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.\"
.IX Title "MRTG-FAQ 1"
.TH MRTG-FAQ 1 "2018-07-13" "2.17.7" "mrtg"
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.SH "NAME"
mrtg\-faq \- How to get help if you have problems with MRTG
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
\&\s-1MRTG\s0 seems to raise a lot of questions. There are a number of resources
apart from the documentation where you can find help for mrtg.
.SH "FAQ"
.IX Header "FAQ"
In the following sections you'll find some additonal Frequently Asked Questions, with Answers.
.ie n .SS "Why is there no ""@#$%"" (my native language) version of \s-1MRTG\s0?"
.el .SS "Why is there no ``@#$%'' (my native language) version of \s-1MRTG\s0?"
.IX Subsection "Why is there no @#$% (my native language) version of MRTG?"
Nobody has contributed a \fI@#$%.pmd\fR file yet. Go into the
\&\fImrtg\-2.17.7/translate\fR directory and create your own translation file.
When you are happy with it send it to me for inclusion with the next mrtg
release.
.SS "I need a script to make mrtg work with my xyz device."
.IX Subsection "I need a script to make mrtg work with my xyz device."
Probably this has already been done. Check the stuff in the
\&\fImrtg\-2.17.7/contrib\fR directory. There is a file called \fI00INDEX\fR in
that directory which tells what you can find in there.
.SS "How does this \s-1SNMP\s0 thing work"
.IX Subsection "How does this SNMP thing work"
There are many resources on the net that explain \s-1SNMP.\s0
Take a look at this article from the Linux Journal by David Guerrero
.PP
.Vb 1
\& http://www.david\-guerrero.com/papers/snmp/
.Ve
.PP
And at this rather long document from \s-1CISCO.\s0
.PP
.Vb 1
\& http://www.cisco.com/univercd/cc/td/doc/cisintwk/ito_doc/snmp.htm
.Ve
.SS "The images created by \s-1MRTG\s0 look very strange."
.IX Subsection "The images created by MRTG look very strange."
Remove the *\-{week,day,month,year}.png files and start \s-1MRTG\s0
again.  Using \s-1MRTG\s0 for the first time, you might have to do this
twice. This will also help when you introduce new routers into the cfg
file.
.SS "What is my Community Name?"
.IX Subsection "What is my Community Name?"
Ask the person in charge of your Router or try 'public', as this is the
default Community Name.
.SS "My graphs show a flat line during an outage. Why ?"
.IX Subsection "My graphs show a flat line during an outage. Why ?"
Well, the short answer is that when an \s-1SNMP\s0 query goes out
and a response doesn't come back, \s-1MRTG\s0 has to assume something to put
in the graph, and by default it assumes that the last answer we got
back is probably closer to the truth than zero.  This assumption is
not perfect (as you have noticed).  It's a trade-off that happens to
fail during a total outage.
.PP
If this is an unacceptable trade-off, use the \fBunknaszero\fR option.
.PP
You may want to know what you're trading off, so in the spirit of
trade-offs, here's the long answer:
.PP
The problem is that \s-1MRTG\s0 doesn't know *why* the data didn't come back, all
it knows is that it didn't come back.  It has to do something, and it
assumes it's a stray lost packet rather than an outage.
.PP
Why don't we always assume the circuit is down and use zero, which will
(we think) be more nearly right?  Well, it turns out that you may be
taking advantage of \s-1MRTG\s0's \*(L"assume last\*(R" behaviour without being aware of
it.
.PP
\&\s-1MRTG\s0 uses \s-1SNMP \s0(Simple Network Management Protocol) to collect data, and
\&\s-1SNMP\s0 uses \s-1UDP \s0(User Datagram Protocol) to ship packets around.  \s-1UDP\s0 is
connectionless (not guaranteed) unlike \s-1TCP\s0 where packets are tracked and
acknowledged and, if needed, retransmitted.  \s-1UDP\s0 just throws
packets at the network and hopes they arrive.  Sometimes they don't.
.PP
One likely cause of lost \s-1SNMP\s0 data is congestion; another is busy routers.
Other possibilities include transient telecommunications problems, router
buffer overflows (which may or may not be congestion-related), \*(L"dirty
lines\*(R" (links with high error rates), and acts of God.  These things
happen all the time; we just don't notice because many interactive
services are TCP-based and the lost packets get retransmitted
automatically.
.PP
In the above cases where some \s-1SNMP\s0 packets are lost but traffic is
flowing, assuming zero is the wrong thing to do \- you end up with a graph
that looks like it's missing teeth whenever the link fills up.  \s-1MRTG\s0
interpolates the lost data to produce a smoother graph which is more
accurate in cases of intermittent packet loss.  But with V2.8.4 and above,
you can use the \*(L"unknaszero\*(R" option to produce whichever graph is best
under the conditions typical for your network.
.SH "AUTHOR"
.IX Header "AUTHOR"
Tobias Oetiker <tobi@oetiker.ch>