OSPF Connectivity Issue

[Paki]

Hi there

Attached herewith is my OSPF network template (Image 1).

Everything is working very good.

PC-1 can PING PC-2 & OSPF is following best possible costs. When I PING PC-2 to PC-1 (& vice versa), the packet follows path as attached in image 2.

But if I remove the link between R1 (192.168.0.17/30) & R5 (192.168.0.18/30), the ICMP packets from any of these both PC(s) do not travel over any other path. They don't PING any other device except their own gateways & their builtin connected ethernet interfaces.

I also noticed that traffic is not flowing via any Serial link.

OSPF is properly establishing neighbor relationship with next hops.

What could be the possible reason for that?

Your professional advise would be appreciated.

Thank/Regards

[Paki]

Thank You Sawant Singh

 I ll redesign my topology & will be in touch with you again if found any problem.

I hope you will help

Thank You

[Satwant Singh]

Not a problem dear

[Paki]

Dear Satwant Singh & Julio Moisa !!!!!

Finally I am done with it.

At router R1, as soon as I changed the network advertisement of 172.16.20.0/16 from wildcard (0.0.255.255) to subnet mask (255.255.0.0); my problem solved.

Previously, It was

R1(config-router)# network 172.16.0.0 0.0.255.255 area 0

Then, I changed it to

R1(config-router)# network 172.16.0.0 255.255.0.0 area 0

Now If I break any link & keep only one route, ICMP from PC-1 to PC-2 & PC-2 to PC-1 reach at their destinations.

I am very thankful to both of your for support; especially Mr. Satwant Singh to you for your quick responses & the hint you provided to me as in case of 10.0.0.1 to change wildcard from 0.255.255.255 to 0.0.0.255. I applied the same technique & succeeded.

Take Care Guys

Bless You

[Satwant Singh]

C:\>tracert 10.0.0.10

Tracing route to 10.0.0.10 over a maximum of 30 hops:

1 0 ms 0 ms 0 ms 172.16.20.1

2 0 ms 0 ms 0 ms 192.168.0.2

3 1 ms 0 ms 0 ms 192.168.0.6

4 0 ms 0 ms 0 ms 192.168.0.26

5 0 ms 1 ms 0 ms 10.0.0.10

Trace complete.

Even i can see here, PC-1 is not taking the optimal path to Pc-2. (while link is up R1 to R5)

The output should like this:

1/  PC-1 => R1 => R5 => R3=> PC-2 (If link R1 to R5 is working)

2/  PC-1 => R1 => R2=> R5 => R3=> PC-2 (If link R1 to R5 is not working)

[Paki]

My dear !!!

I ll get back to you. Tonight I will try this topology again. Lets c what will happen?

[Paki]

You said, "Secondly, Advertise the 10.0.0.0/8 network correctly with 0.0.0.255 wild card mask." After this, the tracert from PC-1 to PC-2 is as under:

C:\>tracert 10.0.0.10

Tracing route to 10.0.0.10 over a maximum of 30 hops:

1 0 ms 0 ms 0 ms 172.16.20.1

2 0 ms 0 ms 0 ms 192.168.0.2

3 1 ms 0 ms 0 ms 192.168.0.6

4 0 ms 0 ms 0 ms 192.168.0.26

5 0 ms 1 ms 0 ms 10.0.0.10

Trace complete.

Now I executed this command with R1 - R5 link established but this time, the packet traveled from R1, R2, R5 & R4.

What that wildcard change command did with route changed?

Then, As you said, I removed the link between R1-R5 & executed show ip route 172.16.20.10 & show ip route 10.0.0.10 on every router as under:

R1#show ip route 172.16.20.10
Routing entry for 172.16.20.0/24
Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via FastEthernet1/0
      Route metric is 0, traffic share count is 1

R1#show ip route 10.0.0.10
Routing entry for 10.0.0.0/8
Known via "ospf 10", distance 110, metric 4, type intra area
  Last update from 192.168.0.2 on FastEthernet0/1, 00:14:47 ago
  Routing Descriptor Blocks:
  * 192.168.0.2, from 192.168.0.26, 00:14:47 ago, via FastEthernet0/1
      Route metric is 4, traffic share count is 1
===============================================================================
R2#show ip route 172.16.20.10
Routing entry for 172.16.20.0/24
Known via "ospf 20", distance 110, metric 2, type intra area
  Last update from 192.168.0.1 on FastEthernet0/1, 00:18:24 ago
  Routing Descriptor Blocks:
  * 192.168.0.1, from 192.168.0.17, 00:18:24 ago, via FastEthernet0/1
      Route metric is 2, traffic share count is 1

R2#show ip route 10.0.0.10
Routing entry for 10.0.0.0/8
Known via "ospf 20", distance 110, metric 3, type intra area
  Last update from 192.168.0.6 on FastEthernet1/0, 00:18:36 ago
  Routing Descriptor Blocks:
  * 192.168.0.6, from 192.168.0.26, 00:18:36 ago, via FastEthernet1/0
      Route metric is 3, traffic share count is 1
================================================================================
R3#show ip route 172.16.20.10
Routing entry for 172.16.20.0/24
Known via "ospf 30", distance 110, metric 4, type intra area
  Last update from 192.168.0.25 on FastEthernet0/1, 00:16:31 ago
  Routing Descriptor Blocks:
  * 192.168.0.25, from 192.168.0.17, 00:16:31 ago, via FastEthernet0/1
      Route metric is 4, traffic share count is 1

