Applying QoS to net management traffic

Answered Question
Apr 29th, 2008
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Hi,


We are using 3750 switches in our core & distribution layer in many sites. WAN links are at a variety of speed (2 M, 5M, 10M up to dark fiber running at 1G)through our MAN provider network. I'm actually designing the QoS strategy and implementation for support Voice, Mission critical traffics, best effort and so on. The only traffics I don't know how to mark them, are network management traffics generated by the network element itself: as SNMP, NTP, Syslog, TFTP, telnet, SSH. Do you have an idea how to do that? I know OSPF is marked by default to dscp 48 which is fine. What about the other net man traffics.


Thanks


Benoit


Correct Answer by JensOsterloh about 8 years 6 months ago

Hi Benoit,


I found out, that for some management protocols (telnet, ssh, snmp) you can set a precedence, dscp or TOS value:


C2960(config)#ip telnet tos ?

<0-FF> TOS value


C2960(config)#ip ssh ?

dscp IP DSCP value for SSH traffic

precedence IP Precedence value for SSH traffic


C2960(config)#snmp-server ip ?

dscp IP DSCP value for SNMP traffic

precedence IP Precedence value for SNMP traffic


Defaults are:


ip telnet tos C0

snmp-server ip precedence 0


According to IOS explanation, "ip ssh dscp 0" is default, but it remains in the config, whatever value you enter (did not try all 64 dscp values ;-)


For other protocols, I didn't find a way to set QoS values, but these three seem to be the most important to me.


HTH,

Jens


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mattcalderon Tue, 04/29/2008 - 13:21
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I would look into the possibility of classifying traffic based on nbar.

A good link from the internetworking guide on using nbar.


http://www.cisco.com/en/US/docs/internetworking/technology/handbook/QoS.html


Also a good link on the configuration of nbar and matched protocols.


http://www.cisco.com/univercd/cc/td/doc/product/software/ios122/122newft/122t/122t8/dtnbarad.htm#wp1074479


Hope this helps!

bdube Wed, 04/30/2008 - 06:43
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Unfortunately, NBAR applies only to routers, not switches nor L3 switches.


But, I have also some routers in the network where we will do shaping/priorizing with cbwfq.


But, my interrogation is not related to traffic passing through the switches (or routers) but to traffic originated by the L2/L3 switches themself. It's mainly management traffic (NTP, SSH, Telnet, Syslog, TFTP...).


Correct Answer
JensOsterloh Thu, 11/13/2008 - 09:39
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Hi Benoit,


I found out, that for some management protocols (telnet, ssh, snmp) you can set a precedence, dscp or TOS value:


C2960(config)#ip telnet tos ?

<0-FF> TOS value


C2960(config)#ip ssh ?

dscp IP DSCP value for SSH traffic

precedence IP Precedence value for SSH traffic


C2960(config)#snmp-server ip ?

dscp IP DSCP value for SNMP traffic

precedence IP Precedence value for SNMP traffic


Defaults are:


ip telnet tos C0

snmp-server ip precedence 0


According to IOS explanation, "ip ssh dscp 0" is default, but it remains in the config, whatever value you enter (did not try all 64 dscp values ;-)


For other protocols, I didn't find a way to set QoS values, but these three seem to be the most important to me.


HTH,

Jens


Joseph W. Doherty Thu, 11/13/2008 - 13:24
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It may also be possible to classify and mark some router originated traffic as it leaves the device using an outbound service policy.


At least on small routers, most device originated traffic usually appears to have a ToS of zero, but besides routing packets having priority, I believe Telnet packets might too.

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