QoS for a VPN VoIP call
Is it possible to provide some type of QoS for a VPN VoIP call? For example: using encapsulation inside the VPN tunnel. Or is it a myth?

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This depends upon the device that is creating the IPSec VPN tunnel.

The idea is that the speech packets arriving at the device that will send the packets through the VPN tunnel are already marked with a specific IP ToS value. If the VPN device simply encapsulates the IP packet with the priority marking, this marking is no longer visible on the outside IP packet.

Some devices that create an IPSec VPN tunnel (such as the ZIP4x5 IP phone from Zultys) look at the IP ToS value of packets arriving at the phone on the LAN interface and set the ToS byte of the outer IP packets to the same value. Again, this capability will depend upon the specific device being used and its configuration.

This was first published in September 2005