VoIP prioritization flags leaving asa

[pbrunnen]

Hello all,

I have a small issue for a customer.  We upgraded their old IOS router to a new ASA 5505 with the install of a new MetroE circuit.  They have a SIP VoIP trunk to the telco coming in on vlan20.

There has been a increase in their network traffic as of late and we have been getting complaints of lost audio from the external party to the internal user, but fine audio from the user to the external party.

What I find is that the priority tags on the 802.1q headers for outbound rtp is 5 (leaving the pbx toward the telco), but inbound rtp is 0 (from the asa to the  pbx) and I believe the rtp streams are dropping out on the switches.  Priority queuing is setup on the internal and external interfaces.

The class-map on the asa is setup for voice to be priority, but I have not found a way to tag the packets with a priority of five.  Is there a way to do this?  I am trying to avoid having to move the pbx trunk to a separate vlan...

Many thanks!

-Peter.

P.S. : The dscp 'expedited forwarding' flags are set, but I am not yet sure if the switches can handle prioritization based on the IP layer.

[malshbou · Accepted solution]

Hi Peter,

The ASA doesn't tag packets for QoS, however it can prioritize/classify flows for QoS using MPF which include matching L3 DSCP.

For QoS across L3 hops, you should utilize DSCP tags (understood by ASAs, routers, and L3 swtiches) as the 802.1q priority value will not be maintinated out of a swtiched network.

HTH

------------------
Mashal Shboul

[pbrunnen]

Hello Mashal,

   I think you had not read my original post correctly.  I am aware that QoS for L3 requires DSCP,  but as I mentioned the DSCP 'ef' value is set.

  The problem appeared to be (and is now confirmed) on the local network between the ASA through the switch to the PBX because the switch is not honoring the DSCP values.

  So basically since there is no way to set a 802.1q priority tag, I will need to move all the voice traffic to the voice vlan on which the phones reside and setup some static routes to the telco on the ASA.

Thanks. -Cheers, Peter.

[pbrunnen]

Side rant:  Aparently when you mark an answer correct... no matter what the original star rating that was given... the user gets 5 stars.   I only gave three stars...  the rating system on the forums here are useless.