If I plug 2 devices talking DECnet into an unconfigured 3550-24 switch will they be able to communicate? If so, is there an article or link with more reference to this?
Yes...If the ports are in the same VLAN(all ports are in VLAN1 by default). Layer 2 switches does not care about higher layer protocols if the devices are in same VLAN. You might also want to enable "spanning-tree portfast" under the interfaces
