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divB
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Why is Mikrotik sending multicast with ptmp? Bug?

Tue Oct 19, 2021 10:09 am

I need to connect Mikrotik OSPF with bird over a non-multicast connection.
I have tried nbma but the neighbors are just not recognized, despite identical configuration.

When I try ptmp, Mikrotik is still sending multicast. Here is what arrives at the Linux box:
07:04:47.192109 IP (tos 0xc0, ttl 1, id 25491, offset 0, flags [none], proto OSPF (89), length 64)
    192.168.56.250 > 224.0.0.5: OSPFv2, Hello, length 44
        Router-ID 192.168.56.249, Backbone Area, Authentication Type: simple (1)
        Simple text password: aaa
        Options [External]
          Hello Timer 10s, Dead Timer 40s, Mask 255.255.255.252, Priority 1
07:04:50.770260 IP (tos 0xc0, ttl 1, id 45191, offset 0, flags [none], proto OSPF (89), length 64)
    192.168.56.249 > 192.168.56.250: OSPFv2, Hello, length 44
        Router-ID 192.168.56.248, Backbone Area, Authentication Type: simple (1)
        Simple text password: aaa
        Options [External]
          Hello Timer 10s, Dead Timer 40s, Mask 255.255.255.252, Priority 1
The second packet is from bird which correctly sends a non multicast packet. The first one is from Mikrotik to the linux box which still sends packet to 224.0.0.5, although it is configured as ptmp.
Also in the OSPF Interfaces, it is shown as "State: point to point".

Thanks!
 
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mrz
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Re: Why is Mikrotik sending multicast with ptmp? Bug?  [SOLVED]

Tue Oct 19, 2021 10:36 am

Because RFC says so (RFC2328 section 8.1 and 9.5):
The IP destination address for the packet is selected as
follows. On physical point-to-point networks, the IP
destination is always set to the address AllSPFRouters.

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