Users Guide

broadcast ARP requests. Control packets, other than ARP requests destined for the VLT peers that reach the
undesired and incorrect VLT node, are dropped if the ICL link is down. Further processing is not done on
these control packets. The VLT node does not perform any action if it receives gratuitous ARP requests for the
VLT peer IP address. Proxy ARP is also supported on secondary VLANs. When the ICL link or peer is down, and
the ARP request for a private VLAN IP address reaches the wrong peer, 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 you add or delete an IP address, 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 stops 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 does not perform proxy ARP for the peer IP addresses. IP address
synchronization occurs again between the VLT peers.
Proxy ARP is enabled only if you enable peer routing 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 you disable peer routing 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 you remove the VLT domain on one of the VLT nodes, the peer routing configuration removal is
notified to the peer. In this case, the VLT peer node disables the proxy ARP. When you remove the ICL link on
one of the VLT nodes 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.
VLT Nodes as Rendezvous Points for
Multicast Resiliency
You can configure VLT peer nodes as rendezvous points (RPs) in a Protocol Independent Multicast (PIM)
domain.
PIM uses a VLT node as the RP to distribute multicast traffic to a multicast group. Messages to join the
multicast group (Join messages) and data are sent towards the RP, so that receivers can discover who the
senders are and begin receiving traffic destined for the multicast group.
To enable an explicit multicast routing table synchronization method for VLT nodes, you can configure VLT
nodes as RPs. Multicast routing needs to identify the incoming interface for each route. The PIM running on
both VLT peers enables both the peers to obtain traffic from the same incoming interface.
You can configure a VLT node to be an RP using the ip pim rp-address command in Global
Configuration mode. When you configure a VLT node as an RP, the (*, G) routes that are synchronized from
the VLT peers are ignored and not downloaded to the device. For the (S, G) routes that are synchronized from
Virtual Link Trunking (VLT) 1171