I have a bunch of /30 thru /27 subnets on my network. OSPF seems to exchange a whole bunch of /32s inside of those and only some of the entire subnets and I can’t understand why.
10.0.1.8/30 would show
10.0.1.9 and
10.0.1.10
etc. . . I have a /27 connected route that only the routeros single IP is getting put into the routing tables as a /32 and not the whole /27. cant figure out why.
4.6 and 4.10
it seems as though this happens when i use PTMP instead of BROADCAST on the network type. I am using ptmp on the wireless links because of the multicast problems. i was using ptmp on the CPE subnets as well because those are wireless, but then i only get the /32 ip of the router and not the entire subnet injected into the routing table. how can i work around this?
hmmm… fo wireless, they recomment nbma, not ptmp
either way, does ospf inject routes differently based on the network type? Shouldn’t a /28 subnet get injected as a /28 rather than a bunch of individual /32s?
Somewhere I read ptmp was more stable for wireless but took longer to converge, and nbma was less stable for wireless but was faster converging. I will find that shortly.
Yes, PtMP interfaces will inject a /32 route for each adjacency, along with one for the router’s own interface address. They will not inject the aggregate.
This is done to support discontinuous subnets, where not all routers in that subnet are directly adjacent. It’s really only useful for carrying routes to OSPF routers, not for anything else that may be in those subnets.
For example, this is useful with multi-point wireless with layer 2 forwarding disabled. You can number the AP and the stations all in a single /24, with the /24 mask; yet each station will end up with a /32 route to each other, via the AP.
PtMP is a bit more intense calculation-wise than Broadcast or NBMA, since all routers must run SPF.
Since there are no DR/BDR dependencies, the failure of a single router is less likely to impact an entire segment, only traffic flowing through the problematic router should be affected. Since switching our network over to PtMP, OSPF stability has dramatically increased.
PtMP still uses multicast hellos however, so if you want pure unicast OSPF, NBMA is the only way to go.
–Eric