Setup Guide

Layer 2 redundancy mechanism, support for configuration of VLT nodes in a PVLAN enables Layer 2 security functionalities. To
achieve maximum VLT resiliency, you should configure the PVLAN IDs and mappings to be identical on both the VLT peer nodes.
The association of PVLAN with the VLT LAG must also be identical. After the VLT LAG is configured to be a member of either
the primary or secondary PVLAN (which is associated with the primary), ICL becomes an automatic member of that PVLAN on
both switches. This association helps the PVLAN data flow received on one VLT peer for a VLT LAG to be transmitted on that
VLT LAG from the peer.
You can associate either a VLT VLAN or a VLT LAG to a PVLAN. First configure the VLT interconnect (VLTi) or a VLT LAG by
using the peer-link port-channel id-number command or the VLT VLAN by using the peer-link port-channel
id-number peer-down-vlan vlan interface number command and the switchport command. After you specify
the VLTi link and VLT LAGs, you can associate the same port channel or LAG bundle that is a part of a VLT to a PVLAN by using
the interface interface and switchport mode private-vlan commands.
When a VLTi port in trunk mode is a member of symmetric VLT PVLANs, the PVLAN packets are forwarded only if the PVLAN
settings of both the VLT nodes are identical. You can configure the VLTi in trunk mode to be a member of non-VLT PVLANs
if the VLTi is configured on both the peers. MAC address synchronization is performed for VLT PVLANs across peers in a VLT
domain.
Keep the following points in mind when you configure VLT nodes in a PVLAN:
● Configure the VLTi link to be in trunk mode. Do not configure the VLTi link to be in access or promiscuous mode.
● You can configure a VLT LAG or port channel to be in trunk, access, or promiscuous port modes when you include the VLT
LAG in a PVLAN. The VLT LAG settings must be the same on both the peers. If you configure a VLT LAG as a trunk port, you
can associate that LAG to be a member of a normal VLAN or a PVLAN. If you configure a VLT LAG to be a promiscuous port,
you can configure that LAG to be a member of PVLAN only. If you configure a VLT LAG to be in access port mode, you can
add that LAG to be a member of the secondary VLAN only.
● ARP entries are synchronized even when a mismatch occurs in the PVLAN mode of a VLT LAG.
Any VLAN that contains at least one VLT port as a member is treated as a VLT VLAN. You can configure a VLT VLAN to be
a primary, secondary, or a normal VLAN. However, the VLT VLAN configuration must be symmetrical across peers. If the VLT
LAG is tagged to any one of the primary or secondary VLANs of a PVLAN, then both the primary and secondary VLANs are
considered as VLT VLANs.
If you add an ICL or VLTi link as a member of a primary VLAN, the ICL becomes a part of the primary VLAN and its associated
secondary VLANs, similar to the behavior for normal trunk ports. VLAN parity is not validated if you associate an ICL to a
PVLAN. Similarly, if you dissociate an ICL from a PVLAN, although the PVLAN parity exists, ICL is removed from that PVLAN.
Association of VLTi as a Member of a PVLAN
If a VLAN is configured as a non-VLT VLAN on both the peers, the VLTi link is made a member of that VLAN if the VLTi link is
configured as a PVLAN or normal VLAN on both the peers. If a PVLAN is configured as a VLT VLAN on one peer and a non-VLT
VLAN on another peer, the VLTi is added as a member of that VLAN by verifying the PVLAN parity on both the peers. In such
a case, if a PVLAN is present as a VLT PVLAN on at least one of the peers, then symmetric configuration of the PVLAN is
validated to cause the VLTi to be a member of that VLAN. Whenever a change in the VLAN mode on one of the peers occurs,
the information is synchronized with the other peer and VLTi is either added or removed from the VLAN based on the validation
of the VLAN parity.
For VLT VLANs, the association between primary VLAN and secondary VLANs is examined on both the peers. Only if the
association is identical on both the peers, VLTi is configured as a member of those VLANs. This behavior is because of security
functionalities in a PVLAN. For example, if a VLAN is a primary VLT VLAN on one peer and not a primary VLT VLAN on the other
peer, VLTi is not made a part of that VLAN.
MAC Synchronization for VLT Nodes in a PVLAN
For the MAC addresses that are learned on non-VLT ports, MAC address synchronization is performed with the other peer if
the VLTi (ICL) link is part of the same VLAN as the non-VLT port. For MAC addresses that are learned on VLT ports, the VLT
LAG mode of operation and the primary to secondary association of the VLT nodes is determined on both the VLT peers. MAC
synchronization is performed for the VLT LAGs only if the VLT LAG and primary-secondary VLT peer mapping are symmetrical.
The PVLAN mode of VLT LAGs on one peer is validated against the PVLAN mode of VLT LAGs on the other peer. MAC
addresses that are learned on that VLT LAG are synchronized between the peers only if the PVLAN mode on both the peers is
identical. For example, if the MAC address is learned on a VLT LAG and the VLAN is a primary VLT VLAN on one peer and not a
primary VLT VLAN on the other peer, MAC synchronization does not occur.
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Virtual Link Trunking (VLT)