• IPv4/IPv6 Multicast should be within the same BGP instance in which IPv4/IPv6 Unicast is configured.
• All configuration changes for a single BGP instance can be committed together. However, configuration
changes for multiple instances cannot be committed together.
• Cisco recommends that BGP update-source should be unique in the default VRF over all instances while
peering with the same remote router.
BGP Prefix Independent Convergence for RIB and FIB
BGP PIC for RIB and FIB adds support for static recursive as PE-CE and faster backup activation by using
fast re-route trigger.
The BGP PIC for RIB and FIB feature supports:
• FRR-like trigger for faster PE-CE link down detection, to further reduce the convergence time (Fast
PIC-edge activation).
• PIC-edge for static recursive routes.
• BFD single-hop trigger for PIC-Edge without any explicit /32 static route configuration.
• Recursive PIC activation at third level and beyond, on failure trigger at the first (IGP) level.
• BGP path recursion constraints in FIB to ensure that FIB is in sync with BGP with respect to BGP
next-hop resolution.
BGP Update Message Error Handling
The BGP UPDATE message error handling changes BGP behavior in handling error UPDATE messages to
avoid session reset. Based on the approach described in IETF IDR
I-D:draft-ietf-idr-error-handling
, the Cisco
IOS XR BGP UPDATE Message Error handling implementation classifies BGP update errors into various
categories based on factors such as, severity, likelihood of occurrence of UPDATE errors, or type of attributes.
Errors encountered in each category are handled according to the draft. Session reset will be avoided as much
as possible during the error handling process. Error handling for some of the categories are controlled by
configuration commands to enable or disable the default behavior.
According to the base BGP specification, a BGP speaker that receives an UPDATE message containing a
malformed attribute is required to reset the session over which the offending attribute was received. This
behavior is undesirable as a session reset would impact not only routes with the offending attribute, but also
other valid routes exchanged over the session.
BGP Attribute Filtering
The BGP Attribute Filter feature checks integrity of BGP updates in BGP update messages and optimizes
reaction when detecting invalid attributes. BGP Update message contains a list of mandatory and optional
attributes. These attributes in the update message include MED, LOCAL_PREF, COMMUNITY etc. In some
cases, if the attributes are malformed, there is a need to filter these attributes at the receiving end of the router.
The BGP Attribute Filter functionality filters the attributes received in the incoming update message. The
attribute filter can also be used to filter any attributes that may potentially cause undesirable behavior on the
receiving router.
Routing Configuration Guide for Cisco NCS 6000 Series Routers, IOS XR Release 6.4.x
44
Implementing BGP
BGP Prefix Independent Convergence for RIB and FIB