03-17-2009 09:09 AM - edited 03-04-2019 03:58 AM
OK, stupid question time.
I have an OSPF router that is learning a default route from 2 ASBRs through the default information originate command.
In the OSPF database, you can see both LSAs with the same cost.
So what does the router use as the tie breaker when deciding whcih default route to use when they both have the same metric.
arcr01#sh ip ospf database nssa-external 0.0.0.0
OSPF Router with ID (19.211.101.154) (Process ID 521)
Type-7 AS External Link States (Area 301)
Routing Bit Set on this LSA
LS age: 220
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 19.213.1.130
LS Seq Number: 80000E78
Checksum: 0x1338
Length: 36
Network Mask: /0
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 1
Forward Address: 19.213.1.130
External Route Tag: 0
Routing Bit Set on this LSA
LS age: 1095
Options: (No TOS-capability, Type 7/5 translation, DC)
LS Type: AS External Link
Link State ID: 0.0.0.0 (External Network Number )
Advertising Router: 19.213.1.154
LS Seq Number: 800011BD
Checksum: 0x4092
Length: 36
Network Mask: /0
Metric Type: 2 (Larger than any link state path)
TOS: 0
Metric: 1
Forward Address: 19.213.1.154
External Route Tag: 0
arcr01#
arcr01#sh ip ro 0.0.0.0
Routing entry for 0.0.0.0/0, supernet
Known via "ospf 521", distance 110, metric 1, candidate default path, type NSSA extern 2, forward metric 256
Last update from 19.210.108.17 on FastEthernet3/0, 18:53:22 ago
Routing Descriptor Blocks:
* 19.210.108.17, from 19.213.1.130, 18:53:22 ago, via FastEthernet3/0
Route metric is 1, traffic share count is 1
Solved! Go to Solution.
03-17-2009 09:22 AM
Hello Victor,
if you have two O E2 routes 0.0.0.0/0 with same seed metric and same metric to fowarding address the local router should install both in its IP routing table
Hope to help
Giuseppe
03-17-2009 09:15 AM
Hello Victor,
I would say the OSPF metric to the fowarding address of each LSA
verify the OSPF metrics for
19.213.1.130
and for
19.213.1.154
the first one should be 256
Known via "ospf 521", distance 110, metric 1, candidate default path, type NSSA extern 2, >> forward metric 256
Hope to help
Giuseppe
03-17-2009 09:18 AM
Yeah, I told you it was a stupid question...LOL..I just realized that one defautl route is learned through an FE interface, while the other is only a T3. I thought they were both the same interface BWs. Sorry.
Now that I opened the can of worms, lets say both interfaces were FEs, how would OSPF select the best default route? If it were any other route to another network, then it can have equal cost paths, I know...but what about the default?
03-17-2009 09:22 AM
Hello Victor,
if you have two O E2 routes 0.0.0.0/0 with same seed metric and same metric to fowarding address the local router should install both in its IP routing table
Hope to help
Giuseppe
03-17-2009 09:29 AM
Interesting, so you CAN indeed do some load sharing by using two distinct default routes and have them both in your routing table.
I thought the router could only select one default route.
Excellent, dude!
By the way, go back to that thread about those Asia routers (ECC and FMC) because I got an update for ya! :-)
Thanks, again
Victor
Find answers to your questions by entering keywords or phrases in the Search bar above. New here? Use these resources to familiarize yourself with the community: