Cabletron Systems CSX1200, CSX1000 manual Secondary IP Addressing

CONFIGURING BASIC IP ROUTING

IP Network Interfaces

with a remote device on a different subnet, the local device will ARP for the remote host’s MAC address.

Since routers do not forward ARP requests across subnets, ARPs sent for hosts which are not on the same physical network segment will go unanswered. The proxy ARP feature will potentially generate an ARP reply for remote hosts. If the CyberSWITCH determines that it provides the best route to the remote device, it will respond with an ARP reply containing the MAC address of the CyberSWITCH. Further communication between the two hosts will then be routed through the CyberSWITCH.

•Secondary IP Addressing

If only one IP network interface (i.e., one subnet) per LAN port is configured, any traffic from hosts on different subnets attached to the LAN port would be dropped.

With the secondary IP addressing feature, multiple IP network interfaces may be configured for each LAN port. All existing subnets which are to be reached will have an associated IP network interface on the CyberSWITCH. By allowing each LAN port to be configured with multiple IP network interfaces, the CyberSWITCH can route packets from hosts on any of the subnets attached to the LAN port. (See following example.)

Example: IP Host Communications in Flattened Networks

To communicate with destination hosts which are not on the same physical wire, you must have a router attached to the edge of the flattened network which can forward packets to those destination networks. In the following illustration, we are using a CyberSWITCH as our “edge” router:

2.2.2.11.1.1.1

Host A Host B

2.2.2.21.1.1.2

3.3.3.3

CSX1200
ISDN	Host D
	1.1.1.3

Host C

Workgroup Remote Access Switch 123