Question : DSCP  46 (EF) How to verify and enable for Asterisk

Say, I was asked by my ISP to do this: "Please ensure that your Asterisk is marking your voip traffic with DSCP
46 (EF) particularly your SIP traffic and you RTP traffic. I think it
should be by default, but just double check it. The best would be to do
a wireshark trace and capture the actual packets the you can check the
marking as they come in and as they come back to you."

How do I do it please?

Answer : DSCP  46 (EF) How to verify and enable for Asterisk

Using wireshark to make sure is a different question you can post in the network section.

To use iptables to mark the traffice checkout
http://www.voip-info.org/wiki/view/QoS+Linux

http://www.ibiblio.org/pub/Linux/docs/HOWTO/other-formats/html_single/ADSL-Bandwidth-Management-HOWTO.html read classifying ip packet

read this http://www.voip-info.org/wiki/index.php?page_id=464&tk=99167a4fa50258d7a476&comments_page=1 then go here http://lartc.org/wondershaper you should be able to mark the traffic.

FYI don't forget to read the links on my comment above.

Good luck.