Does a 2900XL switch support both ISL & 802.1q trunking or like the 2950 just 802.1q????
The original 2900XL, or 4MB version does not support trunking at all.
Yes it does support both ISL as well as dot1q.
According to this document, Inter-Switch Link (ISL) trunking is supported on the 2900XL since Cisco IOS Release 11.2(8)SA4 (Enterprise Edition Software):
NOTE: The Catalyst 2940 and 2950/2955 series switches do not support ISL encapsulation.
HTH, please rate if it does help,
it only supports dot1q