[c-nsp] OSPF router gets separated from a broadcast domain

[Gabor Ivanszky]

Hello,


Ed Ravin wrote:
>
>      d1   d2   d3                          d4   d5   d6
>       \    |   /                            \    |   /
>        \   |  /                              \   |  /
>         switch---------leased line------------switch
>            |                                     |
>        Router A                               Router B
>            |                                     |
>            +-- -- -- -- backup tunnel -- -- -- --+
>
>
> I think the answer to the diagram above is "don't do that", or at
> least "don't do that unless all the devices speak OSPF, and you've
> made sure that none of your important traffic uses the IP addresses
> in the broadcast domain that could be unreachable if the Ethernet gets
> partitioned".
>
> The network works fine as long as every device in the broadcast
> domain speaks OSPF and can follow the announced routes whether they
> come from the broadcast domain or from elsewhere.  But for the
> devices that don't speak OSPF, there's no way to reach them from
> the "other side" of the leased line when it is down unless I play
> tricks with /32 routes.
>
>   
the point is that even if all your devices speak OSPF, they will suffer 
from this issue as well.
d4 speaking OSPF doesn't help Router A not to use it's connected 
interface to try to reach the network, and d4 also(and all the possible 
networks behind d4), still creating the blackhole, as far as our tests 
shows.

Gabor