# Understanding the Burst Size against policer for 1G/10G interfaces in Juniper MX

We are facing one confusion with regards to burst size value against rate limit or policer in Juniper MX. Need to understand two things :-

(1) Is the `burst size limit` defined in firewall policer dependent or calculated based on physical interface speed and independent of bandwidth limit (Mbps) defined under a policer for a user?

For example , suppose we have 1G interface and 2 x customers are terminated on this interface . One customers need 2 Mbps while other need 10 Mbps. Since interface is 1G , the burst size against both of these customers would be same i.e. 625,000 bytes while bandwidth limit would be 2 Mbps and 10 Mbps respectively if burst-size-limit is dependent on physical interface and independent of bandwidth limit value? Please correct if am wrong.

``````(2) How to calculate the burst size for 10G interface in Juniper?
``````

This is taken from JNCIA Study Guide (Old Book) , Chapter No.10.

Suppose you have a Gigabit Ethernet interface in your router. The interface can receive 1000 megabits per second. The burst-size-limit is entered in bytes per second, so we translate 1000Mbps into 125MBps. That further translates into 125,000KBps and finally 125,000,000Bps. In a single millisecond, the interface receives 125,000 bytes, so a total of 625,000 bytes are received in 5 milliseconds. `The policer statement becomes burst-size-limit 625000.`

Based on above reference , if the burst size of 1G interface is 625 ,000 bytes then burst size of 10G interface would be 625 , 000 x 10 = 6250 , 000. Is this correct? If not , please guide as per the Juniper best practices.

• Did any answer help you? if so, you should accept the answer so that the question does not keep popping up forever, looking for an answer. Alternatively, you could post and accept your own answer. Dec 23, 2021 at 16:10