topic Re: OSPF stuck in Exchange/DR in Switching

OSPF stuck in Exchange/DR

mistryj — Wed, 06 Mar 2019 12:11:01 GMT

We have a point to point 100MG connection between a 6509 gig interface and a 3750G-48TS Gig interface.

Its a basic point o point but the OSPF fails to load and gets stuck in Exchange/DR as below.

The circuit has been tested by the provider and they have said that there are no issues and MTU has been set correctly to 1500.

Has anyone come across this problem before and how we can over come this ?

Neighbor ID Pri State Dead Time Address Interface

10.137.243.1 1 EXCHANGE/DR 00:00:14 10.128.0.173

Re: OSPF stuck in Exchange/DR

Giuseppe Larosa — Mon, 23 Feb 2009 11:28:48 GMT

Hello Jaya,

try to use

debug ip ospf adj

on your side to see what is happening.

Being the C6509 a multi layer switch it can have different ip settings at physical interface level and at the SVI (interface vlan) if the port is not a routed port.

A MTU mismatch is probably the reason.

Also check the ospf network type with

sh ip ospf interface

have you used

ip ospf network point-to-point on your side or on the provider side they used it ?

feel to free to post debug outputs if public ip addresses are not involved

Hope to help

Giuseppe

Re: OSPF stuck in Exchange/DR

mistryj — Mon, 23 Feb 2009 12:09:26 GMT

Hi Giuseppe,

Please find attached outputs as requested.

Regards,

Jaya

Re: OSPF stuck in Exchange/DR

Giuseppe Larosa — Mon, 23 Feb 2009 13:47:33 GMT

Hello Jaya,

to be able to distingush from different possible problems I would suggest to remove OSPF authentication configuration.

From the debugs we see that the C3750 is elected DR and tries to send first Database Descriptor packet but it never receives an ack from the C6500.

So after some attempts 14 the neighbor state is restarted.

02.554 GMT: OSPF: Send DBD to 10.134.243.2 on GigabitEthernet1/0/2 seq 0x17DA opt 0x52 flag 0x7 len 32

001170: *Mar 1 18:22:02.554 GMT: OSPF: Send with youngest Key 1

001171: *Mar 1 18:22:02.554 GMT: OSPF: Retransmitting DBD to 10.134.243.2 on GigabitEthernet1/0/2 [11]

001172: *Mar 1 18:22:03.141 GMT: OSPF: Send with youngest Key 1

001173: *Mar 1 18:22:03.477 GMT: OSPF: rcv. v:2 t:1 l:48 rid:10.134.243.2

aid:0.0.0.0 chk:0 aut:2 keyid:1 seq:0x4980537F from GigabitEthernet1/0/2

I think you need to verify if NTP in sync in the second device :

the second device thinks it March 1

the c6500 thinks it is Feb 23

this can make them to use a different key.

then also enable datetime in logging

on C3750 with

service timestamps log datetime msec

service timestamps deb datetime msec

So disable the authentication and see what happens

Hope to help

Giuseppe

Re: OSPF stuck in Exchange/DR

mistryj — Tue, 24 Feb 2009 16:41:17 GMT

Hi Giuseppe,

The clock was set manually on the 3750 and removed ip ospf authentication message-digest and message-digest key.

But still no change.

The ospf works if you put another 3750 instead of using the 6509, why is that ?

Re: OSPF stuck in Exchange/DR

glen.grant — Tue, 24 Feb 2009 23:42:55 GMT

Also check to make sure your network statements are correct on each side with the correct masking .

Re: OSPF stuck in Exchange/DR

CSCO11188854 — Wed, 25 Feb 2009 01:29:54 GMT

Try on the 6509 interface facing the 3750

switch-if#ip ospf mtu-ignore

see how that goes.

Re: OSPF stuck in Exchange/DR

Peter010101 — Wed, 25 Feb 2009 03:43:42 GMT

Hi Jaja,

Did you remove authentication on both the 6500 and the 3750?

Looking at the show ip ospf int config both the 6500 and 3750 think its the DR.

On one of the interfaces add ip ospf priority 255 and on the other ip ospf priority 0.

ip ospf priority 255 - higher # is preferred. - Always become the DR.

ip ospf priority 0 - never become the DR

Let me know of this works for you.

Re: OSPF stuck in Exchange/DR

mistryj — Wed, 25 Feb 2009 10:46:24 GMT

Thank you all for you replies unfortunately no change tried all the following suggestions :-

1. The Network statements have correct subnet masks.

2. I have tried removing the following authentication but no change.

ip ospf authentication message-digest

ip ospf message-digest-key 1 md5 7 050F5501351C40

3. I set 6509 interface to priority to 255 and 3750 to priority to 0. Still no change its now stuck in Exchange/DROTHER.

4. I have 'ip ospf mtu-ignore' set on both interfaces but no change same results.

Re: OSPF stuck in Exchange/DR

Giuseppe Larosa — Wed, 25 Feb 2009 17:37:19 GMT

Hello Jaya,

after removing the authentication and changing the ip ospf priority the problem is still there.

I would suggest you to do the following:

sh system mtu

on the C3750

a) remove ip ospf mtu-ignore on both sides

apply

ip mtu 1500

b) collect output of debug ip ospf adj on both sides

if you have changed the system MTU on c3750 there can be a side effect on SVIs and size of DBD packets.

I now remember I had problems with a C3550 to build OSPF adjacency with routers.

Hope to help

Giuseppe

Re: OSPF stuck in Exchange/DR

Peter010101 — Thu, 26 Feb 2009 00:22:08 GMT

Giuseppe,

With ip ospf mtu-ignore then the MTU is ignored so it does not matter if the MTU on one side is different. I've used this successfully where the switch MTU was 1504 and the router MTU was 1500.

What issues have you run into using ospf mtu-ignore?

Jaya for troubleshooting please remove it as Giuseppe suggests.

Re: OSPF stuck in Exchange/DR

Peter010101 — Thu, 26 Feb 2009 00:24:01 GMT

"The ospf works if you put another 3750 instead of using the 6509, why is that?"

What is the difference between the two configurations?

Re: OSPF stuck in Exchange/DR

Peter010101 — Thu, 26 Feb 2009 00:26:23 GMT

Please paste the output of the following commands from both ends.

show ip ospf

show ip ospf neighbor

debug ip ospf adj

debug ip ospf events

Re: OSPF stuck in Exchange/DR

mistryj — Thu, 26 Feb 2009 11:33:21 GMT

Hello all,

Please find attached debug files.

I have removed ip ospf mtu-ignore but left the ospf authentication statements in.

The outputs include :-

3750_CS01#sh system mtu

System MTU size is 1500 bytes

System Jumbo MTU size is 1500 bytes

Routing MTU size is 1500 bytes

3750_CS01#

show ip ospf

show ip ospf neighbor

debug ip ospf adj

debug ip ospf events

Re: OSPF stuck in Exchange/DR

Peter010101 — Thu, 26 Feb 2009 22:28:06 GMT

Neighbor ID Pri State Dead Time Address Interface

10.137.243.1 1 EXCHANGE/DR 00:00:15 10.128.0.173

3750_CS01#sh ip ospf nei

Neighbor ID Pri State Dead Time Address Interface

10.134.243.2 1 INIT/DROTHER 00:00:13 10.128.0.174 GigabitEthernet1/0/47

OSPF: Nbr 10.134.243.2 10.128.0.174 GigabitEthernet1/0/47 is currently ignored

Common causes are

INIT - ACL blocking, corrupt database

EXSTART/EXCHANGE mtu mismatch- fix mtu or ip ospf mtu-ignore

Take a look at the acl's on the 6509.

Re: OSPF stuck in Exchange/DR

Mohamad Qayoom — Thu, 26 Feb 2009 22:41:33 GMT

Did you try removing CoS on the 6509 switch?

Re: OSPF stuck in Exchange/DR

Giuseppe Larosa — Fri, 27 Feb 2009 06:15:51 GMT

Hello Jaya,

I noticed that when the C6500 sends a bigger DBD with size 1412 bytes it is never received by c3750

example from your logs

255334: .Feb 26 11:04:46.296 GMT: OSPF: Send DBD to 10.137.243.1 on GigabitEthernet7/48 seq 0x99B opt 0x52 flag 0x2 len 1412

255335: .Feb 26 11:04:46.296 GMT: OSPF: Send with youngest Key 1

if you look in C3750 log and search for string Rcv DBD you can find only:

005726: .Feb 26 11:05:48.618: OSPF: Rcv DBD from 10.134.243.2 on GigabitEthernet1/0/47 seq 0x11BC opt 0x52 flag 0x7 len 32 mtu 1500 state EXSTART

005727: .Feb 26 11:05:48.618: OSPF: First DBD and we are not SLAVE

on the c6500 the same search gives much more matches

So the question can be at the physical layer check cables:

it looks like that small frames are received but when C6500 says it sending a DBD with size 1412 bytes it is not seen on the other side

check for errors in interfaces

with sh int g1/0/47

sh int g7/48

Hope to help

Giuseppe

Re: OSPF stuck in Exchange/DR

mistryj — Fri, 27 Feb 2009 13:48:55 GMT

Hi All,

I have tried removing access-lists and COS but no luck.

Giuseppe there are no errors on the interface and I do feel there is some configuration missing on the provider side. Do they need to have DF bit set on their equipment along with MTU 1500 ?

Hence the reason 6509 is not sending more than 1400 bytes ?

Re: OSPF stuck in Exchange/DR

Giuseppe Larosa — Sat, 28 Feb 2009 11:04:50 GMT

Hello Jaya,

I've never realized up to now there is another device in the middle or at least a L2 transport service of a service provider.

DF can be set on packets not on equipment. In our case DBD packets have the DF bit set in the IPv4 header.

Call them and explain that packets from one side (C6500) are not received on the other end (C3750) if their size is near to 1500.

the c6500 sends a DBD packet of 1412 bytes or with payload 1412 bytes but it is not seen on the C3750 side

You can also check yourself using extended ping and debug ip icmp if there are MTU issues on the link.

You can use the sweep option to explore a range of packet sizes while you have debug ip icmp on the other switch.

Hope to help

Giuseppe

Re: OSPF stuck in Exchange/DR

mistryj — Wed, 04 Mar 2009 21:42:54 GMT

Hi Giuseppe,

I have connected a laptop at one end and PC at the other end of the circuit and tested ping using different packet sizes and this was fine.

The provider configured a router and connected at the 6509 end with the 3750 at the other end and the connection worked for them. They are saying the circuit is fine and are not helping to resolve this any more.

What I cant understand is what different the 6509 IOS switch is doing compared to a Cisco 3750/Cisco Router. If I have a Cisco 3750 switch connected at both ends OSPF works fine.

Its getting to the point where we will have to put in a 3750 infront of the 6509 just to get this to work, its not a solution we want but we are running out of time.