Surfing the Network Topology
An Overview of the “Topology” Tab
Zenmap's “Topology” tab provides an interactive,
animated visualization of the connections between hosts on a
network. Hosts are shown as nodes on a graph that extends radially
from the center. Click and drag to pan the display, and use the
controls provided to zoom in and out. Click on a host and it becomes
the new center. The graph rearranges itself in a smooth animation to
reflect the new view of the network. Run a new scan and every new
host and network path will be added to the topology automatically.
The topology view is most useful when combined with Nmap's
option, because that's the option that discovers the network path to
a host. You can view a network inventory that doesn't have
traceroute information in the topology, but network paths will not
be visible. Remember, though, that you can add traceroute
information to a network inventory just by running another scan
thanks to Zenmap's scan
Initially the topology is shown from the point of view of localhost,
with you at the center. Click on a host to move it to the center and
see what the network looks like from its point of view.
The topology view is an adaptation of the
program by João Paulo
The topology view uses many symbols and color conventions. This
section explains what they mean.
Each regular host in the network is represented by a little
circle. The color and size of the circle is determined by
the number of open ports on the host. The more open ports,
the larger the circle. A white circle represents an
intermediate host in a network path that was not port
scanned. If a host has fewer than three open ports, it will
be green; between three and six open ports, yellow; more
than six open ports, red.
If a host is a router, switch, or wireless access point, it
is drawn with a square rather than a circle.
Network distance is shown as concentric gray rings. Each
additional ring signifies one more network hop from the
Connections between hosts are shown with colored lines.
Primary traceroute connections are shown with blue lines.
Alternate paths (paths between two hosts where a different
path already exists) are drawn in orange. Which path is
primary and which paths are alternates is arbitrary and
controlled by the order in which paths were recorded. The
thickness of a line is proportional to its round-trip time;
hosts with a higher RTT have a thicker line. Hosts with no
traceroute information are clustered around localhost,
connected with a dashed black line.
If there is no RTT for a hop (a missing traceroute entry),
the connection is shown with a blue dashed line and the
unknown host that makes the connection is shown with a blue
The controls appear in a column when the
“Controls” button is clicked. The controls are
divided into sections.
The controls in the “Action” section control
what happens when you click on a host. The buttons in this section
are, from left to right, “Change focus”,
“Show information”, “Group
children”, and “Fill region”. When
the mode is “Change focus”, clicking on a
host rearranges the display to put the selected host at the
center. When the mode is “Show information”,
clicking on a host brings up a window with information about it.
When the mode is “Group children”, clicking a
host collapses into it all of its children—those nodes that
are farther from the center. When a host is grouped it appears
Clicking on a grouped node ungroups it again. This diagram shows
the process of grouping.
Figure 12.7. Grouping a host's children
When the mode is “Fill region”, clicking a
host highlights the region of the display occupied by the host and
its children. The highlighted hosts are exactly the same as those
that would be grouped in “Group children”
mode. You can choose different colors to highlight different
regions. This diagram shows an example of several regions
highlighted in different colors.
Figure 12.8. Highlighting regions of the topology
The controls in the “Interpolation” section
control how quickly the animation proceeds when part of the graph
There are two options for the automatic layout of nodes. Symmetric
mode gives each subtree of a host an equal-sized slice of the
graph. It shows the network hierarchy well but hosts far from the
center can be squeezed close together. Weighted mode gives hosts
with more children a larger piece of the graph.
The checkboxes in the “View” section enable and
disable parts of the display. For example, disable
“hostname” to show only an IP address for each
host, or disable “address” to use no labels at
all. The “latency” option enables and disables
the display of the round-trip times to each host, as determined by
--traceroute option. If
“slow in/out” is checked, the animation
will not be linear, but will go faster in the middle of the
animation and slower at the beginning and end.
The compass-like widget pans the screen in eight directions. Click
the center to return to the center host. The ring around the
outside controls the rotation of the entire graph.
“Zoom” and “Ring gap” both
control the overall size of the graph. “Zoom”
changes the size of everything—hosts, labels, connecting
lines. “Ring gap” just increases the spacing
between the concentric rings, keeping everything else the same
size. “Lower ring gap” gives a minimum spacing
for the rings, useful mainly when fisheye is enabled.
The fisheye controls give more space to a selected ring,
compressing all the others. The slider controls which ring gets
the most attention. The “interest factor” is
how many times greater the ring spacing is for the chosen ring
than it would be with no fisheye. The “spread
factor” ranges from −1 to 1. It controls
how many adjacent rings are expanded around the selected ring,
with higher numbers meaning more spread.
The topology display recognizes these keyboard shortcuts:
|c||Return the display to the center host.|
|a||Show or hide host addresses.|
|h||Show or hide hostnames.|
|i||Show or hide host icons.|
|l||Show or hide latency.|
|r||Show or hide the rings.|
The host viewer is an alternative way to get details about hosts.
Activate the viewer by clicking the “Hosts
Viewer” button. All the hosts in the inventory are
presented in a list. Select any host to get details about it.