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Network Diagramming and Monitoring with Scotty

Brent Bice

Like many open source tools, Scotty is actually a collection of tools that have grown together. It can be used as a network-diagramming tool in addition to an SNMP network console. After you use Scotty to draw a network diagram, you can then use it to monitor and troubleshoot the objects in your diagram.


You must first have Perl, gcc, and Tcl/Tk installed, then you can download Scotty from its homepage:
At the time of this writing, 2.1.11 is the latest stable version, but the release of 3.0 is expected soon. After downloading Scotty, extract, configure, and compile the source:

zcat scotty-2.1.11.tar.gz |tar xf -
cd scotty-2.1.11/unix
./configure --enable-gcc
make install
make sinstall
You may want to use a --prefix=<dir> option to the configure command to specify where you want to install Scotty if you don't like the default location of /usr/local. If configure has trouble finding your Tcl/Tk installation, you may need to use the --with-tcl-config=<dir> and --with-tk-config=<dir> options. For instance, I had to do:

./configure --enable-gcc --prefix=/usr/local/tools/scotty2.1.11 \
            --with-tcl-config=/usr/local/tools/tcltk8.3.3/lib \
Also, if you have Tcl/Tk installed in an unusual place, you must set up your environment appropriately before running make. This means you need to have LD_LIBRARY_PATH set to include the lib directories for both Tcl and Tk. You may also need to do the su command before the first make install command if the installation location isn't writable by you (e.g., /usr or /usr/local are usually only writable by root).

Lastly, if you install Tcl/Tk in an unusual location or if you install Scotty in a different location, make sure your LD_LIBRARY_PATH and TCLLIBPATH environment variables are set correctly before you fire up Scotty. I wrote a wrapper script that does it for me:

# I like all my diagrams in one tidy spot
cd ~/tkined

# prepend the tcl/tk library dirs
setenv LD_LIBRARY_PATH /usr/local/tools/tcltk8.3.3/lib:$LD_LIBRARY_PATH
setenv TCLLIBPATH "/usr/local/tools/tcltk8.3.3/lib/tk8.3 \
                   /usr/local/tools/scotty2.1.11/lib/tnm2.1.11 \

setenv PATH /usr/local/tools/scotty2.1.11/bin:$PATH
tkined1.4.11 &
Network Diagramming

Start up the network diagram part of Scotty by running tkined1.4.11 to see the interface. The left mouse button selects, the middle mouse button moves, shift-left mouse button selects more objects without deselecting currently selected objects, and the right mouse button brings up a context-sensitive menu.

The frame on the left side of the tkined window is for selecting different modes (Figure 1). The "Select" button lets you use the mouse cursor to select items, "Resize" allows you to resize objects, and "Text" lets you place text objects in the window.

A square box containing a question mark (not shown in Figure 1) is an "unknown device" object, and the default icon is the "unknown device" icon (hence the question mark). The icon menu will allow you to change the icon you have currently selected for placement, or to change the icon of selected objects, which will be described more later.

The thick line is used to draw subnets, and the thin line is used to draw connections between subnets and devices. The squiggly cloud is a group (there are other, more meaningful, group icons as well), and the hand is a reference object.

I'll start with a simple example that will lead into the more interesting aspects of Scotty. If you want to see what some finished diagrams might look like, you can download some sample diagrams I made of a fictitious company at To start making your own diagram, begin by selecting the thick subnet line, then click once in the drawing panel, drag the mouse a few inches away, and click again to finish drawing a subnet line. Click and hold the right mouse button on this subnet object and select "Edit all Attributes" so you can enter a name for your subnet (e.g., "" or "San Mateo LAN").

Next, click on the "unknown device" icon, and click once an inch or two from your subnet to drop a device object. Use the right mouse button again to get a menu for that object and edit its attributes to enter the name of a device (preferably one that has SNMP enabled). Don't worry about the IP address right now.

Click on the thin line in the mode panel and then click on the device object and the subnet object to connect them. You can continue adding devices and subnets, but first I'll show how to group the device and subnet into a group object. To do this, select all the objects you want to group. The easiest way is to select the "Select" button on the mode panel, then click and hold the left mouse button on the drawing panel and drag a "bounding box" around all the objects to select.

After you've selected the objects, pull down the Structure menu and select "Group". Notice the letters on the far right side of the menu and you'll see that there is a "g" next to "Group", so you could just press "g" instead of clicking through the menu. I also use "e" and "c" frequently to "expand" and "collapse" groups. Now change the icon of the new group from the squiggly cloud to something better. To do this, pull down the Icon menu and pull right on "Group" and "Topology" and select "Bus" while the group object is selected.

If you press "e" to expand your group, you'll see the individual objects again but selected as one group; note the gray line around them. You can click on them and select them individually or you can select the entire group by clicking on the gray border. You can also set a more useful name for your group (other than "group 0") by using the right mouse button on the gray border and selecting "edit all attributes". Don't diagram your entire network right now. Scotty can "Discover" networks and do a large portion of the initial work for you, which will be covered later in this article.


Besides drawing network diagrams, Scotty can perform SNMP queries on the objects. In fact, Scotty can keep running strip charts, monitor TCP/IP reachability, and monitor things like CPU and Disk activity on servers running rstatd. Because you now have a small diagram with a few real devices with real hostnames in it, let's look at a few of those tools next. Before you can use these tools, the objects must have IP addresses set. Pull down "Tools" and select "IP Layout".

This tool is useful for quickly filling in the IP addresses you left blank. As long as your device names are correct and can be found in DNS, you can simply select all the objects, then pull down the new IP-Layout menu and select "Set Address". It switches the names displayed to the IP and not the name itself, but you can switch that back with the "Set Name" function of IP-Layout. If you prefer shortened machine names, you can also use "Unique Names" in the IP-Layout menu. IP-Layout saves hours when you diagram a network with hundreds of devices.

Now that the objects have real IP addresses, there are other interesting tools to try. Pull down "Tools" and select "IP-Monitor" and "SNMP-Monitor", then select one of your objects. If the object represents a UNIX machine running rstatd, try pulling down IP-Monitor and selecting "CPU activity". Of course, you can select "Reachability" under the IP-Monitor menu for any IP device. If the object can't be pinged, the object will change to red, flash, and will switch back after the object is reachable again. This reachability check is performed once per minute by default, and can be modified with the IP-Monitor "Set Parameter" menu.

Select a device that has SNMP enabled and pull down the "SNMP-Monitor" menu and select "Set SNMP Parameter". If your SNMP device has a community name other than public, you can set it here. Click on "Accept" when you're done with the settings, then pull down SNMP-Monitor and select "Interface Load". If your SNMP device is answering SNMP queries and all your settings are correct, you'll see a strip chart for every interface pop up. Use the middle mouse button to rearrange them. If you use the right mouse button on one, you'll see that you can change the scale of each strip chart, too. These strip charts also update once per minute by default.

If you get an SNMP error, check the SNMP settings in SNMP-Monitor again. If they're correct, then check the device in question and see if it really does have SNMP enabled. On a Cisco router, here's what you might need to add to the config (Cisco config fragment to enable SNMPv1 with read-only access using "public" for the community):

snmp-server community public RO
snmp-server trap-authentication
snmp-server location San Mateo, CA
! NOTE - there are other traps you can enable too
snmp-server enable traps config
snmp-server enable traps frame-relay
snmp-server enable traps rtr
snmp-server host public
Every vendor will have different ways to enable and configure SNMP access, so you may have to refer to the documentation if SNMP isn't already enabled. Scotty is supposed to support SNMP version 1, verion 2c, and version 2u, but as of this writing I've only tried SNMP version 1.

SNMP-Monitor is useful for monitoring SNMP devices using well-known parts of the MIB tree, such as MIB2 (or even for vendor-specific parts of the MIB tree if you have their MIB files loaded and you know the OID or variable name). However, if you want to explore the MIB tree, use the MIB Browser.

Pull down Tools again and select "SNMP-Browser", then pull down SNMP-Browser and you'll see that you can quickly find and query specific parts of the MIB tree by pulling right on some of the menu entries (such as MIB-2). Once you configure Scotty to read vendor-specific MIB files, you'll see additional menu entries.

You can also browse the MIB tree by pulling down SNMP-Browser and selecting "MIB Browser". In the resulting window (Figure 2), you can click on the items in "<>" (such as <mgmt>, <mib-2>, and <system>) to navigate around the MIB tree. Once you click on something that is a leaf in the MIB tree, you'll see another window pop up with the results of the SNMP query. <--up--> takes you to the previous node in the MIB tree, and <--walk--> queries every node in the tree beyond your current position. Use <--walk--> carefully because it can take a long time to walk, for instance, the entire <private> branch, even if only one device is selected. You can also select <--monitor--> to open up a strip chart for the device variable.

To teach Scotty about a vendor's MIB branch, get the vendor-specific MIB file or files. Find the file that contains what you'd like to be able to see from Scotty, and then find out whether it requires any other MIBs to be loaded first. For instance, in one of the MIB files for a Cisco Catalyst 6506 switch, there is:


