Restrict the Internet Bandwidth

Unanswered Question
Apr 5th, 2009

ear all,

I have 1841 Router with 3 interfaces, one fo r LAN and two for Inrenet as follows:

- Fa0/1 used for LAN

- Se0/0 used for Leased-Line (1Mpbs)

- adsl interface used for ADSL connection (4Mpbs)

Waht I need is to limit the traffic Bandwidth which is coming from specific IP from my Internal LAN ( which is the IP of our Mail Server ) to 300kbps because it is now taking the whole Bandwidth when sending morning messages and nobody can access our online services during this time.

Can I do this?

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thotsaphon Mon, 04/06/2009 - 00:19


You can. Which link does the mail server send traffic out?

I would use CBWFQ. This will work as soon as the interface got congestion.


ip access-l ext MAIL-SERVER

permit ip host any


class-map match-all MAIL

match access-group name MAIL-SERVER


policy MAIL-300K

class MAIL

bandwidth 300

class class-default






service-policy output MAIL-300K.


Unfortunately, This will help you on outgoing traffic. Incoming traffic cannot be guaranteed.



m.metwally Mon, 04/06/2009 - 03:16

Dear toshi,

thanks a lot for your assistance but actually I configured my router exactly as you described, but the traffic still reaching 950Kbps !

should I enable something to activate this?

JamesLuther Mon, 04/06/2009 - 03:50


The "bandwidth" command under the policy map will reserve 300k (not limit) and allow you to burst above.

To limit the amonut of bandwidth then use the police command ie

policy MAIL-300K

class MAIL

police cir 300000 conform-action transmit exceed-action drop


Joseph W. Doherty Mon, 04/06/2009 - 04:01

What might work for you is WFQ on the serial interface (usually the default) and a traffic shaper on the ADSL interface limited to upstream bandwidth. (The latter might be done with the traffic-shape command or with a CBWFQ policy with embedded shaper.)

You shouldn't need to "cap" your mail flow outbound, but instead just insure it doesn't adversely impact other traffic flows.

As Toshi's notes, inbound can be a problem, but outbound shouldn't be.


James, correctly notes the reason why you're see mail traffic using more than 300 Kbps. Besides policing, you could also shape within the class.

The disadvantage of policing or shaping, it limits mail transfers bandwidth utilization even when the bandwidth is available.

thotsaphon Mon, 04/06/2009 - 04:04


Did that happen when the interface got congestion?

Please post the configuration and the output of a "sh policy-map inter " command.

If the WAN interface can handle the traffic(hardware queue is available), the mail server may uses more than 300 Kb.

Note : As James stated, You can police if you want. But what I thought is that you can let them go as long as the interface can handle it. You can define the other class to reserve BW for online services.

Keep in mind,Policing will not allow you to send more than 300Kb all the time. If that was your policy, then go configure it.




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