OSPF Multilink routing issue

From: Rob Phillips <rrphillips_at_swankav.com>
Date: Tue, 22 Sep 2009 19:49:21 -0500

I have an issue that has been racking my brain and I just can not figure it
out.

I have 3 routers Using Multilink PPP. R6 ----- R2 ------ R5

When all links are up R2 believes any routes behind R5 are actually reachable
through R6. The example below is a loopback on R5 (5.5.5.5). In all cases it
knows that 143.43.65.5 is the next hop, however the router believes to get to
143.43.65.5 is through Multilink 2 when it has to route. (aka pinging
143.43.65.5 works from R2, but every route in the routing table shows
143.43.65.5 via Multilink 2 when it should actually follow Multilink 1)

Area 0 is on a loopback on R2.

Any help would be great. I am pulling out the few hairs I have left on the
top of my head. I have tried every show command I and think of and even
started trying show commands I never heard off. Tried several different
debugs but nothing!

If I don't figure it out soon, my head may get so bare and shiney that light
bouncing off of it may blind a proctor during my lab. How many points do you
lose for that?

R2

interface Multilink1
 ip address 143.43.65.2 255.255.255.0
 ip ospf network point-to-multipoint
 ip ospf hello-interval 10
 ppp multilink
 ppp multilink group 1
!
interface Multilink2
 ip address 143.43.65.2 255.255.255.0
 ip ospf network point-to-multipoint
 ip ospf hello-interval 10
 ppp multilink
 ppp multilink group 2

interface Serial0/1/0
 no ip address
 encapsulation frame-relay
 frame-relay traffic-shaping
 frame-relay interface-dlci 205 ppp Virtual-Template1
 frame-relay interface-dlci 206 ppp Virtual-Template2
 frame-relay interface-dlci 215 ppp Virtual-Template1
 frame-relay interface-dlci 216 ppp Virtual-Template2
 frame-relay interface-dlci 225 ppp Virtual-Template1
 frame-relay interface-dlci 226 ppp Virtual-Template2
 no frame-relay inverse-arp
!
interface Virtual-Template1
 no ip address
 ppp multilink
 ppp multilink group 1
!
interface Virtual-Template2
 no ip address
 ppp multilink
 ppp multilink group 2

router ospf 1
 router-id 2.2.2.2
 log-adjacency-changes
 area 0.0.37.128 virtual-link 5.5.5.5
 redistribute eigrp 24 subnets
 network 143.43.65.2 0.0.0.0 area 0.0.37.128

Routing entry for 5.5.5.5/32
  Known via "ospf 1", distance 110, metric 1191, type inter area
  Redistributing via eigrp 24
  Advertised by eigrp 24 metric 1 1 1 1 1
  Last update from 143.43.65.5 on Multilink2, 00:35:54 ago
  Routing Descriptor Blocks:
  * 143.43.65.5, from 5.5.5.5, 00:35:54 ago, via Multilink2
      Route metric is 1191, traffic share count is 1

Neighbor ID Pri State Dead Time Address Interface
5.5.5.5 0 FULL/ - - 143.43.65.5 OSPF_VL0
6.6.6.6 0 FULL/ - 00:01:32 143.43.65.6 Multilink2
5.5.5.5 0 FULL/ - 00:01:48 143.43.65.5 Multilink1

R5

interface Multilink1
 ip address 143.43.65.5 255.255.255.0
 ip ospf network point-to-point
 ppp multilink
 ppp multilink group 1

interface Serial0/1/0
 no ip address
 encapsulation frame-relay
 frame-relay traffic-shaping
 frame-relay interface-dlci 502 ppp Virtual-Template1
 frame-relay interface-dlci 512 ppp Virtual-Template1
 frame-relay interface-dlci 522 ppp Virtual-Template1
 no frame-relay inverse-arp
interface Virtual-Template1
 no ip address
 ppp multilink
 ppp multilink group 1
!
router ospf 1
 router-id 5.5.5.5
 log-adjacency-changes
 area 0.0.37.128 virtual-link 2.2.2.2
 network 143.43.65.5 0.0.0.0 area 0.0.37.128
!

Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 0 FULL/ - - 143.43.65.2 OSPF_VL0
192.168.2.8 1 FULL/DR 00:00:38 143.43.200.2
FastEthernet0/0
2.2.2.2 0 FULL/ - 00:01:30 143.43.65.2 Multilink1

R6

interface Multilink2
 ip address 143.43.65.6 255.255.255.0
 ip ospf network point-to-point
 ppp multilink
 ppp multilink group 2.

interface Serial0/1/0
 no ip address
 encapsulation frame-relay
 frame-relay traffic-shaping
 frame-relay interface-dlci 602 ppp Virtual-Template1
 frame-relay interface-dlci 612 ppp Virtual-Template1
 frame-relay interface-dlci 622 ppp Virtual-Template1
 no frame-relay inverse-arp

interface Virtual-Template1
 no ip address
 ppp multilink
 ppp multilink group 2
!
router ospf 1
 router-id 6.6.6.6
 log-adjacency-changes
 network 143.43.65.6 0.0.0.0 area 0.0.37.128

Neighbor ID Pri State Dead Time Address Interface
2.2.2.2 0 FULL/ - 00:01:56 143.43.65.2 Multilink2
143.43.96.9 0 FULL/ - 00:00:39 143.43.96.9 MFR1.1

  Known via "ospf 1", distance 110, metric 2381, type inter area
  Last update from 143.43.65.2 on Multilink2, 00:44:10 ago
  Routing Descriptor Blocks:
  * 143.43.65.2, from 5.5.5.5, 00:44:10 ago, via Multilink2
      Route metric is 2381, traffic share count is 1

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Received on Tue Sep 22 2009 - 19:49:21 ART

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