        MODULE-IDENTITY, OBJECT-TYPE, Integer32, IpAddress, TimeTicks,
        Counter32, Counter64, NOTIFICATION-TYPE
                FROM SNMPv2-SMI
        DisplayString, RowStatus
                FROM SNMPv2-TC
        fddimibPORTSMTIndex, fddimibPORTIndex
                FROM FDDI-SMT73-MIB
        OwnerString, ifName, ifIndex
                FROM IF-MIB
                FROM SNMPv2-CONF
                FROM CISCO-TC
                FROM CISCO-SMI
                FROM TOKEN-RING-RMON-MIB;
All things under "IMPORTS" are types or objects that must already be loaded before loading this MIB file. The "FROM" lines provide a clue to what the names of the MIB files that must first be loaded are likely to be. Note that some of them may already be defined in MIB files that come with Scotty. For instance, if you look in the /usr/lib/tnm2.1.11/mibs directory, you'll see that there are a lot of files with rfc numbers for part of their file names. These are MIBs that are already being loaded by Scotty. With the Cisco MIB files, you generally only need to load the MIBs that are prefixed with "CISCO-". In this case, we need to load CISCO-TC and CISCO-SMI before we load this MIB file.

Once you have the MIB files you want to load, cd to /usr/lib/tnm2.1.11 and if it's not already there, make the site directory. (tnm2.1.11 could be located elsewhere if you installed Scotty in a different location, so check /usr/local/lib/tnm2.1.11 or under the path you specified in your configure command.) In this site directory, create a file named init.tcl. Here's a sample file:

# MIBs for Livingston
lappend tnm(mibs) /home/bbice/mibs/livingston/le38.mib
lappend tnm(mibs) /home/bbice/mibs/livingston/le38trap.mib

# MIBs for VPNet
lappend tnm(mibs) vpnet3.mib

# MIBs for Cisco Catalyst 6506
lappend tnm(mibs)
lappend tnm(mibs)
lappend tnm(mibs)
Note that lappend lines that load a file don't start with a "/" character. If an absolute path isn't specified, it's assumed the file you specify to lappend is in your tnm2.1.11/mibs directory. When adding MIBs to site/init.tcl, add them one at a time. Modify init.tcl, then use the Tools menu to load SNMP-Browser. If you didn't see any errors in the terminal window from which you ran tkined, then you can pull down the SNMP-Browser and select "Delete SNMP-Browser" to remove it, change site/init.tcl again, and reload the SNMP-Browser, and so on, until you have all the MIBs added. You can add them all at once, but it can sometimes make discovering the bad MIB file more difficult.

After you have the vendor-specific MIBs loaded, the SNMP-Monitor and SNMP-Browser tools will show you vendor-specific items, such as air intake temperatures, the number and types of modules in your Catalyst 6506 switch, the modem statistics for your Portmaster 3, the number of security associations your VPNet gear has running, and so forth. If it's in a loaded MIB, you can view, monitor, graph, or receive traps about it with Scotty.

Finally, if you have a large network to diagram, it can be tedious to diagram everything the first time. Scotty has a shortcut -- pull down Tools and select "IP-Discover". As of this writing, Scotty can "discover", to a limited degree, what your network looks like. It currently only knows how to discover Class A, B, or C networks, which means that if your network is broken into smaller, variable-length subnets, IP-Discovery won't be as useful for you. This is something the next version of Scotty may have fixed.

However, if you have a Class C network you can try it out on, pull down IP-Discover and select "Discover IP Network". Enter in a partial IP address, such as 10.1.110, and Scotty will proceed to ping and SNMP query every IP address in that network. Do not, however, do a discovery on someone else's network.

When Scotty finishes discovering the network, you'll see a mass of objects, one or more networks, and a web of thin lines connecting them all. Press "a" to select all the objects, and then pull down IP-Layout and select "All of the above". This feature strips off redundant domain names from the labels, arranges the objects around their subnets, groups them, sets icon types when possible, and results in a tidier diagram. You'll still need to do some arranging and you'll want to select groups one at a time (press "e" to expand and arrange them, then press "c" to collapse them again), but it can save you time and effort.

To determine which icon to set, Scotty does DNS queries to look for HINFO records, which can tell it the hardware and OS of a device. If your DNS server has no HINFO records, it will also try some SNMP queries to figure out whether the device is a switch, router, bridge, etc.

It's also possible to have one network diagram refer to another entire network diagram using "Reference Objects". For an example of this, see Figure 3. You'll see two network diagram icons on a world map -- the world-view of a fictitious company, Beltway Bandits, Inc. These diagram icons are reference objects with the name of another .tki file set in the address attribute. If you were able to right click on one and select "Open (new view)" you'd see another window open up with a diagram of that office's network.

Scotty is a great complement for other tools, such as MRTG and RRDTool, and there are too many useful things you can do with Scotty to cover in one article.


Scotty homepage:

Scotty FAQ:

Getting Started page:

Tcl and SNMP history:

A series of SNMP-related Web pages and Web sites

The SimpleWeb:

The SimpleTimes:

Example diagrams:

Brent Bice has worked as a programmer, network admin, or systems admin on a variety of UNIX-based systems since 1989. He is currently employed at Persistence Software Inc as Senior System/Network Admin and can be reached at: