Routing Information Protocol (RIP)
The Routing Information Protocol (RIP)
facilitates the exchange
of routing information on a NetWare internetwork.
Like IPX, the
RIP protocol was derived from XNS.
However, an extra field, ``Number of ticks'', was added to
the packet structure to improve the decision criteria for
selecting the fastest route to a destination.
This change
prohibits the straight integration of NetWare's RIP with
strictly conforming XNS implementations.
The broadcast of RIP packets allows:
For more information on routers and the functions they perform,
see the Novell NetWare documentation.
The RIP packet structure is shown in Figure 4-5. This structure is enveloped within the data area of IPX.
Figure 4-5 RIP packet structure
The packet contains the following fields:
The ``Operation'' field can be followed by one or more sets of information, each consisting of a network number and the number of hops and ticks to that network number. A RIP packet can contain a maximum of 50 sets of network number information.
The original XNS definition of the RIP did not include the ``Number of Ticks'' field. The ``Number of ticks'' field was added by the developers of NetWare so that the NetWare shell could estimate how long it should wait for a response from a file server. Also, if multiple routes exist to a network number, a router uses the route with the smallest number of ticks when forwarding packets to that network number.
If a RIP packet is a request for information, only the ``Network Number'' field applies; the ``Number of hops'' and ``Number of ticks'' fields are essentially nulled out. A response packet can be either a reply to a request from a router or workstation or a periodic broadcast by a router.