Topology Graph (graphviz) Output Module

graph output module create a description of network topology in graphviz DOT format. You can use that description with graphviz commands to create topology diagrams in numerous output formats.

Note: The network topology graph description contains nodes and links but no placement information. graphviz is pretty good at figuring out how to draw the required graph, but it pays out to test out various layout engines (hint: use the name of the layout engine as the CLI command).

The graph output module is invoked with the netlab graph command or by specifying the -o graph parameter in the netlab create command. It takes an optional destination file name (default: graph.dot).

A single formatting modifier can be used to specify the graph type:

topology (default) – Display inter-node links, multi-access- and stub subnets. When the network topology contains BGP information, the graph groups nodes into autonomous systems. Alternatively, you could set defaults.outputs.graph.groups attribute to use topology groups to group graph nodes.
bgp – Include autonomous systems, nodes, and BGP sessions. With the rr option (specified with netlab create -o graph:bgp:rr), RR-client sessions are drawn as directed arrows.

Modifying Graph Attributes

Graphing routines use default topology settings to modify the generated DOT file’s node- or link parameters. These defaults influence how your graphs look:

outputs.graph.as_clusters (default: True) – use BGP AS numbers to create graph clusters
outputs.graph.groups – use the specified list of groups (or all groups when set to True) to create graph clusters
outputs.graph.interface_labels – Add IP addresses to links in topology graph. Results in a cluttered image (but feel free to fix that and submit a pull request).
outputs.graphs.node_address_label (default: True) – add node loopback IP addresses or IP addresses of the first interface (for hosts) to node labels.
outputs.graph.rr_sessions (default: False) – draw IBGP sessions between BGP route reflectors and clients as directional connections.

Modifying Link and Node Attributes

You can use the graph link and node attributes to change the style of individual nodes or links. The following attributes are built into netlab[1]:

graph.color – line color (color GraphViz attribute)
graph.fill – fill color (fillcolor GraphViz attribute)
graph.width – line width (penwidth GraphViz attribute)

You can also use the graph.linkorder link attribute to change the order of links in the D2 graph description file, which can sometimes improve the diagrams’ appearance. Links with lower graph.linkorder values (default: 100) appear earlier in the list of links.

Object Styles

You can also change the formatting of individual graph objects with the outputs.graph.styles.object defaults:

Object	Description
graph	Generic graph formatting
node	Device formatting
edge	Link formatting
as	Autonomous system/group container formatting
stub	Subnet formatting
ibgp	IBGP session formatting
ebgp	IBGP session formatting

Each styles parameter is a dictionary of Graphviz attributes and their values (see the following printout for an example).

You can also change graph colors and margins with old-style defaults:

outputs.graph.colors.object – Specify background color for as, node, stub subnet, ibgp or ebgp session.
outputs.graph.margins.as – Inner margin for graph clusters (BGP autonomous system or groups).

You could specify the graph defaults in your topology file (where you would have to prefix them with defaults), in per-user topology defaults, or with environment variables (even more details). You could also specify them with the -s parameter of the netlab create command, yet again prefixed with defaults (more details).

The system defaults in netlab release 25.09 are included below; you can always inspect them with netlab show defaults outputs.graph

% netlab show defaults outputs.graph

netlab default settings within the outputs.graph subtree
=============================================================================

as_clusters: true
attributes:
  link:
    _keys:
      linkorder:
        max_value: 200
        min_value: 1
        type: int
      type:
        type: str
        valid_values:
        - lan
    type: dict
  shared:
  - linkorder
interface_labels: false
node_address_label: true
styles:
  as:
    bgcolor: '#e8e8e8'
    color: '#c0c0c0'
    fontname: Verdana
    margin: 16
  ebgp:
    color: '#b21a1a'
    penwidth: 2
  edge:
    fontname: Verdana
    labeldistance: 1.5
    labelfontsize: 8
  graph:
    bgcolor: transparent
    nodesep: 0.5
    ranksep: 1
  ibgp:
    color: '#613913'
    penwidth: 2
  node:
    bgcolor: '#ff9f01'
    fillcolor: '#ff9f01'
    fontname: Verdana
    margin: 0.3,0.1
    shape: box
    style: rounded,filled
  stub:
    bgcolor: '#d1bfab'
    fillcolor: '#d1bfab'
    fontsize: 11
    margin: 0.3,0.1