Administrator Guide

Table Of Contents
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.
VLT Nodes as Rendezvous Points for Multicast
Resiliency
You can configure 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 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 through 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 the VLT peer, after the RP starts receiving
multicast traffic 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 traffic from the source to the receiver.
You can configure VLT nodes, which function as RP, as Multicast Source Discovery Protocol (MSDP) peers in different domains.
However, you cannot configure 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, configure 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 configure VLT nodes as RPs.
Backup RP is not supported if the VLT peer that functions as the RP is statically configured. With static RP configuration, 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 configured
through the multicast peer-routing timeout value command. You can configure 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 configured 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.
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 portchannel ID
1050
Virtual Link Trunking (VLT)