# 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?
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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.