Dbeacon, Frequently Asked Questions
Introduction
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What does 'dbeacon' mean?
'dbeacon' stands for Distributed Beacon. This named was adopted since it doesn't require a centralized server.
Why should i run 'dbeacon'?
'dbeacon' might be useful if you are deploying intra or inter-domain multicast in your network. It is a tool that might help you find connectivity problems as well as to collect statistics about the current connectivity.
Why doesn't dbeacon use RTP/RTCP?
Historically, dbeacon was designed to be compatible with the DAST/NLANR java beacon version which doesn't use RTP/RTCP. After dropping down the compatibility we considered implementing RTCP to gather various multicast figures because it would have been possible to plug dbeacon to any RTP/RTCP application. Finally we decided that dbeacon was a specialized application and to implement additional features such as using SSM would require a new protocol.
What is ASM? and SSM?
ASM and SSM are two multicast models. ASM stands for Any Source Multicast while SSM for Source Specific Multicast. ASM provides a simple bidirectional multicast model for hosts at the expense of router complexity while SSM is a simpler unidirectional model.
Do i need to be 'root' to run dbeacon?
No, dbeacon is able (and should be) run as a simple user.
Can i deploy several dbeacons in the same host?
Yes, you may run as many dbeacons as your OS has resources for. A dbeacon is identified by a tuple (source address/source port), and multiple dbeacons running on the same machine are differenciated by their source port.
Where should i deploy dbeacon in my network?
The rule is simple: wherever you want to check your multicast connectivity status. If you have 5 multicast enabled subnetworks it makes sense to deploy a dbeacon on each subnetwork. Also, be carefull of IGMP/MLD snooping issues: you may encounter multicast problems with IGMP/MLD snooping and in those cases should deploy a dbeacon on each switched segment of your network.
How can i make my country's flag show up in the matrix page?
To make your flag show up in the matrix page, specify your Two Letter Country Code when running dbeacon. For instance:
./dbeacon [...] -C EU
I read the usage of 'ntpd' is recommended, why is that?
'dbeacon' relies on the several beacon hosts to have their clocks properly synchronized in order to collect good delay statistics. 'ntpd' provides this feature.
How do i setup the history feature?
The history feature depends on the RRDs (Round Robin Database) perl module. So before setting it up you must be sure have this module available (if you are running Debian you may install librrds-perl, if not you may install it from rrdtool's source code.
After RRDs is installed, set $history_enabled to 1 in your matrix.conf and either run matrix.pl periodicly via dbeacon, using the parameters -I 60 -L contrib/matrix.pl or from cron.
How much disk space is required for the history feature?
The History feature may take a lot of disk space, depending of the number of sources you are storing data for. The current implementation takes approximatively 30Mb per tuple (source, destination), so beware that for 10 sources it would take 300Mb of disk space. This space however is constant and doesn't increase with time due to the nature of the Round Robin Database.
May i run a matrix page without history support?
Yes, the history feature may be disabled via matrix.conf.
My beacon is in the 'Beacons that report no received sources' list. What does it mean and how can i fix it?
This means that while some (or all) beacons are able to receive your multicast packets, your beacon isn't receiving any other sources. This is due to a broken multicast setup, the current dbeacon relies on ASM for source discovery and it might be broken in your network. You should investigate your routers for problems (connectivity or configuration) or contact your network administrator.
Alternatively, if you are running a host based firewall,l such as iptables, you should check that packets with the relevant multicast group as the destination are allowed into your host in the input direction. A general rule to allow multicast packets inwards could be achieved by including something like this as part of your input chain in iptables:
ACCEPT 0 -- anywhere BASE-ADDRESS.MCAST.NET/4
Or you could be more specific and allow only certain sources and specific multicast groups as the destination.
Contributed by Anthony Ryan
How much bandwidth will dbeacon consume?
It depends on the current number of beacons in the group. Due to adaptive intervals 'dbeacon' usually consumes bandwidth in a direct proportion to the number of beacons. For instance, for 14 beacons, it usualy consumes around 10Kb/s if SSM is being used.
Is IPv4 supported?
Yes, for ASM and SSM.
Is my Operating System supported?
It depends on what Operating System you run. At this moment dbeacon is known to work in the following systems:
- Linux 2.4 and 2.6, with SSM support in versions >= 2.6.11.
- BSD variants (you need the latest KAME kit to support SSM).
- Solaris (no SSM support)
Where can i find a dbeacon Debian package?
Check dbeacon's website.
What debian packages do i need to install in order to setup a matrix?
Besides a web server (such as apache) you need perl and libxml-parser-perl. If you wish to use the history feature you must also install librrds-perl.
How do i setup my Apache to run a matrix page?
Just add the following line to your apache configuration:
ScriptAlias /matrix/ /path/to/matrix.pl
Refer to contrib/apache-matrix-conf included with the source distribution for further information on how to setup Apache and the dbeacon matrix.
What do 'TTL', 'Loss', 'Delay' and 'Jitter' in the matrix page mean?
These are the various values gathered by the multicast beacon. The TTL is derived from the Time to live value (Hop count) of the packets and represents the number of multicast routers separating two specific sources. The Loss represents the mean percentage of packet loss between two sources. The Delay is a distance between two sources but expressed in miliseconds, it represents the time for a packet to travel from one source to another. Jitter represents the additionnal interarrival time between each probe.
Why are some matrix cells painted in a lighter green than others?
When in 'SSM or ASM' view (the default one), a bright green cell means that the currently displayed value was obtained via SSM, while a lighter green points to ASM only and a darker green to SSM only.
How does dbeacon's protocol work?
For a detailed explanation on dbeacon's protocol read the PROTOCOL file included with the source code.
What does the sign '#' means in the source info listing ?
This means that the source is ssmpingable : you can ssmping it with the ssmping tool from http://www.venaas.no/multicast/ssmping/ . To announce to others beacons that you are ssmpingabe, use the option -F ssmping.
