BMP Extension for Path Status
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 before and after being processed by the
BGP best-path selection algorithm. This extension makes use of the TLV
mechanims described in draft-ietf-grow-bmp-tlv and draft-lucente-grow-bmp-tlv-ebit.
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 that facilitate 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 Status TLV to convey the BGP
path status to the BMP server. The BMP Path Status TLV is carried in the
BMP Route Monitoring (RM) Message.This document defines two types of Path Status TLVs: one is the
IANA-registered Path Status TLV, and the other is the
Enterprise-specific Path Status TLV.E bit: For an IANA-registered TLV, the E bit MUST be set to
0.Type = TBD2 (15 Bits): indicates that it is the IANA-registered
Path Status TLV.Length (2 Octets): indicates the length of the value field of
the Path Status TLV. The value field further consists of the
Path-Status field and Reason Code field.Index (2 Octets): indicates the prefix that this TLV is describing.
The index is the encapsulation order, starting from 0, of the
prefix in the BGP Update PDU.Path Status (4 Octets): indicates the path status of the BGP
Update PDU encapsulated in the RM Message. Currently 8 types of
path status are defined, as shown in Table 1. All zeros are
reserved.Reason Code (2 Octets, optional): indicates the reason of
the path status indicated in the Path Status field. The reason
code field is optional. If no reason code is carried, this field
is empty. If a reason code is carried, the reason code is
indicated by a 2-byte value, which is defined in Table 2.The Path Status field contains a bitmap where each bit
encodes a specific role of the path. Multiple bits may be set
when multiple path status apply to a path.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. Back-up routes are considered non-selected,
while the best 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.
The path status TLV does not force a BMP client to send any
of these paths. It just provides a method to mark the paths that
are available with their status.
E bit: For an Enterprise-specific TLV, the E bit MUST be set to
1.Type = 1 (15 Bits): indicates that it's the Enterprise-specific
Path Status TLV.Length (2 Octets): indicates the length of the value field of
the Path Status TLV. The value field further consists of the
Path-Status field and Reason Code field.Index (2 Octets): indicates the prefix that this TLV is describing.
The index is the encapsulation order, starting from 0, of the
prefix in the BGP Update PDU.PEN Number (4 octets): indicates the IANA enterprise number
IANA-PEN.Path Status (4 Octets): indicates the enterprise-specific path
status. The format is to be determined w.r.t. each PEN number.Reason Code (2 octets, optional): indicates the reasons/explanations of
the path status indicated in the Path Status field. The format is
to be determined w.r.t. each PEN number.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.Type = TBD1 (15 Bits): indicates that it is the IANA-registered Path
Status TLV.It is not believed that this document adds any additional security
considerations.