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OSPF database inconsistency

OK, so I've got Routers F,G,H forming Area 0 along a 10.4.4.0/24 token ring segment. Router F's PPP link to Router E forms Area 1. (215.0.0.4/30 (.5=E; .6=F).

For consistent OSPF Router ID's, I've given each router a loopback of 222.1.x.1/24; where x equals the router's letter (E/5, F/6, G/7, H/8).

When I do a sh ip ospf database on Router F, I get this:

=======================================

OSPF Router with ID (222.1.6.1) (Process ID 100)

Router Link States (Area 0)

Link ID ADV Router Age Seq# Checksum Link count

222.1.6.1 222.1.6.1 22 0x80000009 0xFB31 2

222.1.7.1 222.1.7.1 393 0x80000005 0x84A2 1

222.1.8.1 222.1.8.1 273 0x80000005 0x2307 2

Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum

10.4.4.8 222.1.8.1 22 0x80000006 0x690D

Summary Net Link States (Area 0)

Link ID ADV Router Age Seq# Checksum

215.0.0.4 222.1.6.1 22 0x80000003 0x4CAE

Router Link States (Area 1)

Link ID ADV Router Age Seq# Checksum Link count

215.0.0.5 215.0.0.5 1887 0x80000002 0x63E9 2

222.1.6.1 222.1.6.1 92 0x80000003 0x50EF 2

Summary Net Link States (Area 1)

Link ID ADV Router Age Seq# Checksum

10.4.4.0 222.1.6.1 92 0x80000002 0xD666

222.1.6.1 222.1.6.1 92 0x80000002 0xD993

222.1.8.1 222.1.6.1 92 0x80000002 0xFF65

=======================================

Some of the many questions I have about this output are:

1) How come only 10.4.4.8 (Router H) is listed as a Net Link (why not .7/Router G?)

2) While network 222.1.6.1 and 222.1.8.1 are in fact declared on their host router's ospf process; 222.1.7.1 is NOT (see Router F's routing table below). Why then does 222.1.7.1 show up as a link ID?

3) Why does 10.4.4.0 show as a Summary Net Link in Area 1? The network 10.4.4.0 0.0.0.255 area 0 command was config'd on Router E - area 0, I say.

Here's Router F's routing table:

======================================

C 222.1.6.0/24 is directly connected, Loopback0

215.0.0.0/24 is variably subnetted, 2 subnets, 2 masks

C 215.0.0.5/32 is directly connected, Serial0

C 215.0.0.4/30 is directly connected, Serial0

10.0.0.0/24 is subnetted, 1 subnets

C 10.4.4.0 is directly connected, TokenRing0

222.1.8.0/32 is subnetted, 1 subnets

O 222.1.8.1 [110/7] via 10.4.4.8, 00:00:07, TokenRing0

2 ACCEPTED SOLUTIONS

Accepted Solutions
Hall of Fame Super Bronze

Re: OSPF database inconsistency

So, why is G's loopback appearing as a Link ID in Router F's database?

I already covered this on my first reply.

Router F's OSPF database is purely displaying the Router-IDs as LSA Type 1. You can change the Router-ID to any non-routable dotted decimal address and it will be displayed in the LSA Type 1 in all routers in the segment.

This is where it lists the links it's advertising outbound into that area?

6.1 is the ABR for Area 1 and it's telling Router E, how to get to 10.4.4.0 .

___

Edison.

Hall of Fame Super Bronze

Re: OSPF database inconsistency

So, the router ID of a neighbor router automatically becomes a Link ID, even if it's the address of a non-participating interface?

Yes.

9 REPLIES
Hall of Fame Super Bronze

Re: OSPF database inconsistency

1) How come only 10.4.4.8 (Router H) is listed as a Net Link (why not .7/Router G?)

You have 3 OSPF speaking routers in a LAN and the one with the highest loopback becomes the DR for that segment.

2) While network 222.1.6.1 and 222.1.8.1 are in fact declared on their host router's ospf process; 222.1.7.1 is NOT (see Router F's routing table below). Why then does 222.1.7.1 show up as a link ID?

