From: Hunt, Richard (LDN-GIS) (Richard.Hunt@interpublic.com)
Date: Thu Mar 12 2009 - 10:50:20 ARST
Thanks Lejoe,
I just realised that in my case ToS is copied as you say to the GRE header and
each hop (which is providers MPLS cloud)does nothing with it to prioritise it
because I haven't asked them to. Therefore unless I engage the provider, I
get no guarantees , doh!
I see my markings at both ends so the pre-classify part isn't needed as you
rightly say.
The question for me remains about the when to use pre-classify exactly. The
link that you sent just re-gurgitates the Cisco link I sent before. If ToS is
Ok and passed on to the new GRE header, then what sort of markings are not OK
?, and therefore need this feature?
Quote:
Apply the policy to a physical interface and enable qos-preclassify on a
tunnel interface when you want to classify packets based on the pre-tunnel
header.
Thanks,
Rich.
From: Styran [mailto:styran@gmail.com]
Sent: 12 March 2009 12:06
To: Hunt, Richard (LDN-GIS)
Cc: ccielab@groupstudy.com
Subject: Re: Qos over GRE using 'pre-classify' command
Hi Richard,
If you're applying the service-policy command under the tunnel interface, you
dont need to add the qos-preclassify under the tunnel interface. IOS copies
the DS-Field or TOS byte of the original IP header to the new the IP header (
eg: in case of GRE tunnel, when the original packet is encapsulated), so
intermediate nodes can examine this field to apply appropriate QOS policies.
As to when to use the qos-preclassify, I believe this might help
http://ccieeverest.blogspot.com/2008/12/qos-pre-classify.html
Lejoe
On Thu, Mar 12, 2009 at 9:52 PM, Hunt, Richard (LDN-GIS)
<Richard.Hunt@interpublic.com<mailto:Richard.Hunt@interpublic.com>> wrote:
Dear All,
I have backup WAN over a provider MPLS that uses GRE tunnels (but it's just a
network with GREs nothing complex). It's hub and spoke in essence. I have a
service-policy that matches my VoIP traffic and is applied to each Tunnel
interface. As far as I could determine it was all marking and sending the
VoIP using LLQ ( I used Netflow to verify this). Now I read about the
'pre-classify' interface command and I'm a little confused as to whether my
receiving tunnel interfaces are able to pass on the original QoS marking
(based on DSCP) and therefore if the rest of the LAN behind can prioritise
this traffic.
My GRE tunnel service-policy is applied outbound on all sites including the
hub site and that seems to give priority based on my match criteria.
Here's the CCO link that has me confused.
http://www.cisco.com/en/US/tech/tk543/tk545/technologies_tech_note09186a00801
7405e.shtml#qoscomm<http://www.cisco.com/en/US/tech/tk543/tk545/technologies_
tech_note09186a00801%0A7405e.shtml#qoscomm>
Can anyone shed any light, has anyone sniffed this on say a LAN Ethernet of a
router that has a GRE to another site? Who knows when you'd use
'pre-classify'?
Thanks in advance.
Richard.
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