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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The route tag entry is used to advertise routes that were learned externally (not in this IGP). OSPF has this capability and allows the OSPF IGP to learn about routes external to the IGP. For example, if the routes were learned via BGP-4 ( a routing protocol used between autonomous systems), the route tag entry could be used for setting the autonomous system from which the routes were learned.
The next-hop field allows the router to learn where the next hop is for the specific route entry. If the entry is 0.0.0.0, then the source address of the update should be used for the route. Over a point-to-point link (to routers connected by a serial line) there is not much use for this entry (the next hop could be extracted from the source IP address in the IP header of the packet). This field does have considerable use in instances where there are multiple routers on a single LAN segment using different IGPs to communicate to multiple LANs.
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