User manual

Frame Relay IP Routing
Page 29-16
An InARP message is sent between the two routers indicating their IP addresses and associ-
ated VC. Once they know each other’s IP address and the DLCI of the VC on each end of the
link (the same VC may have a different DLCIs on each end), then they can begin normal rout-
ing of RIP frames, etc.
The Frame Relay Subnet and “Split Horizon”
The IP protocol must account for the Frame Relay network in making routing decisions. After
all, the WAN network is more than just a single cable, or even several cables, attaching two
routers. The solution is to assign the Frame Relay network a unique IP subnet.
Frame Relay Network Is an IP SubNet
In the configuration shown above, one virtual circuit connects the
WSX router on IP Subnet
1.1.1.x and the other router on IP Subnet 3.3.3.x. The Frame Relay network, for routing
purposes, is considered to be IP Subnet 2.2.2.x. Routing decisions are straightforward in this
setup. But if another Router and another IP Subnet were added, a special routing technique
must be devised.
R
WSX
Subnet 1.1.1.X
Subnet 3.3.3.X
Subnet 2.2.2.X
Frame Relay network consid-
ered a unique IP Subnet by IP.
Virtual circuit connects
two WAN Routers.