Hi, Jina:

    When a net range is configured for an area, it is possible that some
prefixes inside the net range do not exist in the area. In other words, the
ABR does not know how to deliever packets to those prefixes. To prevent
routing loops, a discard route is configured for each netrange. When a
packet destined for a prefix in the net range is received by an ABR, the ABR
checks its routing table to find a route. If the destination prefix is
inside the area, a more specific match than the discard route will be found
and the packet will be delivered. If the destination prefix is not inside
the area, the discard route will be found and the packet will be discarded.
    Depending on the implementation, a flag can be used to distinguish
discard routes with normal routes.

Feng Xie

-----Original Message-----
From: Wu Jina [mailto:jinawucnYAHOO.COM.CN]
Sent: Wednesday, July 18, 2001 7:38 AM
To: OSPFDISCUSS.MICROSOFT.COM
Subject: About routing table loopup.

Hello, everyone.

Now, I am reading the RFC2328, but I found one question, can your help me?

In Section 11.1:
....
Before the lookup begins, "discard" routing table entries should
be inserted into the routing table for each of the router's active area
address ranges (see Section 3.5). (An area range is considered "active"
if the range contains one or more networks reachable by intra-area
paths.) The destination of a "discard" entry is the set of addresses
described by its associated active area address range, and the path type
of each "discard" entry is set to "inter-area".[10]
...

I don't know what is the "discard route", why need this step?

Thanks.

Jina.

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