[j-nsp] Routing loop with OSPFv3 NSSA and external routes

[Alex Arseniev]

Looks like R2 has 2 equal-cost Ext routes, both with metric-type 2.
What happens if you redistribute on SW1 with metric-type 1?
Also, what do your link metrics look like? Are they BW-related or just 1 for 
any link (LAG or single 1/10GE)?
Lastly, what happens if R1 has "no-nssa-abr" configured?
Thanks
Alex

----- Original Message ----- 
From: "Tore Anderson" <tore at fud.no>
To: "Juniper List" <juniper-nsp at puck.nether.net>
Sent: Thursday, February 21, 2013 11:55 AM
Subject: [j-nsp] Routing loop with OSPFv3 NSSA and external routes


> Hi list,
>
> I'm scratching my head over an OSPFv3 routing loop to an external NSSA
> destination that happens when extending the area to another router in
> the backbone.
>
> This is (hopefully) all the relevant parts of the currently (working)
> setup. The two routers R1 and R2 are MX-es running JUNOS 12.2R3,
> SW1 is an EX4200 VC running 10.4R6.
>
> 2001:db8::1/128 gets advertised to SW1 by a host using RIPng, and SW1
> exports this route into OSPFv3.
>
>  2001:db8::1/128
>    | (RIPng-advertised)
>    ~
>    |
>  [SW1 - ID 192.0.2.40]
>    |
>    | (NSSA area 10.0.0.0)
>    |
>    | xe-1/2/0.5
>  [R2 - ID 192.0.2.4]
>    | ae0.0     | xe-1/2/0.6
>    |           |
>    | (area 0)  | (area 0)
>    |           |
>    | ae0.0     | xe-1/2/0.6
>  [R1 - ID 192.0.2.5]
>
>
> On R2 I can see the external NSSA route appear fine:
>
> R2> show ospf3 route 2001:db8::1 extensive
> Prefix                                       Path  Route      NH   Metric
>                                             Type  Type       Type
> 2001:db8::1/128                              Ext2  Network    IP   2
>  NH-interface xe-1/2/0.5, NH-addr fe80::3
>  Area 10.0.0.0, Origin 192.0.2.40, Type 7, P-bit, Fwd NZ, Priority medium
>
> ...and on R1 I can see that the ABR R2 translated it into a normal
> external route and advertised it into area 0:
>
> R1> show ospf3 route 2001:db8::1 extensive
> Prefix                                       Path  Route      NH   Metric
>                                             Type  Type       Type
> 2001:db8::1/128                              Ext2  Network    IP   2
>  NH-interface ae0.0, NH-addr fe80::2
>  NH-interface xe-1/2/0.6, NH-addr fe80::62:2
>  Area 0.0.0.0, Origin 192.0.2.4, Fwd NZ, Priority medium
>
> The problem occurs when I attempt to include R1 into area 10.0.0.0.
> This I do by adding ae0.0 on R1 and R2 into the area in secondary
> mode. My problem is that as soon as I do so, traffic to
> 2001:db8::1/128 starts to loop between R1 and R2.
>
> As expected, R1 now sees the type-7 LSA generated by SW1 (and
> readvertises it into area 0 since it's now an ABR):
>
> R1> run show ospf3 route 2001:db8::1 extensive
> Prefix                                       Path  Route      NH   Metric
>                                             Type  Type       Type
> 2001:db8::1/128                              Ext2  Network    IP   2
>  NH-interface ae0.0, NH-addr fe80::2
>  Area 10.0.0.0, Origin 192.0.2.40, Type 7, P-bit, Fwd NZ, Priority medium
>
> R2, on the other hand, for seam prefers the area 0 external route that
> was generated by R1 over the NSSA route generated by SW1:
>
> R2> run show ospf3 route 2001:db8::1 extensive
> Prefix                                       Path  Route      NH   Metric
>                                             Type  Type       Type
> 2001:db8::1/128                              Ext2  Network    IP   2
>  NH-interface ae0.0, NH-addr fe80::1
>  NH-interface xe-1/2/0.6, NH-addr fe80::62:1
>  Area 0.0.0.0, Origin 192.0.2.5, Fwd NZ, Priority medium
>
> I have the exact same topology set up for IPv4/OSPFv3/RIPv2, and then
> R2 prefers the route it learned from SW1's Type-7 LSA within area
> 10.0.0.0, instead of the normal external route received from R1. I would
> have expected the same to happen with OSPFv3, but for some reason the
> priorities are the other way around.
>
> Anyone have an idea as to whether this is a bug or if I'm doing
> something wrong here?
>
> BR,
> -- 
> Tore Anderson
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