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

Paul Horrocks (phorrock) phorrock at cisco.com
Tue Aug 15 11:37:21 EDT 2006

Yes 'l2tp ip tos reflect is not supported on LTS - LNS only.  

The below is the workaround as detailed in CSCee27441

It has been found that the correct mode of operation where the TOS field
is reflected correctly
into the L2TP header can be achieved by adding the following config
below. This was tested with
12.3(4)T5 and 12.3(7.11)T. However, it still has to be determined
whether it should be necessary
to make the changes below or whether the TOS relfect feature needs to be
corrected for the
C7X00 platforms.

class-map match-all QOS-Group7
 match qos-group 7
class-map match-all QOS-Group6
 match qos-group 6
class-map match-all QOS-Group5
 match qos-group 5
class-map match-all QOS-Group4
 match qos-group 4
class-map match-all QOS-Group3
 match qos-group 3
class-map match-all QOS-Group2
 match qos-group 2
class-map match-all QOS-Group1
 match qos-group 1
class-map match-all QOS-Group0
 match qos-group 0
class-map match-all Tos0
 match ip precedence 0
class-map match-all Tos1
 match ip precedence 1
class-map match-all Tos2
 match ip precedence 2
class-map match-all Tos3
 match ip precedence 3
class-map match-all Tos4
 match ip precedence 4
class-map match-all Tos5
 match ip precedence 5
class-map match-all Tos6
 match ip precedence 6
class-map match-all Tos7
 match ip precedence 7
policy-map Outbound-Policy
 class QOS-Group0
  set precedence 0
 class QOS-Group1
  set precedence 1
 class QOS-Group2
  set precedence 2
 class QOS-Group3
  set precedence 3
 class QOS-Group4
  set precedence 4
 class QOS-Group5
  set precedence 5
 class QOS-Group6
  set precedence 6
 class QOS-Group7
  set precedence 7
policy-map Inbound-Policy
 class Tos0
  set qos-group 0
 class Tos1
  set qos-group 1
 class Tos2
  set qos-group 2
 class Tos3
  set qos-group 3
 class Tos4
  set qos-group 4
 class Tos5
  set qos-group 5
 class Tos6
  set qos-group 6
 class Tos7
  set qos-group 7
interface GigabitEthernet0/1
 ip address
 service-policy input Inbound-Policy
 service-policy output Outbound-Policy
 duplex full
 speed 1000
 media-type gbic
 negotiation auto

> -----Original Message-----
> From: cisco-bba-bounces at puck.nether.net 
> [mailto:cisco-bba-bounces at puck.nether.net] On Behalf Of 
> Oliver Boehmer (oboehmer)
> Sent: Tuesday, August 15, 2006 4:28 PM
> To: Tony Redstone; cisco-bba at puck.nether.net
> Subject: Re: [cisco-bba] L2TP tunnel switching not copying 
> dscp bitsbetweensession L2TP tunnel switching not copying 
> dscp bitsbetweensession headers
> 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..
> 	oli
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