Need bandwidth usage explanation

[Raja_D]

How to determine how much amount of "Datagram size" can be applied on a 500mb mpls link or 1gb link or whatever the bandwidth of the link provided by provider. 

The below output is taken from a 12mb link but I would like to know how much of size can be applied on this 12mb link and what is meant by burstable bandwidth ? In specific do we have any specific calculation method that can be used to determine the size that can be applied, if so please guide

ping 10.25.104.50 re 100 size 6000
Type escape sequence to abort.
Sending 100, 6000-byte ICMP Echos to 10.25.104.50, timeout is 2 seconds:
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Success rate is 100 percent (100/100), round-trip min/avg/max = 1/1/12 ms

Kindly clarify. 

[Morne Vermeulen]

Hi Danraj,

As far as I can make out, you are playing with MTU sizes. The size of a packet that can be sent through any interface depends on the interface, not the bandwidth of the actual link. 

In otherwords, if you send 100 Megabits of data on a 100Mb/s link, with the default MTU of 1500 Bytes, it will send your data in one second. The data will be fragmented into 1500 Byte packets, those packets will be sent at 100Mb/s. But upping the packet size will cause issues on interfaces that do not support jumbo frames (basically anything with an MTU of above 1500). 

You'll have to inspect the interfaces of the link, not the bandwidth of the link. As far as I know, these two factors don't have anything to do with each-other. But I could be wrong.

Still new to networking. 

I hope this helps! 

[Raja_D]

Thank you Morne for the explanation...

[Joseph W. Doherty]

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Posting

If you don't set the DF bit, your logical datagrams can be as large as supported by IP and your ping source.  The former, for IPv4, should be up to 64 KB, the latter, for a Cisco router, might be about 18 KB.  (For your ping 10.25.104.50 re 100 size 6000, try ping 10.25.104.50 re 100 size ? and see what your Cisco devices lists as the maximum size.)

If you set the DF bit, your logical datagrams will be limited by the smallest link's MTU within your end-to-end path.

As also noted by Morne, the above is independent of link bandwidth.

". . . and what is meant by burstable bandwidth ? "

Many service providers will provide logical bandwidth caps less than media supports, e.g. you're logically limited to 500 Mbps of a physical gigabit circuit.  As such circuits always transmit at full link speed, you can "burst" above your logical maximum.  The provider should provide a specification limit for how long you can consume full link bandwidth before they will discard packets.

[Raja_D]

Thank you Joseph