What is the difference between ISL (inter switch link) on Fiber Channel and trunk links on Ethernet switching?

Are they essentially the same thing?

2 Answers 2


ISL on Fiber Channel networks has nothing to do with the ISL trunking protocol known on Ethernet networks. In Fiber Channel networks, it is simply a way to describe the connection between two Fiber Channel switches.

In Ethernet networks it's a trunking protocol tagging frames with the appropriate VLAN information (as 802.1Q does, which is actually the standard). ISL is a Cisco proprietary trunking protocol pre-dating 802.1Q; it's deprecated and is already removed from the newest switches.

  • 802.1q is vlan and priority tagging. It has nothing at all to do with LACP (802.3ad) But yeah, when you say "ISL" in an ethernet context, people will think Cisco's VLAN tagging method.
    – Ricky
    Commented May 12, 2015 at 20:03

Essentially ISL in fiber channel and trunk link on ethernet channel carry same task... but difference is its two type of reduntet path of data transmission. ISL in fiber channel is its own path of data transmission which connect two fiber links and trunk link in ethernet switching is its path of data transmission, which use the TCP/IP protocol.

The path of network changes according to the network and protocol. FSPF(fabric shortest path first) is the protocol of fiber link and TCP/IP for ethernet link.

  • This is just wrong in so many ways. TCP/IP has absolutely nothing to do with tagged/trunk ports nor with Ethernet. TCP/IP can just as easily use some other L2 protocol just as Ethernet supports other L3/L4 protocols. For example, tagged/trunk ports will function in exactly the same manner in an IPX/SPX environment as they do in a TCP/IP environment.
    – YLearn
    Commented May 13, 2015 at 1:34
  • @YLearn Thank you for correct me, now I understand the TCP/IP.
    – jeremy
    Commented May 13, 2015 at 2:45

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