Jaycee's Networking

June 12, 2010

Enable/Establish BGP

Filed under: BGP, IOS — Tags: , — Jaycee @ 7:54 pm

I. BGP Overview:

1. Path Vector EGP – used to exchange prefix information b/w ASs.

2. Uses TCP port 179 for transport:

a. Required underlying IGP
b. Network cannot route on BGP alone

II. Enabling BGP:

1. Enable the global process

router bgp [AS]

*Only one processes per router

2. Establish BGP Peerings

neighbor [address] remote-as [AS]

*Need to have ip reach-ability

III. Establishing BGP Peerings:

1. Two types of peers:

iBGP – member of the same AS
EBGP – members of different ASs

2. TCP 179 for transport

Normal TCP operations apply

3. Listen for address starting a TCP session at port 179:

neighbor remote-as 100

(router is doing “show ip route”, and do router recursion process to the interface – source of the BGP packet is from)

4. TCP server must agree on where the session is coming from. Need to know which one is TCP Client and which one is TCP Server.


5. TCP Client has the higher BGP router-id

6. If server doesn’t expect session it will refuse

7. Packet sourced from outgoing interface in the routing table

BGP update source

*If there are multiple links b/w BGP peers, you can use “bgp update source” to update the BGP source interface.




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