Max-Burst-Size and Egress Rate Limiting

[Stephen_Elliot1]

Hello Everybody,

Can anyone explain the 'max-burst-size' variable as it relates to egress rate limiting in the command below?

configure ports rate-limit egress [no-limit | [Kbps| Mbps | Gbps] {max-burst-size [Kb | Mb]}]

More specifically, if I've been provided a Telco Ethernet WAN link with a CIR of 100Mbps over a 1Gbps bearer, what max-burst-size should I use and why?

Many thanks!
Stephen

[Manoharan__Sent]

Yes.
Max-burst-size is a finite amount of data which is the maximum volume of data send out on that port.ex FTP.
Hope you understand.

[Stephen_Elliot1]

Thanks Senthil but that's not quite my understanding. Max-burst-size is a finite amount of data (Mbits or Kbits), not a throughput speed (in Kbps or Mbps) which is why I've tried to work out how much data I can send at CIR for a given time period.
Of course, this calulation comes out considerably less than the CIR. (400Kbits for a 100Mbps CIR)
Happy to be corrected.

[Manoharan__Sent]

Stephen,
First I will try to answer for your first query.

More specifically, if I've been provided a Telco Ethernet WAN link with a CIR of 100 Mbps over a 1 Gbps bearer, what max-burst-size should I use and why?

Max-burst-size depends on customer requirement.
For Example in ISP's shared data center a customer X opted 100 Mbps bandwidth for their server but they need bandwidth width up to 1 Gbps & they are connected to core switch whose link speed is 10 Gbps.
So ISP configure provide rate limit of 100 Mbps & max-burst-size of 1 Gbps.
Meaning is 100 Mbps of guaranteed bandwidth & they can use up to 1 Gbps.
Above 1 Gbps they cant use the bandwidth.i.e.Servers internet speed is limited up to max of 1 Gbps not more than that.
Remember one-thing max burst size should be greater than CIR value.

But ExOS CLI accepts max max burst size lower than CIR.

[Stephen_Elliot1]

That's excellent and very helpful - thanks Joshua.

It's still tricky to get a steer on exactly what max-burst-size to use although I think I've got my head round it now.

Our Telco suggests a 4ms burst window. So I've calulated the amount of traffic that can be transmitted at the CIR during the window and have configured that as the max burst size.

So, for a 100Mbps CIR
0.004 (4ms) X 100,000,000 = 400,000 bits (400Kbits)

conf port 1:1 rate-limit egress 100 Mbps max-burst-size 400 Kb

It seems to work and I'm getting no local congestion drops although I can't easily tell if the telco is dropping traffic - if anyone else has a better method of calculation please feel free to comment.

: )