OSPF MTU adjustement

RouterOS Forwarding Protocols
1

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.

2

Did u Try rising mtu mannualy in Mikrotik?

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3

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.

4

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.

5

Pode ser tb, todos os equipamentos participantes devem comportar o tamanho do pacote.

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