Example Roadmap: Configuring a Basic Bridge Domain Environment

Example Topology

Consider the network in Figure 1. The figure shows three MX Series routers acting as Layer 2 devices.

Figure 1: Bridging Network with MX Series Routers

The three routers each have a series of hosts on their Ethernet interfaces, as well as aggregated Ethernet links between them. Router 2 and Router 3 are linked to the Internet, and Router 1 and Router 3 are also linked to switches configured with a range of VLANs, as shown in the figure. Because the VLAN tags are important, the routers run Multiple STP (MSTP) on the links connecting them to prevent bridging loops (Rapid STP, or RSTP, does not recognize VLAN tags and blocks ports without regard for VLAN tagging).

Example Scenario

• The six Gigabit Ethernet links between Router 1 and the other routers (ge-2/1/0 through ge-2/1/5) are gathered into two aggregated Ethernet (AE) links mixing bridged traffic from the VLANs. AE1 will consist of the first three links and AE2 will use the last three links. The same approach is taken for the links on Router 2 and Router 3.
• The Gigabit Ethernet links from Router 1 to the customer devices (ge-2/2/1 and ge-2/2/6 ) will be bridged and include VLAN tag 100 on ge-2/2/1 and VLAN tag 200 on ge-2/2/6. The other two routers, Router 2 and Router 3, also have two ports configured to handle VLAN 100 on one port (ge-2/2/2) and VLAN 200 on the other (ge-3/3/3).
• Router 2 and Router 3 have IRB configured so that they can pass traffic to other routers in the rest of the network.
• Router 1 has an access interface which provides bridging on VLAN 205 and is connected to a customer device configured on ge-2/2/2. Router 3 has an access interface which provides bridging on VLAN 200 and is connected to a customer device configured on ge-2/2/6.
• Router 1 and Router 3 are configured with a trunk interface to a switch for VLANs 200–205. On both routers, this interface is ge-2/2/4.

Example Configuration Summary

1. Configure the Ethernet interfaces and VLAN tags on all three routers, as described in Example Step: Configuring Interfaces and VLAN Tags
2. Configure the bridge domains on all three routers, as described in Example Step: Configuring Bridge Domains.
3. Configure the Spanning Tree Protocol on all three routers, as described in Example Step: Configuring Spanning Tree Protocols
4. Configure IRB, as described in Example Step: Configuring Integrated Bridging and Routing