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I need to be able to ping a device and classify the data with a TOS value (184).
We have a Cisco site-to-site link working perfectly, but I'm trying to prioritise voice traffic between two voice servers (non cisco - one at each site). The voice servers are apparently tagging all inter-site traffic with a TOS value of 184 (tos=0xB8). I've created a policy-map to match outgoing DSCP EF traffic on the WAN interfaces, but I don't seem to be getting any matches when I make an inter-site voice call.
If I use a Cisco Wireless Access Point to run an extended ping and input the TOS value of 184 then I get matches so I know that the router policy-map is working correctly. The thing I don't know is if the Cisco routers can only detect Cisco traffic. I need a ping tool where I can set a TOS value to the ICMP traffic to see if I get matches.
I've tried a ping from an XP machine where the ping -v command is supported, and this traffic doesn't 'match' in the policy-map.
I'm also trying to find a way to capture the packets to and from each voice server to see if the packets are actually tagged with the correct TOS value. Any ideas how to do this? (I have wireshark but can't seem to work out how to monitor a remote device).
Any ideas?
Cheers, Andy
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The capture filter equivalent of "ip.dsfield==184" would be "ip[1]=184".
Furthermore, when the dsfield value is 184, the dscp value is actually 46, as the dscp field consists of the higher 6 bits of the dsfield, the other two bits are for ECN (Explicit Congestion Notification).
Im assuming your filter "ip.dsfield==184" will only show packets with DSCP value 46 and both ECN bits zero. So you might miss packets that have an ECN bit set. It's better to use the display filter "ip.dsfield.dscp==46", for which the capture filter equivalent is "ip[1]>>2=46"
Hope this helps.
Thank you for the suggestion. I may have to revert to this option if I can't get the TOS / DSCP values to match. Now that I've started along the TOS / DSCP route I'd quite like to get it working this way.
The_Warlock
Thank you for that. I've managed to capture packets from the voice server while a call was being made to the other site. From what I can tell, the inter-site traffic is being tagged with a DSCP value of 0 (DSCP 0x00) which is probably why the Cisco router isn't matching the traffic.
The voice server uses TOS, and I'm inputting a TOS value of 184 (tos=0xB8), and the Cisco router is trying to match DSCP EF (46). Is the TOS value correct for this?
Cheers, Andy
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Routers
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A router is a networking device that forwards data packets between computer networks. Routers perform the "traffic directing" functions on the Internet. The most familiar type of routers are home and small office cable or DSL routers that simply pass data, such as web pages, email, IM, and videos between computers and the Internet. More sophisticated routers, such as enterprise routers, connect large business or ISP networks up to the powerful core routers that forward data at high speed along the optical fiber lines of the Internet backbone. Though routers are typically dedicated hardware devices, use of software-based routers has grown increasingly common.