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Services Are Interrupted After an ME60 Changes to Advertise BGP Routes Instead of the Original OSPF Routes

Publication Date:  2019-04-19 Views:  48 Downloads:  0
Issue Description

Simplified networking:

Terminal--switch--ME60--NE5000E---Internet

A user terminal obtains an IP address from an ME60 for Internet access through PPPoE dialup. The ME60 originally imports UNRs in OSPF and advertises the UNRs to an NE5000E. Services are normal in this situation. After the ME60 advertises routes using BGP, the terminal fails to access the Internet.

Handling Process

1. Check whether the BGP peer relationship is properly established on the ME60.

<ME60>display bgp peer 

 BGP local router ID : 1.1.1.1

 Local AS number : 65003

 Total number of peers : 1                Peers in established state : 1

  Peer            V          AS  MsgRcvd  MsgSent  OutQ  Up/Down       State PrefRcv

  10.138.172.1   4       65003   419308    33923     0 0565h17m Established   18958

 

2. Run the display bgp routing-table peer 10.138.172.1 advertised-routes command on the ME60 to check whether BGP routes are properly advertised to the NE5000E. It is found that the BGP routes are properly advertised to the NE5000E.

3. Run the display bgp routing-table peer 1.1.1.1 received-routes command on the NE5000E to check whether routes can be properly received from the ME60.

<HUAWEI> display bgp routing-table peer 1.1.1.1 received-routes 11.11.1.0 24

 BGP Local router ID is 10.138.172.1

 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

 *>i  11.11.1.0/24       1.1.1.1         0          100        0      ?

4. On the NE5000E, check that the service route received from the ME60 is a blackhole route.

<HUAWEI> display ip routing-table 11.11.1.0 24

Route Flags: R - relay, D - download to fib

------------------------------------------------------------------------------

Routing Tables: Public

Summary Count: 1

Destination/Mask    Proto  Pre  Cost  Flags  Nexthop  Interface

   11.11.1.0/24     Static  200    0     D    0.0.0.0   NUll0

5. Check that the NE5000E is configured with a static blackhole route with the priority of 200 and the same mask/prefix as that of the BGP routes learned from the ME60. The BGP priority of the NE5000E is by default 255. As a result, the NE5000E preferentially matches the blackhole route with the priority of 200 over the service routes received from the ME60.

Root Cause

The NE5000E is configured with a static blackhole route with the same mask/prefix as that of the BGP routes learned from the ME60 but a higher priority than that of BGP routes. As a result, the NE5000E preferentially matches the blackhole route over the BGP routes, causing service interruptions.

Solution

1. Delete the blackhole route on the NE5000E.

undo ip route-static 11.11.1.0 24 NULL 0

2. On the NE5000E, change the priority of BGP routes to be greater than that of blackhole routes.

bgp 65003

 #

 ipv4-family unicast

  preference 20 20 20

END