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Extending ICMP for Interface and Next-Hop Identification.
A. Atlas, Ed., R. Bonica, Ed., C. Pignataro, Ed., N. Shen, JR. Rivers. April 2010.

 
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Internet Engineering Task Force (IETF) A. Atlas, Ed. Request for Comments: 5837 BT Category: Standards Track R. Bonica, Ed. ISSN: 2070-1721 Juniper Networks C. Pignataro, Ed. N. Shen Cisco Systems JR. Rivers Consultant April 2010 Extending ICMP for Interface and Next-Hop Identification Abstract This memo defines a data structure that can be appended to selected ICMP messages. The ICMP extension defined herein can be used to identify any combination of the following: the IP interface upon which a datagram arrived, the sub-IP component of an IP interface upon which a datagram arrived, the IP interface through which the datagram would have been forwarded had it been forwardable, and the IP next hop to which the datagram would have been forwarded. Devices can use this ICMP extension to identify interfaces and their components by any combination of the following: ifIndex, IPv4 address, IPv6 address, name, and MTU. ICMP-aware devices can use these extensions to identify both numbered and unnumbered interfaces. Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc5837. Atlas, et al. Standards Track [Page 1]
RFC 5837 ICMP Unnumbered April 2010 Copyright Notice Copyright (c) 2010 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. This document may contain material from IETF Documents or IETF Contributions published or made publicly available before November 10, 2008. The person(s) controlling the copyright in some of this material may not have granted the IETF Trust the right to allow modifications of such material outside the IETF Standards Process. Without obtaining an adequate license from the person(s) controlling the copyright in such materials, this document may not be modified outside the IETF Standards Process, and derivative works of it may not be created outside the IETF Standards Process, except to format it for publication as an RFC or to translate it into languages other than English. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions Used In This Document . . . . . . . . . . . . . . 5 3. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Application to Traceroute . . . . . . . . . . . . . . . . 5 3.2. Policy and MTU Detection . . . . . . . . . . . . . . . . . 6 4. Interface Information Object . . . . . . . . . . . . . . . . . 6 4.1. C-Type Meaning in an Interface Information Object . . . . 7 4.2. Interface IP Address Sub-Object . . . . . . . . . . . . . 9 4.3. Interface Name Sub-Object . . . . . . . . . . . . . . . . 10 4.4. Interface Information Object Examples . . . . . . . . . . 10 4.5. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 13 5. Network Address Translation Considerations . . . . . . . . . . 14 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 9.1. Normative References . . . . . . . . . . . . . . . . . . . 16 9.2. Informative References . . . . . . . . . . . . . . . . . . 16 Atlas, et al. Standards Track [Page 2]
RFC 5837 ICMP Unnumbered April 2010 1. Introduction IP devices use the Internet Control Message Protocol (ICMPv4 [RFC0792] and ICMPv6 [RFC4443]) to convey control information. In particular, when an IP device receives a datagram that it cannot process, it may send an ICMP message to the datagram's originator. Network operators and higher-level protocols use these ICMP messages to detect and diagnose network issues. In the simplest case, the source address of the ICMP message identifies the interface upon which the datagram arrived. However, in many cases, the incoming interface is not identified by the ICMP message at all. Details follow: According to [RFC1812], when a router generates an ICMPv4 message, the source address of that message MUST be one of the following: o one of the IP addresses associated with the physical interface over which the ICMPv4 message is transmitted o if that interface has no IP addresses associated with it, the device's router-id or host-id is used instead. If all of the following conditions are true, the source address of the ICMPv4 message identifies the interface upon which the original datagram arrived: o the device sends an ICMPv4 message through the same interface upon which the original datagram was received o that interface is numbered However, the incoming and outgoing interfaces may be different due to an asymmetric return path, which can occur due to asymmetric link costs, parallel links, or Equal Cost Multipath (ECMP). Similarly, [RFC1122] provides guidance for source address selection for multihomed IPv4 hosts. These recommendations, like those stated above, do not always cause the source address of an ICMPv4 message to identify the incoming interface. ICMPv6 is somewhat more flexible. [RFC4443] states that for responses to messages sent to a non-local interface, the source address must be chosen as follows: o the Source Address of the ICMPv6 packet MUST be a unicast address belonging to the node. The address SHOULD be chosen according to the rules that would be used to select the source address for any Atlas, et al. Standards Track [Page 3]
