OSPF multi-level hierarchy: Necessary at all?

There's a better solution: decrease the number of nodes by replacing
clusters with bigger boxes. This has an additional advantage of reducing
number of hops (and, consequently, latency variance).

K.I.S.S. rulez :slight_smile:

--vadim

PS. Using DUAL or DASM instead of SPF helps, too -- these algorithms tend
    to eliminate updates which "do not matter" unlike SPF-based algorithms
    which have to inform everyone about local topology changes.

Side question:

At what point do we stop aggregating customers onto a single box? The
technology exists now to have hundreds if not thousands of customers on a
signle box, but, Do we want that many?

-Steve

Anyway, do you aggregate the customers to the single box, or do not, 2
level hierarchy scheme (backbone + AREA for big nodes) is quite
satisfacted.

Another problem - how do you flood small updates. For example, if we here
allocate dial-up addresses from the central cache, amd I inject this host
addresses into the network. Through, both methods (OSPF or IBGP) works
fine for the middle-size dialup pop's, and I don't think you need to do
it instead of using local address-pools in case of large dialup pop's.

Alex.

Another problem - how do you flood small updates. For example, if we here
allocate dial-up addresses from the central cache, amd I inject this host
addresses into the network.

Although our network is not yet large enough to run into scaling issues,
this is exactly our problem. Our OSPF is relatively stable except for
two things, both on our dialup pools:
o Host level routes appearing from wandering static-ips
o Wandering networks from dial-on-demand networks.

We have more than one physical dialin POP, so summarization can't
take place on the netblocks that these items are allocated from.
As these users connect and disconnect this generates most of our
churn in our OSPF.

Any suggestions on solving this churn issue?

Although our network is not yet large enough to run into scaling issues,
this is exactly our problem. Our OSPF is relatively stable except for
two things, both on our dialup pools:
o Host level routes appearing from wandering static-ips
o Wandering networks from dial-on-demand networks.

We have more than one physical dialin POP, so summarization can't
take place on the netblocks that these items are allocated from.
As these users connect and disconnect this generates most of our
churn in our OSPF.

Any suggestions on solving this churn issue?

As has been said before:

If address allocation fails to match the topology, then you must exchange more
routing information. The only ways to address this are to either change the
point of aggregation (e.g. merge your POP's address space, containing the churn
to these two POPs) or to disallow the migration of addresses between POPs.

TANSTAAFL (There Ain't No Such Thing As A Free Lunch)

Tony