Dell PowerSwitch S4820T Configuration Guide for the S4820T System 9.112.0P1 - Page 1000

VLT Nodes as Rendezvous Points for Multicast Resiliency, Configuring VLAN-Stack over VLT

Page 1000 highlights

When a VLT node detects peer up, it does not perform proxy ARP for the peer IP addresses. IP address synchronization occurs again between the VLT peers. Proxy ARP is enabled only if you enable peer routing 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 you disable peer routing 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 you remove the VLT domain on one of the VLT nodes, the peer routing configuration removal is notified to the peer. In this case, the VLT peer node disables the proxy ARP. When you remove the ICL link on one of the VLT nodes 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 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 using 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 using the multicast peerrouting 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, using the multicast peer-routing-timeout command in VLT DOMAIN mode. Using the bootstrap router (BSR) mechanism, you can configure both the VLT nodes in a VLT domain 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 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. 1000 Virtual Link Trunking (VLT)

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When a VLT node detects peer up, it does not perform proxy ARP for the peer IP addresses. IP address synchronization occurs again
between the VLT peers.
Proxy ARP is enabled only if you enable peer routing 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 you disable peer routing 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 you remove the VLT domain on one of the VLT nodes, the peer routing
configuration
removal is
notified
to the peer. In this case, the
VLT peer node disables the proxy ARP. When you remove the ICL link on one of the VLT nodes 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
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 using 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
using 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, using the
multicast peer-routing-timeout
command in VLT
DOMAIN mode. Using the bootstrap router (BSR) mechanism, you can
configure
both the VLT nodes in a VLT domain 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
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.
1000
Virtual Link Trunking (VLT)