Reference Guide

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.
Whenever a change occurs in the VLAN mode of one of the peers, this modification is synchronized with the other peers.
Depending on the validation mechanism that is initiated for MAC synchronization of VLT peers, MAC addresses learned on a
particular VLAN are either synchronized with the other peers, or MAC addresses synchronized from the other peers on the
same VLAN are deleted. This method of processing occurs when the PVLAN mode of VLT LAGs is modified.
Because the VLTi link is only a member of symmetric VLT PVLANs, MAC synchronization takes place directly based on the
membership of the VLTi link in a VLAN and the VLT LAG mode.
PVLAN Operations When One VLT Peer is Down
When a VLT port moves to the Admin or Operationally Down state on only one of the VLT nodes, the VLT Lag is still considered
to be up. All the PVLAN MAC entries that correspond to the operationally down VLT LAG are maintained as synchronized
entries in the device. These MAC entries are removed when the peer VLT LAG also becomes inactive or a change in PVLAN
configuration occurs.
PVLAN Operations When a VLT Peer is Restarted
When the VLT peer node is rebooted, the VLAN membership of the VLTi link is preserved and when the peer node comes back
online, a verification is performed with the newly received PVLAN configuration from the peer. If any differences are identified,
the VLTi link is either added or removed from the VLAN. When the peer node restarts and returns online, all the PVLAN
configurations are exchanged across the peers. Based on the information received from the peer, a bulk synchronization of MAC
addresses that belong to spanned PVLANs is performed.
During the booting phase or when the ICL link attempts to come up, a system logging message is recorded if VLT PVLAN
mismatches, PVLAN mode mismatches, PVLAN association mismatches, or PVLAN port mode mismatches occur. Also, you can
view these discrepancies if any occur by using the show vlt mismatch command.
Interoperation of VLT Nodes in a PVLAN with ARP Requests
When an ARP request is received, and the following conditions are applicable, the IP stack performs certain operations.
● The VLAN on which the ARP request is received is a secondary VLAN (community or isolated VLAN).
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Virtual Link Trunking (VLT)