Supported Platforms
Understanding EX8200 Virtual Chassis Topologies
An EX8200 Virtual Chassis is composed of one or two XRE200 External Routing Engines interconnected with up to four Juniper Networks EX8200 Ethernet Switches.
This topic explains the topologies that you can use to connect these devices.
The topic covers:
Understanding the Full Mesh EX8200 Virtual Chassis Topology
We recommend that you use a full mesh topology for all EX8200 Virtual Chassis whenever possible.
In a full mesh topology, every possible Virtual Chassis port (VCP) connection within the Virtual Chassis is established. Both external Routing Engines have connections to all switches in addition to having connections to each other. The switches are connected together by a user-configured VCP link—preferably multiple VCP links, which will automatically form a VCP link aggregation group (LAG)—to provide another link for Virtual Chassis Control Protocol (VCCP) traffic within the Virtual Chassis. Each member switch has a VCP link to every other member switch.
Figure 1 shows a full mesh EX8200 Virtual Chassis topology with four member switches.
Figure 1: EX8200 Virtual Chassis Full Mesh Topology with Four EX8200 Member Switches
Figure 2 shows a full mesh EX8200 Virtual Chassis topology with two member switches.
Figure 2: EX8200 Virtual Chassis Full Mesh Topology with Two EX8200 Member Switches
A full mesh Virtual Chassis topology has several advantages over other topologies. Because there are multiple paths to all devices in the Virtual Chassis, a single link failure does not disable any path from one device to another. Because the multiple VCP links connect all devices together, the VCCP has more flexibility when sending traffic through the Virtual Chassis than it does in other topologies.
Understanding the Ring EX8200 Virtual Chassis Topology
In a ring topology, each device in the EX8200 Virtual Chassis has at least one path to every other device in the Virtual Chassis. The paths are not necessarily direct and traffic might be required to travel across multiple hops to reach another device within the same Virtual Chassis.
Figure 3 shows a ring EX8200 Virtual Chassis topology.
Figure 3: EX8200 Virtual Chassis Ring Topology
VCCP traffic often has to travel multiple hops to communicate with other devices in the Virtual Chassis. When a VCP link fails in a ring topology, additional hops are added for VCCP traffic in the Virtual Chassis ring topology. VCP link failures are problematic in a ring topology, as the shortage of VCP links in the topology increases the potential for a single link failure to cause the EX8200 member switches to split from the Virtual Chassis.
An EX8200 Virtual Chassis full mesh topology is always recommended. Use the ring topology in cases where some of the VCP links in a full mesh topology have failed or when the equipment to configure a full mesh topology is unavailable.
The Role of XRE200 External Routing Engine Redundancy in a Virtual Chassis Topology
A backup XRE200 External Routing Engine provides redundancy to a master XRE200 External Routing Engine. If a master external Routing Engine fails, the backup external Routing Engine takes control of the Virtual Chassis, allowing network traffic to continue to pass through the Virtual Chassis with minimal network disruption.
 | Note: A backup XRE200 External Routing Engine is recommended in all EX8200 Virtual Chassis configurations. |
When a backup external Routing Engine is included in the EX8200 Virtual Chassis, one link must be used to connect the master external Routing Engine to the backup external Routing Engine. Both EX8200 switches must also have connections to the backup external Routing Engine.
EX8200 Virtual Chassis Basic Topology
The most basic EX8200 Virtual Chassis topology has one XRE200 External Routing Engine connecting two EX8200 switches into a Virtual Chassis.
Figure 4 shows a basic EX8200 Virtual Chassis topology.
Figure 4: EX8200 Virtual Chassis Basic Topology
In this topology, all VCCP traffic has to travel on one of the two links, which is problematic because the switches have to send traffic through the external Routing Engine to communicate with each other.
There is no link redundancy in this topology. If either link fails, one of the switches is no longer participating in the Virtual Chassis.
There is no redundant external Routing Engine in this topology. If the external Routing Engine fails, the Virtual Chassis is no longer active.
An EX8200 Virtual Chassis full mesh topology is always recommended. Use the basic topology only when VCP links have failed or when the equipment to configure a full mesh topology is unavailable.
