1841 router - limit bandwidth with priority for voice.

[ciscokalpesh]

Hi,

We have some point-to-point sites linked with  our HO with 10-30mbps speed. We have provided DID telephone lines to  these sites as well.

We want to limit the bandwidth  with 1mb bandwidth only and also make sure that the voice traffic (DID  telephone lines) gets the priority over all other traffic even if they  are utilitizing the 1mb link completely. We have some Cisco 1841 routers  that we are planning to configure on the main uplink on each of these  sites.

Can someone guide on the configuration part  about how to give the priority to the voice traffic yet limiting the  bandwidth to 1mb.

Thanks in advance.

K

[Laurent Aubert]

HI,

This link should help: http://www.cisco.com/en/US/partner/docs/ios/qos/configuration/guide/congstion_mgmt_oview_ps6350_TSD_Products_Configuration_Guide_Chapter.html

Thanks,

Laurent.

[Latchum Naidu · Accepted solution]

Hi,

If you have a seperate Vlan for Voice then it would be possible to allocate bandwidth under the vlan's

See the below two individual steps may help in your scenario.

STEP-1:

Apply rate-limit on each L3 vlan interface in your 2851
Example (for 1024kbits for vlan 2):

Router# conf t
Router(config)# int vlan 2
Router(config-if)#rate-limit input 1000000 187500 375000 conform-action transmit exceed-action drop
Router(config-if)#rate-limit output 1000000 187500 375000 conform-action transmit exceed-action drop

STEP-2:

Policy a specific VLAN number on VLAN interface.

class-map vlan5
match vlan 5
match class-map class-default

policy-map vlan5-limit
class vlan5
police 2000000 250000 exceed-action drop

int vlan5
service-policy input vlan5-limit

After you apply this configuration, the traffic with VLAN 5 coming from any will be policed at 2Mbps.

Hope this will help you.

Please rate the helpfull posts.
Regards,
Naidu.

[ciscokalpesh]

Hi,

Thanks for reply.

We do not have VLAN configured for our network. It is FLAT with VLAN1.

STEP 1:

This will only fix the bandwidth upto 1mb. What if i add access-list to it and try to give priority to the desired traffic ? I want to assign 512kbps for desired traffic (as per access-list) and rest to be using 1mb. The total bandwidth allocated to them will be 1mb out of which the desired traffic should get 512 always. Example -

ip access-list extended 100
permit udp 10.1.253.0 0.0.0.240 any
permit udp any 10.1.253.0 0.0.0.240

permit tcp host 192.168.168.48 any eq 1494
permit tcp any host 192.168.168.48 eq 1494

interface FastEthernet0/0
description ETH-LAN

ip address 192.168.168.199 255.255.255.0

rate-limit input access-group 100 512000 512000 512000 conform-action set-prec-transmit 5 exceed-action set-prec-continue 0
rate-limit output access-group 100 512000 512000 512000 conform-action set-prec-transmit 5 exceed-action set-prec-continue 0
rate-limit input 1024000 8000 8000 conform-action transmit exceed-action drop
rate-limit output 1024000 8000 8000 conform-action transmit exceed-action drop
duplex auto
speed auto

Please guide.

Thanks again,

K

[Latchum Naidu]

Hi,

Thats even good idea. The only thing now is that your router need to support rate-limit commands.
And that Vlans based rate limit is what I brought from the best practices.

Please click on the correct answer if this answered your question.
Regards,
Naidu.

[ciscokalpesh]

Hi,

The router 1841 does support rate-limt command.

Also ip nbar is good option to check the traffic and police accordingly.

Thanks for the guidance.

K

[Latchum Naidu]

YES,

NBAR can be used to monitor both input and output traffic also and may be applied with or without a service policy enabled.

Below is the sample config for your reference...

interface ethernet 1/3
ip nbar protocol-discovery

#sh ip nbar protocol-discovery

Please rate the helpfull posts.
Regards,
Naidu.

[ciscokalpesh]

Hi,

My doubts are mostly clear, except below !

In the "rate-limit" command, if i want to limit to 512k, we get 3 options,

1) Bits per seconds (Here i will mention 512000 for 512kbps bandwidth)

2) Normal burst bytes (What this should be ? Same 512000 ?)

3) Maximum burst bytes (What this should be ?)

Please guide.

Thanks in advance.

K

[Latchum Naidu]

Hi,

See the below link will clear all your doubts.
http://slaptijack.com/networking/inbound-rate-limiting-on-cisco-catalyst-switches/

Please rate the helpfull posts.
Regards,
Naidu.