Dell Configuration Guide for the S4048–ON System 9.14.2.5

Because the VLT LAG interfaces are terminated on two different nodes, PVLAN configuration of VLT VLANs and VLT LAGs are symmetrical and identical on both the VLT peers. PVLANs provide Layer 2 isolation between ports within the same VLAN. A PVLAN partitions a traditional VLAN into sub-domains identified by a primary and secondary VLAN pair. With VLT being a 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.

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).

• Layer 3 communication between secondary VLANs in a private VLAN is enabled by using the ip local-proxy-arp command in INTERFACE VLAN configuration mode.

• The ARP request is not received on the ICL

Under such conditions, the IP stack performs the following operations:

• The ARP reply is sent with the MAC address of the primary VLAN.

• The ARP request packet originates on the primary VLAN for the intended destination IP address.

The ARP request received on ICLs are not proxied, even if they are received with a secondary VLAN tag. This behavior change occurs because the node from which the ARP request was forwarded would have replied with its MAC address, and the current node discards the ARP request.

Scenarios for VLAN Membership and MAC Synchronization With VLT Nodes in PVLAN

The following table illustrates the association of the VLTi link and PVLANs, and the MAC synchronization of VLT nodes in a PVLAN (for various modes of operations of the VLT peers):