Administrator Guide

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 ushed. 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 notication is sent to the VLT peer to disable the proxy ARP. If peer routing is disabled when
ICL link is down, a notication 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 conguration removal will be notied 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, ushes 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 congure virtual link trunking (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 trac 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 trac destined for the multicast
group.
To enable an explicit multicast routing table synchronization method for VLT nodes, you can congure 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 trac from
the same incoming interface.
You can congure a VLT node to be an RP through the ip pim rp-address command in Global Conguration mode. When you
congure 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 the VLT peer, after the RP starts receiving multicast trac via these routes, these (S, G)
routes are considered valid and are downloaded to the device. Only (S, G) routes are used to forward the multicast trac from the source
to the receiver.
You can congure VLT nodes, which function as RP, as Multicast Source Discovery Protocol (MSDP) peers in dierent domains. However,
you cannot congure the VLT peers as MSDP peers in the same VLT domain. In such instances, the VLT peer does not support the RP
functionality.
If the same source or RP can be accessed over both a VLT and a non-VLT VLAN, congure better metrics for the VLT VLANs. Otherwise,
it is possible that one VLT node chooses a non-VLT VLAN (if the path through the VLT VLAN was not available when the route was
learned) and another VLT node selects a VLT VLAN. Such a scenario can cause duplication of packets. ECMP is not supported when you
congure VLT nodes as RPs.
Backup RP is not supported if the VLT peer that functions as the RP is statically congured. With static RP conguration, if the RP
reboots, it can handle new clients only after it comes back online. Until the RP returns to the active state, the VLT peer forwards the
packets for the already logged-in clients. To enable the VLT peer node to retain the synchronized multicast routes or synchronized multicast
Virtual Link Trunking (VLT)
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