03-03-2012 08:20 PM - edited 03-04-2019 03:32 PM
Hello,
In a lab, I have a router with 2 EIGRP adjacencies. Both neighbors are advertising a route for the 10.254.254.1/32 subnet. One of them has an internal route and the other is an external route (redistributed from OSPF).
With both adjacencies up, when I do a sh ip ei topo I only see the internal route:
Remote2#sh ip ei topo 10.254.254.1/32
EIGRP-IPv4 Topology Entry for AS(100)/ID(10.254.254.4) for 10.254.254.1/32
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 156160
Descriptor Blocks:
10.100.1.1 (FastEthernet1/1), from 10.100.1.1, Send flag is 0x0
Composite metric is (156160/128256), route is Internal
Vector metric:
Minimum bandwidth is 100000 Kbit
Total delay is 5100 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 1
Originating router is 10.254.254.1
If I shutdown the interface on which I receive the internal route and do another sh ip ei topo, I now see the external route:
Remote2#sh ip ei topo 10.254.254.1/32
EIGRP-IPv4 Topology Entry for AS(100)/ID(10.254.254.4) for 10.254.254.1/32
State is Passive, Query origin flag is 1, 1 Successor(s), FD is 412160
Descriptor Blocks:
10.1.3.1 (FastEthernet1/0), from 10.1.3.1, Send flag is 0x0
Composite metric is (412160/409600), route is External
Vector metric:
Minimum bandwidth is 100000 Kbit
Total delay is 15100 microseconds
Reliability is 255/255
Load is 1/255
Minimum MTU is 1500
Hop count is 1
Originating router is 10.1.3.1
External data:
AS number of route is 100
External protocol is OSPF, external metric is 20
Administrator tag is 0 (0x00000000)
Why the external route does no appear in the sh ip ei topo when both links are up?
Thank you
Solved! Go to Solution.
03-03-2012 11:06 PM
Hi Barney,
Most probably, this happens because if the internal route is available, it is propagated to the router performing OSPF-to-EIGRP redistribution, but on that router, the EIGRP route is more preferred (the AD=90 as opposed to OSPF's AD=110) and is placed into the routing table. Therefore, the redistributing router does not redistribute this route from OSPF to EIGRP because in its routing table, the route is not learned from OSPF in the first place.
Remember that in order for a route to be redistributed from protocol A to protocol B, it must first be present in the routing table as learned by protocol A, and will always stay that way, even after redistribution.
Please feel welcome to ask further, this is is a commonly confusing topic.
Best regards,
Peter
03-03-2012 11:06 PM
Hi Barney,
Most probably, this happens because if the internal route is available, it is propagated to the router performing OSPF-to-EIGRP redistribution, but on that router, the EIGRP route is more preferred (the AD=90 as opposed to OSPF's AD=110) and is placed into the routing table. Therefore, the redistributing router does not redistribute this route from OSPF to EIGRP because in its routing table, the route is not learned from OSPF in the first place.
Remember that in order for a route to be redistributed from protocol A to protocol B, it must first be present in the routing table as learned by protocol A, and will always stay that way, even after redistribution.
Please feel welcome to ask further, this is is a commonly confusing topic.
Best regards,
Peter
03-04-2012 09:19 AM
It makes sense, thanks for the clear explanation!
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