IPSec and DSCP

QoS and IPSec interactions | CCIE, the beginning!
http://cciethebeginning.wordpress.com/2011/02/02/qos-and-ipsec-interactions/

Enterprise QoS Solution Reference Network Design Guide - IPSec VPN QoS Design [Design Zone for IPv6] - Cisco
http://www.cisco.com/c/en/us/td/docs/solutions/Enterprise/WAN_and_MAN/QoS_SRND/QoS-SRND-Book/IPSecQoS.html#pgfId-44642

Feature #166: DSCP config in StrongSwan
http://wiki.strongswan.org/issues/166

strongSwan does not provide DSCP specific functionality but the DSCP example in our test suite might give you an idea how to configure it using iptables and XFRM marks.

Test ikev2/net2net-psk-dscp
http://www.strongswan.org/uml/testresults/ikev2/net2net-psk-dscp/index.html

[strongSwan] DSCP support in new version of strongswan
https://lists.strongswan.org/pipermail/users/2010-October/000853.html