RFC 5837 ICMP Unnumbered April 2010 other packet originated by the node, given the destination address of the packet. However, it MAY be selected in an alternative way if this would lead to a more informative choice of address reachable from the destination of the ICMPv6 packet. When a datagram that cannot be processed arrives on an unnumbered interface, neither ICMPv4 nor ICMPv6 is currently capable of identifying the incoming interface. Even when an ICMP message is generated such that the ICMP source address identifies the incoming interface, the receiver of that ICMP message has no way of knowing if this is the case. ICMP extensions are required to explicitly identify the incoming interface. Using the extension defined herein, a device can explicitly identify the incoming IP interface or its sub-IP components by any combination of the following: o ifIndex o IPv4 address o IPv6 address o name o MTU The interface name SHOULD be identical to the first 63 octets of the ifName, as defined in [RFC2863]. The ifIndex is also defined in [RFC2863]. Using the same extension, an IP device can explicitly identify by the above the outgoing interface over which a datagram would have been forwarded if that datagram had been deliverable. The next-hop IP address, to which the datagram would have been forwarded, can also be identified using this same extension. This information can be used for creating a downstream map. The next-hop information may not always be available. There are corner-cases where it doesn't exist and there may be implementations where it is not practical to provide this information. This specification provides an encoding for providing the next-hop IP address when it is available. The extension defined herein uses the ICMP multi-part message framework defined in [RFC4884]. The same backward compatibility issues that apply to [RFC4884] apply to this extension. Atlas, et al. Standards Track [Page 4]
RFC 5837 ICMP Unnumbered April 2010 2. Conventions Used In This Document 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 RFC 2119 [RFC2119]. 3. Applications 3.1. Application to Traceroute ICMP extensions defined in this memo provide additional capability to traceroute. An enhanced traceroute application, like older implementations, identifies nodes that a datagram visited en route to its destination. It differs from older implementations in that it can explicitly identify the following at each node: o the IP interface upon which a datagram arrived o the sub-IP component of an IP interface upon which a datagram arrived o the IP interface through which the datagram would have been forwarded had it been forwardable o the IP next hop to which the datagram would have been forwarded Enhanced traceroute applications can identify the above listed entities by: o ifIndex o IPv4 address o IPv6 address o name o MTU The ifIndex can be utilized within a management domain to map to an actual interface, but it is also valuable in public applications. The ifIndex can be used as an opaque token to discern whether or not two ICMP messages generated from the same router involve the same interface. Atlas, et al. Standards Track [Page 5]
RFC 5837 ICMP Unnumbered April 2010 3.2. Policy and MTU Detection A general application would be to identify which outgoing interface triggered a given function for the original packet. For example, if an access control list (ACL) drops the packet and Dest Unreachable/ Admin Prohibited denies the packet, being able to identify the outgoing interface might be useful. Another example would be to support Path MTU Discovery (PMTUD), since this would allow identification of which outgoing interface can't support a given MTU size. For example, knowledge of the problematic interface would allow an informed request for reconfiguration of the MTU of that interface. 4. Interface Information Object This section defines the Interface Information Object, an ICMP extension object with a Class-Num (Object Class Value) of 2 that can be appended to the following messages: o ICMPv4 Time Exceeded o ICMPv4 Destination Unreachable o ICMPv4 Parameter Problem o ICMPv6 Time Exceeded o ICMPv6 Destination Unreachable For reasons described in [RFC4884], this extension cannot be appended to any of the currently defined ICMPv4 or ICMPv6 messages other than those listed above. The extension defined herein MAY be appended to any of the above listed messages and SHOULD be appended whenever required to identify an unnumbered interface and when local policy or security considerations do not supersede this requirement. A single ICMP message can contain as few as zero and as many as four instances of the Interface Information Object. It is illegal if it contains more than four instances, because that means that an interface role is used more than once (see Section 4.5). A single instance of the Interface Information Object can provide information regarding any one of the following interface roles: o the IP interface upon which a datagram arrived Atlas, et al. Standards Track [Page 6]
