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Re: (ASCEND) Making IGP work on a Max



At 03:32 PM 7/16/98 -0700, Bruce Robertson wrote:
>>>>>> "Matt" == Matt Holdrege <matt@ascend.com> writes:
>
>    Matt> You should be summarizing so that each OSPF router only sees
>    Matt> the supernet addresses.
>
>No, you don't want to do that, unless you like having packets traverse
>your LAN more than once.  Consider the case of several Maxen on the
>same LAN.  Static IP dialup users on different Maxen may wish to
>communicate with each other.  If you summarize just the supernets, the
>traffic between those users must go through the default route, and
>then be bounced back on the same LAN.  If you maintain OSPF external
>routes for each of those users, they can communicate directly.
>
>This isn't restricted to static dialup, either.  We also use Maxen to
>concentrate permanent ISDN customers with supernets.  It's even more
>likely that customers of this type will want to communicate directly.

If your customers talk to each other, then yes, you want a different
design. Most ISP's don't have a lot of this type of traffic and the extra
hop isn't a big problem.

>Also, consider the situation of multiple ABRs on the same LAN as the
>Maxen.  If each router has a path to a given supernet, I want the OSPF
>on the Maxen to know about all of the paths, so that they have direct
>connectivity to the supernet if one router should go down.

OSPF allows you to weight routes so that you can have a backup route to the
supernet if one of the ABR's goes down. That is perfectly natural.

Matt Holdrege		http://www.ascend.com	matt@ascend.com
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