So there I was pondering the problem of getting the IPv6 DSCP coding
onto the outer IPv4 packets of my '6in4' tunnel (kindly provided for
free by Hurricane Electric) when I stumbled across this in a man page:


       ip tunnel { add | change | del | show | prl } [ NAME ]
               [ mode MODE ] [ remote ADDR ] [ local ADDR ]
               [ [i|o]seq ] [ [i|o]key KEY ] [ [i|o]csum ] ]
               [ encaplimit ELIM ] [ ttl TTL ]
               [ tos TOS ] [ flowlabel FLOWLABEL ]
               [ prl-default ADDR ] [ prl-nodefault ADDR ] [ prl-delete
ADDR ]
               [ [no]pmtudisc ] [ dev PHYS_DEV ] [ dscp inherit ]

dscp inherit - just what I need!  Unfortunately it turns out it's for
'things being tunnelled over ipv6' and not 'ipv6 being tunnelled over
ipv4'.   Aaaarrghhh!  So close.