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New Member


hi, i had a doubt.

our network is ip N/w and our service provider is C&W MPLS N/w , we had configured Qos in our routers and marking done by using DSCP for voice traffic and for IPSEC traffic we are using access-list , i know few thing like if our data want to cross MPLS network, DSCP to IP Precedence mapping will be done in Provider Edge router because MPLS Qos is based on MPLS exp bit 3 bit , but my doubt is how the ipsec data will be marked in PE router of C&w which we had mark it by using Access-list...


Re: MPLS Qos

HI Hariharan, [Pls RATE if HELPS]

For the IPSec marking's to work please enable "qos pre-classify" command in CE Router.

When packets are encapsulated by encryption headers, QoS features are unable to examine the original packet headers and correctly classify the packets. Packets traveling across the same tunnel have the same encrypted headers, so the packets are treated identically if the physical interface is congested. With the Quality of Service for Virtual Private Networks (VPNs) feature, packets can now be classified before the encryption occur.

The qos pre-classify command enables the QoS for VPNs feature .

Hope this Helps. Please Rate if HELPS

Best Regards,

Guru Prasad R.

New Member

Re: MPLS Qos

hi guru,

first i should say thanks for ur Reply

but u r talking about VPN Qos , my doubt is in MPLS QOS

1.ip precedence value will be automatically copied int MPLS EXP bit

(3 bits). so if we are using DSCP for Marking Voice or Video traffic, manual mapping from DSCP to ip precedence should be done in PE router so that in MPLS core router (LSR) Marking of traffic will be done by using MPLS exp bit

here in our n/w for (IPSEC and applications traffic ) we are not using NBAR to mark the traffic, we had used access-list in order to mark the traffic.

so my doubt is how the packets marked by access-list in our (CE) router will be marked in (MPLS)PE router for Qos.

Re: MPLS Qos

HI Hariharan,

In SP Network, the QoS marking delivered to the destination network corresponds to the marking received when the traffic entered the MPLS network.

Consider on your LAN Interface the Application Traffic is marked with Precedence 3. Let's assume the COLOR of 3 is RED.

The same RED packet will be matched in the MPLS PE Routers directly on the Customer landing Interface.

Hope this Helps.

Best Regards,

Guru Prasad R

New Member

Re: MPLS Qos


Normally DSCPs are values are backward compatible with IP precedence. When converting between IP precedence and DSCP, match the three most significant bits. So What ever dscp marking is done on , IP prec is set accordingly. Example DSCP = 46 ( priority class traffic ) , wiil have IP prec = 5 , and when in MPLS world it will automatically mapped to EXP = 5 in a labeled packet.



New Member

Re: MPLS Qos

yes, What ever dscp marking is done, IP prec is set accordingly

but what will happen when i dint marked the traffic by using using DSCP or IP pre ? and i marked it by using access-group command

after gone through few documents i came to know that in (MPLS)service provider PE

router they will use CAR and by using rate limit access-list they can mark the traffic.

is it correct........

Super Bronze

Re: MPLS Qos

Although it's possible a particular MPLS provider could remark your packets, as Guru describes, normally one would expect MPLS providers to preserve your original marking. I.e. what the CE provides to the PE, the far side PE should provide to the CE.

The serveral MPLS providers I've encountered, when you exceed a contracted bandwidth, either will drop your packets outright, or mark the packets as being out-of-contract within their MPLS cloud, and more likely to be dropped if there's congestion, but still preserve the original ToS if the packet makes it to the other side.

For any particular provider, you would need to determine what they do.

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