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Routing distribution issue?

Hello,

I'm not sure what problem that I'm facing but hoping any expert here could help.

Customer router, CE HQ site is connected to 2 ISP PE router , PE-a and PE-b using OSPF. PE-a act as active link and PE-b act as backup link.

All customer branches sites are using  CE HQ as a gateway to internet.

Then, when active link down, all the branches cannot access to internet. Further check, default route cannot be learn from other branch.

When I checked the config at router PE-a, configuration for default-information originate for both OSPF and BGP were in place but NOT in router PE-b.

So while investigate the Active link PE-a (that was down at that time), default-information originate for both OSPF and BGP were added at router PE-b.

After that, customer branches site can access to internet.

When the Active PE-a router up, traffic still goes thru PE-b instead off router PE-a. Config default-information originate at PE-b had to be remove back so that traffic could flow back thru PE-a.

Do you guys have any idea why this happen?

Sample config at PE router

#####Active link (Router PE-a)########

!

router ospf 2627 vrf V739:ABC

log-adjacency-changes

redistribute bgp 24645 subnets

network 114.133.89.212 0.0.0.3 area 0

default-information originate

!

!

router bgp 24645

!

address-family ipv4 vrf V739:ABC

  redistribute connected

  redistribute static

  redistribute ospf 2627 vrf V739:ABC metric 1 match internal external 1 external 2

  default-information originate

  no auto-summary

  no synchronization

exit-address-family

end

#####Backup link Router PE-b####

router ospf 2627 vrf V739:ABC

log-adjacency-changes

redistribute static subnets

redistribute bgp 24645 subnets

network 27.146.93.64 0.0.0.3 area 0

!

!

router bgp 24645

!

address-family ipv4 vrf V739:ABC

  redistribute connected

  redistribute static

  redistribute ospf 2627 vrf V739:ABC match internal external 1 external 2

  no auto-summary

  no synchronization

exit-address-family

end

Thanks

4 REPLIES 4
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Hall of Fame Mentor

At the remote branches, from a distribution switch, were you able to see 2 default routes in OSPF or just one?

Can you verify both routers were injecting the default route into OSPF by issuing the command:

show ip ospf database external 0.0.0.0

(we need to perform this command while having both routers with default-information originate configured)

It is expected to have 2 entries. If you want PE-A to be primary and PE-B to be secondary, you can add the metric-type option on the default-information originate command. Metric-Type 1 for the primary and leave the other as is which will result Metric-Type 2 (default).

Highlighted

Hello Edison,

Thanks for replying. Very helpful

Btw, is the any reason or where I should start to check when there is only one entry of default  route when issuing command show ip ospf database external 0.0.0.0?

Highlighted

Your remote sites will use the default route learned via OSPF and the command I suggested will verify if both routers are advertising it, which they should.

For OSPF troubleshooting, it is recommended to see the OSPF table then the routing table.

BTW, the default-information originate in BGP should only be apply on the PE routers where the internet is connected, not in the branch routers, that's how it is configured?

In the branch routers, you should only have default-information originate under OSPF.

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Thank you