BMP Extension for Path Marking
TLVNTT164-168, Carrer de NumanciaBarcelona08029Spaincamilo@ntt.netNTTSiriusdreef 70-72HoofddorpWT2132Netherlandspaolo@ntt.netINSA-LyonLyonFrancePierre.Francois@insa-lyon.frHuaweiHuawei Bld., No.156 Beiqing Rd.Beijing100095Chinaguyunan@huawei.comSwisscomBinzring 17Zurich8045Switzerlandthomas.graf@swisscom.comThe BGP Monitoring Protocol (BMP) provides an interface for obtaining
BGP Path information. BGP Path Information is conveyed within BMP Route
Monitoring (RM) messages. This document proposes an extension to BMP to
convey the status of a BGP path after being processed by the BGP
best-path selection algorithm. This extension makes use of the TLV
mechanims described in draft-lucente-bmp-tlv.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
RFC 2119RFC
8174 when, and only when, they appear in all capitals, as shown
here.For a given prefix, multiple paths with different path status, e.g.,
the "best-path", "back-up path" and so on, may co-exist in the BGP RIB
after being processed by the local policy and the BGP decision process.
The path status information is currently not carried in the BGP Update
Message RFC4271 or in the BMP Update
Message RFC7854.External systems can use the path status for various applications.
The path status is commonly checked by operators when performing
troubleshooting. Having such status stored in a centralized system can
enable the development of tools facilitating this process. Optimisation
systems can include the path status in their process, and also use the
status as a validation source (since it can compare the calculated state
to the actual outcome of the network, such as primary and backup path).
As a final example, path status information can complement other
centralized sources of data, for example, flow collectors.This document defines a so-called Path Marking TLV to convey the BGP
path status information to the BMP server. The BMP Path Marking is
defined to be prepended in the BMP Route Monitoring (RM) Message.As per RFC4271, the BMP RM Message
consists of the Common Header, Per-Peer Header, and the BGP Update PDU.
According to draft-lucente-bmp-tlv , optional
trailing data in TLV format is allowed in the BMP RM Message to convey
characteristics of transported NLRIs (i.e. to help stateless parsing) or
vendor-specific data. Such TLV types are to be defined for each
application.To include the path status along with each BGP path, we define the
Path Marking TLV, shown as follows.Type = TBD1 (2 Octets): indicates that it's the Path Marking
TLV.Length (2 Octets): indicates the length of the value field of the
Path Marking TLV. The value field further consists of the
Path-Status field and Reason Code field.E bit (1 Bit) for Path Status: indicates if any
enterprise-specific path status is used after the IANA-registered
path status code.Path Status (4 Octets): indicates the path status of the BGP
Update PDU encapsulated in the RM Message. Currently 7 types of path
status are defined, as shown in Table 1.E bit (1 Bit) for Reason Code: indicates if any
enterprise-specific reason code is used after the IANA-registered
reason code.Reason Code (Variable): indicates the reasons/explanations of the
path status indicated in the Path Type field. The detailed Reason
Code field is defined in Section 2.2.The Path Status field contains a bit field where each bit encodes a
specific role of the path. Multiple bits may be set when multiple
path status apply to a path.Two encoding options for Path Status are described in the following
two sections. E bit (1 Bit): set to 0, indicating that only IANA-registered
path status is used in this TLV.IANA-registered Path Status (2 octets): indicates the
IANA-registered path status, as specified in Table 1. The best-path is defined in RFC4271 and the best-external path is
defined in draft-ietf-idr-best-external.An invalid path is a route that does not enter the BGP decision process.A non-selected path is a route that is not selected in the BGP decision process.
In other words, Best route and ECMP routes are not considered as non-selected.A primary path is a recursive or non-recursive path whose
nexthop resolution ends with an adjacency draft-ietf-rtgwg-bgp-pic. A
prefix can have more than one primary path if multipath is
configured draft-lapukhov-bgp-ecmp-considerations.
A best-path is also considered as a primary path.A backup path is also installed in the RIB, but it is not used
until some or all primary paths become unreachable. Backup paths are
used for fast convergence in the event of failures.A non-installed path refers to the route that is not installed into the IP
routing table.For the advertisement of multiple paths for the same address
prefix without the new paths implicitly replacing any previous
ones, the add-path status is applied RFC7911.E bit (1 Bit): set to 1, indicating enterprise-specific path
status is used in this TLV.Enterprise-specific Path Type (4 octets): indicates
enterprise-specific path status, which remains to be
defined.Enterprise Number (4 octets): indicates the IANA enterprise
number IANA-PEN.The Reason Code field contains a bit field where each bit encodes a
specific reason. Multiple bits may be set when multiple reasons
apply to a path.E bit (1 Bit): set to 0, indicating that only IANA-registered
reason code is used in this TLV. With the E bit set to 0, the
Length field of the Path Marking TLV SHOULD be set to 8.IANA-registered Reason Code (4 octets): indicates the
IANA-registered reason code of the path status.E bit (1 Bit): set to 1, indicating enterprise-specific
reason code is also used in this TLV.IANA-registered Reason Code (4 octets): indicates the
IANA-registered reason code of the path status.Enterprise Number (4 octets): indicates the IANA enterprise
number IANA-PEN.E-specific Reason Code (Variable): indicates
enterprise-specific reason code of the path status.We would like to thank Jeff Haas for his valuable comments.This document requests that IANA assign the following new parameters
to the BMP parameters name space.This document defines the Path Marking TLV with Type = TBD1: Path
Marking (Section 2).It is not believed that this document adds any additional security
considerations.