Border Gateway Protocol. Interdomain routing protocol that replaces EGP. BGP exchanges reachability information with other BGP systems. It is defined by RFC1163.
(Source: CISCO)

BGP Uses TCP Port 179 To communicate between other BGP Routers
It will only exchange info between routers specified in the config file.

64512 to 65534
Only these asn's can be used on a private network the other are for public (the Internet)

Here is a basic config (parts taken from node fut)
For quagga BGPD
 ! BGPD.conf
 !-*- bgp -*-
 !
 !BGPd sample configuratin file
 !
 hostname bgpd
 password XXXX or zebra
 !enable password please-set-at-here
 !
 !bgp mulitple-instance  -? only if you need to run BGPD more than once Unlikely  on mw.
 !
 router bgp 7675  -? your routers ASN Should be with in this range 64512 to 65534 and connot be the same as another routers in this situation.
 bgp router-id 10.10.129.145 -? this is your routers id most likey the same as in your ospf.conf
 redistribute ospf -? this will redistribute routes collected by ospfd to bgpd
 redistribute connected -? This  will distribute Directly connected networks to bgp
 !DAN'S COMMENT: be careful using redistribute connected - you don't want to
 !distribute your local area network subnet onto the melbwireless network!
 !bgp should automaticlly distribute routes covered by the network statement
 network 10.10.0.0/16 -? you can use this for mw or add each subnet that you are
 !connected to i.e: network 0.10.128.0/28 network 10.10.129.144/29 and so on
 neighbor 10.10.128.97 remote-as 7676 -? for each router on the a subnet that is running bgp will have its own ip(duh!) and its own asn you will need to add a line for each router and there asn here.
 !
 !access-list all permit any most likely you will not need any access list unless you need to.
 !
 !The debug section is optional.
 debug bgp events
 debug bgp filters
 debug bgp fsm
 debug bgp keepalives
 debug bgp updates
 !log file bgpd.log
 !
 log stdout


! Simple example for the 10.10.128.0/28 subnet

So in The end your config might look like this if you were on the subnet 10.10.128.0 (example) This is only if the rest of the networks used ospf

 !-*- bgp -*-
 hostname bgpd
 password zebra
 !enable password please-set-at-here
 !
 router bgp 64512
 bgp router-id 10.10.128.1
 redistribute ospf
 network 10.10.0.0/16
 neighbor 10.10.128.3 remote-as 64513
 neighbor 10.10.128.5 remote-as 64515
 neighbor 10.10.128.7 remote-as 64517
 neighbor 10.10.128.8 remote-as 64518
 !
 !log file bgpd.log
 !
 log stdout



! BGP ASN allocation
Node ID is the Mw node ID
Router No. Is the router at the node, as you may have more than 1.
ASN 64512 to 65534 try to leave a 5 No. gap between each node.

||Node ID||||Router No.||||ASN||
||FUT||||1||||64515||
||FUT||||2||||64516||
||FUU||||1||||64520||
||FUU||||2||||64521||
||GMR||||1||||64525||
||GHO||||1||||64530||
||GWS||||1||||64535||
||FUS||||1||||64540||
||FKR||||1||||64545||
||FSA||||1||||64646||
||GUR||||1||||64550||
||HKF||||1||||64555||
||IKD||||1||||64560||
||KWQ||||1||||64565||
||JQD||||1||||64570||
||DCG||||1||||64574||
||AJJ||||1||||64575||
||KXW||||1||||64580||
||KZZ||||1||||64585||
||LAA||||1||||64586||
||ICQ||||1||||64590||
||WXW||||1||||64595||
||KEI||||1||||64600||
||KWH||||1||||64605||
||WZJ||||1||||64610||
||GDW||||1||||64615||
||KOR||||1||||64620||
||KVK||||1||||64625||
||WWW||||1||||65000||