FAQ for mrtg-dynip version 0.41b

0. What are the problems that gave rise to mrtg-dynip?
  0.1  What is dynamic IP
  0.2  What is static or fixed IP
  0.3  What is SNMP and what information can it provide?
  0.4  What is MRTG?
  0.5  Can the configuration file MRTG runs on remain unchanged? 
1.  What does mrtg-dynip do?
  1.1  Can mrtg-dynip act as a front end to MRTG?
  1.2  Can mrtg-dynip monitor modem banks?
2. What do I need to run mrtg-dynip and where can I get it?
3. What platforms does mrtg-dynip run on?
4. Are there special considerations to running mrtg-dynip?
  4.1 How do I make mrtg-dynip executable?
  4.2 How can I ensure mrtg-dynip can write to directories and files
5. How do I prevent errors and interpret error messages?
  5.0 What problems external to mrtg-dynip affect it?
     5.0.1 Why am I getting losts of weird email from cron?
     5.0.2 Why does the mrtg-dynip log have weird messages from snmp
         modules? 
  5.1 Why doesn't my email address and web page link show?
  5.2 I have configured everything, yet my index page does not update
  5.3 Your crontab example looks really odd, please explain.
6. Why do the in and out graphs closely follow each other in my modem bank
        graphs? 
7. I cannot find a solution to my problem in the docmentation and web
   sites.  What support exists and is there a mailing list?


0. What are the problems that gave rise to mrtg-dynip?

The initial problem that gave rise to the creation of mrtg-dynip is that
MRTG relies on snmp target numbers having a fixed association with file
names representing physical interfaces.  In environments where the snmp
target number of a physical interface can vary, such as in a PPP dial in
environment, it is necessary to ensure that file names associated with real
physical interfaces are associated with the current snmp target number for
the device.  This is what mrtg-dynip does.

0.1  What is dynamic IP

To someone dialling in, dynamic IP means when they dial a rotary
number they do not get a consistent IP address.  To the service provider it
means a unique IP number is assinged to each telephone line/modem/port.

0.2  What is static or fixed IP

To someone dialling in, static or fixed IP means that their user name is
approved to use a unique IP address, whether they dial into a rotary for a
modem bank or into a non rotary number.  To the service provider, it means
if someone is dialling into a rotary for a modem pool, they allow the modem
port use a unique approved IP number for that user, that overrides the IP
address used when a dial in user does not request a fixed or static IP.

0.3  What is SNMP and what information can it provide?

SNMP stands for Simple Network Management Protocol. Like much relating to
the Internet, it is described by a set of Internet Engineering Task Force
documents known as RFCs (Requests for Comments).  SNMP is a means by which
network linked devices can have a wide variety of device status information
reported from them, and have action performed on them, according to known
protocols.

0.4  What is MRTG?

MRTG stands for 'Multi Router Traffic Grapher'. Among much else, it provides
a means for graphing traffic quantity information through various
interfaces, typically routers, in web acessible means, using information
reurned from SNMP requests.

0.5  Can the configuration file MRTG runs on remain unchanged?

Not in environmants that the SNMP target number varies for physical
interface devices you are interested in gathering information on.

1.  What does mrtg-dynip do?

#Mrtg-dynip is a contribution to mrtg, enabling mrtg to generate multi
#interface traffic graphs for IP interfaces on hosts that do not provide
#consistent SNMP target numbers for their interfaces.  Such IP interfaces
#include IP active serial interfaces attached to modems in a PPP dial in
#environment. The hosts must run snmp agents.  For completeness, information
#about interface devices with unvarying SNMP target numbers, such as
#ethernet cards, can be configured to be included.

#Mrtg-dynip's configuration is simplest where static (or fixed) IP is not
#used for dial into a rotary modem pool.

#Mrtg-dynip can be considred to have sophisticated modem bank monitoring
#capacity, when the modems carry PPP or SLIP traffic.

#Regenerates a named 'mrtg.cfg' file to ensure snmp data remains with a
#consistent IP number, or overridable IP number of a real physical device
#in a dial in IP environment, rather than with an interface name which
#can get assinged to different real physical devices, and runs mrtg on
#the generated file.

#Generates a web index file of stats web pages.