R3#show ip route 10.0.0.10
Routing entry for 10.0.0.0/8
Known via "connected", distance 0, metric 0 (connected, via interface)
  Routing Descriptor Blocks:
  * directly connected, via FastEthernet1/0
      Route metric is 0, traffic share count is 1
====================================================================================
R4#show ip route 172.16.20.10
Routing entry for 172.16.20.0/24
Known via "ospf 40", distance 110, metric 4, type intra area
  Last update from 192.168.0.30 on FastEthernet0/1, 00:17:22 ago
  Routing Descriptor Blocks:
  * 192.168.0.30, from 192.168.0.17, 00:17:22 ago, via FastEthernet0/1
      Route metric is 4, traffic share count is 1

R4#show ip route 10.0.0.10
Routing entry for 10.0.0.0/8
Known via "ospf 40", distance 110, metric 3, type intra area
  Last update from 192.168.0.30 on FastEthernet0/1, 00:20:10 ago
  Routing Descriptor Blocks:
  * 192.168.0.30, from 192.168.0.26, 00:20:10 ago, via FastEthernet0/1
      Route metric is 3, traffic share count is 1
=======================================================================================
R5#show ip route 172.16.20.10
% Network not in table

R5#show ip route 10.0.0.10
% Network not in table

The question arises that even routers are showing connected status of 172.16.20.10 & 10.0.0.10, then why these both PC can not access any interface of R2, R3, R4 & R5 except their immediate connected WAN interfaces. I mean no ICMP packet can get at any router interfaces on any IP.

Dear Sir!!!

I am thankful for your swift replies & for your interest solving my problem.

[Satwant Singh]

Dear Aziz, 

Also share the traceroute output from PC1 to PC2  in both cases (with and without link between R1 to R5)

[Paki]

Please check output of tracert from PC-1 to PC-2 with R1-R5 link established & link broken.

Check file name for distinction.

Also please check Output of "R5 with Link Broken between R1 - R5"

&

Output of "R2 with R1-R5 Link Broken".

[Paki]

One more issue... (when we remove link between R1 & R5)

PC-2 can not PING any interface except the one configured at R3 i-e; 192.168.0.22, 192.168.0.26, 192.168.0.10 & it's own gateway 10.0.0.1.

Similarly, PC-1 can not PING any interface except the one configured at R1 i-e; 192.168.0.1, 192.168.0.17 (down due to link detachment), 192.168.0.13 & it's own gateway 10.0.0.1.

Now, the result is that traffic is not flowing over Serial links & PC-2 can not reached at R5.

I have concluded three results from this:

1)   The link between R1 & R5 is acting as main link & OSPF has not configured any backup link.

2)   I have not configured "keepalive" value on serial. What should be the "keepalive" value assigned to each serial link? (But how is this possible that if "keepalive" is not set at serial interfaces, then why PC-1 & PC-2 can PING each & every node at network when R1 & R3 link is established? Because if "keepalive" is not set, then they should not PING to every serial node. So may be "keepalive" is not problem cause.)

3)   OSPF is configured properly but is not remembering any backup path? This may be due to it is not advertising updates after every 10/30 seconds.

What should be done?

[Paki]

One more issue... (when we remove link between R1 & R5)

PC-2 can not PING any interface except the one configured at R3 i-e; 192.168.0.22, 192.168.0.26, 192.168.0.10 & it's own gateway 10.0.0.1.

Similarly, PC-1 can not PING any interface except the one configured at R1 i-e; 192.168.0.1, 192.168.0.17 (down due to link detachment), 192.168.0.13 & it's own gateway 10.0.0.1.

Now, the result is that traffic is not flowing over Serial links & PC-2 can not reached at R5.

I have concluded three results from this:

1)   The link between R1 & R5 is acting as main link & OSPF has not configured any backup link.

2)   I have not configured "keepalive" value on serial. What should be the "keepalive" value assigned to each serial link? (But how is this possible that if "keepalive" is not set at serial interfaces, then why PC-1 & PC-2 can PING each & every node at network when R1 & R3 link is established? Because if "keepalive" is not set, then they should not PING to every serial node. So may be "keepalive" is not problem cause.)

3)   OSPF is configured properly but is not remembering any backup path? This may be due to it is not advertising updates after every 10/30 seconds.

What should be done?

[Julio E. Moisa]

Hi

OSPF should be running on your interfaces, for example, the serial interface in R1 and R4, R4 and R3 are up? and OSPF running on them? Try to enable clock rate 64000 on R4's serial interfaces. 

You could verify if the subnets are configured correctly under the router ospf process. For testing purposes you could configure under the serial interfaces the following command line assuming you are using area 0

interface serial x/y
ip ospf <Ospf process> area 0

Could you please share the config of R1, R4 and R3 just to check that path?

Thank you in advance. 

[Paki]

Dear Julio Moisa

I have already set clock rate to 64000 at my router's DCE but it is not working.

I have set "ip ospf <process id> area 0" but it is still not functional.

As per your demand, attached herewith are outputs of "show run" at R1, R4 & R3.

Please review & adivse as per your expert opinion.

Thanks for your help & valuable time