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 fields in the RIP packets are:
| Command | Description | |
|---|---|---|
| 1 | Request for partial or full routing table information | |
| 2 | Response packet containing a routing table | |
| 3–4 | Turn on (3) or off (4) trace mode (obsolete) | |
| 5 | Sun Microsystems’ internal use |
Version. Used to indicate the version of RIP. Currently set to 1 for RIP version 1.
Family of net x. Used to show the diversity of the RIP protocol and to indicate the protocol that owns the packet. It will be set to 2 for IP. Since XNS could possibly be running on the same network as IP, the RIP frames would be similar. This shows that the same RIP frame can be used for multiple protocol suites. AppleTalk, Novell NetWare’s IPX, XNS, and TCP/IP all use the RIP packet. Each packet is changed a little for each protocol.
IP address. Indicates the IP address of a specific destination network. This would be filled in by the requesting station. An address of 0.0.0.0 indicates the default route (explained later). The address field needs only 4 bytes of the available 14 bytes, so all other bytes must be set to 0. This will be explained in RIP Version 2.
If this is a request packet and there is only one entry, with the address family ID of 0 and a metric of 1, then this is a request for the entire routing table.
As for the distance-to-network field, only the integers of 1 to 16 are allowed. An entry of 16 in this field indicates that the network is unreachable.
The next entry in the field would start with the IP address field through the metric field. This would be repeated for each table entry of the router to be broadcast. The maximum size of this packet is 512 bytes.
The RIP protocol relies on the transport-layer protocol of the User Datagram Protocol (UDP, discussed in the next section on transport-layer protocols). In this will be the specification for the length of the RIP packet. Also, for those interested, RIP operates on UDP port number 520 (port numbers are discussed in the UDP section).
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