Question on throttling traffic on 3845

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Sep 23rd, 2008
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Is thbis possible?

I have 3845 and the traffic outbound is email and web. When a spike in traffic happens for email, the web is naturaly slowed down. Is there a way to throttle the mail outbound traffic so that the web inbound traffic is not too much affected?


The link to the ISP is FastE 50mb


The internal interface is setup as HSRP and wan side is BGP.


Thanks

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John Blakley Tue, 09/23/2008 - 08:33
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I'm not an expert by any means, but you may want to look into QoS and prioritization.


--John

Joseph W. Doherty Tue, 09/23/2008 - 12:01
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Outbound, yes. Normally your options are to shape, rate-limit or prioritize.


If you have a FastEthernet connection, but the ISP is only providing 50 Mbps, if you don't already have a shaper, that alone might help you.


Try:

fastethernet #

traffic-shape rate 45000000


The above can be tuned, or we can get more involved using CBWFQ.

pipsadmin Wed, 09/24/2008 - 03:32
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Where can I get more details on the options available to me?

pipsadmin Wed, 09/24/2008 - 06:21
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so what would be the best option to take for this:


we have bursts of SMPT traffic going outbound.

When this bursts happens, the inbound HTTP is considerably slowed down and in some cases the HTTP is timing out.

Joseph W. Doherty Wed, 09/24/2008 - 08:42
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What QoS, if any, is configured now? If none, did you try the shaper from my first post?


If the shaper alone doesn't cure the problem, I would next deprioritize SMTP, if you're positive it's the cause of your slow downs.


e.g.


class-map match-any Background

match protocol smtp


policy-map Yourname

class Background

bandwidth percent 1

class class-default

fair-queue


policy-map Shaper

class class-default

shape average percent 45

service-policy Yourname


interface FastEthernet#/#

service-policy output Shaper

pipsadmin Wed, 09/24/2008 - 10:26
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no i have not tried the shapper as I'm unsure where to put it... on the WAN or LAN side?


Fa3/0 is WAN and G0/1 is LAN

pipsadmin Wed, 09/24/2008 - 11:27
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is this correct?


class-map match-any SMTP_TRAFFIC_SHAPPING

match protocol smtp

!

!

policy-map PM-SHAPPER

class SMTP_TRAFFIC_SHAPPING

bandwidth percent 75

class class-default

fair-queue

policy-map SHAPPER

class class-default

shape average percent 75

service-policy PM-SHAPPER


Then I add:

service-policy output SHAPPER to the External WAN interface Fa3/0 ?


But what I dont understand is why have 2 policy-map but only 1 is applied to the interface?!?

Joseph W. Doherty Wed, 09/24/2008 - 12:03
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You want to place policy on your outbound Ethernet interface, also configured for outbound.


i.e.

fastethernet3/0

service-policy outbound SHAPPER


The reason for two policies, one is nested within the other. The outer controls the overall data rate, the inner controls how congestion is managed.


PS:

If your link is 100 Mbps, but you're only supposed to use 50, you want to shape to insure a) you don't exceed the 50, b) you account for Ethernet overhead. (10% less than nomimal rate is a good place to start.)


Since you believe SMTP is what's causing the poor web performance, we want to guarantee it little bandwidth, but allow it to use more if the bandwidth is otherwise not being used.


i.e.


policy-map PM-SHAPPER

class SMTP_TRAFFIC_SHAPPING

bandwidth percent 1 adjust up if too little but at the expense of other traffic

class class-default

fair-queue

policy-map SHAPPER

class class-default

shape average percent 45 50 Mbps - 10% = 45 Mbps or 45% of 100

service-policy PM-SHAPPER


pipsadmin Wed, 09/24/2008 - 12:14
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so if I want to keep 75% of available bandwidth for SMTP and 25% for web, is my bellow ok?


And how do I monitor to make sure this is what's going on?


class-map match-any SMTP_TRAFFIC_SHAPPING

match protocol smtp

!

!

policy-map PM-SHAPPER

class SMTP_TRAFFIC_SHAPPING

bandwidth percent 75

class class-default

fair-queue

policy-map SHAPPER

class class-default

shape average percent 75

service-policy PM-SHAPPER


pipsadmin Wed, 09/24/2008 - 12:33
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So after some thoughts, maybe i should garantee bandwidth to HTTP instead of SMTP ? As you can see, im a litle confused... when I see outbound SMTP spikes, my page loads for inbound HTTP go from 2-3 seconds to well over 15 seconds.


So maybe I should garantee a maximum bandwidth to web and allow SMTP to use what's available whichout windering HTTP traffic inbound?

Joseph W. Doherty Wed, 09/24/2008 - 14:32
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The policies I've posted will give HTTP much more bandwidth than SMTP.

pipsadmin Thu, 09/25/2008 - 03:34
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Thanks Joe,


Yesterday, before I left, I changed the settings to match yours exactly:


class-map match-any SMTP_TRAFFIC_SHAPPING

match protocol smtp

!

!

policy-map PM-SHAPPER

class SMTP_TRAFFIC_SHAPPING

bandwidth percent 1

class class-default

fair-queue

policy-map SHAPPER

class class-default

shape average percent 45

service-policy PM-SHAPPER



Although, when spikes happen, I am still getting some http and https timeouts...

Joseph W. Doherty Sun, 09/28/2008 - 09:33
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Sorry for the delay in responding - I was out-of-town last 3 days (w/o Internet access).


This is the type of situation that's hard to diagnose without seeing it. For instance, we're only managing outbound traffic and often the problem is caused by inbound congestion too. Also, we're working on your assumption that just SMTP is causing the issue.


It might help if you can post interface stats and policy stats when the issue arises (i.e. sh interface and show policy-map interface).

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