| Internet-Draft | ICMP extension to include underlay infor | June 2024 |
| Rajamanickam, et al. | Expires 20 December 2024 | [Page] |
Network operators operating overlay networks require the ability to identify hops in an underlay network when traceroute in the overlay. This document defines an ICMP Error extension message to carry the underlay error information to the overlay network endpoint.¶
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The mechanism allowing ICMP messages to carry additional information is [RFC4884]. ICMP message extensions, describing the mechanisms for extending ICMP messages to carry additional information about the system where the error occurred are defined in [RFC5837], [RFC8335] and [RFC8883]. These messages are transmitted to the source node to provide deeper insight into the error in relation to the node where it occurred.¶
Network operators who administer and overlay and underlay network, such as those with VPN segmentation within their network and an SRv6 core connecting them, find it particularly useful to have ICMP underlay information transmitted to source nodes for the purpose of using traceroute. This ICMP underlay information provides details about errors and failures in the underlay network.¶
The underlay error information described in this document satisfy the need of these network operators.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
This section defines a new ICMP extension object called Underlay Information Object (UIO) that is encoded as part of ICMP extension message. A new Class-Num value TBA (To Be Assigned) is assigned to identify the UIO. As per [RFC4884], this object MAY be appended to one of the following ICMP messages:¶
ICMPv4 Time Exceeded¶
ICMPv4 Destination Unreachable¶
ICMPv4 Parameter Problem¶
ICMPv6 Time Exceeded¶
ICMPv6 Destination Unreachable¶
This section described the UIO object format.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length | Class-Num=TBA | C-Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ ~ Object-Payload (Other ICMP Extension Objects...) ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
UIO ICMP extension object contains the following fields:¶
Length: 16 bits¶
Length of the object, measured in octets, including UIO ICMP extension object header and object payload¶
Class-Num: 8 bits¶
Identifies object class. In the case of UIO, a new value TBA will be assigned from IANA "ICMP Extension Object Classes and Class Sub-types" registry. This object could co-exist with the other ICMP extension objects¶
C-Type: 8 bits¶
Identifies object sub-type. This value MUST be transmitted as zeros and ignored upon receipt.¶
Object-Payload: Variable Length¶
UIO Object payload contains one or more other ICMP Extension Objects that are related to the underlay nodes.¶
This ICMP extension object acts as an envelope to carry other ICMP extension objects related to the underlay. Primarily, the UIO ICMP extension object is encoded in the ICMP extension message by the underlay head-end when it receives an ICMP error message from one of its intermediate nodes.¶
This UIO ICMP extension object can encapsulate one or more relevant ICMP extension objects that are related to the underlay node. When the underlay head-end encodes its ICMP extension object, the first object MUST contain the ICMP extension object that carries IP address or the hostname of the node where the initial ICMP error was generated. The ICMP extension objects encoded within the UIO ICMP extension objects can belong to any address family, irrespective of the address family of the source node that decapsulates the UIO ICMP extension objects, as opposed to what is stated in [RFC5837] Section 4.2.¶
When the UIO is encoded, the total length of the ICMP message, including extensions, MUST NOT exceed the minimum reassembly buffer size.¶
If the node decoding the ICMP extension header does not recognize the UIO ICMP extension message, it SHOULD ignore this message and continue processing the other messages.¶
An underlay head-end node generates an ICMP error directed to a host in the overlay network. The specifics of the ICMP error content are beyond the scope of this document. The error is triggered by the receipt of an underlay error message from an IPv4/IPv6 interface. The encoding and processing of the underlay error are also outside the scope of this document.¶
The underlay head-end appends a UIO ICMP extension object to the ICMP error it generates to the overlay host.¶
In most of the cases the overlay and underlay networks are owned by different operators, so it may not be advisable to permit the transmission of the underlay information to an arbitrary recipient. The inclusion of this information should be configurable and must default to being disabled. An implementation should decide which objects can be appended as part of the UIO ICMP extension message.¶
The extensions defined in this document are intended for use in administrative debugging and troubleshooting. They provide additional information in ICMP responses. These mechanisms are not designed for use in non-debugging applications.¶
This document requests that IANA allocate a value (TBA - To Be Assigned) for the UIO ICMP extension object class value from the "ICMP Extension Object Classes and Class Sub-types" registry to indicate the presence of the UIO ICMP extension class, referred to as TBA above.¶
This section lists the UIO example encoding format¶
In this example, a host receives an IPv4 ICMPv4 Time Exceeded error message in response to an ICMP Echo Request as part of the traceroute application. It also contains an UIO ICMP extension object with IPv6 interface address information as follows.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ ~ IPv4 Header ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type=11 | Code=0 | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Unused | Length=32 | Unused | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ ~ Part of Original Datagram (128 bytes) ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ver=2 | Unused | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length=28 | Class-Num=TBA | C-Type=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length=24 | Class-Num=2 | C-Type=4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AFI=2 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ ~ IPv6 Address (Original Error Device) ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The traceroute application displays the IPv6 Address in the UIO to allow an administrator to trace the underlay path of the route being traced.¶
In this example, a host receives an IPv6 ICMPv6 Time Exceeded error message in response to an ICMP Echo Request as part of the traceroute application. It contains a UIO ICMP extension object with IPv4 interface address information as follows.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ ~ IPv6 Header ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type=3 | Code=0 | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length=32 | Unused | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ~ ~ Part of Original Datagram (128 bytes) ~ ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Ver=2 | Unused | Checksum | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length=16 | Class-Num=TBA | C-Type=0 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Length=12 | Class-Num=2 | C-Type=4 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | AFI=1 | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Address (Original Error Device) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The traceroute application displays the IPv4 Address in the UIO to allow an administrator to trace the underlay path of the route being traced.¶
This document derives text heavily from [RFC4884] and [RFC5837].¶
The following people have substantially contributed to this document:¶
Tamilselvan Murugan Cisco Systems, Inc. Email: tammurug@cisco.com Dhilip Sekar Cisco Systems, Inc. Email: dhsekar@cisco.com