Example: VPLS Multihoming, Improved Convergence Time

This example uses the following hardware and software components:

• Three M Series, MX Series, or T Series routers

• Junos OS Release 12.2 or later

If you are using M Series or T Series routers, the PE routers must have either virtual loopback tunnel (vt) interfaces or label-switched interfaces (LSIs). On M Series and T Series routers, VPLS uses tunnel-based PICs to create virtual ports on vt interfaces. If you do not have a tunnel-based PIC installed on your M Series or T Series router, you can still configure VPLS by using LSIs to support the virtual ports. Use of LSIs requires Ethernet-based PICs installed in an Enhanced Flexible PIC Concentrator (FPC).

You do not need to use routers for the CE devices. For example, the CE devices can be EX Series Ethernet Switches.

All PE routers in a VPLS network operate like a large, distributed Ethernet switch to provide Layer 2 services to attached devices. This example illustrates a network of PE routers and CE devices configured to use VPLS multihoming.. The topology consists of six routers: four PE routers and two CE devices. Device CE1 is multihomed to Routers PE1 and PE2. The PE routers are configured with the best-site and mac-flush statements to improve the convergence time in the event the connection between Device CE1 and one of its multihomed PE routers fails.

This example includes the following settings:

• best-site—Uses the B-bit of the control flags bit vector (the third bit counting from the most significant bit) within the Layer 2 information extended community to indicate that the site is preferred. Each VPLS site configured with the best-site statement signals to the other PE routers that it is the preferred site. The Layer 2 information extended community includes the following information:

  • Extended community type (2 octets)

  • Encapsulation type (1 octet)

  • Control flags (1 octet)

  • Layer 2 MTU (2 octets)

  • Reserved (2 octets)

  When a neighboring PE router within the VPLS routing instance receives the label block advertisement, it knows that the corresponding PE router is the most preferable router of those remote PE routers multihomed to that site. If a neighboring PE router does not support the best site feature, the standard local site selection process is used. For example, if Router PE1 does not receive a B-bit from any of the label blocks advertisements received from Router PE3, Router PE1 proceeds to assume that Router PE3 does not support the best site feature. It creates a virtual circuit based on its minimum-designated site. For the other PE routers that do support the best site feature, Router PE1 builds virtual circuits using the locally tagged best site.

• mac-flush—Enables media access control (MAC) flush processing for the VPLS routing instance or for the mesh group under a VPLS routing instance. MAC flush processing removes MAC addresses from the MAC address database that have been learned dynamically. With the dynamically learned MAC addresses removed, MAC address convergence requires less time to complete.

Topology

Figure 1 shows the topology used in this example. Router PE2 is configured with the best-site statement and acts as the preferred gateway for traffic from Device CE1.

Figure 1: VPLS Multihoming Topology with Router PE2 Configured as the Best Site

• CLI Quick Configuration
• Router PE1
• Router PE2
• Router PE3