Usually when that occurs, the reason is that there is only one encapsulation type that is supported. On Cisco switches, your choices are ISL or dot1q. There are certain switches that do only support one type and therefore do not give you the option to choose your vlan encapsulation type. 2960's are newer switches and they may only support dot1q.
Cisco had their own trunk protocol called ISL. Some switches support only one and some support both.
If there is no choice you do not need the switchport trunk encap command.
PT maybe reflecting the 2900 switch rather than a 3750
Ah, that makes sense.
I take back everything i said about packet tracer
Here is a data sheet for the switch you mentioned. http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps6406/product_data_sheet0900aecd80322c0c.html
As you can see, there is only support for dot1q vlan tagging. ISL is not mentioned or supported on this particular model. Typically, Cisco has come out with their own proprietary technologies, until there is one that becomes standard. If that new standard is not their own, it seems that they eventually drop their own proprietary technology and support just the standard. Now, I am not saying that Cisco no longer supports all of their proprietary technologies, but there are those technologies that they don't support any more.
A good example is the old IGRP routing protocol or the Pre-standard PoE before 802.3af was ratified. It looks as if they are starting to do the same thing with ISL.
Thats good information, good idea checking out the specs on the kit.
I am following the wireless book and putting it into tracer.
The 2960 is derived from an "acquired" line of switches. So the ASIC for ISL wasn't integrated in it as far as I've been told.
802.1Q has more features/capabilities than ISL did, so it may also just be a furthering of the shift towards 802.1Q-only.
Don't forget the Feature Navigator can be helpful for capability lookups! (www.cisco.com/go/fn)
Good part of the Cisco site that.
No problems. There's LOTS of good stuff on the Cisco site. Some of it, though, they keep moving around and it's really a pain to find.