Tag Archives: confederation



LPref, MED and next-hop are kept across sub-AS eBGP!

network backup – set distance 200

MED, Local-pref, NLRI are sent as TLVs.

When an IGP (in this example OSPF) route is redistributed in to BGP it is considered locally generated by BGP and gets assigned a weight of 32768.

Best Path Selection

AIGP – optiona notransitive 8 octet. If AIGP is configured AND the bgp bestpath aigp ignore command is not configured, the decision process considers the AIGP metric.

An AS_SET counts as 1, no matter how many ASs are in the set.

AIGP after Local Preference. AIGP metric reflects IGP cost. Lowest wins.
BGP prefers the path with the AIGP attribute by default.


The default BGP ConnectRetry timer is 120 seconds. Only after this time passes does the BGP process check to see if the passive TCP session is established. If the passive TCP session is not established, then the BGP process starts a new active TCP attempt to connect to the remote BGP speaker. During this idle 120 seconds of the ConnectRetry timer, the remote BGP peer can establish a BGP session to it. Presently, the Cisco IOS ConnectRetry timer cannot be changed from its default of 120 seconds.

Internet == 0:0 == match all; no such community in RFC

Redistribute & MED
— If the injected BGP route, using the network or redistribute command, is
from an IGP, the BGP MED is derived from the IGP metric.
— If the injected BGP route (using the network or redistribute command) is
from a connected route, the BGP MED is set to 0.
— If the route is injected by the aggregate-address command, MED is not set.

Capability 64
For IPv4, the end-of-RIB marker is a BGP Update message with no reachable NLRI and
empty withdrawn NLRI. Additional address families indicate the end-of-RIB with a BGP
Update containing only the MP_UNREACH_NLRI attribute with no withdrawn routes for
that AFI/SAFI.
Restart Time indicates how long a peer of the restarting router should maintain prefix
information received from the restarting router. The restart time should be less than the holdtime for the BGP peer.
The reception of a BGP-GR capability with no AFI/SAFI information indicates that the sending peer supports the end-of-RIB marker and can support peers that can maintain forwarding state and that want to utilize BGP-GR. The reception of a BGP-GR capability with AFI/SAFI information indicates that the sending peer wants to perform BGP-GR for the included AFI/SAFIs.
Mark all prefixes as stale.
After restart:
The receiving BGP router sends the BGP-GR capability to the restarting BGP router, with
the Restart State set to 0, unless the receiving BGP router also is reset. The receiving BGP
router receives a BGP-GR capability from the restarting BGP router with a Restart State of 1.
This triggers the receiving BGP router to send the initial routing update, followed by the
end-of-RIB marker.