White Papers

Table Of Contents
VLT Unicast Routing
VLT unicast locally routes packets destined for the L3 endpoint of the VLT peer.
This method avoids sub-optimal 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 both IPV6 / IPv4 . 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 you enable VLT unicast, VLAN wildcarding is enabled to support up to 4094 VLANs. If you enable VLT unicast, the
following actions occur:
L3 routing is enabled on any new IP address / IPV6 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.
NOTE: If the CAM is full, do not enable peer-routing.
NOTE: The peer routing and peer-routing-timeout is applicable for both IPv6/ IPv4.
Configuring VLT Unicast
To enable and configure VLT unicast, follow these steps.
1. Enable VLT on a switch, then configure a VLT domain and enter VLT-domain configuration mode.
CONFIGURATION mode
vlt domain domain-id
2. Enable peer-routing.
VLT DOMAIN mode
peer-routing
3. Configure the peer-routing timeout.
VLT DOMAIN mode
peer-routingtimeout value
value: Specify a value (in seconds) from 1 to 65535.
Non-VLT ARP Sync
In the Dell Networking OS version 9.2(0.0), ARP entries (including ND entries) learned on other ports are synced with the VLT
peer to support station move scenarios.
Prior to Dell Networking OS version 9.2.(0.0), only ARP entries learned on VLT ports were synced between peers.
Additionally, ARP entries resulting from station movements from VLT to non-VLT ports or to different non-VLT ports are
learned on the non-VLT port and synced with the peer node. The peer node is updated to use the new non-VLT port.
NOTE: ARP entries learned on non-VLT, non-spanned VLANs are not synced with VLT peers.
Virtual Link Trunking (VLT) 855