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Knowledge Base

The Change of BGP MED Value Is Not Displayed on the NE5000E

Publication Date:  2019-07-17  |   Views:  405  |   Downloads:  0  |   Author:  SU1001733910  |   Document ID:  EKB0000325903

Contents

Issue Description

            ip ip-prefix list-1 index 1 permit xxx.xxx.96.0 19 
route-policy set-med permit node 10
 if-match ip-prefix list-1
 apply cost 200
route-policy set-med permit node 20
 apply cost 1
bgp xxxx
 peer xxx.xxx.254.193 as-number xxxx
 ......
 network xxx.xxx.96.0 255.255.224.0
 network xxx.xxx.128.0 255.255.224.0 route-policy set-med
 .......
 peer xxx.xxx.254.193 route-policy set-med export
On the NE5000E, display the routes advertised to the peer. The following information is displayed:
[NE5000E-bgp]disp bgp rou peer xxx.xxx.254.193 advertised-routes
 Total Number of Routes: 42
 BGP Local router ID is xxx.xxx.252.132
 Status codes: * - valid, > - best, d - damped,
               h - history,  i - internal, s - suppressed, S - Stale
               Origin : i - IGP, e - EGP, ? - incomplete
      Network            NextHop        MED        LocPrf    PrefVal Path/Ogn
 *>   xxx.xxx.96.0/19     0.0.0.0         0                     0      i
 *>   xxx.xxx.128.0/19   0.0.0.0        200                 0      i
......
Although the policy set-med is applied to the routes exported to the peer in the network segment xxx.xxx.96.0/19, the med value of the EBGP routes advertised to the peer is still 0 instead of the changed200 inthe display information of the disp bgp rou peer xxx.xxx.254.193 advertised-routes command. In the network segment xxx.xxx.128.0/19, the policy set-med is applied and the med value of the EBGP routes advertised to the peer is the changed value, 200, in the display information of the disp bgp rou peer xxx.xxx.254.193 advertised-routes command.

Alarm Information

Null

      

Handling Process

The preceding indicates that the display is normal and no action is required. The implementation of the device of Company C is the same. You can check whether the configuration takes effect or not on the peer device or use the debug bgp command on the local device to verity whether the changed police take effect or not.

      

Root Cause

Each router that runs BGP maintains a local BGP RIB table. The BGI RIB table records all the routes generated and imported by the local router and the routes received from IBGP and EBGP peers. The NE5000E selects the optimized route and records the route in the local IP RIB table after comparing the routes in the BGP RIB with other protocol routes. BGP records routes of a network segment directly in the local BGP RIB. If there is a policy changing BGP route properties, BGP records the route properties changed by the policy to the BGP RIB together with the route.
1. If the policy is applied to the exported routes, BGP does not record the changed properties of BGP routes to the local BGP RIB.
2.
If the policy is applied to the exported routes, BGP records the changed properties of BGP routes to the local BGP RIB.
Description of the display bgp routing-table peer ip-address {advertised-routes | received-routes} command:
The keyword advertised-routes is used to display the routes in the BGP RIB table that are advertised to the peer. Therefore, changed properties of exported routes are not recorded.
The keyword received-routes is used to display the routes received from the peer. The routes are not obtained from the local BGP RIB table. Therefore, changed properties of exported routes are recorded and displayed.
To view the routes in the local BGP RIB table, run the following command:
display bgp routing-table

            

Suggestions

Null