Dynamic Port VSAN Membership (DPVM) – Cisco CCNP and CCIE

Port VSAN membership on the switch is assigned on a port-by-port basis. By default, each port belongs to the default VSAN. You can assign VSANs to ports either statically or dynamically. To assign dynamic VSAN membership to ports, you assign VSANs based on the device WWN. This method is referred to as Dynamic Port VSAN Membership (DPVM). DPVM offers flexibility and eliminates the need to reconfigure the port VSAN membership to maintain fabric topology when a host or storage device connection is moved between two Cisco fabric switches or two ports within a switch. DPVM retains the configured VSAN regardless of where a device is connected or moved.

DPVM configurations are based on port World Wide Name (pWWN) and node World Wide Name (nWWN) assignments. DPVM contains mapping information for each device pWWN/nWWN assignment and the corresponding VSAN. The Cisco NX-OS software checks DPVM active configuration during a device FLOGI and obtains the required VSAN details.

The pWWN identifies the host or device, and the nWWN identifies a node consisting of multiple devices. You can assign any one of these identifiers or any combination of these identifiers to configure DPVM mapping. If you assign a combination, preference is given to the pWWN.

DPVM can be configured to automatically learn (autolearn) new devices within each VSAN. DPVM autolearn can be enabled or disabled at any time. Learned entries are created by populating device pWWNs and VSANs. DPVM should be activated before autolearn can be enabled. Autolearned entries can also be manually deleted. The autolearned entries become permanent when DPVM autolearn is disabled.

DPVM uses the Cisco Fabric Services infrastructure to allow efficient database management and distribution. DPVM uses the application-driven, coordinated distribution mode and the fabric-wide distribution scope.

VSAN Trunking

VSAN trunking enables interconnected ports to transmit and receive frames in more than one VSAN. Trunking is supported on E ports and F ports. VSAN trunking is supported on native Fibre Channel interfaces and virtual Fibre Channel interfaces.

The trunking protocol is important for E port and TE port operations. It supports the following capabilities:

Dynamic negotiation of operational trunk mode

Selection of a common set of trunk-allowed VSANs

Detection of a VSAN mismatch across an ISL

Trunking configurations are applicable only to E ports. If trunk mode is enabled in an E port and that port becomes operational as a trunking E port, it is referred to as a TE port, as shown in Figure 8-23. The trunk-allowed VSANs configured for TE ports are used by the trunking protocol to determine the allowed-active VSANs in which frames can be received or transmitted. If a trunking-enabled E port is connected to a third-party switch, the trunking protocol ensures seamless operation as an E port.

Figure 8-23 VSAN Trunking Between Cisco-Cisco and Cisco-Third-Party Switches

If you misconfigure VSAN configurations across E ports, issues can occur, such as the merging of traffic in two VSANs (causing both VSANs to mismatch), as shown in Figure 8-24. The VSAN trunking protocol validates the VSAN interfaces at both ends of an ISL to avoid merging VSANs. The trunking protocol cannot detect merging of VSANs when a third-party switch is placed in between two Cisco SAN switches, as shown in Figure 8-25.

Figure 8-24 VSAN Mismatch Between Cisco Switches

Figure 8-25 VSAN Mismatch Between Cisco Switches with Third-Party Switch in Between

VSAN 2 and VSAN 3 are effectively merged with overlapping entries in the name server and the zone applications. Cisco MDS 9000 Fabric Manager helps detect such topologies.

By default, the VSAN trunking protocol is enabled. If the trunking protocol is disabled on a switch, no port on that switch can apply new trunk configurations. Existing trunk configurations are not affected: the TE port continues to function in trunk mode but only supports traffic in VSANs that it negotiated with previously (when the trunking protocol was enabled). Other switches that are directly connected to this switch are similarly affected on the connected interfaces. If you need to merge traffic from different port VSANs across a nontrunking ISL, disable the trunking protocol.

By default, trunk mode is enabled in all Fibre Channel interfaces. However, trunk mode configuration takes effect only in E port mode. You can configure trunk mode as on (enabled), off (disabled), or auto (automatic). The default trunk mode is on. The trunk mode configurations at the two ends of the link determine the trunking state of the link and the port modes at both ends, as shown in Table 8-11.

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