#Please see the section 6 of this FAQ for this version for information on
#for differences in interpreting graphs between some devices

1.1  Can mrtg-dynip act as a front end to MRTG for traffic graphing?

In a sense yes for interface or router traffic, but this is not ADVISABLE or
necessarily efficient, see above.  Future versions may make mrtg-dynip more
suitable as a front end to MRTG for some purposes, see the TODO file.

2.  What do I need to run mrtg-dynip?

You need the contribution to MRTG called mrtg-dynip.  Latest version
available from http://www.heenan.ironbark.id.au/mrtg-dynip.

MRTG needs to be successfully installed.  MRTG can be obtained from
http://www.ee.ethz.ch/~oetiker/webtools/mrtg/mrtg.html.  MRTG itself needs
the GD graphics library, see the MRTG package for details. 

3. What platforms does mrtg-dynip run on?

mrtg-dynip should run on all platforms MRTG runs on, including Windows NT. 
Mrtg-dynip's comments are oriented towards running on UNIX style systems.
such as Linux.  There are some comments on configuring directoy names for
Windows NT. Issues involved in differences between running Perl scripts on
UNIX systems and NT systems should be known to you, if you run run MRTG on
an NT machine. 

4. Are there special considerations to running mrtg-dynip?

Not really.  You must of course ensure mrtg-dynip is executable and can
write to directories and files it needs to when executed.

4.1 How do I make mrtg-dynip executable?

In UNIX the command 
chmod 744 mrtg-dynip
will make the file executable to the owner of the file

4.2 How can I ensure mrtg-dynip can write to directories and files

You need to ensure directories (and files if they exist already) have
appropriate write permissions.  This is beyond the scope of this FAQ. 
Basically if you have mrtg working, you will be able to get mrtg-dynip
working.

5. How do I prevent errors and interpret error messages?

Please see section 4 above. Set up log file generation as indicated in the
install file. With regard to starup error messages from rateup, see MRTG. 
Confirm SNMP agents are running correctly.  After a reboot I have found it
sometimes necesary to stop and restart the snmp daemon.  Changing order
around in startup file may have fixed this problem.  I have found running
mrtg-dynip manually outside its crond schedule may alter graph data,
starting anew on some.

5.0 What problems external to mrtg-dynip have been experienced?

Such is the burden of the system adminstrator to be the victim of cryptic
error messages
  
5.0.1 Why am I getting losts of weird email from cron?

Check you only have one crond running.  If more than one is running then
expect weird mesages and data loss.

5.0.2 Why does the mrtg-dynip log have weird messages from snmp modules?

If you think your configuration is correct, try killing your snmp daemon,
restarting it and wait to see if the messages come up again before worrying
about the messages.

5.2 Why doesn't my email address and web page link show?

Did you remove the comment symbol '#' in the configuration file?

5.3 I have configured everything, yet my index page does not update

The default option is to die if there are any response problems.  Try
changing the $suicidal option. Examine the log file.

5.4 Your crontab example looks really odd, please explain.

First the script gets mrtg to run on the regenerated 'mrtg-dynip.cfg' file. 
The crontab entry is designed to send any error mwessages from standard
output and error to a log file with a date and time indicator.  If you don't
do this you may end up perplexing/annoying/frightening those on the root
email distribution list (who are automatically emailed unredirected standard
output and error from cron jobs), if you run the script as user root. The
error messages can be confusing to those inexperienced with mrtg and snmp,
and can be lengthy and frequent!

6. Why do the in and out graphs closely follow each other in my modem bank
graphs?

This has to do with the way information is reported by by the snmp agent for
the interface devices.  On mainstream ISDN router devices, 'in' appears to
indicate incoming packets on one side and 'out' appears to be outgoing
packets on the same side.  

For some interfaces, 'in' appears to indicate incoming packets to both sides
and 'out' appears to mean the forwarded packet out of the interface from
either sides.

It appears as snmp counts both sides of an interface for counting on some
devices but one side for other devices.  This problem needs to be sorted
out.

7. I cannot find a solution to my problem in the docmentation and web
sites.  What support exists and is there a mailing list?

This depends on the problem.  For problems to do with mrtg there is an
active mailing list and extensive archive.  For problems specific to
mrtg-dynip please send an email to me at john@heenan.ironbark.id.au.
I will set up a mailing list if necessasry.