved for HTTP traffic, while port 22 is used for SSH.

Registered ports are used by specific applications or services and are assigned by IANA upon request. These ports are typically used by proprietary applications or custom services. Dynamic or private ports, on the other hand, are not assigned and can be used by any application or service as needed.

Ports Master provides information about the port numbers in each range, along with their associated services and any relevant notes or considerations.

Securing Network Ports: Best Practices

Network port security is crucial to protect against unauthorized access, data breaches, and other security threats. Ports Master offers valuable insights and best practices for securing network ports. Some key recommendations include:

• Closing unnecessary ports: Disable or block any ports that are not required for the intended services or applications.
• Implementing firewalls: Use firewalls to control inbound and outbound traffic based on port numbers and protocols.
• Enabling access control: Restrict access to specific ports based on IP addresses, subnets, or user authentication.
• Keeping software up to date: Regularly update operating systems, applications, and services to patch any known vulnerabilities.
• Monitoring port activity: Implement monitoring tools to detect and alert on suspicious port activity or unauthorized access attempts.

Ports Master provides detailed guides and best practices for securing network ports, helping IT professionals and network administrators to fortify their network infrastructure against potential threats.

Troubleshooting Port-Related Issues

When encountering port-related issues, such as connectivity problems or service disruptions, Ports Master can be a valuable resource for troubleshooting. The database provides information about common port-related issues and offers step-by-step guidance on resolving them.

Some common port-related issues include:

• Port conflicts: When multiple services or applications attempt to use the same port, resulting in connectivity issues.
• Firewall blockages: Firewalls may inadvertently block legitimate traffic on specific ports, causing service disruptions.
• Incorrect port configurations: Misconfigured ports or incorrect port assignments can lead to connectivity problems.

Ports Master’s troubleshooting guides cover these and other port-related issues, providing practical solutions and diagnostic steps to help users identify and resolve problems quickly and effectively.

Ports Master: A Valuable Resource for IT Pros

Ports Master is an indispensable resource for IT professionals, network administrators, and developers who work with network ports regularly. The database offers several key benefits:

• Comprehensive port information: Ports Master provides detailed information about a wide range of port numbers, their associated protocols, and common services.
• Up-to-date data: The database is regularly updated to reflect the latest port assignments and changes in port usage.
• Best practices and security guidance: Ports Master offers valuable insights and recommendations for securing network ports and implementing best practices.
• Troubleshooting assistance: The database provides step-by-step guides and solutions for resolving common port-related issues.

By leveraging Ports Master’s extensive knowledge base, IT professionals can streamline their work, enhance network security, and effectively manage port-related tasks.

Staying Up-to-Date with Ports Master’s Database

To ensure that users have access to the most current and accurate port information, Ports Master regularly updates its database. The team behind Ports Master monitors changes in port assignments, new service releases, and emerging security threats to keep the database up to date.

Users can stay informed about the latest updates and changes by:

• Subscribing to Ports Master’s newsletter: Users can sign up for email notifications to receive regular updates about new port assignments, database enhancements, and security advisories.
• Following Ports Master on social media: Ports Master maintains an active presence on platforms like Twitter and LinkedIn, where users can stay informed about the latest news and updates.
• Checking the Ports Master website regularly: The Ports Master website features a dedicated section highlighting recent updates, changes, and important announcements.

By staying up to date with Ports Master’s database, IT professionals can ensure that they have access to the most accurate and reliable port information for their network management and security needs.

Ports Master is a comprehensive and invaluable resource for anyone working with network ports. By providing detailed information about port numbers, associated protocols, and common services, Ports Master empowers IT professionals, network administrators, and developers to effectively manage and secure their network infrastructure.

With its user-friendly interface, up-to-date data, and practical guidance, Ports Master has become an essential tool in the IT industry. By leveraging Ports Master’s extensive knowledge base and staying informed about the latest updates, users can streamline their work, enhance network security, and confidently navigate the complex world of network ports.

• Chat with a consultant

Find a list of standard network port designations

For a complete list of port assignments, consult the IANA's Port Numbers .

If you are using a Unix-like operating system such as macOS or Linux , you can view the services file under the /etc directory by entering at the Unix shell prompt:

This is document acia in the Knowledge Base. Last modified on 2023-06-28 11:00:49 .

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Best TCP port number range for internal applications [closed]

I work in a place where each of our internal applications runs on an individual Tomcat instance and uses a specific TCP port. What would be the best IANA port range to use for these apps in order to avoid port number collisions with any other process on the server?

Based on http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xml , these are the options as I currently see them:

• System Ports (0-1023): I don't want to use any of these ports because the server may be running services on standard ports in this range
• User Ports (1024-49151): Given that the applications are internal I don't intend to request IANA to reserve a number for any of our applications. However, I'd like to reduce the likelihood of the same port being used by another process, e.g., Oracle Net Listener on 1521.

a. I configure one of my applications to use port X b. The application is down for a few minutes or hours (depending on the nature of the app), leaving the port unused for a little while, c. The operating system allocates port number X to another process, for instance, when that process acts as a client requiring a TCP connection to another server. This succeeds given that it falls within the dynamic range and X is currently unused as far as the operating system is concerned, and d. The app fails to start because port X is already in use

• 3 I answered a similar question here stackoverflow.com/a/38141340/3333759 which you may find helpful. –  adrianwadey Commented Apr 9, 2018 at 14:34

3 Answers 3

I decided to download the assigned port numbers from IANA, filter out the used ports, and sort each "Unassigned" range in order of most ports available, descending. This did not work, since the csv file has ranges marked as "Unassigned" that overlap other port number reservations. I manually expanded the ranges of assigned port numbers, leaving me with a list of all assigned port numbers. I then sorted that list and generated my own list of unassigned ranges.

Since this stackoverflow.com page ranked very high in my search about the topic, I figured I'd post the largest ranges here for anyone else who is interested. These are for both TCP and UDP where the number of ports in the range is at least 500.

Source (via the CSV download button):

http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml

• "It's both tcp and udp" as in - I can open all of those ports lets say 44100-44199 looks easy to remember because audio 44100 sampling on both udp and tcp securely? Both udp 44100-44199 and tcp 44100-44199 are free? –  Lapsio Commented Sep 4, 2016 at 18:27
• 1 Unfortunately no. There have been additional reservations since I posted. There is a port in your range now. "z-wave-tunnel 44123 tcp Z-Wave Secure Tunnel" –  David Vereb Commented Sep 4, 2016 at 20:21
• well luckily I don't think I'm going to install Z-Wave smart home security systems on development server lol. Previously used port ranges covered a lot of important stuff including some VMWare tools so it was much worse. If that's the only collision for now then I'm cool with that thanks :) –  Lapsio Commented Sep 4, 2016 at 22:24
• 3 So I decided to run the list again to come up with a new set of ranges based on newer data. It turns out that the "Unassigned" ranges don't seem to be numbered properly. For example, 43124-44320 is marked as unassigned, yet 44123, which is in that range, is listed just above it as being assigned. It seems I'll have to manually come up with the unassigned ranges as they appear to be incorrectly calculated. –  David Vereb Commented Sep 6, 2016 at 12:44

I can't see why you would care. Other than the "don't use ports below 1024" privilege rule, you should be able to use any port because your clients should be configurable to talk to any IP address and port!

If they're not, then they haven't been done very well. Go back and do them properly :-)

In other words, run the server at IP address X and port Y then configure clients with that information. Then, if you find you must run a different server on X that conflicts with your Y , just re-configure your server and clients to use a new port. This is true whether your clients are code, or people typing URLs into a browser.

I, like you, wouldn't try to get numbers assigned by IANA since that's supposed to be for services so common that many, many environments will use them (think SSH or FTP or TELNET).

Your network is your network and, if you want your servers on port 1234 (or even the TELNET or FTP ports for that matter), that's your business. Case in point, in our mainframe development area, port 23 is used for the 3270 terminal server which is a vastly different beast to telnet. If you want to telnet to the UNIX side of the mainframe, you use port 1023. That's sometimes annoying if you use telnet clients without specifying port 1023 since it hooks you up to a server that knows nothing of the telnet protocol - we have to break out of the telnet client and do it properly:

If you really can't make the client side configurable, pick one in the second range, like 48042, and just use it, declaring that any other software on those boxes (including any added in the future) has to keep out of your way.

• Thanks. After reading your answer and giving it a bit of more thought I decided to go with the option of using a port within the second range. We picked 46xxx as IANA currently has very few ports assigned in this subrange link . We didn't pick the third range because of the theoretically possible (although highly unlikely) scenario I described. –  Juanal Commented May 8, 2012 at 4:07

Short answer: use an unassigned user port

Over achiever's answer - Select and deploy a resource discovery solution. Have the server select a private port dynamically. Have the clients use resource discovery.

The risk that that a server will fail because the port it wants to listen on is not available is real; at least it's happened to me. Another service or a client might get there first.

You can almost totally reduce the risk from a client by avoiding the private ports, which are dynamically handed out to clients.

The risk that from another service is minimal if you use a user port. An unassigned port's risk is only that another service happens to be configured (or dyamically) uses that port. But at least that's probably under your control.

The huge doc with all the port assignments, including User Ports, is here: http://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.txt look for the token Unassigned.

• 7 Isn't it better to use an assigned port for a protocol that will never be used on your network? An unassigned port could become assigned at any time and give you problems. –  adrianwadey Commented Jul 1, 2016 at 9:12

Not the answer you're looking for? Browse other questions tagged networking tomcat or ask your own question .

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Port Number Lookup

If you are not sure that Port Numbers you are going to use has been assignned for what purpose. You can lookup our TCP ports database and find details related to assignment Port or Protocol assigned by IANA (Internet Assigned Numbers Authority).

Port Numbers and Protocols

TCP and UDP are two different protocols that are used for transmitting data over a network. TCP (Transmission Control Protocol) is a connection-oriented protocol that ensures that data is delivered reliably and in the correct order. UDP (User Datagram Protocol) is a connectionless protocol that does not guarantee the delivery of data or the order in which it is delivered.

Here are some common port numbers that are used by TCP and UDP:

TCP port numbers:

• Port 80: HTTP (Hypertext Transfer Protocol)
• Port 443: HTTPS (HTTP Secure)
• Port 21: FTP (File Transfer Protocol)
• Port 22: SSH (Secure Shell)
• Port 25: SMTP (Simple Mail Transfer Protocol)
• Port 155: NETSC

UDP port numbers:

• Port : DNS (Domain Name System)
• Port 67: DHCP (Dynamic Host Configuration Protocol)
• Port 69: TFTP (Trivial File Transfer Protocol)
• Port 123: NTP (Network Time Protocol)

Note that these are just a few examples, and there are many other port numbers that are used for various purposes.

For port numbers lookup, the official database of ports and protocols from IANA (Internet Assigned Numbers Authority) is used. IANA is an organization that manages Internet protocol parameters, as well as IP address spaces and top-level domains.

Diffrent Port Number Ranges?

The entire range of port numbers (from 0 to 65535) is divided into three categories.

0 - 1023  Well-Known Ports The  numbers are reserved by IANA for system processes or network programs with administrative rights. Ports from this category should not be used without registering with IANA.

1024 - 49151  Registered Ports  Ports registered for use by conventional programs and application layer protocols. This category of ports is most popular for commercial software. Registration is also required to use any port.

49152 - 65535  Dynamic ports  Designed for free but temporary use. Registration of ports in this category is not possible.

Our Port checker tool allows you to test open ports in your system. You can easily verify if any port is opened or not not by typing your IP address or domain name and desired port number.

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Suspected attacks by Yemen's Houthi rebels target 2 ships in the Red Sea, officials say

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Suspected attacks by Yemen 's Houthi rebels targeted two ships in the Red Sea on Monday, authorities said, near where crews hope to salvage a tanker loaded with oil and still ablaze after another assault by the group.

The attacks are believed to be the latest in the Iranian-backed rebels’ campaign that has disrupted the $1 trillion in goods that pass through the Red Sea each year over the Israel-Hamas war in the Gaza Strip as well as halted some aid shipments to conflict-ravaged Sudan and Yemen.

Meanwhile, the efforts to salvage the still-burning Sounion seek to head off the potential ecological disaster posed by its cargo of 1 million barrels of crude oil.

In Monday's first assault, ballistic missiles hit the Panama-flagged oil tanker Blue Lagoon I, and a third exploded near the ship, the multination Joint Maritime Information Center overseen by the U.S. Navy said.

“All crew on board are safe (no injury reported),” the center said. "The vessel sustained minimal damage but does not require assistance."

The Blue Lagoon I is traveling south through the Red Sea to an unlisted destination. The vessel was coming from Russia's port of Ust-Luga on the Baltic Sea and had been broadcasting that it had Russian-origin cargo on board.

In recent months, the Blue Lagoon I traveled to India, which gets more than 40% of its oil imports from Russia despite Moscow's ongoing war on Ukraine and the international sanctions it faces over it.

The Greek-based firm operating the ship could not be immediately reached. The Joint Maritime Information Center said it assessed the ship “was targeted due to other vessels within its company structure making recent port calls in Israel.”

Later on Monday morning, the British military's United Kingdom Maritime Trade Operations center reported a second attack off the Houthi-controlled port city of Hodeida. The private security firm Ambrey said an aerial drone hit a merchant ship, though no damage or injuries were reported. The attack happened only a few kilometers (miles) from where the Blue Lagoon I attack happened, Ambrey said.

The Houthis did not immediately claim responsibility for the attacks. However, it can take the rebels hours or even days to acknowledge their assaults.

The Houthis have targeted more than 80 vessels with missiles and drones since the war in Gaza started in October. They seized one vessel and sank two in the campaign that also killed four sailors. Other missiles and drones have either been intercepted by a United States-led coalition in the Red Sea or failed to reach their targets.

The rebels maintain that they target ships linked to Israel, the U.S. or the U.K. to force an end to Israel’s campaign against Hamas in Gaza. However, many of the ships attacked have little or no connection to the conflict, including some bound for Iran.

Meanwhile on Monday, a salvage effort appeared to be underway to tow away the Sounion oil tanker, which was earlier hit by the Houthis and abandoned by its crew. Jamel Amer, an official with the Houthis, wrote online Saturday that tug boats assigned to pull the Sounion away should arrive Sunday.

However, NASA fire satellites showed a blaze at the site where the Sounion had been abandoned on Monday morning. Later photos published by the European Union's Operation Aspides naval mission in the Red Sea of the Sounion taken Monday showed no tugboats near the still-burning vessel.

“Private companies are involved in the salvage operation that is about to start,” the operation said. “Upon their request, EUNAVFOR ASPIDES will provide protection to the tug boats, that will deal with the salvage operation and facilitate their efforts to prevent an environmental disaster.”

It added: “Currently, several fires continue to burn on the vessel’s main deck. The vessel remains anchored without drifting, and there are no visible signs of an oil spill.”

The Sounion was carrying some 1 million barrels of oil when the Houthis initially attacked it on Aug. 21 with small arms fire, projectiles and a drone boat. A French destroyer operating as part of Operation Aspides rescued the Sounion’s crew of 25 Filipinos and Russians, as well as four private security personnel, after they abandoned the vessel and took them to nearby Djibouti.

Last week, the Houthis released footage showing they planted explosives on board the Sounion and ignited them in a propaganda video, something the rebels have done before in their campaign.

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