Version Capability for BGP

In modern data center designs, we tend to have conventional routers participating in the routing process. And the fleet of routers has different versions of routing daemon. This means that knowing which versions of the routing daemons are running the various routers in the network can be a crucial factor in quickly identifying the root cause of any protocol or network problems. This BGP capability is an optional advertisement. Implementations are not required to advertise the version nor to process received advertisements. Information about the version of the routing daemon could also be exchanged in protocols such as LLDP and CDP. However, in containerized environments, it is very hard and not recommended to exchange this information between background processes. Therefore, and to help minimize operational costs, it is helpful to exchange the routing daemon information between BGP peers directly.

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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

Capabilities advertisements with BGP are defined in [RFC5492]. They utilize the BGP Capabilities Optional Parameter that contains one or more triples <Capability Code, Capability Length, Capability Value>. This document defines a new BGP capability, the Version Capability, with Capability Code TBD and Capability Length and Capability Value as described below. The inclusion of the Version Capability is OPTIONAL. If an implementation supports the inclusion of the capability, the implementation MUST include a configuration switch to enable or disable its use, and that switch MUST be off by default. The Version Capability is intended principally more to non-production environments where more visibility is needed for troubleshooting purposes. It is NOT RECOMMENDED for use outside single Autonomous System domain or Autonomous System Confederations, except you have a topology with a number of routers each with a separate Autonomous Number. An implementation that does not recognize or support the Version Capability but which receives one MUST respond as described in [RFC5492] by ignoring the option. An implementation that wishes to complain that its neighbor does not support the Version Capability MAY use the 'Unsupported Capability' Error Subcode of a Notification message as described in [RFC5492]. The triple for the Version Capability is as follows: Capability Code TBD by IANA Capability Length The Capability Length for the Version Capability MUST be greater than zero. A value of zero SHALL be treated as an encoding error and the entire triple MUST be ignored. The Capability Length SHOULD be no greater than 64. This is the limit to allow other capabilities as much space as they require. Capability Value The Capability Value field is encoded in UTF-8 [RFC3629]. It is unstructured data and can be formatted in any way that the implementor decides.

Version Length: The number of characters in the Version Version: The Version encoded via UTF-8

As defined in [RFC5492] the total length of capabilities that can be carried by the BGP Capabilities Optional Parameter is 255 bytes. If an implementation is constructing a BGP Capabilities Optional Parameter and its length exceeds 255 bytes, it is RECOMMENDED to exclude the Version Capability. An implementation may optimally achieve this by making the Version Capability the last capability triple to add to the Parameter, and only adding it if there is sufficient space to do so.

The Version Capability MUST only be used for displaying the version of a BGP speaker's router daemon to make troubleshooting easier. Consider a group of routers each with a number of upstream nodes, and suppose that each router has a different operating system and different routing daemon at a different version installed. Assuming that a specific feature is not working or that there is a bug which has not been fixed in a particular version of the code, knowledge of the routing daemon versions would allow an operator to quickly identify the pattern of which versions are affected. Enabling (i.e., turning on) this capability requires bouncing all existing BGP sessions and the feature MUST be explicitly configured before an implementation advertizes the Version Capability.

Below is an example of implementation in how it looks like with version advertised by a BGP sender:

| jq '."198.51.100.1".neighborCapabilities.versions' { "advertisedVersion": "FRRouting 7.2-dev-MyOwnFRRVersion", "receivedVersion": "FRRouting 7.2-dev-MyOwnFRRVersion-gc68bb14" } ]]>

IANA maintains the "Border Gateway Protocol (BGP) Parameters" registry with a subregistry called "Capabilities Codes". IANA is requested to assign a capability number from the First Come First Served range for the Version Capability in this document as follows: Value Description Reference TBD Version Capability [This.I-D]

The Version Capability should be treated as sensitive information: it could be easier for an attacker to exploit the system if they know the specific version of a BGP speaker. This information could be gathered by inspecting BGP OPEN messages that carry the Version Capability defined in this document. Using encryption to protect the information exchanged in BGP sessions SHOULD, therefore, be carefully considered when this feature is enabled. Suitable encryption can be achieved by protecting the BGP session using TLS [RFC5246]. Furthermore, knowledge of which versions of code is running on a given router and from which vendor it comes may facilitate a number of social-engineering attacks. This further adds to the desire to protect this information through encryption. Modifying the information advertised by a router might lead to attacks including bogus software upgrades and also might mask the causes of faults in the network. This can be mitigated by protecting the BGP session using TLS. Many BGP implementations leave TCP port 179 open in order to be able to establish sessions with new neighbors. This could lead to an attack where a rogue BGP implementation attempts to open a session and learns the version information from the responding peer. The Version Capability MUST be configurable with a vendor-specific knob to be able to enable or disable the capability. The vendor might implement to disable this capability per neighbor. It would be safe to enable this for iBGP or inside the same tenant where you have full control and the BGP speaker is behind the exit points. This capability is NOT RECOMMENDED for eBGP use. Sensitive information leaks can be minimized by using the [RFC5082] mechanism or firewalls to filter out TCP 179 port from untrusted networks. This capability can be disabled per neighbor, thus the sensitive information can't be disclosed to untrusted neighbors.