[c-nsp] Bandwidth Statement - Tunnel Interface

[Jay Hennigan]

sky vader wrote:
> Hi,
> 
> Just curious, since the default bandwidth for tunnel interface is 9k
> (cisco platform), does that mean the maximum bandwidth I can have is 9k?

No.

> What's the purpose of setting bandwidth statement on a tunnel interface?
> Does that mean I get bandwidth that is set or what the router will
> report via snmp?

Three things come to mind, there are likely other subtle ones...

1.  Dynamic routing protocols use the interface bandwidth for path 
selection.  Manually specifying the bandwidth to something sane for the 
physical path over which the tunnel rides may be needed for proper route 
selection.

2.  MRTG and similar tools will use the configured bandwidth as the 
default maximum for graphing and analysis purposes.  Leaving it at 9K is 
likely to result in graphs topped at that value.  SNMP of the actual 
traffic counts will be accurate, but configuration tools of graphing 
software will get the configured bandwidth on setup and may behave as if 
this is the physical limit.

3.  QoS and traffic shaping applied to the interface will use the 
configured bandwidth for percentage calculations and the like.  This 
will almost certainly cause results that aren't what you expect unless 
the tunnel is running over a dialup link.

If you are doing none of these, then the configured bandwidth statement 
really doesn't affect anything in terms of operation that I've noticed.

--
Jay Hennigan - CCIE #7880 - Network Engineering - jay at impulse.net
Impulse Internet Service  -  http://www.impulse.net/
Your local telephone and internet company - 805 884-6323 - WB6RDV