ISL vs dot1q

[danshelb]

I was wondering if there were any technical or performance advantages of using ISL trunking vs. dot1q. I understand that dot1q is the open standard and ISL is Cisco only, but I haven't been able to find if either have inherent advantages over the other. Any info or advice would be appreciated.

Dan

 

[Whoheard]

The best advantage to dot1q is the compatability with other hardware. If you configure ISL and install a non-cisco device and try to use dot1q, it will not work.

bob

I know what I know and that's all I know. What I don't know I'll find out.

 

[Patryn]

And there are certain situations in which ISL is not supported.
Like in MAN (Metro Area Networks) there can be a need for double tagging, what can only be done with dot1q.

 

[NetEng631]

Go with dot1q. From what I have been hearing is Cisco is looking to phase ISL out.

NetEng

 

[danshelb]

Thanks guys, I inherited a site that has ISL to go along with my site which is dot1q. This sort of settles the debate about which way I'll standardize. Thanks again.

Dan

 

[baddos]

ISL is great... It exentends the frame size so your switch doesn't have to fragment the packets going over the trunk link.

I read that ISL is being phased out too, which is bad. The good thing though, is that you can use jumbo MTU on your trunk ports if you are using dot1q, so you don't fragement your frames.

 

[rainman]

I believe that 802.1q also allows for 4096 VLAN's, compared to ISL's limit of 1024. 4 times the amt of VLANs works for me plus interoperability.


-Rainman

 

[lockesurf]

Mr. Rainman.
I am Mr. Locke, and I will tell you the difference between ISL and 802.1q trunking protocols... Simply put, ISL is cisco propietary, which means if a switch has some 802.1q trunks, and some ISL trunks, it will negotiate to the ISL. If ISL is proprietary, then why did they make 802.1q?
because 802.1q works with other vendors, i.e. Enterasys, 3com, etc... so if you are going to be migrating a crappy network to a cisco backbone, you will end up using 802.1q to span your broadcast domains into your existing switches, all the while still segmenting your network into broadcast domains ( number one reason for using cisco switches , in my book )..,,

so they both work, but if your using cisco to cisco , then use ISL, if not , use 802.1q.