Packet Prioritization Through a VPN

[mike-greene]

Hello everyone, I'm going to post this in this forum fist because it has to do with packet prioritization over a full meshed VPN topology. Here’s the question……..

We have a client that has three sites with 2600’s and one site with a 3640. They connect up to an ISP via T1 connections. All four sites terminate on a 3640 at the ISP. All four sites are a fully meshed VPN using 3DES. Now, they just recently setup VOIP between the sites going through the VPN tunnel and it is horrible. We were thinking about doing some packet prioritization on the remote routers and the ISP router. The ISP router I think is going to be pretty easy because we can prioritize ESP traffic going out the serial interfaces on the 3640 at the core (the ISP). The question we have is on the remote client routers. If we setup prioritization coming into those routers, will it prioritize the traffic before the router puts the packets in the VPN tunnel? What I want is to set the prioritization on the Ethernet side on the remote routers, this way it sends VOIP traffic through the VPN tunnel before any other traffic.

Will this work…….Thanks in advance

[dtodd]

Mike:

The prioritization of the traffic will only effect the traffic w/in the routers buffer and memory. This will have no effect on the ISP links or any traffic going to/from the ISP which is your desitination (unless you have a guarenteed end to end Service Contract w/your ISP).

I would assume that your delay is not due to serialization delay but due to latency on ISP links between your offices. Once you hit a delay of 300ms or so your voice quality will be horrible. You NEED to keep the delay down to 150 or so from what I remember.

First your traffic is encrypted so priorization will not have any effect on the packet going through the ISPs.

Second: Unless you have an agreement w/the ISP or other ISPs your delay will be uncontrollible. Thus voice is unpredictable.

Third:

If you need to prioritize traffic in/out of your router I would look at somethink like CBQ or PBQ methods that give you control over the traffic entering/leaving the router.

There are people who have done this but the variability of the internet and vpn traffic has lead to patchy results.

==DMT>