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DGS-3312SR
Инструкция по эксплуатации Страница: 141

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DGS-3312SR Stackable Gigabit Layer 3 Switch

RIP

The Routing Information Protocol is a distance-vector routing protocol. There are two types of network devices running

assive routers update their routing tables based upon RIP messages that active routers

econds, a router running RIP broadcasts a routing update containing a set of pairs of network addresses and a

f hops or routers between the advertising router and the remote network). So, the

nce is measured by the number of routers between the local router and the

distance (or hop count).

to as ‘cost’). So

restarted every time this route is

clude an authorization

a router from learning erroneous routes from unauthorized routers.

have a low maximum value. Infinity (that is, the

ork is more than 16 routers from the source, the

local router w c

RIP can also

RIP messages pro .

Slow converg c

back to the interfa

Hold down c b

route update h s b

to a route’s advertisement. This is usually used in

diate broadcast when an update of an unreachable

RIP - active and passive. Active devices advertise their routes to others through RIP messages, while passive devices listen

to these messages. Both active and p

exchange. Only routers can run RIP in the active mode.

Every 30 s

distance (represented by the number o

vector is the network address and the dista

remote network.

RIP measures distance by an integer count of the number of hops from one network to another. A router is one hop from a

directly connected network, two hops from a network that can be reached through a router, etc. The more routers between a

source and a destination, the greater the RIP

There are a few rules to the routing table update process that help to improve performance and stability. A router will not

replace a route with a newly learned one if the new route has the same hop count (sometimes referred

learned routes are retained until a new route with a lower hop count is learned.

When learned routes are entered into the routing table, a timer is started. This timer is

advertised. If the route is not advertised for a period of time (usually 180 seconds), the route is removed from the routing

table.

RIP does not have an explicit method to detect routing loops. Many RIP implementations in

mechanism (a password) to prevent

To maximize stability, the hop count RIP uses to measure distance must

network is unreachable) is defined as 16 hops. In other words, if a netw

ill onsider the network unreachable.

be slow to converge (to remove inconsistent, unreachable or looped routes from the routing table) because

pagate relatively slowly through a network

en e can be solved by using split horizon update, where a router does not propagate information about a route

ce on which it was received. This reduces the probability of forming transient routing loops.

an e used to force a router to ignore new route updates for a period of time (usually 60 seconds) after a new

a een received. This allows all routers on the network to receive the message.

A router can ‘poison reverse’ a route by adding an infinite (16) hop count

conjunction with triggered updates, which force a router to send an imme

network is received.

RIP Version 1 Message Format

There are two types of RIP messages: routing information messages and information requests. Both types use the same

format.

The Command field specifies an operation according the following table:

Command Meaning

1 Request for partial or full routing information

Response containing network-distance pairs from

sender’s routing table

3 Turn on trace mode (obsolete)

4 Turn off trace mode (obsolete)

5 Reserved for Sun Microsystem’s internal use

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