BGP Route Advertisement – Comprehensive Guide

Does BGP dynamically advertises its route like IGPs or I have to configure the network statement for loopback and neighbor statements?

This question is confusing. Even with IGPs, you need to tell the routing protocol what to advertise. For example, you use network statements to tell OSPF which interfaces participate in OSPF (and possibly redistribution to advertise networks), which doesn't automatically advertise every interface address (e.g. loopbacks) or network in the router.

With BGP, you use network statements to tell BGP which prefixes (that already exist in the routing table, including directly connected networks) to advertise. A loopback network will exist in the routing table, so you can use a network statement to advertise it, or you can redistribute connected networks, just like you can do with OSPF.

BGP will not simply try to connect to a peer on an interface, the way some IGPs do when they are configured to use a network interface. You don't tell BGP which interfaces are to participate in the routing protocol; you specifically tell BGP a peer address and AS because BGP uses TCP. If the AS is the same as the router AS, then it is iBGP, otherwise it is eBGP.

Further does this command advertise routes to its neighboring AS:

neighbor x.x.x.x remote-as xxxx activate

Without anything that restrict what is advertised, e.g. a prefix list, that command will advertise any prefixes in the BGP table to an eBGP peer, but iBGP has a rule that it will not advertise iBGP-learned routes to an iBGP peer.