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OSPF Question

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#

4 REPLIES

Re: OSPF Question

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.

Re: OSPF Question

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

Blue

Re: OSPF Question

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?

Hall of Fame Super Silver

Re: OSPF Question

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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