The way that I read the license agreement indicates that Boden is quite right to ask the question and that legally he does not have the right to use the licensed software on a router that he may have purchased from somewhere like Ebay.
Here is part of the license agreement that we must accept when we download software from Cisco:
License. Conditioned upon compliance with the terms and conditions of the Agreement, Cisco grants to Customer a nonexclusive and nontransferable license to use for Customer's internal business purposes the Software and the Documentation for which Customer has paid the required license fees to an Approved Source.
In particular it says that the license is non transferable.
And here is another section of the license agreement:
Customer specifically agrees not to:
(i) transfer, assign or sublicense its license rights to any other person or entity (other than in compliance with any Cisco relicensing/transfer policy then in force), or use the Software on Cisco equipment not purchased by the Customer from an Approved Source or on secondhand Cisco equipment, and Customer acknowledges that any attempted transfer, assignment, sublicense or use shall be void;
Here is a link to the complete agreement
http://www.cisco.com/en/US/docs/general/warranty/English/EU1KEN_.html
So Boden's concern is well founded. As a practical matter many people purchase used equipement from various non-authorized sources and use the equipment with the existing copy of software. But as a legal question they do not have a legal right to do this.
HTH
Rick
HTH
Rick
