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Frequent Contributor

OSPF To many retransmissions

Hi all,

We have MAN conenction between two sites and both sites use OSPF  as Routing protocol.

I see on Link A and B  router following logs

000717: Mar  4 22:34:09.187 EST: %OSPF-5-ADJCHG: Process 3738, Nbr on GigabitEthernet4/4 from EXSTART to DOWN, Neighbor Down: Dead timer expired
000718: Mar  4 22:35:59.155 EST: %OSPF-5-ADJCHG: Process 3738, Nbr on GigabitEthernet4/4 from EXSTART to DOWN, Neighbor Down: Dead timer expired
000719: Mar  4 22:42:15.531 EST: %OSPF-5-ADJCHG: Process 3738, Nbr on GigabitEthernet4/4 from EXSTART to DOWN, Neighbor Down: Too many retransmissions
000720: Mar  4 22:43:15.531 EST: %OSPF-5-ADJCHG: Process 3738, Nbr on GigabitEthernet4/4 from DOWN to DOWN, Neighbor Down: Ignore timer expired
000721: Mar  4 22:45:25.620 EST: %OSPF-5-ADJCHG: Process 3738, Nbr  on GigabitEthernet4/4 from EXSTART to DOWN, Neighbor Down: Too many retransmissions
000722: Mar  4 22:46:25.620 EST: %OSPF-5-ADJCHG: Process 3738, Nbr on GigabitEthernet4/4 from DOWN to DOWN, Neighbor Down: Ignore timer expired
000723: Mar  4 22:49:09.148 EST: %OSPF-5-ADJCHG: Process 3738, Nbr  on GigabitEthernet4/4 from EXSTART to DOWN, Neighbor Down: Too many retransmissions
000724: Mar  4 22:50:09.148 EST: %OSPF-5-ADJCHG: Process 3738, Nbr  on GigabitEthernet4/4 from DOWN to DOWN, Neighbor Down: Ignore timer expired
000725: Mar  4 22:55:45.952 EST: %OSPF-5-ADJCHG: Process 3738, Nbr  on GigabitEthernet4/4 from EXSTART to DOWN, Neighbor Down: Too many retransmissions
000726: Mar  4 22:56:45.952 EST: %OSPF-5-ADJCHG: Process 3738, Nbr  on GigabitEthernet4/4 from DOWN to DOWN, Neighbor Down: Ignore timer expired
000727: Mar  4 23:00:40.885 EST: %OSPF-5-ADJCHG: Process 3738, Nbr  on GigabitEthernet4/4 from LOADING to FULL, Loading Done

Both sides show OSPF  is down due to Too many retransmissions

Can someone expalinme please what is Too many retransmissions  and how can we fix this?

Is this telco issue or something in cabling or config?

thanks

mahesh

2 ACCEPTED SOLUTIONS

Accepted Solutions
Cisco Employee

Re: OSPF To many retransmissions

Hi Mahesh,

I have seen this "too many retranmission" error message along with EXSTART to DOWN, when you have MTU issue (not MTU mismatch) between the neighbors.

In other words, when your MTU on the interface is say 2000 while for some reason, the router is not able to process pakt of size 2000. In this case, when OSPF is enabled, after initial DBD mesage exchange (with MTU value of 2000 advertised in DBD ), neighbor STATE will be moved to EXSTART and will start sending actual DBD with LSA headers.This DBD packet size will be based on interface MTU. In this case, it will be 2000 which the neighbor may not be able to process. So no ACK or LSA request will be received from neighbor. This will result in moving neighbor STATE from EXSTART to DOWN and same process will continue.

Simply try sending ping traffic to size of outgoing MTU in interface and DF bit set. That will show if you are hitting MTU issue.

HTH,

Nagendra

View solution in original post

Rising star

Re: OSPF To many retransmissions

Hi, You need to use the extended ping command. See below

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f22.shtml

See also a handy MTU mismatch troubleshooting guide between two OSPF routers

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f0d.shtml

View solution in original post

5 REPLIES 5
Cisco Employee

Re: OSPF To many retransmissions

Hi Mahesh,

I have seen this "too many retranmission" error message along with EXSTART to DOWN, when you have MTU issue (not MTU mismatch) between the neighbors.

In other words, when your MTU on the interface is say 2000 while for some reason, the router is not able to process pakt of size 2000. In this case, when OSPF is enabled, after initial DBD mesage exchange (with MTU value of 2000 advertised in DBD ), neighbor STATE will be moved to EXSTART and will start sending actual DBD with LSA headers.This DBD packet size will be based on interface MTU. In this case, it will be 2000 which the neighbor may not be able to process. So no ACK or LSA request will be received from neighbor. This will result in moving neighbor STATE from EXSTART to DOWN and same process will continue.

Simply try sending ping traffic to size of outgoing MTU in interface and DF bit set. That will show if you are hitting MTU issue.

HTH,

Nagendra

View solution in original post

Frequent Contributor

Re: OSPF To many retransmissions

Hi,

Thanks for reply.

how can i do the ping test and check the size of mtu?

mahesh

Rising star

Re: OSPF To many retransmissions

Hi, You need to use the extended ping command. See below

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f22.shtml

See also a handy MTU mismatch troubleshooting guide between two OSPF routers

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080093f0d.shtml

View solution in original post

Frequent Contributor

Re: OSPF To many retransmissions

Hi all,

Many thanks for the update.

regards

mahesh

Beginner

Re: OSPF To many retransmissions

@Nagendra 

You only discussed what's happening but you didn't mention a solution. 

How do we resolve this?

I'm also getting EXSTART to DOWN. I have 9100 ip mtu configured on both ends (one Cisco and one is a different vendor). 

When I configure ip mtu-ignore, the OSPF neighborship comes but, but I don't want to use mtu-ignore. 

Why can't one of the routers process a 9100 mtu packet?  

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