Routing Updates - Bay Networks Nautica 200 Reference Manual

NauticaRS Release 4.1 Reference Guide

Routing Updates

1-16
When a router becomes active on a Novell network, it starts to
listen to all SAP broadcasts. The server information is then added
to the router's server information table, so that the router can send
SAP broadcasts to each attached Novell network.
The process of regular routing update broadcasts used in IPX and
IP works well with a leased circuit or permanent type connection,
where the circuit is either functioning (passing data and routing
updates) or not functioning (in which case routing updates are not
received). In this case there is a time-out mechanism which
removes the relevant routes from the routing tables after no
updates have been received for a defined period.
Using ISDN as the connection medium adds another circuit state
to the equation, in that the connection can be functioning but no
data or routing updates are being passed because the call is
currently closed. If this state were to exist for longer than the
routing protocol time-out (normally 3 minutes), the routes would
decay and be removed from the tables at each end of the link. If
this were to happen, then no routing could take place between the
units at either end of the ISDN link.
To overcome this problem, Nautica series routers automatically
treat routes learned over ISDN as semi-permanent. This means
that they are not decayed (removed), but they can be updated by
any received routing protocol updates if any of the metrics (e.g.,
hop counts) have changed since the last update.
Another issue with passing routing updates across ISDN is
whether a call is either made, or left connected, only for passing
routing information. Nautica series routers do not make calls to
pass routing updates, but simply "piggy-back" the routing update
on to the next user data call.
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