[mrtg] Re: Graphing the lo

[Rich Adamson]

The lo (or loopback) interface can be used for several things on
various boxes. Three such examples include:
a) two applications on the same box can communicate nicely through
   the loopback. If I write an app that listens on tcp/udp port 999
   and write another app that tries to connect to that port using
   the address 127.0.0.1, the loopback counters that you are referring
   to are supposed to count that traffic.
b) if a unix system is misconfigured (including some incorrectly
   stated static routes), packets intended for some other destination
   may get sent to the loopback instead.
c) routers are often times configured to send packets for certain
   destinations to a black hole (which on some boxes are counted in
   the loopback).
Whether the mrtg graphs of the loopback mean anything to you requires
you to understand what is running on the box and how it was intended
to communicate. In example (a), the mrtg chart will display the traffic
expected from app's written in that manner. In (b), the chart is
indicative of a problem that has not been resolved. In (c), the chart
would indicate the number of packets that matched the intended
"black hole" configuration.

> 
> As far as I know, lo doesn't do anything.  Any traffic 
> would be on eth0, eth1, etc.  I've played around with 
> lo, and there has never been traffic on it.
> 
> Paul
> 
> >>> Cliff <cliff at acsalaska.net> 04/22/02 22:29 PM >>>
> 
> Hi Folks
> 
> If I uncomment the lo part of my config file
> I assume it'll graph just fine.
> 
> Why would I want to do that?
> 
> Would it tend to show me if the linux box itself
> was being used to surf with instead of just sitting
> there doing it's appointed job of gatewaying for the lan?
> 
> Is it considered uninteresting information - hence it's
> commented out by default in the config file?
> 
> 
> Best regards,
>  Cliff
> 
> 
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