Fibre Channel (SAN)

Occasional Contributor
Posts: 13
Registered: ‎06-27-2014
Accepted Solution

Broken of an ISL within a Trunk

Hi Experts,


I have a dummy question again.


|                     | ------ ISL_1------ |                     |

|                     | ------ ISL_2------ |                     |

|                     |                              |                     |

| Switch_A  |                              | Switch_B  |

|                     |                              |                     |

|                     | ------ ISL_3------ |                     |

|                     | ------ ISL_4------ |                     |


I have two Trunks:

  1. Upper_Trunk: formed by ISL_1 and ISL_2.
  2. Lower_Trunk: formed by ISL_3 and ISL_4.


Let's say Host_X is sending frames from Switch_A to Switch_B through ISL_1; at the same time, ISL_1 is broken.



  1. Will the traveling frames, auto reroute to ISL_2 or may be ISL_3 and ISL_4 without, again, without the need to reinstate/resend by Host_X?
  2. Or, the travelling frames for sure will be discarded in ISL_1, and Host_X needs to reinstate/resend the frames?

Thank you for your guidance in advance.






Regular Contributor
Posts: 164
Registered: ‎05-11-2011

Re: Broken of an ISL within a Trunk

Hi Swee,


if ISL_1 goes down and there was a frame on it, frame will be lost.

When farme is lost, the whole exchange which the lost frame was part of, have to be resend.


All exchanges traversing trunk isl_1/isl_2 having no frame lost will be uninterrupted on isl_2 only.


Depending on your routing policy on the switches, the next exchanges will be routed either via trunk isl_3/4 or isl_2.

Kind Regards
Occasional Contributor
Posts: 13
Registered: ‎06-27-2014

Re: Broken of an ISL within a Trunk

Thank you Ralf!

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