RFC 5837 ICMP Unnumbered April 2010 o the sub-IP component of an IP interface upon which a datagram arrived o the IP interface through which the datagram would have been forwarded had it been forwardable o the IP next hop to which the datagram would have been forwarded The following are examples of sub-IP components of IP interfaces upon which a datagram might arrive: o Ethernet Link Aggregation Group Member o Multilink PPP bundle member o Multilink frame relay bundle member To minimize the number of octets required for this extension, there are four different pieces of information that can appear in an Interface Information Object. 1. The ifIndex of the interface of interest MAY be included. This is the 32-bit ifIndex assigned to the interface by the device as specified by the Interfaces Group MIB [RFC2863]. 2. An IP Address Sub-Object MAY be included if either of the following conditions is true: a) the eliciting datagram is IPv4 and the identified interface has at least one IPv4 address associated with it, or b) the eliciting datagram is IPv6 and the identified interface has at least one IPv6 address associated with it. The IP Address Sub-Object is described in Section 4.2 of this memo. 3. An Interface Name Sub-Object, containing a string of no more than 63 octets, MAY be included. That string, as specified in Section 4.3, is the interface name and SHOULD be the MIB-II ifName [RFC2863], but MAY be some other human-meaningful name of the interface. 4. A 32-bit unsigned integer reflecting the MTU MAY be included. 4.1. C-Type Meaning in an Interface Information Object For this object, the C-Type [RFC4884] is used to indicate both the role of the interface and the information that is included. This is illustrated in Figure 1. Atlas, et al. Standards Track [Page 7]
RFC 5837 ICMP Unnumbered April 2010 Bit 0 1 2 3 4 5 6 7 +-------+-------+-------+-------+-------+-------+-------+-------+ | Interface Role| Rsvd1 | Rsvd2 |ifIndex| IPAddr| name | MTU | +-------+-------+-------+-------+-------+-------+-------+-------+ Figure 1: C-Type for the Interface Information Object The following are bit-field definitions for C-Type: Interface Role (bits 0-1): These bits indicates the role of the interface being identified. The enumerated values are given below: Value 0: This object describes the IP interface upon which a datagram arrived Value 1: This object describes the sub-IP component of an IP interface upon which a datagram arrived Value 2: This object describes the IP interface through which the datagram would have been forwarded had it been forwardable Value 3: This object describes the IP next hop to which the datagram would have been forwarded Reserved 1 (bit 2): This bit is reserved for future use and MUST be set to 0 and MUST be ignored on receipt. Reserved 2 (bit 3): This bit is reserved for future use and MUST be set to 0 and MUST be ignored on receipt. ifIndex (bit 4) : When set, the 32-bit ifIndex of the interface is included. When clear, the ifIndex is not included. IP Addr (bit 5) : When set, an IP Address Sub-Object is present. When clear, an IP Address Sub-Object is not present. The IP Address Sub-Object is described in Section 4.2 of this memo. Interface Name (bit 6): When set, an Interface Name Sub-Object is included. When clear, it is not included. The Name Sub-Object is described in Section 4.3 of this memo. MTU (bit 7): When set, a 32-bit integer representing the MTU is present. When clear, this 32-bit integer is not present. The information included does not self-identify, so this specification defines a specific ordering for sending the information that must be followed. Atlas, et al. Standards Track [Page 8]
