3Com Switch 4500 26-Port, Руководство по настройке

Страница: 113 / 396

RIP 111
■
Next hop address — The address of the next router that an IP packet will pass
through for reaching the destination.
■
Interface — The interface through which the IP packet should be forwarded.
■
Cost — The cost for the router to reach the destination, which should be an
integer in the range of 0 to 16.
■
Timer — The length of time from the last time that the routing entry was
modified until now. The timer is reset to 0 whenever a routing entry is
modified.
RIP is controlled by three timers as follows:
■
Period update — Triggered periodically to send all RIP routes to all neighbors.
■
Timeout — If a RIP route has not been updated when the timer times out (i.e
the Switch has not received update packets from the neighbors) the route will
be considered unreachable.
■
Garbage-collection — If Garbage-collection times out before the unreachable
route is updated by the packets from the neighbors, then the route will be
deleted from the routing table.
The process of RIP startup and operation is as follows:
1 If RIP is enabled on a router for the first time, the router broadcasts or multicasts a
request packet to the adjacent routers. When they receive the request packet,
adjacent routers (on which RIP is also enabled) respond to the request by returning
response packets containing information about their local routing tables.
2 After receiving the response packets, the router that sent the request modifies its
own routing table and sends a modification triggering packet to the neighbor
router. The neighbor router sends this packet to all its neighbor routers. After a
series of modification triggering processes, each router can get and keep the
updated routing information.
3 RIP broadcasts its routing table to the adjacent routers every 30 seconds. The
adjacent routers maintain their own routing table after receiving the packets and
elect an optimal route. They then advertise the modification information to their
adjacent network to make the updated route globally available. RIP uses the
timeout mechanism to handle timed out routes to ensure the timeliness and
validity of the routes. With these mechanisms, RIP, an interior routing protocol,
enables the router to learn the routing information of the entire network.
RIP has become one of the most popular standards of transmitting router and host
routes. It can be used in most campus networks and regional networks that are
simple yet extensive. RIP is not recommended for larger and more complicated
networks.
RIP configuration is described in the following sections:
■
Configuring RIP
■
Troubleshooting RIP
Configuring RIP Only after RIP is enabled can other functional features be configured. But the
configuration of the interface-related functional features is not dependent on
whether RIP has been enabled.