Configuring the E-ports on the Cisco FC switch

You must configure the FC switch ports that connect the inter-switch link (ISL). These are the E-ports, and configuration must be done for each port. To do so, you must calculate the correct number of buffer-to-buffer credits (BBCs).

All ISLs in the fabric must be configured with the same speed and distance settings.

This task must be performed on each ISL port.

Use the following table to determine the adjusted required BBCs per kilometer for possible port speeds.
To determine the correct number of BBCs, you multiply the Adjusted BBCs required (determined from the following table) by the distance in kilometers between the switches. An adjustment factor of 1.5 is required to account for FC-VI framing behavior.
Speed in Gbps BBCs required per kilometer Adjusted BBCs required (BBCs per km x 1.5)
1 0.5 0.75
2 1 1.5
4 2 3
8 4 6
16 8 12
For example, to compute the required number of credits for a distance of 30 km on a 4-Gbps link, make the following calculation:
- Speed in Gbps is 4
- Adjusted BBCs required is 3
- Distance in kilometers between switches is 30 km
- 3 x 30 = 90
Issue the following command to enter configuration mode: config t
Specify the port you are configuring: interface port-name
Shut down the port: shutdown
Set the rate mode of the port to dedicated:switchport rate-mode dedicated
Set the speed for the port: switchport speed speed
Set the buffer-to-buffer credits for the port: switchport fcrxbbcredit number of buffers
Set the port to E mode: switchport mode E
Enable the trunk mode for the port: switchport trunk mode on
Add the ISL virtual storage area networks (VSANs) to the trunk:switchport trunk allowed vsan 10 switchport trunk allowed vsan add 20
Add the port to port channel 1:channel-group 1

Speed in Gbps	BBCs required per kilometer	Adjusted BBCs required (BBCs per km x 1.5)
1	0.5	0.75
2	1	1.5
4	2	3
8	4	6
16	8	12

Repeat the previous steps for the matching ISL port on the partner switch in the fabric.

The following example shows port fc1/41 configured for a distance of 30 km and 8 Gbps:

FC_switch_A_1# conf t
FC_switch_A_1# shutdown
FC_switch_A_1# switchport rate-mode dedicated
FC_switch_A_1# switchport speed 8000
FC_switch_A_1# switchport fcrxbbcredit 60
FC_switch_A_1# switchport mode E
FC_switch_A_1# switchport trunk mode on
FC_switch_A_1# switchport trunk allowed vsan 10
FC_switch_A_1# switchport trunk allowed vsan add 20
FC_switch_A_1# channel-group 1
fc1/36 added to port-channel 1 and disabled
 
FC_switch_B_1# conf t
FC_switch_B_1# shutdown
FC_switch_B_1# switchport rate-mode dedicated
FC_switch_B_1# switchport speed 8000
FC_switch_B_1# switchport fcrxbbcredit 60
FC_switch_B_1# switchport mode E
FC_switch_B_1# switchport trunk mode on
FC_switch_B_1# switchport trunk allowed vsan 10
FC_switch_B_1# switchport trunk allowed vsan add 20
FC_switch_B_1# channel-group 1
fc1/36 added to port-channel 1 and disabled

Issue the following command on both switches to restart the ports: no shutdown
Repeat the previous steps for the other ISL ports in the fabric.
Add the native VSAN to the port-channel interface on both switches in the same fabric: interface port-channel number switchport trunk allowed vsan add native_san_id

Verify configuration of the port-channel:show interface port-channel number

The port channel should have the following attributes:

The port-channel is trunking.
Admin port mode is E, trunk mode is on.
Speed shows the cumulative value of all the ISL link speeds.
For example, two ISL ports operating at 4 Gbps should show a speed of 8 Gbps.
Trunk vsans (admin allowed and active) shows all the allowed VSANs.
Trunk vsans (up) shows all the allowed VSANs.
The member list shows all the ISL ports that were added to the port-channel.
The port VSAN number should be the same as the VSAN that contains the ISLs (usually native vsan 1).

FC_switch_A_1(config-if)# show int port-channel 1
port-channel 1 is trunking
    Hardware is Fibre Channel
    Port WWN is 24:01:54:7f:ee:e2:8d:a0
    Admin port mode is E, trunk mode is on
    snmp link state traps are enabled
    Port mode is TE
    Port vsan is 1
    Speed is 8 Gbps
    Trunk vsans (admin allowed and active) (1,10,20)
    Trunk vsans (up)                       (1,10,20)
    Trunk vsans (isolated)                 ()
    Trunk vsans (initializing)             ()
    5 minutes input rate 1154832 bits/sec,144354 bytes/sec, 170 frames/sec
    5 minutes output rate 1299152 bits/sec,162394 bytes/sec, 183 frames/sec
      535724861 frames input,1069616011292 bytes
        0 discards,0 errors
        0 invalid CRC/FCS,0 unknown class
        0 too long,0 too short
      572290295 frames output,1144869385204 bytes
        0 discards,0 errors
      5 input OLS,11  LRR,2 NOS,0 loop inits
      14 output OLS,5 LRR, 0 NOS, 0 loop inits
    Member[1] : fc1/36
    Member[2] : fc1/40
    Interface last changed at Thu Oct 16 11:48:00 2014

Exit interface configuration on both switches: end

Copy the updated configuration to the startup configuration on both fabrics: copy running-config startup-config

FC_switch_A_1(config-if)# end
FC_switch_A_1# copy running-config startup-config
 
FC_switch_B_1(config-if)# end
FC_switch_B_1# copy running-config startup-config

Repeat the previous steps on the second switch fabric.

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