Lancom Systems LCOS 3.50

 Chapter 7: Routing and WAN connections LANCOM Reference Manual LCOS 3.50

Routing and WAN

connections

column shows which router has revealed this route. This leaves the 'Time'. The

dynamic table thus shows how old the relevant route is. The value in this col-

umn acts as a multiplier for the intervals at which the RIP packets arrive. A '1',

therefore, stands for 30 seconds, a '5' for about 2.5 minutes and so on. New

information arriving about a route is, of course, designated as directly reach-

able and is given the time setting '1'. The value in this column is automatically

incremented when the corresponding amount of time has elapsed. The dis-

tance is set to '16' after 3.5 minutes (route not reachable) and the route is

deleted after 5.5 minutes.

Now if the router receives an IP RIP packet, it must decide whether or not to

incorporate the route contained into its dynamic table. This is done as follows:

The route is incorporated if it is not yet listed in the table (as long as there

is enough space in the table).

The route exists in the table with a time of '5' or '6'. The new route is then

used if it indicates the same or a better distance.

The route exists in the table with a time of '7' to '10' and thus has the dis-

tance '16'. The new route will always be used.

The route exists in the table. The new route comes from the same router

which notified this route, but has a worse distance than the previous

entry. If a device notifies the degradation of its own static routing table in

this way (e.g. releasing a connection increases the distance from 1 to 2,

see below), the router will believe this and include the poorer entry in its

dynamic table.

RIP packets from the WAN will be ignored and will be rejected imme-

diately. RIP packets from the LAN will be evaluated and will not be

propagated in the LAN.

The interaction of static and dynamic tables

The router uses the static and dynamic tables to calculate the actual IP routing

table it uses to determine the path for data packets. In doing so, it includes

the routes from the dynamic table which it does not know itself or which indi-

cate a shorter distance than its own (static) route with the routes from its own

static table.

Routers without IP RIP support

Routers which do not support the Routing Information Protocol are also occa-

sionally present on the local network. These routers cannot recognize the RIP