[j-nsp] nssa default route

[Harry Reynolds]

Sounds like a case of "active backbone detection". A feature where if the abr loses its area 0 adjacency it ceases to adv the default.

There is a hidden (unsupported) command to disable:

set protocols ospf no-active-backbone

started with 7.2, IIRC:

http://www.juniper.net/techpubs/software/junos/junos72/rn-sw-72/rn-new-features.html#rn-new-features




OSPF active backbone detection-The JUNOS software now supports active backbone detection. There are two changes in Open Shortest Path First (OSPF) default behavior associated with active backbone detection, but there are no new configuration statements. First, if an Area Border Router (ABR) loses its OSPF adjacency to backbone area 0, then the router no longer announces the default into connected stub areas or not-so-stubby areas (NSSAs) via the configuration under the nssa or stub default-metric statements at the [edit protocols ospf] hierarchy level. This makes it possible to reroute traffic through another ABR that has an active adjacency to backbone area 0. Second, an ABR with no active backbone area 0 adjacency now considers inter-area traffic destined to areas that are not directly connected to that ABR. This change does not obviate the need for virtual links in the case of a partitioned area. [Routing Protocols] 




-----Original Message-----
From: juniper-nsp-bounces at puck.nether.net [mailto:juniper-nsp-bounces at puck.nether.net] On Behalf Of ryanL
Sent: Thursday, August 16, 2012 10:48 AM
To: juniper-nsp at puck.nether.net
Subject: [j-nsp] nssa default route

tl;dr - when i kill one of my mx's, the default route disappears on my ex's. and, the remaining ospf database entry is for the router that died, not the router that remains active.

i might be a little slow on the uptick here, but this seems pretty straight forward to me. i can't figure out what's up. i'm pretty new to junos, so bear with me.

m = mx
e = ex
standard physical full mesh

mx1 lo0 = 1.1.1.1
mx2 lo0 = 1.1.1.2

m - m
| x |
e - e

my mx are ospf area 0 and area 1 nssa. the ex are area 1 nssa only.
mx's inject default into nssa.

config on mx:

//
area 0.0.0.0 {
    interface lo0.0 {
        passive;
    }
    interface ae0.0 {
        interface-type p2p;
        bfd-liveness-detection {
            minimum-interval 300;
            multiplier 3;
            full-neighbors-only;
        }
    }
}
area 0.0.0.1 {
    nssa {
        default-lsa default-metric 10;
        no-summaries;
    }
    interface ae1.0 {
        interface-type p2p;
        bfd-liveness-detection {
            minimum-interval 300;
            multiplier 3;
            full-neighbors-only;
        }
    }
    interface ae2.0 {
        interface-type p2p;
        bfd-liveness-detection {
            minimum-interval 300;
            multiplier 3;
            full-neighbors-only;
        }
    }
}
//

config on ex:

//
area 0.0.0.1 {
    nssa;
    interface lo0.0 {
        passive;
    }
    interface ae1.0 {
        interface-type p2p;
        bfd-liveness-detection {
            minimum-interval 300;
            multiplier 3;
            full-neighbors-only;
        }
    }
    interface ae2.0 {
        interface-type p2p;
        bfd-liveness-detection {
            minimum-interval 300;
            multiplier 3;
            full-neighbors-only;
        }
    }
    interface ae0.0 {
        interface-type p2p;
        bfd-liveness-detection {
            minimum-interval 300;
            multiplier 3;
            full-neighbors-only;
        }
    }
}
//

routes before killing mx2:
>show route 0.0.0.0

inet.0: 28 destinations, 28 routes (28 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

0.0.0.0/0          *[OSPF/10] 00:08:40, metric 15
                    > to 10.254.1.2 via ae1.0
                      to 10.254.1.4 via ae2.0

ospf database before killing mx2:
> show ospf database

    OSPF database, Area 0.0.0.1
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Router  *10.255.1.1       10.255.1.1       0x8000048e  2283  0x20 0x7c36 168
Router   10.255.1.2       10.255.1.2       0x80000486  2284  0x20 0x1e89 168
Router   1.1.1.1     1.1.1.2     0x800003e2   513  0x20 0x7006  72
Router   1.1.1.2     1.1.1.2     0x800003e8  1082  0x20 0x7bf2  72
Summary  0.0.0.0          1.1.1.1     0x80000001   513  0x20 0xeaa8  28
Summary  0.0.0.0          1.1.1.2     0x800000b4  1082  0x20 0x7d61  28



routes after killing mx2:
> show route 0.0.0.0
#<----nothing here
{master:0}

ex ospf database after killing mx2:
> show ospf database

    OSPF database, Area 0.0.0.1
 Type       ID               Adv Rtr           Seq      Age  Opt  Cksum  Len
Router  *10.255.1.1       10.255.1.1       0x80000490    41  0x20 0x286f 144
Router   10.255.1.2       10.255.1.2       0x80000488    42  0x20 0x6030 144
Router   1.1.1.1     1.1.1.2     0x800003e2   612  0x20 0x7006  72
Router   1.1.1.2     1.1.1.2     0x800003e8  1181  0x20 0x7bf2  72
Summary  0.0.0.0          1.1.1.2     0x800000b4  1181  0x20 0x7d61
28  #<---dead router!

so, what happened to my remaining router's ospf database entry, and that secondary default route?

thanks for any insight. i'm going to open a case with jtac as well.

ryanL
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