Table Of Contents
Configuring Trunking
About Trunking
About the Trunking Protocol
Enabling or Disabling the Trunking Protocol
Configuring Trunk Mode
Configuring the Trunk Mode
Trunk-Allowed VSAN Configuration
Configuring an Allowed-Active List of VSANs
Trunking Configuration Guidelines
Displaying Trunking Information
Default Settings
Configuring Trunking
This chapter describes the trunking feature provided in Cisco MDS 9000 switches. It includes the following sections:
•About Trunking
•About the Trunking Protocol
•Configuring Trunk Mode
•Trunk-Allowed VSAN Configuration
•Trunking Configuration Guidelines
•Displaying Trunking Information
•Default Settings
About Trunking
Trunking, also known as VSAN trunking, is a feature specific to switches in the Cisco MDS 9000 Family. Trunking enables interconnect ports to transmit and receive frames in more than one VSAN, over the same physical link, using Enhanced ISL (EISL) frame format (see Figure 12-1).
Figure 12-1 Trunking
The trunking feature includes the following restrictions:
•Trunking configurations are only applicable 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.
•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.
About the Trunking Protocol
The trunking protocol is important for E-port and TE-port operations. It supports the following:
•Dynamic negotiation of operational trunk mode.
•Selection of a common set of trunk-allowed VSANs.
•Detection of a VSAN mismatch across an ISL.
By default, the 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). Also, other switches that are directly connected to this switch are similarly affected on the connected interfaces. In some cases, you may need to merge traffic from different port VSANs across a non-trunking ISL. If so, disable the trunking protocol.
Tip To avoid inconsistent configurations, disable all E ports with a shutdown command before enabling or disabling the trunking protocol.
Enabling or Disabling the Trunking Protocol
To enable or disable the trunking protocol, follow these steps:
|
Command
|
Purpose
|
Step 1
|
switch# config t
|
Enters configuration mode.
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Step 2
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switch(config)# no trunk protocol enable
switch(config)#
|
Disables the trunking protocol.
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switch(config)# trunk protocol enable
switch(config)#
|
Enables trunking protocol (default).
|
Configuring Trunk Mode
By default, the trunk mode is enabled in all Fibre Channel interfaces. However, the trunk mode configuration takes effect only in E-port mode. You can configure the trunk mode as on (enabled), off (disabled), or auto (automatic). The default trunk mode is on. The trunk mode configuration at the two ends of an ISL, between two switches, determine the resulting trunking state of the link and the port modes at both ends (see Table 12-2).
Table 12-2 Trunk Mode Status Between Switches
Your Trunk Mode Configuration
|
Resulting State and Port Mode
|
Switch 1
|
Switch 2
|
Trunking State
|
Port Mode
|
On
|
Auto or on
|
Trunking (EISL)
|
TE port
|
Off
|
Auto, on, or off
|
No trunking (ISL)
|
E port
|
Auto
|
Auto
|
No trunking (ISL)
|
E port
|
Tip The preferred configuration on the Cisco MDS 9000 Family switches is one side of the trunk set to auto and the other set to on.
Note When connected to a third-party switch, the trunk mode configuration has no effect—the ISL is always in a trunking disabled state.
Configuring the Trunk Mode
To configure the trunk mode, follow these steps:
|
Command
|
Purpose
|
Step 1
|
switch# config t
|
Enters configuration mode.
|
Step 2
|
switch(config)# interface fc1/1
switch(config-if)#
|
Configures the specified interface.
|
Step 3
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switch(config-if)# switchport trunk mode on
|
Enables (default) the trunk mode for the specified interface.
|
switch(config-if)# switchport trunk mode off
|
Disables the trunk mode for the specified interface.
|
switch(config-if)# switchport trunk mode auto
|
Configures the trunk mode to auto mode, which provides automatic sensing for the interface.
|
Trunk-Allowed VSAN Configuration
Each Fibre Channel interface has an associated trunk-allowed VSAN list. In TE-port mode, frames are transmitted and received in one or more VSANs specified in this list. By default, the VSAN range (1 through 4093) is included in the trunk-allowed list.
The common set of VSANs that are configured and active in the switch are included in the trunk-allowed VSAN list for an interface, and they are called allowed-active VSANs. The trunking protocol uses the list of allowed-active VSANs at the two ends of an ISL to determine the list of operational VSANs in which traffic is allowed.
In Figure 12-1, switch 1 has VSANs 1 through 5, switch 2 has VSANs 1 through 3, and switch 3 has VSANs 1, 2, 4, and 5 with a default configuration of trunk-allowed VSANs. All VSANs configured in all three switches are allowed-active. However, only the common set of allowed-active VSANs at the ends of the ISL become operational as shown in Figure 12-1.
