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Of these two, the Jetdirect 635n (also known as J7961G) allegedly has IPv6 support, and is therefore a suitable candidate to upgrade our Laserjet 4250, who's . This is not a reasonably new printer, but the embedded J7949E doesn't do IPv6. Funnily enough the configuration pages of the J7949E explicitly list IPv4, probably HP wanted to make very clear that it is IPv4, and not IPv6.
After receiving the box I was happy to see the golden version of the IPv6 ready Gold logo 
. The card itself is not very spectacular, it features the only notable things are a SafeXcel 1141 crypto coprocessor, and a Broadcom BCM5788 Gbic.
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After adding the new card, the "Networking" tab has a fresh new look, and now all kinds of new stuff is configurable: