Learning default routes from OSPF rather than the EIGRP

[zulkarnain]

Hi All.

We have a scenario when ASBR router has redistribution between OSPF and EIGRP, we can see that the default routes coming from OSPF rather than the EIGRP (where it should). The diagram is as attached

At the B_UP & B_DOWN we have the route-map as follow:

route-map EIGRP-TO-OSPF deny 10
match tag 3000
route-map EIGRP-TO-OSPF permit 20
match ip address prefix-list DEFAULT
set tag 3001
route-map OSPF-TO-EIGRP deny 10
match tag 3001
route-map OSPF-TO-EIGRP deny 20
match ip address prefix-list DEFAULT
route-map OSPF-TO-EIGRP permit 30
set tag 3000

ip prefix-list DEFAULT seq 5 permit 0.0.0.0/0

IN B_UP

router ospf 1
router-id 10.188.207.101
default-information originate route-map EIGRP-TO-OSPF
redistribute direct route-map EIGRP-TO-OSPF
redistribute static route-map STATIC-MAP
redistribute eigrp xxx route-map EIGRP-TO-OSPF

router eigrp xxx
address-family ipv4 unicast
autonomous-system 1
router-id 10.188.207.101
redistribute ospf 1 route-map OSPF-TO-EIGRP

IN B_DOWN

router ospf 1
router-id 10.188.207.101
default-information originate route-map EIGRP-TO-OSPF
redistribute direct route-map EIGRP-TO-OSPF
redistribute static route-map STATIC-MAP
redistribute eigrp xxx route-map EIGRP-TO-OSPF

router eigrp xxx
address-family ipv4 unicast
autonomous-system 1
router-id 10.188.207.101
redistribute ospf 1 route-map OSPF-TO-EIGRP

Question:

How we want to remove the B_UP seeing the default routes learning from the OSPF?

[Enes Simnica]

hello @zulkarnain The reason B_UP is still seeing the default routes from OSPF is that default-information originate generates a default route in OSPF independently of redistribution, so it doesn’t get tagged by your existing route-map statements. As a result, when OSPF is redistributed back into EIGRP, the default route is not matched by match tag 3001 (since it has no tag), and it is permitted by the final permitclause.

Which means that to prevent B_UP from learning the OSPF default route in EIGRP, u should explicitly tag the originated default route and ensure ur redistribution filters it.

In B_UP and B_DOWN:

 ip prefix-list DEFAULT seq 5 permit 0.0.0.0/0

Route-maps:

route-map EIGRP-TO-OSPF deny 10
 match tag 3000

route-map EIGRP-TO-OSPF permit 20
 match ip address prefix-list DEFAULT
 set tag 3001

route-map OSPF-TO-EIGRP deny 10
 match tag 3001

route-map OSPF-TO-EIGRP deny 20
 match ip address prefix-list DEFAULT

route-map OSPF-TO-EIGRP permit 30
 set tag 3000

OSPF config:

router ospf 1
 default-information originate route-map EIGRP-TO-OSPF
 redistribute eigrp <asn> route-map EIGRP-TO-OSPF

EIGRP config: 

router eigrp <asn>
 address-family ipv4 unicast
  redistribute ospf 1 route-map OSPF-TO-EIGRP

and what this does is that it is going to ensure the default route is originated into OSPF (for OSPF neighbors) but never gets redistributed back into EIGRP..... Hope it helps and PEACE!

-Enes

[zulkarnain]

Hi Enes Siminica.

I'm not actually get it what are your statement. I have the set tag of 3001 for the default route in EIGRP-TO-OSPF and match ip address prefix-list DEFAULT and have deny it in route-map OSPF-TO-EIGRP deny 10. Need your help where was wrong.

Thank Yoo

[MHM Cisco World]

https://www.cisco.com/c/en/us/support/docs/ip/enhanced-interior-gateway-routing-protocol-eigrp/8606-redist.html#toc-hId-1078908562

I take fast review' but you use tag for defualt route and dont use it?

This tag can use for filter list

Or 

You can make ospf external have high AD more than 170 (like 200) <<- checl link I share for this solution 

MHM

[MHM Cisco World]

I only change the AD of ospf to be 200 which is higher than 170 of eigrp

[MHM Cisco World]

Warning My suggestion is only if you have lab 
if you have real network I need more info like area you use and how you redistribute the default into ospf 

MHM