I don't disagree that a firewall has some basic routing abilities as part of the firewall design. See e.g. http://www.petri.co.il/csc_routers_switches_and_fw_%E2%80%93_Learn_how_they_are_different.htm . Rather, they are complimentary and nay be integrated into a single device. I'd differentiate between then by way of functionality, don't buy a firewall if you need a router and vice versa, unless you go for integrated devices.
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There are two types of vessels, submarines and targets.