IGPs in use

Tue Oct 13 22:18:00 UTC 1998

hcb at clark.net (Howard C. Berkowitz) writes:

> When I gave my OSPF tutorial at NANOG in June, I stressed OSPF shouldn't be
> thought of purely as a 2-level hierarchy with a routing domain consisting
> of an area 0 and a set of nonzero areas.   Some of the OSPF scaling
> problems I see, and these are probably equally likely in IS-IS, come from
> people trying to put everything into a single OSPF routing domain.  Aside
> from performance issues, this can become a network administration nightmare.
> 
> Splitting the interior network into several IGP routing domains, and
> linking these with a backbone-of-backbones, helps both performance and
> administration.  The backbone group doesn't need to be concerned with LAN
> installations in a POP or customer site. Depending on the particular
> network, you might link IGP routing domains with:
> 
>        -- static routes
>        -- iBGP, putting all IGPs in a single AS
>        -- iBGP and eBGP in a confederation
>        -- Hybrid layer 2/3 techniques, such as linking IGP-routed domains
>           to internal layer 2 "superhubs"
> 
> How much IGP support you need will depend on your network. A large
> enterprise, or a provider of both connectivity and content, will probably
> need more IGP stuff than a pure connectivity provider.

Howard,

Yes, those sound like a list of administrative nightmares.  ;-)

Wouldn't it be much easier to make use of a three or four level
hierarchical IGP?

Tony