[c-nsp] Loopback Advertise in OSPF

[Mark Tinka]

On Wednesday 27 February 2008, Darryl Dunkin wrote:

> If you're using /32 masks for your loopbacks (as you
> should): router ospf ####
>   redistribute connected subnets
>
> The key part is to define 'subnets'.

I'd advise against using 'redistribute' to announce any kind 
of prefixes into any kind of routing protocols (with the 
exception of MPLS/VPN's, as that is scope is quite more 
limited [VRF instances] and easily manageable/predictable).

Rather, specify your networks within the OSPF process, 
explicity:

router ospf 1
 network 1.2.3.4 0.0.0.0 area 0

Alternatively, if you have the opportunity to run IOS 12.4, 
you can now deploy OSPFv2 directly on an interface:

int lo0
 ip address 1.2.3.4 255.255.255.255
 ip ospf 1 area 0

I find the above approach to be more manageable, 
cosmetically appealing as well as less prone to mistakes, 
e.g., forgeting to add the (correct) 'network' statement 
under the OSPF process, e.t.c.

The scalable approach - use OSPF to carry ONLY your 
infrastructure and Loopback addresses. DO NOT carry your 
customer's IPv4/IPv6 addresses in OSPF, do this in iBGP 
instead.

Cheers,

Mark.
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