Working Of Proxy Arp For Vlt Peer Nodes - Dell C9000 Series Networking Configuration Manual

Working of Proxy ARP for VLT Peer Nodes

Proxy ARP is enabled only when peer routing is enabled on both the VLT peers. If peer routing is disabled on
one of the VLT peers, proxy ARP is not performed when the ICL link goes down. Proxy ARP is performed only
when the VLT peer's MAC address is installed in the database. Proxy ARP is stopped when the VLT peer's MAC
address is removed from the ARP database because of the peer routing timer expiry. The source hardware
address in the ARP response contains the VLT peer MAC address. Proxy ARP is supported for both unicast and
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, 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.
Virtual Link Trunking (VLT) 1212