| Internet-Draft | BGP Flow Specification for SRv6 | August 2021 |
| Li, et al. | Expires 11 February 2022 | [Page] |
This document proposes extensions to BGP Flow Specification for SRv6 for filtering SRv6 packets that match a sequence of conditions.¶
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].¶
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[RFC8955] describes in details about a new BGP NLRI to distribute a flow specification, which is an n-tuple comprising a sequence of matching criteria that can be applied to IP traffic. [RFC8956] extends [RFC8955] to make it also usable and applicable to IPv6 data packets. [I-D.ietf-idr-flowspec-l2vpn] extends the flow-spec rules for layer 2 Ethernet packets. [I-D.hares-idr-flowspec-v2] specifies BGP Flow Specification Version 2.¶
Segment Routing (SR) for unicast traffic has been proposed to cope with the usecases in traffic engineering, fast re-reroute, service chain, etc. SR architecture can be implemented over an IPv6 data plane using a new type of Segment Routing Header (SRH) [I-D.ietf-6man-segment-routing-header]. SRv6 Network Programming [RFC8986] defines the SRv6 network programming concept and its most basic functions. An SRv6 SID may have the form of LOC:FUNCT:ARGS::.¶
LOC: Each operator is free to use the locator length it chooses. Most often the LOC part of the SID is routable and leads to the node which instantiates that SID.¶
FUNCT: The FUNCT part of the SID is an opaque identification of a local function bound to the SID. (e.g. End: Endpoint, End.X, End.T, End.DX2 etc.).¶
ARGS: A function may require additional arguments that would be placed immediately after the FUNCT.¶
This document specifies one new BGP Flow Specification (FS) component type to support Segment Routing over IPv6 data plane (SRv6) filtering for BGP Flow Specification Version 2. The match field is destination address of IPv6 header, but it's a SID from SRH rather than a traditional IPv6 address (refer to Figure 1). To support these features, a Flowspec version that is IPv6 capable (i.e., AFI = 2) MUST be used. These match capabilities of the features are only permitted to match when there is an accompanying SRH.¶
+-----------------------------+
IPv6 Header| SA | DA |<--Match field of this document
+--------------------^--------+
|
+--------------------|--------+
| +-------------+ | +-------------------+
| | Segment[0] +-------> Loc | Func | Args |
| +-------------+ | +-------------------+
| | Segment[1] | |
| +-------------+ |
| | ... | |
SR Header| +-------------+ |
| | Segment[n] | |
| +-------------+ |
| +-------------+ |
| ~ Option TLV ~ |
| +-------------+ |
+-----------------------------+
The Flow Specification NLRI-type consists of several optional components, each of which begins with a type field (1 octet) followed by a variable length parameter. 13 component types are defined in [RFC8955] and [RFC8956] for IPv4 and IPv6. This document defines one component type for SRv6.¶
[RFC8986] defines the format of SID is LOC:FUNCT:ARGS::. In some scenarios, traffic packets can just match Locator, Function ID, Arguments or some combinations of these different fields. In order to match a part of SID, its prior parts need to be examined and matched first. For example, in order to match the Function ID (FUNCT), the Locator (LOC) needs to be examined and matched first. The new component type TBD1 defined below is for matching some parts of SID.¶
Encoding: <type, LOC-Len, FUNCT-Len, ARGS-Len, [op, value]+>¶
The total of three lengths (i.e., LOC length + FUNCT length + ARGS length) MUST NOT be greater than 128. If it is greater than 128, an error occurs and Error Handling is applied according to [RFC7606] and [RFC4760].¶
The operator (op) byte is encoded as:¶
0 1 2 3 4 5 6 7 +---+---+---+---+---+---+---+---+ | e | a | field type|lt |gt |eq | +---+---+---+---+---+---+---+---+¶
where the behavior of each operator bit has clear symmetry with that of [RFC8955]'s Numeric Operator field.¶
e - end-of-list bit. Set in the last {op, value} pair in the sequence.¶
a - AND bit. If unset, the previous term is logically ORed with the current one. If set, the operation is a logical AND. It should be unset in the first operator byte of a sequence. The AND operator has higher priority than OR for the purposes of evaluating logical expressions.¶
field type:¶
For an unknown type, Error Handling is applied according to [RFC7606] and [RFC4760].¶
lt - less than comparison between data' and value'.¶
gt - greater than comparison between data' and value'.¶
eq - equality between data' and value'.¶
The data' and value' used in lt, gt and eq are indicated by the field type in a operator and the value field following the operator.¶
The value field depends on the field type and has the value of SID's some parts rounding up to bytes (refer to the table below).¶
+-----------------------+------------------------------+ | Field Type | Value | +=======================+==============================+ | SID's LOC | value of LOC bits | +-----------------------+------------------------------+ | SID's FUNCT | value of FUNCT bits | +-----------------------+------------------------------+ | SID's ARGS | value of ARGS bits | +-----------------------+------------------------------+ | SID's LOC:FUNCT | value of LOC:FUNCT bits | +-----------------------+------------------------------+ | SID's FUNCT:ARGS | value of FUNCT:ARGS bits | +-----------------------+------------------------------+ | SID's LOC:FUNCT:ARGS | value of LOC:FUNCT:ARGS bits | +-----------------------+------------------------------+¶
An example of a Flow Specification NLRI encoding for: all SRv6 packets to LOC 2001:db8:3::/48 and FUNCT {range [0100, 0300]}.¶
Some Parts of SID
|
length v LOC==20010db80003 FUN>=100 FUN<=300
0x12 0f 30 10 40 01 2001 0db8 0003 4b 0100 bd 0300
^ ^ ^
| | |
Length of LOC FUN ARGS¶
Decoded:
Value
0x12 length 18 octets (if len<240, 1 octet)
TBD1(0x0f) type type TBD1(0x0f) - Some Parts of SID
0x30 LOC Length = 48 (bits)
0x10 FUNCT Length = 16 (bits)
0x40 ARGS Length = 64 (bits)
0x01 op LOC ==
0x2001 value LOC's value = 2001:db8:3
0x0db8
0x0003
0x4b op "AND", FUNCT >=
0x0100 value FUNCT's value = 0100
0xbd op end-of-list, "AND", FUNCT <=
0x0300 value FUNCT's value = 0300
¶
No new security issues are introduced to the BGP protocol by this specification over the security considerations in [RFC8955] and [RFC8956].¶
Under "Flow Spec IPv6 Component Types" registry, IANA is requested to assign the following values:¶
+-----------+-------------------+----------------+ | Value | Name | Reference | +-----------+-------------------+----------------+ | TBD1 (15) | Some Parts of SID | This Document | +-----------+-------------------+----------------+¶
The authors would like to thank Joel Halpern, Jeffrey Haas, Ketan Talaulikar, Aijun Wang, Shunwan Zhuang and Rainsword Wang for their valuable suggestions and comments on this draft.¶