by Matthew G. Naugle
Wiley Computer Publishing, John Wiley & Sons, Inc.
ISBN: 0471196568 Pub Date: 11/01/98
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Illustrated TCP/IP
by Matthew G. Naugle Wiley Computer Publishing, John Wiley & Sons, Inc. ISBN: 0471196568 Pub Date: 11/01/98 |
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Receiving a route report is a different matter. There are many checks done on the received information. Route reports are processed only by those sent by a known neighbor; otherwise, they are discarded. Generally, two rules are followed: If the route entry is new and the metric is less than infinity, the route is added. That’s the simple one. The second rule is tougher and is shown in the table.
If the route entry exists, perform the following checks:
| If New Metric < infinity AND New metric > existing metric | If the same neighbor is reporting it, update the entry; otherwise, discard the entry. |
| If New Metric < infinity AND New metric < existing metric | Update the entry with the route and if necessary, update the reporting neighbor. |
| If New Metric < infinity AND New metric = existing metric | Refresh the route and if the new neighbor has a lower IP address, update that entry. |
| If New Metric = infinity AND New gateway = existing gateway | Route is now unreachable, update the entry. |
| If New Metric = infinity AND New gateway not equal to existing gateway | Ignore |
| If New metric is between route infinity and 2x infinity | Neighbor considers the receiving router to be upstream for the indicated and that router is dependent on the receiving router for the route indicated. If the receiving neighbor router considers that router to be downstream, the receiving router marks that neighbor as dependent for that route; otherwise, discard the packet, for a dependent router cannot be considered to be upstream. |
| If the metric is greater than 2x infinity | Ignore |
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