1. Customer network use NE 80 router and has been configured with BGP routing.
But when display the BGP routing table, the best routing path selected is the link with Local Pref 400, it is selected over the link with Local Pref 500.
2. Customer need to use the link with Local Pref 500 as their best path for routing.
Refer to attachment (NE 80 BGP Route Selection.txt).
1. Check the physical link condition.
--- no physical link faulty.
--- if link is down the route will not be selected in the bgp routing priority.
2. Check all router the network topology.
--- there is no router down.
--- if the next hop for the link is down, it will not be selected in the routing.
3. Check if there is any routing protocol applied in the network.
---no other routing protocol applied is affecting the routing table.
---if there is, it will select the route based on these routing protocol sequence ospf, is-is, ebgp, static, rip, and ibgp.
4. Check the bgp routing protocol by execute the command "display bgp routing-table".
--- Check the attributes and policies for bgp to select best route priority and found that the link with Local Pref 400 have the smaller value for preference ( pre value )
i. "pre value" - smaller the value, higher the priority.
5. Change the "pre value" for Local Pref 500 link from "pre 200" to "pre 10", after change execute the "refresh bgp" command line.
6. Execute again "display bgp routing-table" and check the best path selected.
7. The link with Local Pref 500 and "pre 10" value will be chosen as the best path.
8. Problem solved.
1. From the "display bgp routing-table" information, found that the "pre 20" with the first route, "pre 200" with the last route . " pre " means protocol priority. It is in the first position priority when BGP selects routes.
2. The best path was selected based to the smaller "pre 20" preference value for the Local Pref 400 link.
3. The preference value for Local Pref 500 link is "pre 200" which is higher than the Local Pref 400 link.
4. The smaller the "pre" value , the higher the priority.
Please remember when configuring the BGP, need to follow the route selection attributes and it policy. The best path will be selected based on the priority of the attributes. Any misconfiguration will affect the routing table sequences.