Ref: 03250411
Title: IB/2 Routing Tables and Aging Times
Date: 12/10/87

Copyright 3Com Corporation, 1991.  All rights reserved.

QUESTION: Can we change the value for the time after which a
routing table entry disappears with Aging ON on the IB/2 ?

ANSWER: Fortunately, you don't need to (and there will probably
not be user configurable aging times in any future release as
there should be no need.)

The routing table on an IB is not the same as the routing table
on a router.

With IB's, if a packet is destined for a box on either net and
the destination box isn't on the routing table, the packet WILL
be forwarded to the other net.  If the destination box is on
either net and in the routing table (and the packet originated on
the same net), the packet will NOT be forwarded.

This is the opposite of what happens with a router where, if the
destination box isn't on the routing table, the packet WILL NOT
be forwarded.

With IB's, once the destination box has acknowledged the packet,
with Learning ON on the IB, the routing table will be updated.
With Learning and Aging ON (recommended), if a box is moved from
one side of the net to the other, the old routing table entry
disappears as it becomes "Old", and when the new box is powered-
up and broadcasts its address (or if the box doesn't do this on
power-up, after acknowledging or sending its first packet), the
routing table will be updated to show the box's new location.

In summary, when you use IB's, you no longer have to worry
about routing tables on those IB's, just the routing tables
on your routers which just show where each network is.
The routing table becomes a diagnostic tool instead of a
concern.  User-assigned entries do not get deleted (for the
unconvinced network manager.)
