Administrator Guide

VLT Proxy Gateway
The Virtual link trucking (VLT) proxy gateway feature allows a VLT domain to locally terminate and route L3 packets that are
destined to a L3 end point in another VLT domain. Enable the VLT proxy gateway using the link layer discover protocol (LLDP)
method or the static configuration.
Topics:
• Proxy Gateway in VLT Domains
• Configuring a Static VLT Proxy Gateway
• Configuring an LLDP VLT Proxy Gateway
Proxy Gateway in VLT Domains
Using a proxy gateway, the VLT peers in a domain can route the L3 packets destined for VLT peers in another domain as long as
they have L3 reachability for the IP destinations.
A proxy gateway in a VLT domain provides the following benefits:
● Avoids sub-optimal routing of packets by a VLT domain when packets are destined to the endpoint in another VLT domain.
● Provides resiliency if a VLT peer goes down by performing proxy routing for the peer’s destination MAC address in another
VLT domain.
A typical scenario is virtual movement of servers across data centers as shown in Topology 1. Virtual movement enables live
migration of running Virtual Machines (VMs) from one host to another without a downtime. Consider a square VLT connecting
two data centers.
If a VM has for example the following scenario, L3 packets destined for C can be routed either by C1 or D1 locally:This behavior
is achieved by installing the local system mac address of C and D in both C1 and D1 so the packets for C and D could have a hit
at C1 /D1 and be routed locally.
● VM1 on Server Rack 1 has C as its default gateway
● VM1 performs a virtual movement to Server Rack 2 with no change in default gateway,
In the following figure, server racks, named Rack 1 and Rack 2, are part of data centers, named DC1 and DC2, respectively. Rack
1 is connected to devices A and B in Layer 2. Similarly, Rack 2 is connected to devices A and B in Layer 2. A VLT Link
Aggregation Group (LAG) is present between A and B. A and B are connected to core routers, C and D. VLT routing is present
between C and D.
Similarly, C1 and D1 are Layer 3 core routers in DC2, in which VLT routing is enabled. The core routers C and D in the local VLT
domain are connected to the core routers C1 and D1 in the remote VLT Domain using VLT links in eVLT fashion. For more
information about the eVLT, see the Virtual Link Trunking (VLT) chapter. The core or Layer 3 routers C and D in local VLT
Domain and C1 and D1 in the remote VLT Domain are then part of a Layer 3 cloud.
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