RFC 5837 ICMP Unnumbered April 2010 If bit 4 (ifIndex) is set, then the 32-bit ifIndex MUST be sent first. If bit 5 (IP Address) is set, an IP Address Sub-Object MUST be sent next. If bit 6 (Name) is set, an Interface Name Sub-Object MUST be sent next. If bit 7 is set, an MTU MUST be sent next. The information order is thus: ifIndex, IP Address Sub-Object, Interface Name Sub-Object, and MTU. Any or all pieces of information may be present or absent, as indicated by the C-Type. Any data that follows these optional pieces of information MUST be ignored. It is valid (though pointless until additional bits are assigned by IANA) to receive an Interface Information Object where bits 4, 5, 6, and 7 are all 0; this MUST NOT generate a warning or error. 4.2. Interface IP Address Sub-Object Figure 2 depicts the Interface Address Sub-Object: 0 31 +-------+-------+-------+-------+ | AFI | Reserved | +-------+-------+-------+-------+ | IP Address .... Figure 2: Interface Address Sub-Object The IP Address Sub-Object contains the following fields: o Address Family Identifier (AFI): This 16-bit bit field identifies the type of address represented by the IP Address field. It also determines the length of that field and the length of the entire sub-object. Values for this field represent a subset of values found in the IANA registry of Address Family Numbers (available from <http://www.iana.org>). Valid values are 1 (representing a 32-bit IPv4 address) and 2 (representing a 128-bit IPv6 address). o Reserved: This 16-bit field MUST be set to zero and ignored upon receipt. o IP Address: This variable-length field represents an IP address associated with the identified interface. If the eliciting datagram was IPv4, the IP Interface Sub-Object MUST represent an IPv4 address. Likewise, if the eliciting datagram was IPv6, the IP Interface Sub-Object MUST represent an IPv6 address. Atlas, et al. Standards Track [Page 9]
RFC 5837 ICMP Unnumbered April 2010 4.3. Interface Name Sub-Object Figure 3 depicts the Interface Name Sub-Object: octet 0 1 63 +--------+-----------................-----------------+ | length | interface name octets 1-63 | +--------+-----------................-----------------+ Figure 3: Interface Name Sub-Object The Interface Name Sub-Object MUST have a length that is a multiple of 4 octets and MUST NOT exceed 64 octets. The Length field represents the length of the Interface Name Sub- Object, including the length and the interface name in octets. The maximum valid length is 64 octets. The length is constrained to ensure there is space for the start of the original packet and additional information. The second field contains the human-readable interface name. The interface name SHOULD be the full MIB-II ifName [RFC2863], if less than 64 octets, or the first 63 octets of the ifName, if the ifName is longer. The interface name MAY be some other human-meaningful name of the interface. It is useful to provide the ifName for cross- correlation with other MIB information and for human-reader familiarity. The interface name MUST be padded with ASCII NULL characters if the object would not otherwise terminate on a 4-octet boundary. The interface name MUST be represented in the UTF-8 charset [RFC3629] using the Default Language [RFC2277]. 4.4. Interface Information Object Examples Figure 4 shows a full ICMPv4 Time Exceeded message, including the Interface Information Object, which must be preceded by an ICMP Extension Structure Header and an ICMP Object Header. Both are defined in [RFC4884]. Although examples show an Interface Name Sub-Object of length 64, this is only for illustration and depicts the maximum allowable length. Atlas, et al. Standards Track [Page 10]
RFC 5837 ICMP Unnumbered April 2010 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Code | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | unused | Length | unused | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Internet Header + leading octets of original datagram | | | | // | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ver=2 | (Reserved) | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length |Class-Num=2 | C-Type=00001010b | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface ifIndex | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Name Sub-Object, 32-bit word 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Name Sub-Object, 32-bit word 16 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: ICMPv4 Time Exceeded Message with Interface Information Object Figure 5 depicts an Interface Information Object representing an incoming interface identified by ifIndex and Name. Class-Num = 2 C-Type = 00001010b // Indicates incoming interface Length = 72 (4 + 4 + 64) 0 1 2 3 +--------------+--------------+--------------+--------------+ | Interface ifIndex | +--------------+--------------+--------------+--------------+ | Length | Name, word 1 | +--------------+--------------+--------------+--------------+ ... ... +--------------+--------------+--------------+--------------+ | Name, word 16 | +--------------+--------------+--------------+--------------+ Figure 5: Incoming Interface: By ifIndex and Name Atlas, et al. Standards Track [Page 11]
