i suspect that there shouldn't be a mention of this for ccnp certification, since most indications that i'm seeing have it at ccie, even if there... but the idea is interesting...
this is simple enough... create a bridge group for legacy non-routable protocols to pass between svi's or l3 interfaces, such as decnet... (is that even out there anymore?)
dls1(config)#bridge 1 protocol vlan-bridge
that statement turns it on, then configure svi's (int vlan x) into a bridge group, say 1...
dls1(config)#int vlan 10
Br Group Mac Address State Type Ports
-------- ----------- ----- ---- -----
1 0009.b73f.ce87 Forward DYNAMIC Vl10 Po1
this is very exciting... chances are you'll never need it nowadays... however, i was alarmed when i read that 3550's might treat ipv6 as a non-routable protocol (read, not ipv4) in older versions of ios...
but no, arteq, you say, this simply cannot be...
dls1#sh ipv6 proto
dls1(config)#do sh ipv6 proto
IPv6 Routing Protocol is "connected"