Users Guide

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 outgoing interface (OIF) maps after a peer node failure, use the timeout value that you congured through the
multicast peer-routing timeout value command. You can congure an optimal time for a VLT node to retain synced
multicast routes or synced multicast outgoing interface (OIF), after a VLT peer node failure, through the multicast peer-
routing-timeout
command in VLT DOMAIN mode. Using the bootstrap router (BSR) mechanism, both the VLT nodes in a VLT
domain can be congured as the candidate RP for the same group range. When an RP fails, the VLT peer automatically takes over
the role of the RP. This phenomenon enables resiliency to be achieved by the PIM BSR protocol.
Virtual Link Trunking (VLT)
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