hi
i feel ur quzzing up about the bgp setup between a customer and a sp if yes do find some points on the same.You would be requiring to setup BGP on your routers mostly when you are multihomed and when u need to do load sharing or reduandcy setup in your network.
multihomed basically meant here as you are connected to 2 different isp.
in this case you cant simply work with static routes and u need to have some dynamic mechansim in place to take care of the routing as well as the traffic flow once theres some issue with the link or to do load sharing.
if you have 2 links connected to a same isp you can always simply use the static routes to take care of the load sharing as well as the reduandancy.
hope this has given somoe fair basic knowledge on why we are setting up the BGP between a customer site and a SP side.
for more info on y we basically need bgp between AS,setting up load sharing,difference between ibgp and ebgp,attributes in bgp,path selection on bgp do refer this link which has the whole lot repository of bgp..
http://cisco.com/en/US/tech/tk365/tk80/tsd_technology_support_sub-protocol_home.html
regds
