CISCO BGP SUMMARY
I have seen static route pointing towards a null0 interface in BGP. Can I know why it is used for?
The static route to null 0 is needed to advertise networks into BGP,
BGP would advertise Networks using any of the bellow methods:
1– with the Network command set.
2– Redistribution into BGP.
3– Aggregate address command.
All of these methods needs an exact match in the routing table , except for the aggregation which
needs at least one route part of the aggregate address exist.
However, doesn’t need the (network command under bgp) as long as the aggregate address along with
one part of the aggregate address exist in the IP routing table.
EG :
ip route 196.196.1.0 255.255.255.0 Null0
router bgp myASN
network 196.196.1.0 mask 255.255.255.0
…
(((
modern way
router bgp myASN
aggregate-address 196.196.0.0 255.255.252.0 summary-only
))))
it is a way to create an aggregate = a summary route
Route Reflectors
Another solution for the explosion of iBGP peering within an AS is Route Reflectors (RRs).
As the iBGP section demonstrates, a BGP speaker does not advertise a route that the BGP speaker
learned via another iBGP speaker to a third iBGP speaker.
You can relax this restriction a bit and provide additional control, which allows a router to
advertise, or reflect, iBGP learned routes to other iBGP speakers. This route reflection reduces the
number of iBGP peers within an AS.
neighbor route-reflector-client
The router with this command is the RR, and the neighbors at which the command points are
the clients of that RR.
Tuning BGP Transport
Tuning BGP transport mechanism is a very important factor for improving BGP performance in
the cases where purely BGP-based re-convergence process is in use. TCP is the underlying transport
used for propagating BGP UPDATE messages,and optimizing TCP performance directly benefits BGP.
If you take the full Internet routing table, which is above 300k prefixes (Y2010), then simply transporting
the prefixes alone will consume over 10 Megabytes, not to count the path attributes and other
information. Tuning TCP transport performance includes the following:
Enabling TCP Path MTU discovery for every neighbor, to allow the TCP selecting optimum MSS size.
Notice that this requires that no firewall blocks the ICMP unreachable messages used during the
discovery process Tuning the router’s ingress queue size to allow for successful absorption of large
amount of TCP ACK messages. When a router starts replicating BGP UPDATES to its peers, every peer
responds with TCP ACK message to normally every second segment sent (TCP Delayed ACK).
The more peers router has, the higher will be the pressure on the ingress queue.
