secondary VLANs. When the ICL link or peer is down, and the ARP request for a private VLAN IP address
reaches the wrong peer, then the wrong peer responds to the ARP request with the peer MAC address.
The IP address of the VLT node VLAN interface is synchronized with the VLT peer over ICL when the VLT
peers are up. Whenever an IP address is added or deleted, this updated information is synchronized with
the VLT peer. IP address synchronization occurs regardless of the VLAN administrative state. IP address
addition and deletion serve as the trigger events for synchronization. When a VLAN state is down, the VLT
peer might perform a proxy ARP operation for the IP addresses of that VLAN interface.
VLT nodes start performing Proxy ARP when the ICL link goes down. When the VLT peer comes up, proxy
ARP will be stopped for the peer VLT IP addresses. When the peer node is rebooted, the IP address
synchronized with the peer is not flushed. Peer down events cause the proxy ARP to commence.
When a VLT node detects peer up, it will not perform proxy ARP for the peer IP addresses. IP address
synchronization occurs again between the VLT peers.
Proxy ARP is enabled only if peer routing is enabled on both the VLT peers. If you disable peer routing by
using the no peer-routingcommand in VLT DOMAIN node, a notification is sent to the VLT peer to
disable the proxy ARP. If peer routing is disabled when ICL link is down, a notification is not sent to the
VLT peer and in such a case, the VLT peer does not disable the proxy ARP operation.
When the VLT domain is removed on one of the VLT nodes, the peer routing configuration removal will
be notified to the peer. In this case VLT peer node disables the proxy ARP. When the ICL link is removed
on one of the VLT nodes by using the no peer-link command, the ICL down event is triggered on the
other VLT node, which in turn starts the proxy ARP application. The VLT node, where the ICL link is
deleted, flushes the peer IP addresses and does not perform proxy ARP for the additional LAG hashed
ARP requests.
Configuring VLAN-Stack over VLT
To configure VLAN-stack over VLT, follow these steps.
1. Configure the VLT LAG as VLAN-stack access or trunk mode on both the peers.
INTERFACE PORT-CHANNEL mode
vlan-stack {access | trunk}
2. Configure VLAN as VLAN-stack compatible on both the peers.
INTERFACE VLAN mode
vlan-stack compatible
3. Add the VLT LAG as a member to the VLAN-stack on both the peers.
INTERFACE VLAN mode
member port-channel port—channel ID
4. Verify the VLAN-stack configurations.
EXEC Privilege
show running-config
1004 Virtual Link Trunking (VLT)