11-10-2008 12:16 PM - edited 03-17-2019 09:33 PM
Hello,
1) I have Snom phones that show them using DSCP CS 5 (0x28) on captures.
2) Asterisk servers showing DSCP AF31-low (0x1a)
I have the following configuration for my Cisco 2560 switches;
#Access-list with Snom SIP & RTP
ip access-list extended voip-traff
permit udp any any range 5060 5061
permit udp any any range 10000 20000
#class-map named ipphone & match acl voip-traff:
class-map match-any ipphone
match access-group name voip-traff
#Policy map named voip, match class-map iphone:
policy-map voip
class ipphone
set dscp cs5
#set interfaces to police policy-map voip:
interface-range gi 0/1 - 48
service-policy input voip
#enable qos globally:
mls qos
#qos on 4500
#map out QOS to COS-DSCP
mls qos map cos-dscp 0 8 16 24 32 46 48 56
My question is can I do a packet re-write and change the DSCP to Expedited Fwdg and if so, how?
Thanks!
11-10-2008 12:45 PM
Yes, you can change your configuration slightly to accomplish this. See the following example.
ip access-list extended voip-sig
permit udp any any range 5060 5061
ip access-list extended voip-media
permit udp any any range 10000 20000
class-map match-any ipphone-sig
match access-group name voip-sig
class-map match-any ipphone-media
match access-group name voip-media
policy-map voip
class ipphone-sig
set dscp cs5
class ipphone-media
set dscp ef
This would set the DSCP for signalling traffic to CS5 and media to EF. You could obviously change the signalling as well. Cisco recommends CS3 for signalling.
Hope this helps. If so, please rate the post.
Brandon
11-10-2008 01:19 PM
Thanks Brandon!
I'm still trying to figure this one out though..
mls qos map cos-dscp 0 8 16 24 32 46 48 56
What does it do?
11-10-2008 01:25 PM
This command changes the default Class of Service to DSCP map. An incoming packet with a COS value gets mapped to a DSCP value. The problem is that the default map does not map these values correctly. I'm not sure why Cisco doesn't change the default map, but they haven't. For example, voice traffic with a COS of 5 should map to DSCP value 46 (EF). This is why the command is necessary. Also, see the following link.
http://www.cisco.com/en/US/docs/ios/qos/command/reference/qos_m2.html#wp1012528
Hope this helps.
Brandon
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