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I am Val Glinskiy, network engineer specializing in data center networks. TIME magazine selected me as Person of the Year in 2006.

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Wednesday, January 04, 2012

IPexpert puzzle

IPexpert posted  interesting puzzle today. Here is my solution:

router ospf 1
 network area 0
 default-information originate
router bgp 5
 no synchronization
 bgp router-id
 bgp log-neighbor-changes
 redistribute ospf 1
 neighbor remote-as 4
 neighbor default-originate route-map DEFAULT
 no auto-summary
ip prefix-list DEFAULT seq 5 permit
route-map DEFAULT permit 10
 match ip address prefix-list DEFAULT
Now let's head to R4 and check BGP routes:
R4#sho ip route bgp
B [20/0] via, 00:55:28 is subnetted, 2 subnets
B [20/2] via, 00:55:28
B [20/0] via, 00:55:28
B* [20/0] via, 00:37:36
I am still trying to find out why OSPF would not redistribute static default route. BGP will not redistribute default route even it's in source protocol routing table. It must be loop prevention mechanism, but I can not come up with a scenario when redistributing default route as oppose to originating it can cause routing loop. Especially in OSPF, where "default-information originate" creates Type5 LSA - same type as "redistribute" command would have created:
R2#sho ip ospf database | begin Type-5
                Type-5 AS External Link States
Link ID         ADV Router      Age         Seq#       Checksum Tag     391         0x80000003 0x001F26 1

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