[cisco-bba] L2TP tunnel switching not copying dscp bits betweensession L2TP tunnel switching not copying dscp bits betweensession headers

Oliver Boehmer (oboehmer) oboehmer at cisco.com
Tue Aug 15 11:28:20 EDT 2006

Tony Redstone <> wrote on Tuesday, August 15, 2006 5:14 PM:
> We're terminating ppp users on the LNS and using "QoS: Per-Session
> Shaping and Queuing on LNS" and "ip tos reflect" under the vpdn-group
> to copy the end user payload dscp bits into the encapsulating L2TP
> header.  This works fine.
> When L2TP traffic is tunnel switched through a cisco 7301 (LTS) the
> dscp bits are reset in the outgoing L2TP session headers on egress
> from the LTS.  This means we can't apply appropriate congestion
> management either directly on egress from the LTS or further upstream.
> [..]
> Any suggestions as to how we can preserve the ToS byte during L2TP
> tunnel switching?

you could try to mark the pkts with a qos-group on ingress (i.e.
match-all on the l2tp traffic and the dscp's) and then set the dscp on
egress depending on the qos-group of the packet. Cumbersome, but I can't
think of any other workaround right now..


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