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brcinko
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Posts: 3
Joined: Wed Jan 03, 2018 10:07 am

OSPF MTU adjustement

Mon Aug 05, 2019 12:53 pm

Hi,

I have a question abuout automatic MTU adjustement in OSPF protocol implementation.

I have two routers - one is Cisco ASR9k - IOS-XR, second is mikrotik RouterOS 6.44.5.

I found an issue with MTU and network types in OSPF. When I use broadcast network type and default MTU of 1500 bytes, everything is working correctly. When i switch to point-to-point network type, neighborship wont come up to FULL state. Reason is MTU mismatch.

Mikrotik change its own MTU for point-to-point network type. MTU is lowered from 1500 to 1482. This is a problem because Ciscos MTU is still the same.
When I change Cisco MTU, OSPF will come to FULL state, but some application have problem with MSS adujstement and dont work correctly.

Is there some way how we can disable auto-mtu adjusements for point-to-point network type on Mikrotik?

Thank you for the reply.
 
faraujo88
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Posts: 14
Joined: Fri Feb 15, 2019 2:28 am

Re: OSPF MTU adjustement

Mon Aug 05, 2019 1:01 pm

Hi,

I have a question abuout automatic MTU adjustement in OSPF protocol implementation.

I have two routers - one is Cisco ASR9k - IOS-XR, second is mikrotik RouterOS 6.44.5.

I found an issue with MTU and network types in OSPF. When I use broadcast network type and default MTU of 1500 bytes, everything is working correctly. When i switch to point-to-point network type, neighborship wont come up to FULL state. Reason is MTU mismatch.

Mikrotik change its own MTU for point-to-point network type. MTU is lowered from 1500 to 1482. This is a problem because Ciscos MTU is still the same.
When I change Cisco MTU, OSPF will come to FULL state, but some application have problem with MSS adujstement and dont work correctly.

Is there some way how we can disable auto-mtu adjusements for point-to-point network type on Mikrotik?

Thank you for the reply.
Did u Try rising mtu mannualy in Mikrotik?

Enviado de meu MI 9 usando o Tapatalk

 
brcinko
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Topic Author
Posts: 3
Joined: Wed Jan 03, 2018 10:07 am

Re: OSPF MTU adjustement

Mon Aug 05, 2019 4:58 pm

Did u Try rising mtu mannualy in Mikrotik?

Enviado de meu MI 9 usando o Tapatalk
I did not. I cant make another outage for client. Ive tried this in lab with same RouterOS version (6.44.5). Everything works perfectly in lab enviroment. Broadcast and Point-to-point have still the same MTU - 1500. Its look like some strage software error or something for that very Mikrotik.
 
ebertyrodrigues
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Posts: 4
Joined: Sun Aug 30, 2015 4:25 am

Re: OSPF MTU adjustement

Tue Aug 06, 2019 1:38 am

Já verificou se não tem outro equipamento entre os 2 que está com MTU mais baixo, porque em laboratório é ligado direto e em campo as vezes temos algum ponto a ponto.
 
faraujo88
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Posts: 14
Joined: Fri Feb 15, 2019 2:28 am

Re: OSPF MTU adjustement

Tue Aug 06, 2019 3:32 am

Já verificou se não tem outro equipamento entre os 2 que está com MTU mais baixo, porque em laboratório é ligado direto e em campo as vezes temos algum ponto a ponto.
Pode ser tb, todos os equipamentos participantes devem comportar o tamanho do pacote.

Enviado de meu MI 9 usando o Tapatalk

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