User Manual
IP IP Routing
6-16
The SCS must be positioned between two networks in order for routing to work correctly. If two or more
SCSs are used, the units cannot be on the same network (as in Figure 6-39).
Figure 6-39: Two Units Used to Link the Same Network
6.7.1 How Packets are Routed
When an IP host tries to send a packet, it looks to see if the destination address is on the same network as
the host’s IP address. If it is, the host sends the packet directly to its destination. If the packet is destined for
a different network, the host sends it to a router (in this case, the SCS).
When the SCS receives the packet, it examines the packet’s destination address, determines the most
efficient route to this address, and forwards the packet to this location. The “most efficient route” is
determined using two factors: the network that the address is part of and the SCS routing table, which is
discussed in the following section.
6.7.2 Routing Tables
The SCS uses a routing table to keep track of which networks are reachable, and the shortest route to each
network. A typical routing table entry consists of the destination network, and which router is the best path
to that network. Routing tables also keep track of the cost or metric required to get to a given network.
6.7.2.1 Types of Routes
There are three types of routes: host, network, and default.
Host Routes A Host Route is a route to a single host. Generally, a host route is entered for
each Remote Node that logs into the SCS.
Network Routes A network route is a route to another network. A network route is used if a host
route to the destination doesn’t exist.
Default Routes A default route is used if a more specific host or network route isn’t available.
It is used to cut down on the size of routing tables and dynamic routing protocol
updates. If, for example, the SCS is the only path for network packets to reach
a much larger group of networks, the SCS can be configured to advertise itself
as the default route.
Note: See Set/Define IP Route Default on page 12-37 and Define Site IP Default on
page 12-142.
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