Juniper Networks

2251 Corporate Park Drive Herndon 20171 Virginia USA rbonica@juniper.net

NTT Communications Corporation

3-4-1 Shibaura, Minato-ku Tokyo 108-8118 Japan y.kamite@ntt.com

KDDI

3-22-7, Yoyogi, Shibuya-ku Tokyo 151-0053 Japan to-niwa@kddi.com

Liquid Telecom

Nairobi Kenya Andrew.Alston@liquidtelecom.com

Verizon

Richardson Texas USA luay.jalil@one.verizon.com

INT Area 6man IPv6 Routing header This document defines two new Routing header types. Collectively, they are called the Compressed Routing Headers (CRH). Individually, they are called CRH-16 and CRH-32.

IPv6 source nodes use Routing headers to specify the path that a packet takes to its destination. The IETF has defined several Routing header types. This document defines two new Routing header types. Collectively, they are called the Compressed 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. Is designed to operate within a network domain. (See ). The following are reasons for encoding the CRH in as few bytes as possible: Many ASIC-based forwarders copy all headers from buffer memory to on-chip memory. As header sizes increase, so does the cost of this copy. Because Path MTU Discovery (PMTUD) 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. of this document addresses security considerations. of this document demonstrates how the CRH can be encoded in fewer bytes than RH0.

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 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: Next Header - Defined in . Hdr Ext Len - Defined in . Routing Type - Defined in . Value TBD by IANA. (For CRH-16, the suggested value is 5. For CRH-32, the suggested value is 6.) Segments Left - Defined in . Type-specific Data - Described in . In the CRH, the Type-specific data field contains a list of Segment Identifiers (SIDs). Each SID represents both of the following: A segment of the path that the packet takes to its destination. An entry in the CRH Forwarding Information Base (CRH-FIB) . SIDs are listed in reverse order. So, the first SID in the list represents the final segment 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 for examples. In the CRH-16, each SID is encoded in 16-bits. In the CRH-32, 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.

Each SID identifies a CRH-FIB entry. Each CRH-FIB entry contains: A IPv6 address. A forwarding method. Method-specific parameters (optional). The IPv6 address represents an interface on the next segment endpoint. It MUST NOT be a link-local address. While the IPv6 address represents an interface on the next segment endpoint, it does not necessarily represent the interface through which the packet will arrive at the next segment endpoint. The forwarding method specifies how the processing node will forward the packet to the next segment endpoint. The following are examples: Forward the packet to the next-hop along the least-cost path to the next segment endpoint. Forward the packet through a specified interface to the next segment endpoint. Some forwarding methods require method-specific parameters. For example, a forwarding method might require a parameter that identifies the interface through which the packet should be 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) or the Network Configuration Protocol (NETCONF). By a distributed routing protocol , , .

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 Parameter Problem, Code 0, message to the Source Address, pointing to the Hdr Ext Len field. Compute L, the minimum CRH length (See ). 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. Resubmit the packet to the IPv6 module for transmission to the new destination, ensuring that it executes the forwarding method specified by the CRH-FIB entry.

The algorithm described in this section accepts the following CRH fields as its input parameters: Routing Type (i.e., CRH-16 or CRH-32). Segments Left. It yields L, the minimum CRH length. The minimum CRH length is measured in 8-octet units, not including the first 8 octets.

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) ]]>

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: Allocate SIDs so that they have domain-wide significance. Allocate SIDs so that they have node-local significance.

PING and TRACEROUTE both operate correctly in the presence of the CRH.

Networks that process the CRH MUST NOT accept packets containing the CRH from untrusted sources. Their border routers SHOULD discard packets that satisfy the following criteria: The packet contains a CRH The Segments Left field in the CRH has a value greater than 0 The Destination Address field in the IPv6 header represents an interface that resides inside of the network. Many border routers cannot filter packets based upon the Segments Left value. These border routers MAY discard packets that satisfy the following criteria: The packet contains a CRH The Destination Address field in the IPv6 header represents an interface that resides inside of the network.

Juniper Networks has produced experimental implementations of the CRH on: A LINUX-based software platform The MX-series (ASIC-based) router Liquid Telecom has deployed the CRH, on a limited basis, in their network. Other experimental deployments are in progress.

SID values 0-15 are reserved for future use. They may be assigned by IANA, based on IETF Consensus. IANA is requested to establish a "Registry of SRm6 Reserved SIDs". Values 0-15 are reserved for future use. IANA is requested to make the following entries in the Internet Protocol Version 6 (IPv6) Parameters "Routing Type" registry:

Thanks to Dr. Vanessa Ameen, Fernando Gont, Naveen Kottapalli, Joel Halpern, Tony Li, Gerald Schmidt, Nancy Shaw, and Chandra Venkatraman for their contributions to this document.

Daniam Henriques Liquid Telecom Johannesburg, South Africa Email: daniam.henriques@liquidtelecom.com Gang Chen Baidu No.10 Xibeiwang East Road Haidian District Beijing 100193 P.R. China Email: phdgang@gmail.com Yifeng Zhou ByteDance Building 1, AVIC Plaza, 43 N 3rd Ring W Rd Haidian District Beijing 100000 P.R. China Email: yifeng.zhou@bytedance.com

IANA International Organization for Standardization

The CRH-16 and CRH-32 encode information more efficiently than RH0. SIDs RH0 CRH-16 CRH-32 1 24 8 8 2 40 8 16 3 56 16 16 4 72 16 24 5 88 16 24 6 104 16 32 7 120 24 32 8 136 24 40 9 152 24 40 10 168 24 48 11 184 32 48 12 200 32 52 13 216 32 52 14 232 32 56 15 248 40 56 16 264 40 60 17 280 40 60 18 296 40 64 reflects Routing header size as a function of Routing header type and number of SIDs contained by the Routing header.

This appendix demonstrates CRH processing in the following scenarios: The SID list contains one entry for each segment in the path . The SID list omits the first entry in the path .

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 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