Route advertisement with AS path

Question

Hello
We are running Multi-homed network, to influence the BGP route selection, we are using AS path attribute with route-maps.
Recently, we observed that the routes advertised on TCL network(ISP 1) were not reflected in global routing table.
For example, we have advertised a network (196.X.X.X/24) on TCL BGP peer as best path and also advertised the same network on another BGP peer with AS path pretend of 10times. But, the network is reaching via Bharti BGP (iSP 2 )peer instead of TCL peer.
Can anyone help understand as why it is preferred route is via Bharti 
Thanks
Viswa Sai

Answer 1

Network statement in BGP configuration is used to identify which networks are being advertised. BGP process then checks the global routing table, if it sees a prefix in global routing table and with exact match (including subnet mask), only then it will advertise that network to other BGP peers. 
Is this network a local network or learned from other routing protocols? If locak, make sure you enter exact mask of the network seen in routing table. If learned from other routing protocols, the better way is to selectively redistribute iGP routes into BGP using prefix-list and route-map.
As far as convergence is concerned, below is explanation:
BGP routers router will not start the BGP Best-Path calculation/selection process until they receives all NLRI from BGP peer. This will be known from UPDATE messages. End of UPDATE messages is usually identified after a KEEPALIVE message is received. 
The time taken to learn new best path is directly proportional to number of NLRIs received from peers. 
Only when your service provider router selects it's best path, and installs into RIB, it is going to send UPDATE message to your routers. If SP routers use line cards with Cisco distributed forwarding, it is going to populate it's FIB and then send UPDATE message.
It depends on how fast your Bharati BGP peer detects your network unreachable and sends UPDATE messages to it's peers to withdraw your network's NLRI from it's routing table.
There are ways to improve this convergence, but at service provider level. In your network, if you want faster re-convergence, static routes (with higher AD) would be a wonderful solution.
Few other ways would be to use:
Bidirectional forwarding detection (BFD)
fast neighbor failover
BGP next hop tracking
BGP best external path (IOS and vendor specific)
BGP prefix convergence (IOS and vendor specific)
Peace and Health,
Ravindra