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Webcast-Catalyst9k
New Member

diffserv and qos

Hi all, is diffserv the layer 3 marking of the packet, whereas 802.1p is the layer 2 marking ? and do we have to map these at between the layer 2/3 boundaries ?

5 REPLIES
Silver

Re: diffserv and qos

Yes the .1p is used within layer2 frame (only in tagged frame) and DSCP and ToS is used within IP header. If you want to preserve the layer2 marking you have to map it to layer3.

Hope it helps, if so pls rate

Krisztian

New Member

Re: diffserv and qos

Hi

when i set the qos value on my switch for the port, If the pc or device does not set its own value say for a paticular application etc, how do i make the switch apply the qos value to the traffic to the incoming frames ?

Silver

Re: diffserv and qos

Hi,

The best way is to apply a policy-map on the ingress interface and classify (based on acl) and mark the packets (set cos, dscp).

This link fairly good describes how qos should be configured:

http://forums.cisco.com/eforum/servlet/NetProf?page=netprof&type=Subscriptions&loc=.1dde8945/1&forum=Network%20Infrastructure&topic=LAN%2C%20Switching%20and%20Routing

Hope it helps, rate if does,

Krisztian

Re: diffserv and qos

Carl,

If your switch supports the features, then you can always classify the packets based on IP address, port no etc, at the ingress and mark them as required.

eg. on a 3750 switch

ip access-list extended VOICE

permit udp 100.100.100.0 0.0.0.127 any range 16384 32767

class-map match-all VOICE

match access-group name VOICE

policy-map VOICE-ACCESS

class VOICE

set ip dscp ef

interface fa 1/0/1

service-policy input VOICE-ACCESS

HTH, rate if it does

Narayan

New Member

Re: diffserv and qos

thanks for your help, I know im a pain but could you explain what each line does? so all we are doing here is creating an access list that defines port number etc, and if there are any matches it applies the ef policy to them? also say if we have a phone that already marks the packets, what would we do here

again , many thanks

Carl

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