If you are referring to the Linksys WRT54GS, it supports IPv6 tunnels, but not with Linksys firmware. The WRT54G and GS (those that do NOT run VxWorks) can alternatively run Tomato, DD-WRT, or OpenWRT firmware, all of which support IPv6 (I have a V.2 GS that I personally upgraded to OpenWRT; the router itself dates to 2005, but the firmware is less than two months old).
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