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An S7700 Fails to Advertise the Default Route Through OSPF

Publication Date:  2019-03-26 Views:  105 Downloads:  0

Issue Description

Software version: V200R010

Problem description: On the network shown in the following figure, the S7700 acts as the network egress and uses OSPF to advertise the default route to the S5700. However, the default route is not found in the S5700's routing table.

Handling Process

1. Check the configuration of the S7700.

 ospf 1 router-id 1.1.1.1

 default-route-advertise always

 import-route direct

 import-route static

The S7700 imports external routes and its role is an ASBR. The always parameter is specified when the S7700 advertises the default route to the S5700. Theoretically, the default route is successfully advertised.

2. Check whether the S7700 generates a Type 5 LSA for the default route.

[S7700]dis ospf lsdb  ase self-originate

OSPF Process 1 with Router ID 1.1.1.1

      Link State Database

  Type      : External

  Ls id     : 0.0.0.0

  Adv rtr   : 1.1.1.1 

  Ls age    : 1095

  Len       : 36

  Options   :  E 

  seq#      : 80000004

  chksum    : 0xdaee

  Net mask  : 0.0.0.0

  TOS 0  Metric: 1

  E type    : 2

  Forwarding Address : 0.0.0.0

  Tag       : 1

  Priority  : Low

The command output shows that the S7700 has generated a Type 5 LSA for the default route.

3. Check whether the S5700 receives the Type 5 LSA of the default route advertised by the S7700.

<NT_BG_putou.14>   dis ospf lsdb ase 0.0.0.0

OSPF Process 1 with Router ID 5.5.5.5

       Link State Database


  Type      : External

  Ls id     : 0.0.0.0

  Adv rtr   : 5.5.5.5 

  Ls age    : 310

  Len       : 36

  Options   :  E 

  seq#      : 80000006

  chksum    : 0x5e59

  Net mask  : 0.0.0.0

  TOS 0  Metric: 1

  E type    : 2

  Forwarding Address : 0.0.0.0

  Tag       : 1

  Priority  : Low


  Type      : External

  Ls id     : 0.0.0.0

  Adv rtr   : 1.1.1.1 

  Ls age    : 1178

  Len       : 36

  Options   :  E 

  seq#      : 80000004

  chksum    : 0xdaee

  Net mask  : 0.0.0.0

  TOS 0  Metric: 1

  E type    : 2

  Forwarding Address : 0.0.0.0

  Tag       : 1

  Priority  : Medium

The command output shows that the S5700 has received the Type 5 LSA of the default route advertised by the S7700. However, the S5700 itself also generates a Type 5 LSA for a default route. In this case, the S5700 considers that the default route already exists and does not add the default route advertised by the S7700 to the routing table.

4. Check the configuration of the S5700.

ospf 1 router-id 5.5.5.5

 default-route-advertise always

It is found that the S5700 also has the configuration for advertising a default route. Therefore, it generates a Type 5 LSA for the default route.

Root Cause

The configuration of advertising a default route has been configured in the OSPF process of the S5700.

Solution

On the S5700, delete the configuration of advertising the default route

  ospf 1 router-id 5.5.5.5

   undo default-route-advertise



Suggestions

If an OSPF-enabled device has been configured to advertise a default route, it cannot add an OSPF default route advertised by another device to the routing table.

END