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Rate Limit to 200Mbit on a Gig Interface, Cisco 3850.

Lee Smitherman
Level 1
Level 1

Hi,

 

I have extended a branch over 1gig Fibre on which we have 200Mbits of bandwidth.  The Interface is configured as an access port on vlan 5.  The depth of QOS options are quite detailed.  Can anyone give me some pointers on how to rate limit to 200Mbits on my interface for all traffic? I would have though this one would be simple, but a little stuck.

 

interface TenGigabitEthernet1/0/11
description xxxxxx
switchport access vlan 5
switchport mode access
bandwidth 200000
ip flow monitor Solar_mon_input input
ip flow monitor Solar_mon_output output
end

 

The Switches are 3850 both ends

 

Switch Ports Model SW Version SW Image Mode
------ ----- ----- ---------- ---------- ----
* 1 16 WS-C3850-12XS 03.07.03E cat3k_caa-universalk9 INSTALL

 

 

 

1 Accepted Solution

Accepted Solutions

Hello Lee,

 

Correct. More appropriately, it catches all traffic not identified by another class. However, since you don't have any other classes, it would catch all traffic. 

-Bradley Selzer
CCIE# 60833

View solution in original post

9 Replies 9

brselzer
Cisco Employee
Cisco Employee

Hello Lee,

 

 You will need to apply a service policy with a policer in order to limit the traffic.

 

https://www.cisco.com/c/en/us/td/docs/switches/lan/catalyst3850/software/release/3se/qos/configuration_guide/b_qos_3se_3850_cg/b_qos_3se_3850_cg_chapter_011.html

 

The bandwidth command does not actually limit the traffic on the interface. It just changes how certain statistics and metrics are calculated.

 

The config will look something like this

 

policy-map POLICE

class class-default

police 200000000  <---Double check my math but that should be 200Mbps

 

int te1/0/11

service-policy out POLICE

 

Hope that helps!

-Bradley Selzer
CCIE# 60833

Thanks for the quick response, but policing drops packets, and if the SP is policing at 200Mbits, then in effect I would be doing the same thing. I need to shape or control the rate of traffic.

Lee.

Hello Lee, 

 

Understood. Sounds like you want a shaper more than a policer. The configuration will be roughly the same:

 

policy-map SHAPE

class class-default

shape average percent 20


If it is a tengig link, you might need to do 2 percent rather than 20 percent. However, you are still limited by the buffers on the 3850 so if your traffic is constantly higher than 200Mbps, you could still see drops.

 

Hope that helps. Thanks!

 

-Bradley Selzer
CCIE# 60833

Hi,

 

Thanks again, so I have this...  will the Class class-default match all traffic with all markings? Its been a while since I have performed any QOS configuration.

 

Policy Map 200mbits
Class class-default
Average Rate Traffic Shaping
cir 200000000 (bps)

 

Int TE1/0/11

   service-policy output 200mbits

 

Lee.

 

 

Hello Lee,

 

Correct. More appropriately, it catches all traffic not identified by another class. However, since you don't have any other classes, it would catch all traffic. 

-Bradley Selzer
CCIE# 60833

Thanks Very much. I`ll get this applied and see how it performs. Appreciate the help.

Lee.

Just to add to the other posts that show shaping for your SP's 200 Mbps, something you could bump into, might be how your 3850 counts bps vs. how the SP counts bps.

SP's often count bps for all bits on the wire. I.e. if they limited your gig link to 100 Mbps, you should obtain the same actual bps capacity of a FE link.

I'm unsure all Cisco shapers or policers account for all L2 overhead. If they don't, and your SP does, you many need to set your shaper (or policer) about 10 to 15% slower than your SP rate to insure you don't overrun it.

Thank you.

 

Lee.

 

Thanksssss a lot that meets my requirement 

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