RFC 5837 ICMP Unnumbered April 2010 Figure 6 depicts an Interface Information Object representing an incoming interface identified by ifIndex, IPv4 Address, and Name. Class-Num = 2 C-Type = 00001110b // Indicates incoming interface Length = 80 (4 + 4 + 8 + 64) 0 1 2 3 +--------------+--------------+--------------+--------------+ | Interface ifIndex | +--------------+--------------+--------------+--------------+ | AFI | Reserved | +--------------+--------------+--------------+--------------+ | IPv4 address | +--------------+--------------+--------------+--------------+ | Length | Name, word 1 | +--------------+--------------+--------------+--------------+ ... ... +--------------+--------------+--------------+--------------+ | Name, word 16 | +--------------+--------------+--------------+--------------+ Figure 6: Incoming Interface: by ifIndex, IPv4 Address, and Name Figure 7 depicts an Interface Information Object representing an incoming interface identified by ifIndex and IPv6 Address. Class-Num = 2 C-Type = 00001100b // Indicates incoming interface Length = 28 (4 + 4 + 20) 0 1 2 3 +--------------+--------------+--------------+--------------+ | Interface ifIndex | +--------------+--------------+--------------+--------------+ | AFI | Reserved | +--------------+--------------+--------------+--------------+ | IPv6 address, 32-bit word 1 | +--------------+--------------+--------------+--------------+ | IPv6 address, 32-bit word 2 | +--------------+--------------+--------------+--------------+ | IPv6 address, 32-bit word 3 | +--------------+--------------+--------------+--------------+ | IPv6 address, 32-bit word 4 | +--------------+--------------+--------------+--------------+ Figure 7: Incoming Interface: By ifIndex and IPv6 Address Atlas, et al. Standards Track [Page 12]
RFC 5837 ICMP Unnumbered April 2010 Figure 8 depicts an Interface Information Object representing an outgoing interface identified by ifIndex and Name. Class-Num = 2 C-Type = 10001010b // Indicates outgoing interface Length = 72 (4 + 4 + 64) 0 1 2 3 +--------------+--------------+--------------+--------------+ | Interface ifIndex | +--------------+--------------+--------------+--------------+ | Length | Name, word 1 | +--------------+--------------+--------------+--------------+ ... ... +--------------+--------------+--------------+--------------+ | Name, word 16 | +--------------+--------------+--------------+--------------+ Figure 8: Outgoing Interface: By ifIndex and Name 4.5. Usage Multiple Interface Information Objects MAY be included within a single ICMP message, provided that each Interface Information Object specifies a unique role. A single ICMP message MUST NOT contain two Interface Information Objects that specify the same role. ifIndex, MTU, and name information MAY be included whenever it is available; more than one instance of each of these three information elements MUST NOT be included per Interface Information Object. A single instance of IP Address information MAY be included in an Interface Information Object under the following circumstances: o if the eliciting datagram is IPv4 and an IPv4 address is associated with the identified interface. In this case, if an IP Address Sub-Object is included, it must specify an IPv4 address. o if the eliciting datagram is IPv6 and an IPv6 address is associated with the identified interface. In this case, if an IP Address Sub-Object is included, it must specify an IPv6 address. In all other circumstances, IP address information MUST NOT be included. An ICMP message that does not conform to these rules and contains multiple instances of the same information is considered illegal; specifically, an ICMP message containing more than one Interface Atlas, et al. Standards Track [Page 13]
RFC 5837 ICMP Unnumbered April 2010 Information Object with the same role, as well as an ICMP message containing a duplicate information element in a given role are considered illegal. If such an illegal ICMP message is received, it MUST be silently discarded. 5. Network Address Translation Considerations [RFC5508] encourages Traditional IP Network Address Translators (Traditional NATs; see [RFC3022]) to support ICMP extension objects. This document defines an ICMP extension that includes IP addresses and therefore contains realm-specific information, and consequently describes possible NAT behaviors in the presence of these extensions. NAT devices MUST NOT translate or overwrite the ICMP extensions described herein. That is, they MUST either remove the extension entirely or pass it unchanged. It is conceivable that a NAT device might translate an ICMP header without translating the extension defined herein. In this case, the ICMP message might contain two instances of the same address, one translated and the other untranslated. Therefore, application developers should not assume addresses in the extension are of the same realm as the addresses in the datagram's header. It also is conceivable that a NAT device might translate an ICMPv4 message into ICMPv6 or vice versa. If that were to occur, applications might receive ICMPv6 messages that contain IP Address Sub-Objects that specify IPv4 addresses. Likewise, applications might receive ICMPv4 messages that contain IP Address Sub-Objects that specify IPv6 addresses. 