Figure 12-1 Default Allowed-Active VSAN Configuration
You can configure a select set of VSANs (from the allowed-active list) to control access to the VSANs specified in a trunking ISL.
Using Figure 12-1 as an example, you can configure the list of allowed VSANs on a per-interface basis (see Figure 12-2). For example, if VSANs 2 and 4 are removed from the allowed VSAN list of ISLs connecting to switch 1, the operational allowed list of VSANs for each ISL would be as follows:
•The ISL between switch 1 and switch 2 shall include VSAN 1 and VSAN 3.
•The ISL between switch 2 and switch 3 shall include VSAN 1 and VSAN 2.
•The ISL between switch 3 and switch 1 shall include VSAN 1, 2, and 5.
Consequently, VSAN 2 can only be routed from switch 1 through switch 3 to switch 2.
Figure 12-2 Operational and Allowed VSAN Configuration
Configuring an Allowed-Active List of VSANs
To configure an allowed-active list of VSANs for an interface, follow these steps:
|
Command
|
Purpose
|
Step 1
|
switch# config t
|
Enters configuration mode.
|
Step 2
|
switch(config)# interface fc1/1
switch(config-if)#
|
Configures the specified interface.
|
Step 3
|
switch(config-if)# switchport trunk allowed vsan 2-4
|
Changes the allowed list for the specified VSANs.
|
switch(config-if)# switchport trunk allowed vsan add 5
updated trunking membership
|
Expands the specified VSAN (5) to the new allowed list.
|
switch(config-if)# no switchport trunk allowed vsan 2-4
|
Deletes VSANs 2, 3, and 4.
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switch(config-if)# no switchport trunk allowed vsan add 5
|
Deletes the expanded allowed list.
|
Trunking Configuration Guidelines
If you misconfigure VSAN configurations across E ports, you could face consequences such as merging the traffic in two VSANs (thus causing both VSANs to mismatch). The trunking protocol validates the VSAN interfaces at both ends of an ISL to avoid VSANs merging (see Figure 12-3).
Figure 12-3 VSAN Mismatch
In this example, the trunking protocol detects potential VSAN merging and isolates the ports involved.
The trunking protocol cannot detect merging of VSANs when a third-party switch is placed in between two Cisco MDS 9000 Family switches (see Figure 12-4).
Figure 12-4 Third-Party Switch VSAN Mismatch
VSANs 2 and 3 get effectively merged with overlapping entries in the name server and the zone applications. The Cisco MDS 9000 Fabric Manager helps detect such topologies. Refer to the Cisco MDS 9000 Family Fabric Manager Configuration Guide.
Displaying Trunking Information
The show interface command is invoked from the EXEC mode and displays trunking configurations for a TE port. Without any arguments, this command displays the information for all of the configured interfaces in the switch. See Examples 12-1 to 12-3.
Example 12-1 Displays a Trunked Fibre Channel Interface
switch# show interface fc1/13
Hardware is Fibre Channel
Port WWN is 20:0d:00:05:30:00:58:1e
Peer port WWN is 20:0d:00:05:30:00:59:1e
Admin port mode is auto, trunk mode is on
Receive B2B Credit is 255
Trunk vsans (admin allowed and active) (1)
Trunk vsans (isolated) ()
Trunk vsans (initializing) ()
5 minutes input rate 0 bits/sec, 0 bytes/sec, 0 frames/sec
5 minutes output rate 0 bits/sec, 0 bytes/sec, 0 frames/sec
233996 frames input, 14154208 bytes, 0 discards
236 frames output, 13818044 bytes, 0 discards
11 input OLS, 12 LRR, 10 NOS, 28 loop inits
34 output OLS, 19 LRR, 17 NOS, 12 loop inits
Example 12-2 Displays the Trunking Protocol
switch# show trunk protocol
Trunk protocol is enabled
Example 12-3 Displays Per VSAN Information on Trunk Ports
switch# show interface trunk vsan 1-1000
Vsan 1000 is down (Isolation due to vsan not configured on peer)
Vsan 1 is up, FCID is 0x760001
Vsan 2 is up, FCID is 0x6f0001
Belongs to port-channel 6
Vsan 1 is up, FCID is 0xef0000
Vsan 2 is up, FCID is 0xef0000
port-channel 6 is trunking
Vsan 1 is up, FCID is 0xef0000
Vsan 2 is up, FCID is 0xef0000
Default Settings
Table 12-3 lists the default settings for trunking parameters.
Table 12-3 Default Trunk Configuration Parameters
Parameters
|
Default
|
Switch port trunk mode
|
On.
|
Allowed VSAN list
|
1 to 4093 user-defined VSAN IDs.
|
Trunking protocol
|
Enabled.
|