[c-nsp] Bandwidth Statement - Tunnel Interface

[sky vader]

see in-line:


Jay Hennigan wrote:
> 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.
-------------------------
So what does tunnel "bandwidth transmit / receive" statement under
tunnel interface do? For example:

interface tunnel0
bandwidth 40000
ip address 192.169.0.1 255.255.255.252
tunnel destination x.x.x.x
tunnel bandwidth transmit 40000
tunnel bandwidth receive 40000


thanks,
sky

> 
>> 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
>