Reference Guide

296 | Virtual Link Trunking (VLT)
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If the VLT node elected as the designated router fails, traffic loss will occur until another VLT node is
elected the designated router.
VLT Unicast
VLT unicast locally routes packets destined for the L3 endpoint of the VLT peer. This method avoids
suboptimal routing. Peer-routing syncs the MAC addresses of both VLT peers and requires two local DA
entries in TCAM. In case a VLT node is down, resiliency is provided by a timer that allows you to
configure the amount of time needed for peer recovery.
VLT unicast also assists in conflict resolution by updating the routing table when a path for an existing
multicast route has been changed. You can enable VLT unicast and multicast routing across multiple
configurations using VLT links. ECMP can be enabled on VLT nodes using VLT unicast; however, ECMP
is not compatible on VLT nodes using VLT multicast. You must use a single VLAN.
VLT unicast is supported on IPv4 only. To enable VLT unicast, both VLT peers must be in L3 mode. Static
route and routing protocols such as RIP, OSPF, ISIS, and BGP are supported. However, point-to-point
configuration is not supported. To enable VLT unicast, VLAN configuration must be symmetrical on both
peers. The same VLAN cannot be configured as Layer 2 on one node and as Layer 3 on the other node.
Configuration mismatches are logged in the syslog and displayed in the output of the
show vlt
inconsistency
command.
When VLT unicast is enabled, VLAN wildcarding is enabled to support up to 4094 VLANs. If VLT unicast
is enabled, the following actions occur:
• L3 routing is enabled on any new IP address configured for a VLAN interface that is up.
• L3 routing is enabled on any VLAN with an admin state of up.
• For PVLAN, if the IP address is configured for the primary VLAN, L3 routing is enabled.
Configuring VLT Unicast
To enable and configure VLT unicast, follow these steps.
Step Task
Command
Syntax Command Mode
1 Enter interface configuration mode.
vlt domain
domain-id
CONFIGURATION
2 Enable peer-routing.
peer-routing
VLT DOMAIN
3 Configure the peer-routing timeout.
peer-routing—
timeout value
value:
Specify a
value (in seconds)
from 1 to 65535.
VLT DOMAIN