| Internet-Draft | IPv6 Compressed Routing Header | January 2024 |
| Bonica, et al. | Expires 7 July 2024 | [Page] |
This document describes an experiment in which two new IPv6 Routing headers are implemented and deployed. Collectively, they are called the Compact Routing Headers (CRH). Individually, they are called CRH-16 and CRH-32.¶
One purpose of this experiment is to demonstrate that the CRH can be implemented and deployed in a production network. Another purpose is to demonstrate that the security considerations, described in this document, can be addressed with access control lists. Finally, this document encourages replication of the experiment.¶
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IPv6 [RFC8200] source nodes use Routing headers to specify the path that a packet takes to its destination. The IETF has defined several Routing header types [IANA-RH]. This document defines two new Routing header types. Collectively, they are called the Compact Routing Headers (CRH). Individually, they are called CRH-16 and CRH-32.¶
The CRH allows IPv6 source nodes to specify the path that a packet takes to its destination. The CRH can be encoded in relatively few bytes. The following are reasons for encoding the CRH in as few bytes as possible:¶
Many ASIC-based forwarders copy headers from buffer memory to on-chip memory. As header sizes increase, so does the cost of this copy.¶
Because Path MTU Discovery (PMTUD) [RFC8201] is not entirely reliable, many IPv6 hosts refrain from sending packets larger than the IPv6 minimum link MTU (i.e., 1280 bytes). When packets are small, the overhead imposed by large Routing Headers is excessive.¶
This document describes an experiment whose purposes are:¶
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.¶
Both CRH versions (i.e., CRH-16 and CRH-32) contain the following fields:¶
In the CRH, the Type-specific data field contains a list of Segment Identifiers (SIDs). Each SID identifies an entry in the CRH Forwarding Information Base (CRH-FIB) (Section 4). Each CRH-FIB entry identifies an interface on the path that the packet takes to its destination.¶
SIDs are listed in reverse order. So, the first SID in the list represents the final interface in the path. Because segments are listed in reverse order, the Segments Left field can be used as an index into the SID list. In this document, the "current SID" is the SID list entry referenced by the Segments Left field.¶
The first segment in the path can be omitted from the list. See Appendix A an example.¶
In the CRH-16 (Figure 1), each SID is encoded in 16-bits. In the CRH-32 (Figure 2), each SID is encoded in 32-bits.¶
In all cases, the CRH MUST end on a 64-bit boundary. So, the Type- specific data field MUST be padded with zeros if the CRH would otherwise not end on a 64-bit boundary.¶
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | Routing Type | Segments Left | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID[0] | SID[1] | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| | ......... +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Next Header | Hdr Ext Len | Routing Type | Segments Left | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + SID[0] + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + SID[1] + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ // // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + SID[n] + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Each SID identifies a CRH-FIB entry.¶
Each CRH-FIB entry contains:¶
The topological function specifies how the processing node forwards the packet to the interface identified by the IPv6 address. The following are examples:¶
Forward the packet through the least-cost path to the interface identified by the IPv6 address (i.e., loose source routing).¶
Forward the packet through a specified interface to the interface identified by the IPv6 address (i.e.,strict source routing)¶
Some topological functions require parameters. For example, a topological function might require a parameter that identifies the interface through which the packet is forwarded.¶
The CRH-FIB can be populated:¶
By an operator, using a Command Line Interface (CLI).¶
By a controller, using the Path Computation Element (PCE) Communication Protocol (PCEP) [RFC5440] or the Network Configuration Protocol (NETCONF) [RFC6241].¶
By a distributed routing protocol [ISO10589-Second-Edition], [RFC5340], [RFC4271].¶
The following rules describe CRH processing:¶
If Segments Left equals 0, skip over the CRH and process the next header in the packet.¶
If Hdr Ext Len indicates that the CRH is larger than the implementation can process, discard the packet and send an ICMPv6 [RFC4443] Parameter Problem, Code 0, message to the Source Address, pointing to the Hdr Ext Len field.¶
Compute L, the minimum CRH length ( Section 5.1).¶
If L is greater than Hdr Ext Len, discard the packet and send an ICMPv6 Parameter Problem, Code 0, message to the Source Address, pointing to the Segments Left field.¶
Decrement Segments Left.¶
Search for the current SID in the CRH-FIB. In this document, the "current SID" is the SID list entry referenced by the Segments Left field.¶
If the search does not return a CRH-FIB entry, discard the packet and send an ICMPv6 Parameter Problem, Code 0, message to the Source Address, pointing to the current SID.¶
If Segments Left is greater than 0 and the CRH-FIB entry contains a multicast address, discard the packet and send an ICMPv6 Parameter Problem, Code 0, message to the Source Address, pointing to the current SID.¶
Copy the IPv6 address from the CRH-FIB entry to the Destination Address field in the IPv6 header.¶
Decrement the IPv6 Hop Limit.¶
