The bandwidth statement doesn't make data move faster or slower by itself, but it can be used by some technologies.
For example, EIGRP and OSPF can look at the bandwidth parameter (either the default, or the configured one), as part of the calculation for the metric or cost of that link/interface.
The bandwidth can also be referenced in QoS applications.
On some IOS versions, GRE tunnels got a super small default bandwidth by default, and protocols like EIGRP doesn't want to use all the bandwidth for routing updates, and may not operate correctly with the default. Another possibly, is that the GRE tunnel may never be used, as the metric is too high, due to default bandwidth that is too small, and that would be another reason for increasing it.
Bandwidth in Network Communication referes to the amount of data that can be transferred in a particular period from one source to destination.
In cisco world with the increase in network speed also increases the bandwidth capabilities i.e. we have default value to set to 1500 bytes now how does we know whether the ISP side supports how much of MTU
Ping<IP address> -l 1500 -f
-l represents send buffer size
Here-f represents don't fragment flag is set
In router also we can do this type of ping for that we need to use the followingcommand :-
Ping<Ip Address> size 1400 df-bit
thus we can increase the bandwidth capabilities of our router thereby increases the throughput. thus it is necessary to find the bandwidth of ISP side to have a better throughput.
Please correct me if i'am misundestood the point.....