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OSPF configuration rules

Fri May 22, 2020 9:55 pm

Hi all,
I have a small network running ospf, but I need to optimize the configuration cause of a lot of messages in logs. I'm not sure on how to correctly configure all routers.
You can find attached a picture showing a simplified layout of my network. Actually I run "broadcast" OSPF on routers R1, R2, R3, and CHR server and it works.
I know that using wireless link, the best ospf network type is NBMA, so I have to choose wich routes will become DR, add NBMA neighbors manually and set the router priority.
Now my questions are:
1) probably R1 is the only candidate to be DR because is the only one that is connected to each others. Is it right?
2) Is it correct to exclude the wireless ptp devices from routers running ospf if I set static route rules into them?
3) working for example on R1, I have to add in the nbma neighbors list, the addresses of routers R2 and R3 (not W1M, W2M, W3M)
4) since I have a redundant link between R1 and R3 I have to add R3 twice on nbma neighbors list?
5) if R1 is the designated router, all its neighnors should have priority 0
6) When I add the intefaces in ospf of R1, the priority and network type are referred to the link to devices W1M, W2M, W3M, directly connected to it, or are referred to its neighbors R2 and R3?

Thank you for your support
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Re: OSPF configuration rules

Thu May 28, 2020 3:33 am

Actually i've found NBMA to be quite buggy on MikroTik and I can't think of any upsides to using it. The only 2 possible scenario's I can think it has any merit whatsoever is
1) You have some really antiquated shitty radio equipment or you are leasing a link from another company that does not support or provide you with VLAN's
2) If it dynamically learned neighbors to slightly reduce configuration time, but it doesn't so its a mute point

Always use point-to-point. And in the case of having multiple routers in the same physical broadcast domain i.e. 3 radio's connected to a multi-point. Setup 1 VLAN interface per router, with its own /30 subnet and OSPF interface setup as point-to-point. Then you won't have any strange convergence issues or missing routes like i've always seemed to have with NBMA. You also avoid the need to a DR/BDR and split-horizon issues

The way I do is is to use VLAN's on every single link in our network between routers, even if they are truly point-to-point. This is because you can use a mangle rule to 'set priority from dscp high 3 bits' so in the case of radio's not being able to read DSCP tags, they use rely on the 3 bit priority field in a VLAN header for QoS. This isn't necessary, but i've found its helped to simplify QoS
And any radio's/switches/etc that need management access they either use a management VLAN, or they just use the native/untagged/no vlan and get their DHCP lease from the upstream router. I.e. R1 in your case
R2 and R3 should only communicate to R1 via the VLAN you setup for them
4) since I have a redundant link between R1 and R3 I have to add R3 twice on nbma neighbors list?'
the way I do that is to setup 2 VLAN's for R1 and R3. i.e. vlan301 and vlan302 for instance. If you make them exactly the same, they'll load balance. However if they should function like as as primary/backup role, just raise the interface cost on the backup links to i.e. 15. Ideally turn BFD on for the primary link to provide much faster fail-over, but leave it off on the backup link
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Re: OSPF configuration rules

Sat May 30, 2020 11:27 am

Hi millenium7 and thankyou for you advice, I will try as you suggested. I suppose that in my case vlan is not necessary, right?

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