That's a good question, can you post the show ip os int brief and show ip ospf neigh from Router F and Router G?

Remember, the OSPF Router ID is selected when enabling OSPF process but it does not automatically advertise the interface into OSPF. The loopback must be included in the network statement to be advertised as well.

3) Why does 10.4.4.0 show as a Summary Net Link in Area 1? The network 10.4.4.0 0.0.0.255 area 0 command was config'd on Router E - area 0, I say.

Can we see show ip os int brief from that router?

__

Edison.

Re: OSPF database inconsistency

Here you go:

Router-F#sh ip os int brief

^

% Invalid input detected at '^' marker.

Router-F#sh ip ospf neigh

Neighbor ID Pri State Dead Time Address Interface

222.1.7.1 1 FULL/BDR 00:00:39 10.4.4.7 TokenRing0

222.1.8.1 1 FULL/DR 00:00:35 10.4.4.8 TokenRing0

222.1.5.1 1 FULL/ - 00:00:37 215.0.0.5 Serial0

Router-F#

Router-G>sh ip os int brief

^

% Invalid input detected at '^' marker.

Router-G>sh ip ospf neigh

Neighbor ID Pri State Dead Time Address Interface

222.1.6.1 1 FULL/DROTHER 00:00:39 10.4.4.6 TokenRing0

222.1.8.1 1 FULL/DR 00:00:35 10.4.4.8 TokenRing0

Router-G>

Router-E#sh ip ospf int brief

^

% Invalid input detected at '^' marker.

Router-E#

Here's the IOS versions we're running:

Router E:

IOS (tm) 2500 Software (C2500-I-L), Version 12.0(8), RELEASE SOFTWARE (fc1)

System image file is "flash:c2500-i-l.120-8.bin"

Router F:

IOS (tm) 2500 Software (C2500-JK8OS-L), Version 12.2(1d), RELEASE SOFTWARE (fc1)

System image file is "flash:/c2500-jk8os-l.122-1d.bin"

Router G:

IOS (tm) 2500 Software (C2500-JK8OS-L), Version 12.2(1d), RELEASE SOFTWARE (fc1)

System image file is "flash:/c2500-jk8os-l.122-1d.bin"

Hall of Fame Super Bronze

Re: OSPF database inconsistency

Very old software :)

Try show ip ospf interface

Re: OSPF database inconsistency

Yeah they're all 2500's (as I guess you could tell from the system image filename).

Router-E>sh ip ospf int

Serial1 is up, line protocol is up

Internet Address 215.0.0.5/30, Area 1

Process ID 100, Router ID 222.1.5.1, Network Type POINT_TO_POINT, Cost: 64

Transmit Delay is 1 sec, State POINT_TO_POINT,

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Hello due in 00:00:01

Neighbor Count is 1, Adjacent neighbor count is 1

Adjacent with neighbor 222.1.6.1

Suppress hello for 0 neighbor(s)

Router-F>sh ip ospf int

Loopback0 is up, line protocol is up

Internet Address 222.1.6.1/24, Area 0

Process ID 100, Router ID 222.1.6.1, Network Type LOOPBACK, Cost: 1

Loopback interface is treated as a stub Host

TokenRing0 is up, line protocol is up

Internet Address 10.4.4.6/24, Area 0

Process ID 100, Router ID 222.1.6.1, Network Type BROADCAST, Cost: 6

Transmit Delay is 1 sec, State DROTHER, Priority 1

Designated Router (ID) 222.1.8.1, Interface address 10.4.4.8

Backup Designated router (ID) 222.1.7.1, Interface address 10.4.4.7

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Hello due in 00:00:08

Index 1/1, flood queue length 0

Next 0x0(0)/0x0(0)

Last flood scan length is 0, maximum is 2

Last flood scan time is 0 msec, maximum is 4 msec

Neighbor Count is 2, Adjacent neighbor count is 2

Adjacent with neighbor 222.1.7.1 (Backup Designated Router)

Adjacent with neighbor 222.1.8.1 (Designated Router)

