Cisco Systems BC-109 manual Configure a Multiport Bridge Using a Virtual Ring

Configure a Multiport Bridge Using a Virtual Ring

A dual-port bridge is a limitation imposed by IBM Token Ring chips; the chips can process only two ring numbers. If you have a router with two or more Token Ring interfaces, you can work around the two-ring number limitation. You can configure your router as multiple dual-port bridges or as a multiport bridge using a virtual ring.

You can define several separate dual-port bridges in the same router. However, the routers on the LANs cannot have any-to-any connectivity; that is, they cannot connect to every other router on the bridged LANs. Only the routers connected to the dual-port bridge can communicate with one another. Figure 46 shows two separate dual-port bridges (T0-T2 and T1-T3) configured on the same router.

Figure 46 Multiple Dual-Port Bridges

	Token
	Ring
	T1
Token T2	T0 Token
Ring	Ring

T3

Token

Ring

S2323

To configure multiple dual-port source-route bridges, use the following command in interface configuration mode for each Token Ring interface that is part of a dual-port bridge:

Command	Purpose
source-bridgelocal-ring bridge-number target-ring	Enable local source-route bridging on
	a Token Ring interface.

If you want your network to use only SRB, you can connect as many routers as you need via Token Rings. Remember, source-route bridging requires you to bridge only Token Ring media.

Configure a Multiport Bridge Using a Virtual Ring

A better solution for overcoming the two-ring number limitation of IBM Token Ring chips is to configure a multiport bridge using a virtual ring. A virtual ring on a multiport bridge allows the router to interconnect three or more LANs with any-to-any connectivity; that is, connectivity between any of the routers on each of the three LANs is allowed. A virtual ring creates a logical Token Ring internal to the Cisco IOS software, which causes all the Token Rings connected to the router to be treated as if they are all on the same Token Ring. The virtual ring is called a ring group. Figure 47 shows a multiport bridge using a virtual ring.

Configuring Source-Route Bridging BC-111