[Cake] Using firewall connmarks as tin selectors

[Pete Heist]

> On Mar 3, 2019, at 12:52 PM, Kevin Darbyshire-Bryant <kevin at darbyshire-bryant.me.uk> wrote:
> 
> The very bad idea:
> 
> And it’s bad ‘cos it’s sort of incompatible with the existing fwmark implementation as described above.  So an awful lot of our shenanigans above is due to DSCP not traversing the internet particularly well.  The solution above abstracts DSCP into ’tins’ which we put into fwmarks.  Another approach would be to put the DSCP *into* the fwmark.  CAKE could (optionally) copy the FWMARK contained DSCP into the diffserv field onto the actual packets.  Voila DSCP traversal across ’tinternet with tin/bandwidth allocation in our local domain preserved.

If I understand it right, another use case for this “very bad idea” is preserving DSCP locally while traversing upstream WiFi links as besteffort, which avoids airtime efficiency problems that can occur with 802.11e (WMM). In cases where the router config can’t be changed (802.11e is mandatory after all) I’ve used IPIP tunnels for this, as it hides DSCP from the WiFi stack while preserving the values through the tunnel, but this would be easier. Neat… :)