6. Security Considerations This extension can provide the user of traceroute with additional network information that is not currently available. Implementations SHOULD provide configuration switches that suppress the generation of this extension based upon role (i.e., incoming interface, outgoing interface, sub-IP data). Implementations SHOULD also provide configuration switches that conceal various types of information (e.g., ifIndex, interface name). It may be desirable to provide this information to a particular network's operators and not to others. If such policy controls are desirable, then an implementation could determine what sub-objects to include based upon the destination IP address of the ICMP message that will contain the sub-objects. The implementation of policy controls could also be based upon the mechanisms described in [TRACEROUTE-EXT] for those limited cases supported. Atlas, et al. Standards Track [Page 14]
RFC 5837 ICMP Unnumbered April 2010 For instance, the IP address may be included for all potential recipients. The ifIndex and interface name could be included as well if the destination IP address is a management address of the network that has administrative control of the router. Another example use case would be where the detailed information in these extensions may be provided to ICMP destinations within the local administrative domain, but only traditional information is provided to 'external' or untrusted ICMP destinations. The intended field of use for the extensions defined in this document is administrative debugging and troubleshooting. The extensions herein defined supply additional information in ICMP responses. These mechanisms are not intended to be used in non-debugging applications. This document does not specify an authentication mechanism for the extension that it defines. Application developers should be aware that ICMP messages and their contents are easily spoofed. 7. IANA Considerations IANA has reserved 2 for the Interface Information Object from the ICMP Extension Object Classes registry available from <http://www.iana.org>. From the Interface Information Object's C-Type, IANA has reserved values as follows: o Bit 0-1: Interface Role field o Bit 2: Unallocated - allocatable with Standards Action o Bit 3: Unallocated - allocatable with Standards Action o Bit 4: ifIndex included o Bit 5: IP Address Sub-Object included o Bit 6: Name Sub-Object included o Bit 7: MTU included IANA has reserved the following values for Interface Role: o Value 0: Incoming IP Interface o Value 1: Sub-IP Component of Incoming IP Interface Atlas, et al. Standards Track [Page 15]
RFC 5837 ICMP Unnumbered April 2010 o Value 2: Outgoing IP Interface o Value 3: IP Next Hop 8. Acknowledgments The authors would like to thank Sasha Vainshtein, Enke Chen, and Joe Touch for their comments and suggestions. They would also like to thank Dr. Ali Assefi. 9. References 9.1. Normative References [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, September 1981. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group MIB", RFC 2863, June 2000. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [RFC4443] Conta, A., Deering, S., and M. Gupta, "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", RFC 4443, March 2006. [RFC4884] Bonica, R., Gan, D., Tappan, D., and C. Pignataro, "Extended ICMP to Support Multi-Part Messages", RFC 4884, April 2007. 9.2. Informative References [RFC1122] Braden, R., "Requirements for Internet Hosts - Communication Layers", STD 3, RFC 1122, October 1989. [RFC1812] Baker, F., "Requirements for IP Version 4 Routers", RFC 1812, June 1995. [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and Languages", BCP 18, RFC 2277, January 1998. Atlas, et al. Standards Track [Page 16]
RFC 5837 ICMP Unnumbered April 2010 [RFC3022] Srisuresh, P. and K. Egevang, "Traditional IP Network Address Translator (Traditional NAT)", RFC 3022, January 2001. [RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT Behavioral Requirements for ICMP", BCP 148, RFC 5508, April 2009. [TRACEROUTE-EXT] Shen, N., Pignataro, C., Asati, R., and E. Chen, "UDP Traceroute Message Extension", Work in Progress, June 2008. Atlas, et al. Standards Track [Page 17]
RFC 5837 ICMP Unnumbered April 2010 Authors' Addresses Alia K. Atlas (editor) BT EMail: alia.atlas@bt.com Ronald P. Bonica (editor) Juniper Networks 2251 Corporate Park Drive Herndon, VA 20171 USA EMail: rbonica@juniper.net Carlos Pignataro (editor) Cisco Systems 7200-12 Kit Creek Road PO Box 14987 Research Triangle Park, NC 27709 USA EMail: cpignata@cisco.com Naiming Shen Cisco Systems 225 West Tasman Drive San Jose, CA 95134 USA EMail: naiming@cisco.com JR. Rivers Consultant EMail: jrrivers@yahoo.com Atlas, et al. Standards Track [Page 18]

   

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