Submit the packet, its topological function and its parameters to the IPv6 module. See NOTE.¶
NOTE: By default, the IPv6 module determines the next-hop and forwards the packet. However, the topological function may elicit another behavior. For example, the IPv6 module may forward the packet through a specified interface.¶
The algorithm described in this section accepts the following CRH fields as its input parameters:¶
It yields L, the minimum CRH length. The minimum CRH length is measured in 8-octet units, not including the first 8 octets.¶
<CODE BEGINS>
switch(Routing Type) {
case CRH-16:
if (Segments Left <= 2)
return(0)
sidsBeyondFirstWord = Segments Left - 2;
sidPerWord = 4;
case CRH-32:
if (Segments Left <= 1)
return(0)
sidsBeyondFirstWord = Segments Left - 1;
sidsPerWord = 2;
case default:
return(0xFF);
}
words = sidsBeyondFirstWord div sidsPerWord;
if (sidsBeyondFirstWord mod sidsPerWord)
words++;
return(words)
<CODE ENDS>¶
In the CRH, the Segments Left field is mutable. All remaining fields are immutable.¶
A CRH contains one or more SIDs. Each SID is processed by exactly one node.¶
Therefore, a SID is not required to have domain-wide significance. Applications can:¶
PING and TRACEROUTE [RFC2151] both operate correctly in the presence of the CRH. TCPDUMP and Wireshark have been extended to support the CRH.¶
A 16-bit SID is represented by a colon (:) followed by four hexadecimal digits. Leading zeros can be omitted. The following are examples:¶
A 32-bit SID is represented by a colon (:), four hexadecimal digits, another colon (:), and another four hexadecimal digits. Leading zeros can be omitted. The following are examples:¶
In this document, one node trusts another only if both nodes are operated by the same party.¶
A node can encounter security vulnerabilities by indiscriminately processing packets that contain Routing Headers [RFC5095]. Therefore, nodes MUST discard packets containing the CRH when both of the following conditions are true:¶
The Source Address does not identify an interface on a trusted node.¶
The Destination Address identifies an interface on the local node.¶
The above-state rule does not protect the node from attack packets that contain a forged (i.e., spoofed) Source Address. In order to mitigate this risk, nodes MAY also discard packets containing the CRH when all of the following conditions are true:¶
The Source Address identifies an interface on a trusted node.¶
The Destination Address identifies an interface on the local node.¶
The packet does not pass an Enhanced Feasible-Path Unicast Reverse Path Forwarding (RPF) [RFC8704],¶
The RPF check eliminates some, but not all packets with forged source addresses. Therefore, a network operator that deploys CRH MUST implement Access Control Lists (ACL) on each of its edge nodes. The ACL discards packets whose source address identifies an interface on a trusted node.¶
Juniper Networks has produced experimental implementations of the CRH on the MX-series (ASIC-based) router¶
Liquid Telecom has produced experimental implementations of the CRH on software based routers.¶
The CRH has carried non-production traffic in CERNET and Liquid Telecom.¶
This document makes the following registrations in the "Internet Protocol Version 6 (IPv6) Parameters" "Routing Types" subregistry maintained by IANA:¶
+-------+------------------------------+---------------+
| Value | Description | Reference |
+=======+==============================+===============+
| 5 | CRH-16 | This document |
+-------+------------------------------+---------------+
| 6 | CRH-32 | This document |
+-------+------------------------------+---------------+
¶
Thanks to Dr. Vanessa Ameen, Dale Carder, Brian Carpenter, Fernando Gont, Naveen Kottapalli, Joel Halpern, Mark Smith, Reji Thomas, Tony Li, Xing Li, Gerald Schmidt, Nancy Shaw, Ketan Talaulikar, and Chandra Venkatraman for their contributions to this document.¶
Gang Chen¶
Baidu¶
No.10 Xibeiwang East Road Haidian District¶
Beijing 100193 P.R. China¶
Email: phdgang@gmail.com¶
This appendix demonstrates CRH processing in the following scenarios:¶
The SID list contains one entry for each segment in the path (Appendix A.1).¶
The SID list omits the first entry in the path (Appendix A.2).¶
----------- ----------- -----------
|Node: S | |Node: I1 | |Node: I2 |
|Loopback: |---------------|Loopback: |---------------|Loopback: |
|2001:db8::a| |2001:db8::1| |2001:db8::2|
----------- ----------- -----------
| |
| ----------- |
| |Node: D | |
---------------------|Loopback: |---------------------
|2001:db8::b|
-----------
Figure 3 provides a reference topology that is used in all examples.¶
| SID | IPv6 Address | Forwarding Method |
|---|---|---|
| 2 | 2001:db8::2 | Least-cost path |
| 11 | 2001:db8::b | Least-cost path |
Table 1 describes two entries that appear in each node's CRH-FIB.¶
In this example, Node S sends a packet to Node D, via I2. In this example, I2 appears in the CRH segment list.¶
| As the packet travels from S to I2: | |
|---|---|
| Source Address = 2001:db8::a | Segments Left = 1 |
| Destination Address = 2001:db8::2 | SID[0] = 11 |
| SID[1] = 2 |
| As the packet travels from I2 to D: | |
|---|---|
| Source Address = 2001:db8::a | Segments Left = 0 |
| Destination Address = 2001:db8::b | SID[0] = 11 |
| SID[1] = 2 |
In this example, Node S sends a packet to Node D, via I2. In this example, I2 does not appear in the CRH segment list.¶
| As the packet travels from S to I2: | |
|---|---|
| Source Address = 2001:db8::a | Segments Left = 1 |
| Destination Address = 2001:db8::2 | SID[0] = 11 |
| As the packet travels from I2 to D: | |
|---|---|
| Source Address = 2001:db8::a | Segments Left = 0 |
| Destination Address = 2001:db8::b | SID[0] = 11 |