| Internet-Draft | BMP Loc-RIB | March 2021 |
| Evens, et al. | Expires 9 September 2021 | [Page] |
The BGP Monitoring Protocol (BMP) defines access to various Routing Information Bases (RIBs). This document updates BMP (RFC 7854) by adding access to the Local Routing Information Base (Loc-RIB), as defined in RFC 4271. The Loc-RIB contains the routes that have been selected by the local BGP speaker's Decision Process.¶
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This document defines a mechanism to monitor the BGP Loc-RIB state of remote BGP instances without the need to establish BGP peering sessions. BMP [RFC7854] does not define a method to send the BGP instance Loc-RIB. It does define in section 8.2 of [RFC7854] locally originated routes, but these routes are defined as the routes originated into BGP. For example, locally sourced routes that are redistributed.¶
Figure 1 shows the flow of received routes from one or more BGP peers into the Loc-RIB.¶
+------------------+ +------------------+
| Peer-A | | Peer-B |
/-- | | ---- | | --\
| | Adj-RIB-In (Pre) | | Adj-RIB-In (Pre) | |
| +------------------+ +------------------+ |
| | | |
| Filters/Policy -| Filters/Policy -| |
| V V |
| +------------------ +------------------+ |
| | Adj-RIB-In (Post)| | Adj-RIB-In (Post)| |
| +------------------ +------------------+ |
| | | |
| Selected -| Selected -| |
| V V |
| +-----------------------------------------+ |
| | Loc-RIB | |
| +-----------------------------------------+ |
| |
| ROUTER/BGP Instance |
\----------------------------------------------------/
Figure 2 (Locally Originated into Loc-RIB) illustrates how redistributed or otherwise originated routes get installed into the Loc-RIB based on the decision process selection in RFC 4271 [RFC4271].¶
/--------------------------------------------------------\ | | | +----------+ +----------+ +----------+ +----------+ | | | IS-IS | | OSPF | | Static | | BGP | | | +----------+ +----------+ +----------+ +----------+ | | | | | | | | | | | | | Redistributed or originated into BGP | | | | | | | | | | | | | V V V V | | +----------------------------------------------+ | | | Loc-RIB | | | +----------------------------------------------+ | | | | ROUTER/BGP Instance | \--------------------------------------------------------/
The following are some use-cases for Loc-RIB access:¶
The Adj-RIB-In for a given peer Post-Policy may contain hundreds of thousands of routes, with only a handful of routes selected and installed in the Loc-RIB after best-path selection. Some monitoring applications, such as ones that need only to correlate flow records to Loc-RIB entries, only need to collect and monitor the routes that are actually selected and used.¶
Requiring the applications to collect all Adj-RIB-In Post-Policy data forces the applications to receive a potentially large unwanted data set and to perform the BGP decision process selection, which includes having access to the IGP next-hop metrics. While it is possible to obtain the IGP topology information using BGP-LS, it requires the application to implement SPF and possibly CSPF based on additional policies. This is overly complex for such a simple application that only needs to have access to the Loc-RIB.¶
This document adds Loc-RIB to the BGP Monitoring Protocol and replaces Section 8.2 of [RFC7854] Locally Originated Routes.¶
Loc-RIB is used to build Adj-RIB-Out when advertising routes to a peer. It is therefore possible to derive the Loc-RIB of a router by monitoring the Adj-RIB-In Pre-Policy from another router. At scale this becomes overly complex and error prone.¶
/------------------------------------------------------\
| ROUTER1 BGP Instance |
| |
| +--------------------------------------------+ |
| | Loc-RIB | |
| +--------------------------------------------+ |
| | | |
| +------------------+ +------------------+ |
| | Peer-ROUTER2 | | Peer-ROUTER3 | |
| | Adj-RIB-Out (Pre)| | Adj-RIB-Out (Pre)| |
| +------------------+ +------------------+ |
| Filters/Policy -| Filters/Policy -| |
| V V |
| +-------------------+ +-------------------+ |
| | Adj-RIB-Out (Post)| | Adj-RIB-Out (Post)| |
| +-------------------+ +-------------------+ |
| | | |
\------------- | ------------------------ | -----------/
BGP | BGP |
Peer | Peer |
+------------------+ +------------------+
| Peer-ROUTER1 | | Peer-ROUTER1 |
/--| |--\ /--| | --\
| | Adj-RIB-In (Pre) | | | | Adj-RIB-In (Pre) | |
| +------------------+ | | +------------------+ |
| | | |
| ROUTER2/BGP Instance | | ROUTER3/BGP Instance |
\------------------------/ \-------------------------/
| |
v v
ROUTER2 BMP Feed ROUTER3 BMP Feed
The setup needed to monitor the Loc-RIB of a router requires another router with a peering session to the target router that is to be monitored. As shown in Figure 3, the target router Loc-RIB is advertised via Adj-RIB-Out to the BMP router over a standard BGP peering session. The BMP router then forwards Adj-RIB-In Pre-Policy to the BMP receiver.¶
BMP lacking access to Loc-RIB introduces the need for additional resources:¶
Complexities introduced by the lack of access to Loc-RIB in order to derive (e.g. correlate) peer to router Loc-RIB:¶
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 2119 [RFC2119] RFC 8174 [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
A new peer type is defined for Loc-RIB to distinguish that it represents Loc-RIB with or without RD and local instances. Section 4.2 of [RFC7854] defines a Local Instance Peer type, which is for the case of non-RD peers that have an instance identifier.¶
This document defines the following new peer type:¶
In section 4.2 of [RFC7854], the "locally sourced routes" comment under the L flag description is removed. If locally sourced routes are communicated using BMP, they MUST be conveyed using the Loc-RIB instance peer type.¶
The per-peer header flags for Loc-RIB Instance Peer type are defined as follows:¶
0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |F| Reserved | +-+-+-+-+-+-+-+-+¶
The Loc-RIB contains all routes selected by the BGP protocol Decision Process as described in section 9.1 of [RFC4271]. These routes include those learned from BGP peers via its Adj-RIBs-In post-policy, as well as routes learned by other means as per section 9.4 of [RFC4271]. Examples of these include redistribution of routes from other protocols into BGP or otherwise locally originated (ie. aggregate routes).¶
As mentioned in Section 4.2 a subset of Loc-RIB routes MAY be sent to a BMP collector by setting the F flag.¶
All peer messages that include a per-peer header section 4.2 of [RFC7854] MUST use the following values:¶
Peer UP notifications follow section 4.10 of [RFC7854] with the following clarifications:¶
The following Peer UP information TLV type is added:¶
Type = 3: VRF/Table Name. The Information field contains a UTF-8 string whose value MUST be equal to the value of the VRF or table name (e.g. RD instance name) being conveyed. The string size MUST be within the range of 1 to 255 bytes.¶
The VRF/Table Name TLV is optionally included. For consistency, it is RECOMMENDED that the VRF/Table Name always be included. The default value of "global" MUST be used for the default Loc-RIB instance with a zero-filled distinguisher. If the TLV is included, then it MUST also be included in the Peer Down notification.¶
Multiple TLVs of the same type can be repeated as part of the same message, for example to convey a filtered view of a VRF. A BMP receiver should append multiple TLVs of the same type to a set in order to support alternate or additional names for the same peer. If multiple strings are included, their ordering MUST be preserved when they are reported.¶
Peer down notification MUST use reason code 6. Following the reason is data in TLV format. The following peer Down information TLV type is defined:¶
Route Monitoring messages are used for initial synchronization of the Loc-RIB. They are also used to convey incremental Loc-RIB changes.¶
As defined in section 4.3 of [RFC7854], "Following the common BMP header and per-peer header is a BGP Update PDU."¶
Loc-RIB route monitor messages MUST use 4-byte ASN encoding as indicated in PEER UP sent OPEN message (Section 5.2) capability.¶
State compression and throttling SHOULD be used by a BMP sender to reduce the amount of route monitoring messages that are transmitted to BMP receivers. With state compression, only the final resultant updates are sent.¶
For example, prefix 192.0.2.0/24 is updated in the Loc-RIB 5 times within 1 second. State compression of BMP route monitor messages results in only the final change being transmitted. The other 4 changes are suppressed because they fall within the compression interval. If no compression was being used, all 5 updates would have been transmitted.¶
A BMP receiver should expect that Loc-RIB route monitoring granularity can be different by BMP sender implementation.¶
Route mirroring is not applicable to Loc-RIB and Route Mirroring messages SHOULD be ignored.¶
Not all Stat Types are relevant to Loc-RIB. The Stat Types that are relevant are listed below:¶
There are several methods for a BGP speaker to implement Loc-RIB efficiently. In all methods, the implementation emulates a peer with Peer UP and DOWN messages to convey capabilities as well as Route Monitor messages to convey Loc-RIB. In this sense, the peer that conveys the Loc-RIB is a local router emulated peer.¶
There MUST be multiple emulated peers for each Loc-RIB instance, such as with VRFs. The BMP receiver identifies the Loc-RIB by the peer header distinguisher and BGP ID. The BMP receiver uses the VRF/Table Name from the PEER UP information to associate a name to the Loc-RIB.¶
In some implementations, it might be required to have more than one emulated peer for Loc-RIB to convey different address families for the same Loc-RIB. In this case, the peer distinguisher and BGP ID should be the same since it represents the same Loc-RIB instance. Each emulated peer instance MUST send a PEER UP with the OPEN message indicating the address family capabilities. A BMP receiver MUST process these capabilities to know which peer belongs to which address family.¶
There maybe be use-cases where BMP receivers should only receive specific routes from Loc-RIB. For example, IPv4 unicast routes may include IBGP, EBGP, and IGP but only routes from EBGP should be sent to the BMP receiver. Alternatively, it may be that only IBGP and EBGP that should be sent and IGP redistributed routes should be excluded. In these cases where the Loc-RIB is filtered, the F flag is set to 1 to indicate to the BMP receiver that the Loc-RIB is filtered. If multiple filters are associated to the same Loc-RIB, a Table Name MUST be used in order to allow a BMP receiver to make the right associations.¶
In case of any change that results in the alteration of behaviour of an existing BMP session, ie. changes to filtering and table names, the session MUST be bounced with a Peer DOWN/Peer UP sequence.¶
The same considerations as in section 11 of [RFC7854] apply to this document. Implementations of this protocol SHOULD require to establish sessions with authorized and trusted monitoring devices. It is also believed that this document does not add any additional security considerations.¶
This document requests that IANA assign the following new parameters to the BMP parameters name space.¶
This document defines a new peer type (Section 4.1):¶
This document defines a new flag (Section 4.2) and proposes that peer flags are specific to the peer type:¶
This document defines the following new BMP PEER UP informational message TLV types (Section 5.2.1):¶
This document defines the following new BMP Peer Down reason code (Section 5.3):¶
The authors would like to thank John Scudder, Jeff Haas and Mukul Srivastava for their valuable input.¶