Dell C1048P Port Extender Networking Configuration Guide for the C9000 Series - Page 1014

VLT Nodes as Rendezvous Points for Multicast Resiliency

Page 1014 highlights

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 peerroutingcommand 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. 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 Virtual Link Trunking (VLT) 1014

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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-
routing
command 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.
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
Virtual Link Trunking (VLT)
1014