11-28-2011 06:54 PM - edited 03-16-2019 08:16 AM
For some reason, a bunch of Cisco phones are marking RTP packets with a DSCP of 11, instead of 46. I've confirmed this with a packet capture as well as looking at the DSCP statistics on the switch ("show mls qos int x statistics" on the Catalyst 3750).
On the same packet capture, I can look at the SKINNY "StartMediaTransmission" packet, and it appears the call manager is telling the phone to use DSCP 46 (well, Wireshark decodes it as "Predecence: 46"... which I assume really meant *DSCP* of 46). Yet, the phone keeps marking it as DSCP 11.
Has anyone see this before? Maybe a bug in the phone's firmware?
Phone is a 7960, running software version P00308000700.
Thanks!
11-28-2011 08:29 PM
It has to be difserv of differentiate serve field for the dscp value in wireshark !!
Sent from Cisco Technical Support iPhone App
11-28-2011 08:49 PM
marwanshawi wrote:
It has to be difserv of differentiate serve field for the dscp value in wireshark !!
Sent from Cisco Technical Support iPhone App
Thanks for the response. But I don't understand what you mean.
When I'm talking about the QoS marking the call manager tells the phone to use, I'm talking about the field in the SKINNY payload of the IP packet that wireshark decodes as "Precedence".
// here is that skinny payload that the call manager sends to the phone:
Skinny Client Control Protocol
Data Length: 108
Reserved: 0x00000000
Message ID: StartMediaTransmission (0x0000008a)
Conference ID: 42593650
PassThruPartyID: 33633647
Remote Ip Address: 10.89.2.52 (10.89.2.52)
Remote Port: 20094
MS/Packet: 20
PayloadCapability: G.711 u-law 64k (4)
Precedence: 46
Silence Suppression: Media_SilenceSuppression_Off (0x00000000)
MaxFramesPerPacket: 0
G723 BitRate: Unknown (0)
// Then this is the very next packet the phone sends (ie an RTP packet to the remote phone):
Internet Protocol, Src: 10.91.2.51 (10.91.2.51), Dst: 10.89.2.52 (10.89.2.52)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x2e (DSCP 0x0b: Unknown DSCP; ECN: 0x02)
0010 11.. = Differentiated Services Codepoint: Unknown (0x0b)
.... ..1. = ECN-Capable Transport (ECT): 1
.... ...0 = ECN-CE: 0
11-29-2011 02:06 AM
What's the switch port config of this phone ?
11-29-2011 03:26 AM
Hi,
I think Marwan is right (+5)
This looks like a bug in the version of wireshark
Please see
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=3320
Looks like the wireshark is reading a field back to front
I am running Version 1.6.0
It seems to be OK
Regards
Alex
11-29-2011 07:47 AM
acampbell wrote:
Hi,
I think Marwan is right (+5)
This looks like a bug in the version of wireshark
Please see
https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=3320
Looks like the wireshark is reading a field back to front
I am running Version 1.6.0
It seems to be OK
Regards
Alex
Interesting. So if we switch the entire byte around.... instead of 0010 1110, it becomes 0111 0100 and then group it into 6 bits for DSCP and 2 for ECN (00 - 101110).... then you're right!! DSCP = 46! I'm running Wireshark version 1.4
But, the counters on the switchport (show mls qos int x) also show DSCP 11 inbound from the phone incrementing.
I'll have to double check everything again. Thanks for the tip!
11-29-2011 07:41 AM
marwanshawi wrote:
What's the switch port config of this phone ?
I don't have access to the network at the moment, but it's configured using auto qos -- to conditionally trust the markings from the phone if CDP is detected.
Also, from the "show mls qos int x statistics" from the switch, the switch itself is seeing DSCP 11 inbound from the phone.
11-29-2011 07:57 AM
Hi,
The key part here is the line
From your trace RTP packet
Differentiated Services Field: 0x2e
So --> 2E (HEX) = 00010 1110 (BIN) = 46 (DEC)
So DSCP 46 (EF)
I still think you need to change your weireshark version
HTH
Alex
Please rate useful posts
11-29-2011 09:01 PM
acampbell wrote:
Hi,
The key part here is the line
From your trace RTP packet
Differentiated Services Field: 0x2e
So --> 2E (HEX) = 00010 1110 (BIN) = 46 (DEC)
So DSCP 46 (EF)
I still think you need to change your weireshark version
HTH
Alex
Please rate useful posts
I just updated Wireshark to 1.6.4 and get the same result.
I also notice that when the phone initiates SKINNY messages, they're marked with DSCP CS3 -- which is correct:
Internet Protocol Version 4, Src: 10.91.2.51 (10.91.2.51), Dst: 10.99.20.7 (10.99.20.7)
Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x60 (DSCP 0x18: Class Selector 3; ECN: 0x00: Not-ECT (Not ECN-Capable Transport))
0110 00.. = Differentiated Services Codepoint: Class Selector 3 (0x18)
.... ..00 = Explicit Congestion Notification: Not-ECT (Not ECN-Capable Transport) (0x00)
So it just seems the RTP stream isn't marked correctly. Plus, the "show mls qos int x statistics" still shows DSCP 11 inbound increment during phone calls.
I'm guessing it's a firmware issue on the phone, but I'll keep everyone posted.
Thanks for the help everyone!
11-29-2011 09:03 PM
marwanshawi wrote:
What's the switch port config of this phone ?
Here's the config, just standard auto-qos conditionally trusting the phone:
interface FastEthernet3/0/9
switchport access vlan 10
switchport mode access
switchport voice vlan 2
switchport port-security maximum 2
switchport port-security
switchport port-security aging time 2
switchport port-security aging type inactivity
srr-queue bandwidth share 10 10 60 20
srr-queue bandwidth shape 10 0 0 0
priority-queue out
mls qos trust device cisco-phone
mls qos trust cos
auto qos voip cisco-phone
no mdix auto
spanning-tree portfast
spanning-tree bpdufilter enable
spanning-tree bpduguard enable
service-policy input AutoQoS-Police-CiscoPhone
11-30-2011 02:19 AM
Hi,
Is the phone on CUCM or CME
Regards
Alex
11-30-2011 07:31 PM
acampbell wrote:
Hi,
Is the phone on CUCM or CME
Regards
Alex
CUCM. We're gonna try upgrading the phone firmware and see what happens.
07-28-2020 11:37 AM
Did the CUCM upgrade worked?
Regards
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