Switch User's Guide

Planning for CSX400 ISDN Configuration
CSX400 and CSX400-DC User’s Guide 33
TCP/IP Route Addresses — If the CSX400 is to direct traffic to networks or stations beyond the
remote router, the routing table in the CSX400 can be “seeded” with static IP routes. An IP route
includes an IP address, subnet mask and metric. The metric is a number representing the perceived
cost in reaching the remote network or station.
The CSX400 routing table must be seeded statically so that it dials out to the appropriate remote
router when IP traffic is targeted to networks and stations beyond that remote router. After the link
is established, RIP update packets are dynamically added to the routing table. Seeding the routing
table is not necessary when the CSX400 never dials out; it discovers remote networks and stations
beyond the calling router as soon as RIP updates arrive (provided the remote router supports RIP
and RIP packets are allowed to flow on the WAN link).
TCP/IP Default Route — One default route should be designated in the routing table for all
traffic that cannot be directed to other specific routes. You need to define the default route for a
remote router if the CSX400 will be placing calls to that remote router.
Source (Target) and Remote WAN IP Addresses — You may need to specify a Source WAN IP
address and/or a Remote WAN IP address for the WAN connection to the remote router depending
on IP address negotiation under PPP. Check with your system administrator for details on whether
the router must communicate in numbered or unnumbered mode and what addresses are required.
In unnumbered mode, neither IP address is defined on the link. In numbered mode, one IP address
is defined on each end of the WAN link. These addresses may or may not belong to the same
subnetwork. They may also be determined automatically, negotiated, or forced by the network
administrator.
The CSX400 automatically determines whether to run in unnumbered mode or numbered mode. If
unnumbered mode negotiation fails, numbered mode is attempted using the Ethernet LAN IP
address as a default. If you have specified a Source WAN IP address, unnumbered mode
negotiation is not performed; i.e., the operating mode is numbered. If a Source WAN IP address is
explicitly defined, the router will not, as a rule, accept another local address from the remote end.
In numbered mode without an explicit Source WAN IP address, this address can be negotiated to a
different value by the remote end.