CCIE Review – BGP

CCIE Review – BGP Border Gateway Protocol BGP is an EGP for routing between autonomous systems. It is described in RFC 4271 in great detail. The primary function of a BGP speaking system is to exchange network reachability information with other BGP systems. This network reachability information includes information about the list of Autonomous […] EBGP, IBGP

here is an older site (2008) devoted to bgp review… it is based on some old school graphics (which i actually like a lot, similar to this one for ospf which is outstanding: and the bgp case studies tech notes on here: EBGP, IBGP

from wendell, r&s The BGP network router subcommand differs significantly from the network command used by IGPs. The BGP network command instructs that router’s BGP process to do the following: Look for a route in the router’s current IP routing table that exactly matches the parameters of the network command; if the IP route exists, […] EBGP, IBGP

from: Generally speaking, for EBGP peering using the BGP standards, we peer based on the IP address of the BGP neighbors’ local interfaces. However, that brings up some challenging permutations. When peering is done via the external network of a BGP edge router within an AS, a BGP edge router will not change the […] EBGP, IBGP

from: Because there is no component route (no classful route or subnet route ) in the R101 IP routing table, the network in not installed in the BGP table. The minimum requirement for a prefix configured under the network command to be installed in a BGP table is to have a component route […] EBGP, IBGP

r3 and r4 are peering using loopback interfaces, update source, and ebgp multihop because they are  in different as’s… although the loopback is on that same router it is considered another hop and the default ttl has to be increased… no surprise there… R3#sh run | b router bgp router bgp 123 bgp log-neighbor-changes neighbor […] EBGP, IBGP

1) a tcp connection request must have a matching source address in a bgp neighbor statement R2#sh tcp brie TCB       Local Address               Foreign Address             (state) 67F71058                       ESTAB 67F709D4                       ESTAB R2#sh run | b bgp 123 router bgp 123 bgp log-neighbor-changes neighbor remote-as 123 neighbor update-source Loopback1 neighbor remote-as […] EBGP, IBGP

the conventional wisdom for directly connected EBGP routers when using loopbacks as the update source is to manually set the ebgp-multihop to a number greater than 1 in order to establish the peering… this manually sets the ttl value  as seen below to a number other than the default… the disable-connected-check accomplishes the same thing […]