Internet A. Atlas, Ed. Internet-Draft BT Expires: May 19, 2008 R. Bonica Juniper Networks JR. Rivers Nuova Systems N. Shen E. Chen Cisco Systems Nov 16, 2007 Extending ICMP to Identify the Receiving Interface draft-atlas-icmp-unnumbered-04 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on May 19, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This memo defines ICMP extensions, using ICMP multi-part messages, through which a router or host can explicitly identify the interface Atlas, et al. Expires May 19, 2008 [Page 1] Internet-Draft ICMP Unnumbered Nov 2007 upon which an undeliverable datagram anrrived. The incoming interface can be identified by ifIndex, name, and/or address, as already used in MIBs and by OSPF. The extensions defined herein are particularly useful when troubleshooting networks with unnumbered interfaces, parallel interfaces and/or asymmetric routing. Table of Contents 1. Conventions Used In This Document . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Applications . . . . . . . . . . . . . . . . . . . . . . . . . 4 3.1. Application to TRACEROUTE . . . . . . . . . . . . . . . . 4 3.2. Policy and MTU Detection . . . . . . . . . . . . . . . . . 4 4. Interface Information Object . . . . . . . . . . . . . . . . . 5 4.1. C-type meaning in an Interface Information Object . . . . 5 4.2. Interface Name Sub-Object . . . . . . . . . . . . . . . . 7 4.3. Interface Information Object Description . . . . . . . . . 8 4.4. Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 10 5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11 8.1. Normative References . . . . . . . . . . . . . . . . . . . 11 8.2. Informative References . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12 Intellectual Property and Copyright Statements . . . . . . . . . . 14 Atlas, et al. Expires May 19, 2008 [Page 2] Internet-Draft ICMP Unnumbered Nov 2007 1. 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 RFC2119 [RFC2119]. 2. Introduction IP devices use the Internet Control Message Protocol (ICMP) [RFC0792] (ICMPv6) [RFC4443] to convey control information. In particular, when an IP device receives a datagram that it cannot forward, 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 nominal case, the source address of the ICMP message identifies the interface upon which the non-forwardable datagram arrived. However, in many cases, the incoming interface is not identified by the ICMP message at all. Details follow: According to RFC1812 [RFC1812], when a router generates an ICMP message, the source address of that ICMP message MUST be one of the following: o one of the IP addresses associated with the physical interface over which the ICMP 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 the following conditions are true, the source address of the ICMP message identifies the interface upon which the non-forwardable datagram arrived: o the device originates an ICMP message through the same interface upon which the non-forwardable datagram was received. o that interface is numbered. However, the transmitting and incoming interfaces may be different due to an asymmetric return path, which can occur due to asymmetric link costs, parallel links or ECMP. For ICMPv6, the asymmetric issues need not be an issue, since there is more flexibility for ICMPv6, as defined in RFC4443 [RFC4443]. For responses to messages sent to addresses that aren't the router's, the source address must be chosen as follows: Atlas, et al. Expires May 19, 2008 [Page 3] Internet-Draft ICMP Unnumbered Nov 2007 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 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. For both ICMP and ICMPv6, when a network uses unnumbered interfaces, it is not possible to identify the incoming interface. The extensions defined in this memo permit an ICMP originator to identify the interface through which the datagram that elicited the ICMP messages arrived. Using the extension defined herein, an IP device can explicitly identify the incoming interface by any or all of the following: o IPv4 address o IPv6 address o name o ifIndex Using the extension defined herein, 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. This can be used for creating a downstream map. The extensions defined herein use the ICMP multi-part message framework defined in [RFC4884]. The same backward compatibility issues that apply to [RFC4884] apply to these extensions. 3. Applications 3.1. Application to TRACEROUTE ICMP extensions defined in this memo require enhancements ([RFC4884]) and provide additional capability to TRACEROUTE. The enhanced TRACEROUTE application, like older implementations, indicates which nodes the original datagram visited en route to its destination. It differs from older implementations in that it also reflects the incoming interface on which the original triggering packet arrived, even when that interface is unnumbered. 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 Atlas, et al. Expires May 19, 2008 [Page 4] Internet-Draft ICMP Unnumbered Nov 2007 an ACL drops the packet and Dest Unreachable/Admin Prohibited denies the packet, being able to identify that might be useful. Another example would be support PMTU, since this would allow identification of which outgoing interface can't support a given MTU size. 4. Interface Information Object This section defines an ICMP extension object that can be appended to the ICMPv4 Time Exceeded, ICMPv4 Destination Unreachable, ICMPv4 Parameter Problem, ICMPv6 Time Exceeded, and ICMPv6 Destination Unreachable messages, as described in [RFC4884]. For the description of the Interface Information Object, the incoming interface is the one upon which the packet which triggered the ICMP message was received. If desired, information about a sub-IP member of the incoming interface can be included. An example of such a sub-IP member would be a member of an Ethernet Link Aggregation Group that forms the incoming interface. To minimize the use of extra octets required for this extension, there are four different pieces of information that can appear in an Interface Information Object. 