C.2.d) “Show ip bgp neighbor ip-address routes”
1. As said previously, when a customer receives routes from its ISP:
a. The customer will be able to send IP-packets from its network to the ISP (and so the Internet),), so the customer uploads packets to the ISP (and reciprocally we can say that the ISP downloads packets from the customer).
b. By receiving prefixes or routes, a customer controls its outbound/egress/upload traffic packets.
2. With this command, we can check if the traffic engineering has been designed rightly on how the customer wants to upload its traffic to the Internet.
Still it will not tell you clearly, how packets for each subnet are leaving from your router, for that you will need to make a traceroute, originated from an IP’s customer.
a. With that command, you will have much information on the route that your peer advertises to you.
b. The as-path column, show the quality of the ISP and its size as a Tier1 or Tier2.
c. The LocalPref will show if our route-map have been applied correctly, and which BGP table is the best by default.
d. The next-hop is obviously the bgp speaker ip address.
3. In our case, ISP-B BGP table is the best one since LocalPref is fixed to 100. Unless a next-hop is fixed to a specific network, default upload traffic should go to ISP-B.
ISP-C’s BGP table is tagged with LocalPref90, in case of ISP-B link is cut, the ISP-C’s BGP table will be the prefered one(it is an Ebgp table, so has priority on RTA’s Ibgp table, even if BGP selection criteria are the same, Localpref 90).