Administrator Guide

• trunk (inter-switch PVLAN hub port)
5. Access INTERFACE VLAN mode for the VLAN to which you want to assign the PVLAN interfaces.
CONFIGURATION mode
interface vlan vlan-id
6. Enable the VLAN.
INTERFACE VLAN mode
no shutdown
7. To obtain maximum VLT resiliency, congure the PVLAN IDs and mappings to be identical on both the VLT peer nodes. Set the
PVLAN mode of the selected VLAN to primary.
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
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.
Virtual Link Trunking (VLT)
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