'bandwidth x' command

[tedauction]

Hello, regading the interface 'bandwidth x' command, I understand it is used by IGRP, EIGRP, and OSPF and also TCP for the prupose of initial retransmission parameters.

What other protocols make use of the 'bandwidth x' command ?

Does BGP utilise it ?

Thank you for any information.

[Philip D'Ath · Accepted solution]

OSPF and TCP do not use the bandwidth command parameter.  BGP does not use it.  SNMP will report it.  It is really only used by EIGRP.

[Julio E. Moisa]

Hi

Bandwidth is used by IGRP (not used anymore) and EIGRP to calculate the metric to a destination, now OSPF does not use Bandwidth command, BGP either but if you want to test BGP load balancing (bgp dmzlink-bw) you can configure the bandwidth command. 

But bandwidth is not part of the metrics for BGP.

I dont think TCP uses bandwidth command.

Note: no matter the value set with the bandwidth command under a interface, it will not change the transmission speed of the interface.

Hope it is useful

:-) 

[Joseph W. Doherty]

Regarding OSPF and using the interface bandwidth statement, contrary to what both Julio and Philip have posted, I've found on Cisco devices that I've used, both OSPFv2 and OSPFv3 use it for computing OSPF's link cost metric unless overridden with a OSPF cost statement.

However, also note, on Cisco devices, it considers 100 Mbps the base cost of 1.  I.e. any link 100 Mbps or faster, will compute its link cost as 1.  This too can be overridden using the auto-cost reference command.

[Julio E. Moisa]

Hi

I agree with Joseph, although the ip ospf cost <value> is widely used to manipulate OSPF traffic.

The formula to find an automatic cost is:

As Joseph mentioned, the default reference bandwidth can be changed but by default is 100Mbps

Default reference bandwidth value used is 100Mbps (10^8).

Interface Cost= 10^8/(interface bandwidth)

:-)