Cisco Systems manual Bridging with a Cisco 700 Series Router, Bridging Example

Bridging with a Cisco 700 Series Router

values for DMS-100 and NI1 switches: ISDN number, 4085551212; SPID 1, 408555121201; SPID 2, 408555121202. In this case the SPID is the 10-digit ISDN number ending with a “01” for SPID 1 and a “02” for SPID 2.

Bridging with a Cisco 700 Series Router

This section describes how to bridge a Cisco 700 series router over an ISDN line to another router. Bridging is used in cases where you do not need a lot of filtering to manage the network. Basically, you are relying on the nodes on the LAN side of the router to determine if a packet should be accepted or dropped. (If you turn routing on, you can filter the packets on the WAN side, reducing your traffic on the LAN side.)

Note Bridging over an ISDN line is not an efficient use of ISDN bandwidth. Routing over the ISDN line helps optimize ISDN bandwidth by reducing traffic to the WAN.

Figure 3-1 illustrates an example of a remote Cisco 700 series router bridging to a router called central at a central site.

Figure 3-1 Bridging Example

IP address 172.16.125.9			IP address 172.16.125.10
Subnet mask 255.255.0.0			Subnet mask 255.255.0.0
	Enterprise	ISDN		San Jose
	CPA765			Central
		network

H5860

You are going to establish a basic connection with another router, relying primarily on the defaults. In this example configuration, a simple user-defined profile is created in your Cisco 700 series router to bridge over an ISDN network to another router.

By default, the Cisco 700 series router automatically “learns” the MAC addresses that exist locally and remotely across the WAN. The router stores the MAC addresses in a MAC address table, so it knows if the unicast packets should remain on the LAN or forwarded

3-8Cisco 700 Series Router Configuration Guide