[j-nsp] Preventing direct routes from forming OSPF summaries

Wayne Tucker wayne at tuckerlabs.com
Thu Aug 30 11:22:31 EDT 2012

On Thu, Aug 30, 2012 at 6:42 AM, Tore Anderson
<tore.anderson at redpill-linpro.com> wrote:
> I have a OSPFv3 network that looks something like this (simplified):
> +-----+                                +-----+
> |MX240|xe-0/0/0 ---(area 0)--- xe-0/0/0|MX240|
> +-----+                                +-----+
> xe-0/1/0                              xe-0/1/0
>    |                                      |
> (area 1)           +------+            (area 1)
>    \------ xe-0/0/0|EX4500|xe-1/0/0 ------/
>                    +------+
>                     ||||||
>                (production stuff)
> I noticed that if the OSPF session between one MX and the EX goes down,
> that MX will continue to install the summary discard route, effectively
> blackholing all traffic destined for area 1.[snip]
> Is there a clever way to avoid this? I'm thinking along the lines of a
> knob that would make it so that a summary wouldn't pop into existence
> unless an active *ospf* route from inside the area-range exists.

None that I know of.  Depending on your overall design you might be able to:

1.) Number the transit links out of a different space.  You can
summarize (or suppress) them separately.
2.) Configure xe-0/0/0 in area 1 of both MXs as a secondary interface.
 That will allow them to exchange the LSDB for that area even when the
downlink to the EX is down.  There are other reasons that you'd
probably want that, anyhow.

Note: I haven't tested #2 with OSPFv3, but it has always worked fine
for me in v2.


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