Edge-Routed Bridging for QFX Series Switches
The edge-routed bridging (ERB) for QFX series switches feature configures the inter-VN unicast traffic routing to occur at the leaf (ToR) switches in an IP CLOS with underlay connectivity topology. The ERB feature introduces the ERB-UCAST-Gateway and CRB-MCAST-Gateway roles. ERB is supported on the following devices running Junos OS Release 18.1R3 and later:
Contrail Networking supports assigning physical roles and routing bridging (overlay) roles to a networking device like a switch. The roles define the routing and bridging responsibilities of the device in the data center. A device can have one physical role and one or more routing bridging roles. In releases prior to Contrail Networking Release 5.1, Contrail Networking supports centrally-routed bridging (CRB) roles on data center devices. In CRB, when you configure the logical router to allow traffic to flow between Ethernet virtual network instances, the routing occurs at the spine device. Traffic is routed from the leaf to the spine and back. IRB interfaces are configured in the overlay at each spine device to route traffic between virtual networks. Contrail Networking Release 5.1, supports the ERB-UCAST-Gateway role in which the routing occurs at the leaf switch. The IRB interfaces are configured at the leaf switch to enable unicast traffic routing at the leaf switch.
Traffic is routed in lesser hops when routed at the leaf switches. For example, consider two bare metal servers belonging to two separate VNs. Unicast traffic between the VNs are routed at the leaf switch and doesn’t need to flow to the spine and back. Traffic is routed through the shortest path.
When you configure the ERB-UCAST-Gateway role on the leaf switches, it is recommended that you also configure the CRB-MCAST-Gateway role for multicast traffic on the corresponding spine devices. The CRB-MCAST-Gateway role is also supported. While unicast traffic can be routed at the leaf switches, multicast traffic routing still occurs at the spine devices. The existing CRB-Gateway role is capable of routing both unicast and multicast traffic at the spine devices. However, in ERB, if leaf switches route the unicast traffic, configuring the CRB-Gateway role on the spine is unnecessary since unicast traffic will never reach the spine device. Instead, you must configure the spine devices with the CRB-MCAST-Gateway role to route multicast traffic when required.
Benefits of ERB
Traffic is routed through the shortest path.
When you extend a logical router to a physical router, you can extend the logical router to leaf switches as well . Previously, logical routers could only be extended to the spine devices.
Optimization of IRB Interfaces Creation in ERB Switches
In an ERB topology with ERB-UCAST-Gateway role configured on ERB switches, when creating a logical router, an integrated routing and bridging (IRB) interface is created for each associated VN on all ERB switches. IRB interfaces are created regardless of a local port or VPG in the associated VNs. This leads to a lot of unnecessary IRB and VRF configurations associated to the logical router being pushed to the ERB switches.
Starting from release 2011, Contrail Networking checks if a VPG is attached to the VN in an ERB switch with ERB-UCAST-Gateway role configured, before pushing IRB interface configuration associated with the logical router to the switch. Only if a VPG is attached to the VN, the IRB interface configuration is pushed to the ERB switch. The routing instance is not created if there are no VPGs.