Compatible Systems 5.4 - Manual (Page 41)

Chapter 2 - IP Routing & Bridging 35
default router see the discussion of the IP Static Route Dialog Box later
in this chapter.
v Note: Some routers, in particular those designed to create very large
corporate backbones, may use other routing protocols such as OSPF (Open
Shortest Path First). These routers can simultaneously use RIP 1 (and in
some cases RIP 2) to communicate with smaller routers, or each of the
smaller routers can be set to use one of these backbone routers as their
default router.
> Update Method
VPN links which are configured to provide “dial-on-demand” service will
bring a connection up (i.e. dial the other end) when there are network packets
which must be transferred over the link. Once a dial-on-demand connection
is up, network traffic passing across the link causes the inactivity timer for the
link to be reset, keeping the connection up.
The RIP protocol periodically sends out update information across a link.
These periodic update packets will cause a VPN link set for dial-on-demand
operation to stay up indefinitely.
• If Triggered is selected with this pull-down menu, the router will modify
the standard RIP behavior for this link to send RIP packets only when
there has been an update to its routing table information, or when it has
detected a change in the accessibility of the next hop router.
• If Periodic is selected with this pull-down menu, the router will use the
standard RIP protocol, which sends RIP packets over the link every 30
seconds.
RIP Split Horizon
Normally, RIP uses a technique called split horizon to avoid routing loops and
allow smaller update packets. This technique specifies that when the device
sends a RIP update out a particular network interface, it should never include
routing information acquired over that same interface.
There is a variation of the split horizon technique called “poison reverse”
which specifies that all routes should be included in an update out a particular
interface, but that the metric should be set to infinity for those routes acquired
over that interface. One drawback is that routing update packet sizes will be
increased when using poison reverse.
• If Split Horizon is selected with this pull-down menu, the device will
apply the split horizon technique to routes being output over this inter-
face.