1. If the interface of interest has at least one IPv4 address and the triggering packet was IPv4, then one of the interface's IPv4 addresses MAY be included. 2. If the interface of interest has at least one IPv6 address and the triggering packet was IPv6, then one of the interface's IPv6 addresses MAY be included. 3. The ifIndex of the interface of interest MAY be included. This is the ifIndex assigned to the interface by the router in as specified by the Interfaces Group MIB [RFC2863]. 4. An Interface Name Sub-Object, containing a string of no more than 62 octets, MAY be included. 4.1. C-type meaning in an Interface Information Object For this object, the c-type is split into two fields, a 2-bit interface-role field and a 6-bit included-information field. This is illustrated below. Atlas, et al. Expires May 19, 2008 [Page 5] Internet-Draft ICMP Unnumbered Nov 2007 Bit 7 6 | 5 4 3 2 1 0 +-------+-------+-------+-------+-------+-------+-------+-------+ | Interface Role| Rsvd | Rsvd | index | IP | Rsvd | descr | +-------+-------+-------+-------+-------+-------+-------+-------+ Interface Role: This 2-bit field [6:7] indicates the role of the interface being identified. The enumerated values are given below. 0 : This object describes the incoming interface. 1 : This object describes the outgoing interface. 2 : This object describes a sub-IP member of the incoming interface. 3 : Reserved Included Information: This 6-bit field [0:5] indicates what information is included in the object. The information must be included in the same order as the bits (leftmost, from highest, 5, to lowest, 0,). bit 5 : This bit is reserved for future use and MUST be set to 0 and MUST be ignored on receipt. 4 : This bit is reserved for future use and MUST be set to 0 and MUST be ignored on receipt. 3 : When set, this bit indicates the ifIndex of the interface is included. When clear, the ifIndex is not included. 2 : When set, this indicates an IP address of the interface is included. When clear, no IP address is included. The version of the IP packet containing the ICMP message will indicate the type of IP address. An IPv4 packet will have an IPv4 address and an IPv6 packet will have an IPv6 address. 1 : This bit is reserved for future use and MUST be set to 0 and MUST be ignored on receipt. 0 : When set, this indicates an Interface Name Sub-object for the interface is included. When clear, it is not included. Figure 1: C-Type for the Interface Information Object The information/sub-objects MUST be sent and received inside the Interface Information Object in the order that they are listed in the final 6-bits included-information field. With the exception of the Atlas, et al. Expires May 19, 2008 [Page 6] Internet-Draft ICMP Unnumbered Nov 2007 Interface Name sub-object, the information included does not self- identify, so this is required to ensure correct parsing. The sender of an Interface Information Object MUST NOT set the Interface Role to 3 and an Interface Role value of 3 MUST be ignored on receipt and the Interface Information Object discarded. It is valid (though pointless until additional bits are assigned by IANA) to receive an Interface Information Object where bits 3,2, and 0 are all 0; this MUST NOT generate a warning or error. 4.2. 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. A one octet "charset type" and a one octet "length" are required and the interface name can be at most 62 octets long. The interface name SHOULD be the MIB-II ifName [RFC2863] but MAY be some other human-meaningful name of the interface. It is useful to rovide the ifName for cross- correlation with other MIB information and for human-reader familiarity. The Interface Name Sub-Object consists of three fields. The first 1-octet field indicates the character set type used by the second field. The second field contains the length of the Interface name Sub-object, including the charset type, the length, and the human- readable 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 third field contains the human-readable name. octet 0 1 2 63 +--------------+--------+---..............-----------------+ | charset type | length | interface name octets 1-62 | +--------------+--------+---..............-----------------+ Figure 2: Interface Name Sub-Object charset type 0 : This indicates that the human-readable interface name MUST be provided in the US-ASCII charset [US-ASCII] using the Default Language [RFC2277]. charset type 1 : This indicates that the human-readable interface name MUST be provided in the UTF-8 charset [RFC3629] using the Default Language [RFC2277]. Atlas, et al. Expires May 19, 2008 [Page 7] Internet-Draft ICMP Unnumbered Nov 2007 4.3. Interface Information Object Description Figure 3 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]. Figure 4 depicts the Interface Information Object, with two of the valid permutations. Although all examples show an Interface Name Sub-object of length 64, this is only for illustration and depicts the maximum allowable length. 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=9 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface ifIndex | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Name, 32-bit word 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ... ... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface Name , 32-bit word 16 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: ICMPv4 Time Exceeded message with Interface Information Object Class-Num = 2 Example 1: Unnumbered Interface with ifIndex and interface name Atlas, et al. Expires May 19, 2008 [Page 8] Internet-Draft ICMP Unnumbered Nov 2007 C-Type = 00001001b // Indicates incoming interface Length = 40 (4 + 4 + 32) 0 1 2 3 +--------------+--------------+--------------+--------------+ | Interface ifIndex | +--------------+--------------+--------------+--------------+ | Interface Name, 32-bit word 1 | +--------------+--------------+--------------+--------------+ ... ... +--------------+--------------+--------------+--------------+ | Interface Name , 32-bit word 16 | +--------------+--------------+--------------+--------------+ Example 2: IPv4 interface with IPv4 address, ifIndex and interface name C-Type = 00001101b // Indicates incoming interface Length = 44 (4 + 4 + 4 + 32) 0 1 2 3 +--------------+--------------+--------------+--------------+ | Interface ifIndex | +--------------+--------------+--------------+--------------+ | IPv4 address | +--------------+--------------+--------------+--------------+ | Interface Name, 32-bit word 1 | +--------------+--------------+--------------+--------------+ ... ... +--------------+--------------+--------------+--------------+ | Interface Name, 32-bit word 16 | +--------------+--------------+--------------+--------------+ Example 3: IPv6 interface with IPv6 address and ifIndex C-Type = 00001100b // Indicates incoming interface Length = 24 (4 + 4 + 16) 0 1 2 3 +--------------+--------------+--------------+--------------+ | Interface ifIndex | +--------------+--------------+--------------+--------------+ | IPv6 address, 32-bit word 1 | +--------------+--------------+--------------+--------------+ | IPv6 address, 32-bit word 2 | +--------------+--------------+--------------+--------------+ Atlas, et al. Expires May 19, 2008 [Page 9] Internet-Draft ICMP Unnumbered Nov 2007 | IPv6 address, 32-bit word 3 | +--------------+--------------+--------------+--------------+ | IPv6 address, 32-bit word 4 | +--------------+--------------+--------------+--------------+ Figure 4: Interface Information Object 4.4. Usage For each interface described by an included Interface Information Object, these are the rules for the information to be included. If the interface in question is unnumbered, then the Interface Information Object SHOULD include the ifIndex and SHOULD NOT include an IP address. If the interface in question is numbered, then the Interface Information Object SHOULD include the IP address. Other fields MAY be included in the Interface Information Object. In an ICMP message, more than one Interface Information Object with a given interface role MUST NOT be included. Multiple Interface Information Objects, each with a different interface role, MAY be included. 5. Security Considerations This extension can provide the user of traceroute with additional network information that is not currently available. 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. 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. Another issue is when a device inside a private region generates an ICMP message with some of these extensions and that ICMP message will transit a NAT to reach its destination. A NAT may choose to remove or overwrite the extensions. Atlas, et al. Expires May 19, 2008 [Page 10] Internet-Draft ICMP Unnumbered Nov 2007 6. IANA Considerations IANA should should reserve from the ICMP Extension Object registry: 2 for the Interface Information Object. From the Interface ID Object's c-type, IANA should reserve as follows: o Bit 0: Interface Name Sub-Object included o Bit 1: Unallocated - allocatable with Standards Action o Bit 2: IP address included o Bit 3: ifIndex include o Bit 4: Unallocated - allocatable with Standards Action o Bit 5: Unallocated - allocatable with Standards Action o Bit 6-7: Interface Role field * Value 0: Incoming Interface * Value 1: Outgoing Interface * Value 2: Incoming Interface - Sub-IP Member * Value 3: Unallocated - allocatable with Standards Action Additionally, the Interface Name Sub-Object has a 1 octet charset type field. IANA should create a registry for it and allocate as follows: o 0 : encoded in ASCII o 1 : encoded in UTF-8 o 2-127: Unallocated - allocatable with Standards Action o 128-255: Unallocated - allocated on first come basis. 7. Acknowledgements The authors would like to thank Carlos Pignataro, Sasha Vainshtein, and Joe Touch for their comments and suggestions. 8. References 8.1. 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. Atlas, et al. Expires May 19, 2008 [Page 11] Internet-Draft ICMP Unnumbered Nov 2007 [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. 8.2. Informative References [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. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [US-ASCII] "Coded Character Set -- 7-bit American Standard Code for Information Interchange, ANSI X3.4-1986". Authors' Addresses Alia K. Atlas (editor) BT Email: alia.atlas@bt.com Ronald P. Bonica Juniper Networks 2251 Corporate Park Drive Herndon, VA 20171 USA Email: rbonica@juniper.net J.R. Rivers Nuova Systems Email: jrrivers@nuovasystems.com Atlas, et al. Expires May 19, 2008 [Page 12] Internet-Draft ICMP Unnumbered Nov 2007 Naiming Shen Cisco Systems 225 West Tasman Drive San Jose, CA 95134 USA Email: naiming@cisco.com Enke Chen Cisco Systems 170 West Tasman Drive San Jose, CA 95134 USA Email: enkechen@cisco.com Atlas, et al. Expires May 19, 2008 [Page 13] Internet-Draft ICMP Unnumbered Nov 2007 Full Copyright Statement Copyright (C) The IETF Trust (2007). 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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 ietf-ipr@ietf.org. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Atlas, et al. Expires May 19, 2008 [Page 14]