FIGURE 39 Conguration for Layer 3 unicast
Layer 3 trac forwarding towards MCT clients
Trac destined to the MCT clients follows normal IP routing. By default, the best route should not involve the ICL link. Only when the
local CCEP is down is trac rerouted to pass over the ICL.
Layer 3 trac forwarding from MCT clients
For Layer 3 forwarding to work on MCT devices, a dynamic trunk must be congured on the MCT client. Routes should be statically
congured or dynamically learned on the MCT cluster devices.
The client routes the trac towards its next hop, which can be either one of the MCT devices. If ECMP is deployed on the client, each
MCT device can be a possible next hop. In such a deployment, the trac can be load balanced at a Layer 3 level over the next two hops.
Because a LAG is deployed at the client, this trac is further subjected to load balancing at the Layer 2 level over the physical ports in
the LAG. Thus, the trac being sent out with the next hop as one of the MCT devices can either reach it directly or through the cluster
peer (where it gets Layer 2 switched towards the intended next hop).
Therefore, almost 50 percent of trac being forwarded from MCT clients (and as much as 100 percent trac in the worst case) can pass
through the ICL. This fact should be considered when designing the ICL capacity in the network.
VRRP or VRRP-E over an MCT-enabled network
To interface a Layer 2 MCT deployment with a Layer 3 network and add redundancy at the Layer 3 level, MCT can be
congured with
Virtual Router Redundancy Protocol (VRRP). The standard VRRP mode is master-backup, and all trac is forwarded through the master.
In VRRP-E server virtualization, multiple VRRP standby devices are supported, and each device can be congured to route to an
upstream Layer 3 network. This provides ecient deployment for both Layer 2 and Layer 3 networks.
The MCT device acting as a backup router will Layer 2 switch all packets destined to VRRP/ VRRP-E virtual MAC address to the VRRP/
VRRP-E master router for routing. The VRRP/VRRP-E backup learns the virtual MAC address while processing the VRRP hello
message from the VRRP master. Both data trac and VRRP/VRRP-E control trac travel through the ICL unless the short-path
forwarding feature is enabled (VRRP-E only).
Layer 3 behavior with MCT
FastIron Ethernet Switch Layer 3 Routing
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