I'm having trouble with the encapsulation command on a router 2611..

[smasherjp1]

Home lab: I’m practicing basic configurations and I was in the process of configuring a router on a stick. I have the switch done, but when I go to the router and go into the subinterface, it doesn’t recognize the encapsulation command. The switch is running STP , and when I run the command “sh interfaces” on the router, it says the interfaces “Encapsulation ARPA”. Do both router and switch have to have the same encapsulation? 

I don't even know if the 2611 can even have STP on it.  This is some output..

router1(config)#router ?
  bgp       Border Gateway Protocol (BGP)
  eigrp     Enhanced Interior Gateway Routing Protocol (EIGRP)
  isis      ISO IS-IS
  iso-igrp  IGRP for OSI networks
  mobile    Mobile routes
  odr       On Demand stub Routes
  ospf      Open Shortest Path First (OSPF)
  rip       Routing Information Protocol (RIP)

[Reza Sharifi]

Not every image on the old 2600 can do encapsulation dot1q. What version of IOS are you running?

sh ver

Also, there is no need for STP on the router and not sure why you posted the options for different routing protocols (confusing).

HTH