Administrator Guide

INTERFACE VLAN mode
private-vlan mode primary
8 Map secondary VLANs to the selected primary VLAN.
INTERFACE VLAN mode
private-vlan mapping secondary-vlan vlan-list
The list of secondary VLANs can be:
• Specied in comma-delimited (VLAN-ID,VLAN-ID) or hyphenated-range format (VLAN-ID-VLAN-ID).
• Specied with this command even before they have been created.
• Amended by specifying the new secondary VLAN to be added to the list.
Proxy ARP Capability on VLT Peer Nodes
The proxy ARP functionality is supported on VLT peer nodes.
A proxy ARP-enabled device answers the ARP requests that are destined for another host or router. The local host forwards the trac to
the proxy ARP-enabled device, which in turn transmits the packets to the destination.
By default, proxy ARP is enabled. To disable proxy ARP, use the no proxy-arp command in the interface mode. To re-enable proxy ARP,
use the ip proxy-arp command in INTERFACE mode. To view if proxy ARP is enabled on the interface, use the show config
command in INTERFACE mode. If it is not listed in the show config command output, it is enabled. Only nondefault information is
displayed in the show config command output.
ARP proxy operation is performed on the VLT peer node IP address when the peer VLT node is down. The ARP proxy stops working either
when the peer routing timer expires or when the peer VLT node goes up. Layer 3 VLT provides a higher resiliency at the Layer 3 forwarding
level. VLT peer routing enables you to replace VRRP with routed VLT to route the trac from Layer 2 access nodes. With proxy ARP, hosts
can resolve the MAC address of the VLT node even when VLT node is down.
If the ICL link is down when a VLT node receives an ARP request for the IP address of the VLT peer, owing to LAG-level hashing algorithm
in the top-of-rack (TOR) switch, the incorrect VLT node responds to the ARP request with the peer MAC address. Proxy ARP is not
performed when the ICL link is up and the ARP request the wrong VLT peer. In this case, ARP requests are tunneled to the VLT peer.
Proxy ARP supported on both VLT interfaces and non-VLT interfaces. Proxy ARP supported on symmetric VLANs only. Proxy ARP is
enabled by default. Routing table must be symmetrically congured to support proxy ARP. For example, consider a sample topology in
which VLAN 100 is congured on two VLT nodes, node 1 and node 2. ICL link is not congured between the two VLT nodes. Assume that
the VLAN 100 IP address in node 1 is 10.1.1.1/24 and VLAN 100 IP address in node 2 is 20.1.1.2/24. In this case, if the ARP request for 20.1.1.1
reaches node 1, node 1 will not perform the ARP request for 20.1.1.2. Proxy ARP is supported only for the IP address belongs to the received
interface IP network. Proxy ARP is not supported if the ARP requested IP address is dierent from the received interface IP subnet. For
example, if VLAN 100 and 200 are congured on the VLT peers, and if the VLAN 100 IP address is congured as 10.1.1.0/24 and the VLAN
200 IP address is congured as 20.1.1.0/24, the proxy ARP is not performed if the VLT node receives an ARP request for 20.1.1.0/24 on
VLAN 100.
Working of Proxy ARP for VLT Peer Nodes
Proxy ARP is enabled only when peer routing is enabled on both the VLT peers. If peer routing is disabled on one of the VLT peers, proxy
ARP is not performed when the ICL link goes down. Proxy ARP is performed only when the VLT peer's MAC address is installed in the
database. Proxy ARP is stopped when the VLT peer's MAC address is removed from the ARP database because of the peer routing timer
expiry. The source hardware address in the ARP response contains the VLT peer MAC address. Proxy ARP is supported for both unicast
and broadcast ARP requests. Control packets, other than ARP requests destined for the VLT peers that reach the undesired and incorrect
VLT node, are dropped if the ICL link is down. Further processing is not done on these control packets. The VLT node does not perform any
action if it receives gratuitous ARP requests for the VLT peer IP address. Proxy ARP is also supported on secondary VLANs. When the ICL
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Virtual Link Trunking (VLT)