(New: 1 October 1996: Multicast virus escapes during Sigcom 96 )

Production Internet routers are only now beginning to support native multicast, and the MBone has provided intermediate support by using a virtual layer of tunnels configured over the physical Internet. The Mbone works by connecting individual multicast-capable subnetworks with these logical tunnels whose endpoints encapsulate multicast packets into normal IP packets and send them across the the unicast path between the tunnel endpoints. Tunnel endpoints are typically Unix workstations with IP multicast support and running the multicast routing daemon mrouted. Currently the widest use of the MBone is for real-time video and audio streams.

A few years ago the Mbone was a new and small enough system that it was possible to draw a complete map of the topology. As the real-time events that were broadcast grew in popularity, keeping the maps up-to-date went from difficult to impossible. We know of no pictorial maps of the current Mbone topology, which makes it difficult at best to debug problems or optimize topologies and configurations. This gap in understanding a system that has grown beyond manageability motivated our investigation.

We present a 3D visualization of MBone connections from a list of MBone links collated by the mrwatch utility developed by Atanu Ghosh at UCL for the MICE project. We have developed a set of tools to convert the mrwatch data into a geographical representation of the tunnels as arcs on a globe. The interactive 3D maps use the VRML file format, which allows the graphical representation of each tunnel to contain a hyperlink pointer to textual information about that tunnel. Our toolkit allows us to highlight different aspects of the tunnel structure by using visualization techniques such as thresholding, shown in the previous sequence, and grouping according to characteristics such as tunnel type or backbone provider.

We visualize the Mbone tunnel structure with a VRML 3D visualization system, drawing the tunnels as arcs on a globe. A VRML browser then supports access to hypertext information about tunnels by interactively clicking on them. We also provide gif images for the VRML-challenged.

This particular set of four figures provides different `views' of the Mbone or subsets of the global tunnel connectivity, as derived from the mrinfo mbone mapping tool by Piete.Brooks in the U.K. For each graph, your browser will let you rotate the globe in order to locate the tunnels of interest, and click on a link to bring up an HTML browser pointing to a text description of the tunnel you selected.

Note: to make these views work you need a VRML browser and may have to appropriately specify a .mime.types entry:

x-world/x-vrml  wrl

and .mailcap entry:

x-world/x-vrml;  <your-VRML-browser-location-here> %s -URL %u

Otherwise you're stuck with the gif snapshots and will not have the interactivity.
Still, the gifs are cool.

The default display shows the full mbone topology as derived from the mrinfo mbone mapping tool by Piete Brooks in the U.K.

The domain display to the left differentiates the mbone tunnels by their backbone status:
all ISP-to-ISP nodes are blue,
ISP-to-non-ISP are red,
and non-ISP-to-non-ISP are yellow.

The backbone display shows the subset of the tunnels by major backbone infrastructure, distinguished by color.

backbone	color
mci	blue
sprintlink	green
bbnplanet	magenta
ans	yellow
alternet	cyan
nasa	red
dren	black
dartnet	white

The PIM display highlights the few tunnels participating in the newer PIM, a more advanced (but still not operationally stable) protocol-independent multicast protocol. In the picture, PIM tunnels are shown in red while all other tunnels are white.








(Note that if you have access to or the inclination to build a compiled version of geomview), that tool will allow you to manipulate components of the mbone representation. For the same four views use: full mbone, by ISP, by TLD, or PIM highlights)

Probably the most tedious aspect of this project was the development of a database and tools that map TCP/IP addresses into geographic locations, We needed to obtain the latitude and longitude of each IP address for each Mbone router in order to draw the arcs. Unfortunately, accurate lat/lon data is remarkably difficult to come: the InterNIC database contains one geographical location per domain, which often only represents a headquarters for a much wider area subnetwork e.g., ISPs. And painstaking to construct (and not totally complete yet.)

Note: to help with such visualization studies, you could put geographical information into your DNS configuration as outlined in RFC 1876. (More info available here).

The magnitude of the breakdown, which is obvious at a glance at the picture, suprised someone deeply involved with mbone deployment. We believe that our results, although preliminary, can facilitate a more rational restructuring of the MBONE tunnel system.
Note: we've outlined steps for cleaning up redundant tunnels that transit your infrastructure.

(One alternative is to allow native peerings to occur at network access points , as depicted to the right; this configuration could would prevent large numbers of tunnels from crossing already stressed multi-provider access points.)