BGP Theory and basic config

Basics
Neighbors are manually configured.
Stage: IDLE, ACTIVE, Open Sent, Open Confirmed, Established

Hello sent every 60 seconds with a hold-down of 180 seconds.
Capable of MD5 authentication

Rule of Synchronization
Routes learnt via iBGP must be validated by the interior routing table before they can be advertised to remote peers - eBGP. Sync can be off/on at bgp router connected to remote ebgp peer.

Rule of Split-Horizon
Routes learnt via IBGP will never be sent to another IBGP peer
Route reflector to overcome this issue.


Attributes (Mandatory, Well-known Optional - transitive/non-transitive)
AS-Path, Next-Hop, Origin (IGP,EGP,Unknown?)
Local Preference(higher better), weight(local router, higher better) = select Exit point
Atomic Aggregate = this route is summarized
MED - used to suggest an entry point into your AS (lower is better)
Aggregator = designates IP addr of the router who performed summarization,
Community = used for route tagging

Basic Configuration
ip address of neighbors must be reachable(eg. via Internal routing protocol); exact subnet mask;
router bgp AS number
neighbor x.x.x.x remote-as 666
network 10.1.0.0 mask 255.255.0.0
neighbor 3.3.3.3 ebgp-multihop 2 -- if interfaces are not directly connected to each other
neighbor 3.3.3.3 update-source loopback 0 - to use if router's bgp address is loopback or not directly connected to neigbor
no auto summary

no synchronization -- turn of rule of synchronization
neighbor 2.2.2.2 next-hop-self -- when ebgp route is advertised back to ibgp

Troubleshooting
debug ip bgp updates