Suppress hello for 0 neighbor(s)

Serial0 is up, line protocol is up

Internet Address 215.0.0.6/30, Area 1

Process ID 100, Router ID 222.1.6.1, Network Type POINT_TO_POINT, Cost: 64

Transmit Delay is 1 sec, State POINT_TO_POINT,

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Hello due in 00:00:09

Index 1/3, flood queue length 0

Next 0x0(0)/0x0(0)

Last flood scan length is 2, maximum is 4

Last flood scan time is 0 msec, maximum is 4 msec

Neighbor Count is 1, Adjacent neighbor count is 1

Adjacent with neighbor 222.1.5.1

Suppress hello for 0 neighbor(s)

Router-F#

Router-G>sh ip ospf int

Serial0 is down, line protocol is down

Internet Address 215.0.0.13/30, Area 0

Process ID 100, Router ID 222.1.7.1, Network Type POINT_TO_POINT, Cost: 64

Transmit Delay is 1 sec, State DOWN,

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

TokenRing0 is up, line protocol is up

Internet Address 10.4.4.7/24, Area 0

Process ID 100, Router ID 222.1.7.1, Network Type BROADCAST, Cost: 6

Transmit Delay is 1 sec, State BDR, Priority 1

Designated Router (ID) 222.1.8.1, Interface address 10.4.4.8

Backup Designated router (ID) 222.1.7.1, Interface address 10.4.4.7

Timer intervals configured, Hello 10, Dead 40, Wait 40, Retransmit 5

Hello due in 00:00:00

Index 1/1, flood queue length 0

Next 0x0(0)/0x0(0)

Last flood scan length is 0, maximum is 1

Last flood scan time is 0 msec, maximum is 0 msec

Neighbor Count is 2, Adjacent neighbor count is 2

Adjacent with neighbor 222.1.6.1

Adjacent with neighbor 222.1.8.1 (Designated Router)

Suppress hello for 0 neighbor(s)

Router-G>

Hall of Fame Super Bronze

Re: OSPF database inconsistency

As I presumed, Router G does not have the loopback under the OSPF process.

As for having the LAN subnet in Area 1 on Router F, that's Router F way of announcing that subnet to Router E as an IA route.

HTH,

Please rate helpful posts

Re: OSPF database inconsistency

Well, I TOLD you Router G didn't have the loopback under the OSPF process (as you can tell from F's routing table, where H's loopback is present and G's isn't). So, why is G's loopback appearing as a Link ID in Router F's database?

For the LAN/Area 1 stuff - This is where it lists the links it's advertising outbound into that area? I thought it was where it listed the links it receives FROM that area.

Hall of Fame Super Bronze

Re: OSPF database inconsistency

So, why is G's loopback appearing as a Link ID in Router F's database?

I already covered this on my first reply.

Router F's OSPF database is purely displaying the Router-IDs as LSA Type 1. You can change the Router-ID to any non-routable dotted decimal address and it will be displayed in the LSA Type 1 in all routers in the segment.

This is where it lists the links it's advertising outbound into that area?

6.1 is the ABR for Area 1 and it's telling Router E, how to get to 10.4.4.0 .

___

Edison.

Re: OSPF database inconsistency

Ah yes, just as I meant to say :-P

See, I'm still pretty new to interarea OSPF; so I guess part of why I'm confused is that you said above that "Remember, the OSPF Router ID is selected when enabling OSPF process but it does not automatically advertise the interface into OSPF. The loopback must be included in the network statement to be advertised as well."

So, since Router G/7's loopback wasn't included I didn't expect to see that loopack address as a Link ID in the Router Link States box. I don't mind seeing it as the Adv Router ID, I just didn't think that loopack address was something it would be Adv'ing.

So, the router ID of a neighbor router automatically becomes a Link ID, even if it's the address of a non-participating interface?

Hall of Fame Super Bronze

Re: OSPF database inconsistency

So, the router ID of a neighbor router automatically becomes a Link ID, even if it's the address of a non-participating interface?

Yes.

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