[FROG] sending routes to one area

[Acee Lindem]

Hi Michael, 

> On Apr 15, 2024, at 16:16, Michael DiDomenico <mdidomenico4 at gmail.com> wrote:
> 
> i'm new to frr and ospf, so this might sound like a simple question.  i have a network of clients separated from the rest of a much larger network by four gateways
> 
> pseudo code follows...
> 
> when i config ospf on the gateways
> router ospf
>   router id 1
>   network 10.0.1.0/24 <http://10.0.1.0/24> area 0
>   network 10.0.2.0/24 <http://10.0.2.0/24> area 1
> 
> and then on the clients
> router ospf
>   router id 100
>   network 10.0.2.0/24 <http://10.0.2.0/24> area 1
> 
> all the routing seems to work find and all the hosts on various networks can see each other.  however, what i can't seem to figure out is how i can distribute a default route
> 
> on linux i would do something like
> 
> ip route add default nexthop 10.0.2.1 nexthop 10.0.2.2 nexthop 10.0.2.3 nexthop 10.0.2.4
> 
> and that works in this instance too, in that the packets will flow over the four gateway machines, however if one of the gateways goes down the route table doesn't get updated since i statically defined the default route
> 
> what i want to do is advertise a default route to all the clients in area 1 only.  i can't seem to figure out a combination of redistribute/route-maps/acl's and i haven't been able to locate a clear example on the internet.
> 
> can anyone lend a hand?

Given that the originated default route is advertised as a OSPF AS External LSA (advertised to all non-stub, NSSA areas), you can’t limit the advertisement to area 1 unless it is an NSSA. In the case of an NSSA area, you’d use:

area A.B.C.D nssa default-information-originate [metric-type (1-2)] [metric (0-16777214)] <https://docs.frrouting.org/en/latest/ospfd.html#clicmd-area-A.B.C.D-nssa-default-information-originate-metric-type-1-2-metric-0-16777214>
Hopes this helps. 
Thanks,
Acee



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