07-13-2009 11:02 AM - edited 03-06-2019 06:44 AM
Hi:
Roueters RIB shows 2 default routes learned from two OSPF neighbors.
Why do I only see one LSA for th default route if two neighbors are sending LSAs?
router 4#sh ip ro 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
Known via "ospf 16586", distance 110, metric 1, candidate default path
Tag 16586, type extern 2, forward metric 3
Last update from 71.22.7.157 on TenGigabitEthernet9/2, 6d18h ago
Routing Descriptor Blocks:
* 71.22.7.165, from 64.13.44.104, 6d18h ago, via TenGigabitEthernet9/1
Route metric is 1, traffic share count is 1
Route tag 16586
71.22.7.157, from 64.13.44.104, 6d18h ago, via TenGigabitEthernet9/2
Route metric is 1, traffic share count is 1
Route tag 16586
router 4#
router 4#
router 4#
router 4#
router 4#
router 4#
router 4#sh ip ospf data ext 0.0.0.0
OSPF Router with ID (64.13.44.112) (Process ID 16586)
Type-5 AS External Link States
Routing Bit Set on this LSA in topology Base with MTID 0
LS age: 25
Options: (No TOS-capability, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 64.13.44.104
LS Seq Number: 8000032A
Checksum: 0x1B3D
Length: 36
Network Mask: /0
Metric Type: 2 (Larger than any link state path)
MTID: 0
Metric: 1
Forward Address: 66.192.62.1
External Route Tag: 16586
router 4#
router 4#
router 4#
router 4#sh ip ospf nei
Neighbor ID Pri State Dead Time Address Interface
64.13.44.111 1 FULL/BDR 808 msec 71.22.7.157 TenGigabitEthernet9/2
64.13.44.105 1 FULL/BDR 836 msec 71.22.7.165 TenGigabitEthernet9/1
router 4#
07-13-2009 11:24 AM
The obvious thought is that the default is generated at one point in your network (64.13.44.104) but you have two equakl cost paths to get to it.
07-13-2009 12:55 PM
Victor,
Router4 has received this information from 64.13.44.104(Advertising Router) who generated Type5LSA. Because this router can reach 66.192.62.1(Forward Address) via 2 paths(equal cost) that's why you see 2 default routes in RIB.
However,This should be posted in the routing forum. J/K (grin)
Toshi
07-13-2009 07:39 PM
Yes, I see...stupid question, really..
One router originated the default and it learned it from two equal cost paths....
Why there are 2 routes in the RIB is easy to understand, I knew that. I just couldnt figure out why there was only one LSA....I guess the only LSA that should appear is from the router that orginated it....right?
07-14-2009 05:41 AM
Hello Victor,
>> .I guess the only LSA that should appear is from the router that orginated it....right?
yes, an LSA is a data structure with a single owner the node that originated it other nodes can just flood it.
Best Regards
Giuseppe
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