Multicast (Pete's notes)
A multicast beacon is a daemon that runs on a host at a site to let other sites check if the
site is reachable. As of 2007-10-07, we run a multicast beacon on the npad machine. The beacon
is /usr/local/bin/beacon.
To: NETS engineers
Subject: Multicast Beacon
Date: Mon, 01 Oct 2007 13:14:41 -0600
From: David Mitchell
NE folks,
I installed a multicast beacon on npad.ucar.edu. It should automatically
restart after reboots, although I haven't tested that. I also updated
the "Tools" page to link to the NLANR primary beacon instead of the
(defunct) Access Grid Beacon.
-David
The
Multicast HOWTO says that you should provide a default route
for multicast traffic. This may be unecessary since there is a
global default route, but if it's needed, the sample "route"
command in the HOWTO isn't quite sufficient - it doesn't get
executed whenever the system boots. To set up a default multicast
route at boot time, I did this:
(as root)
cat > /etc/sysconfig/static-routes
any net 224.0.0.0 netmask 240.0.0.0 dev eth0
^D
The
Multicast HOWTO says
...multicast-capable hosts join the all-hosts group at start-up,
so "pinging" 224.0.0.1 returns all hosts in the network that
have multicast enabled.
Try it.
If you have sdr installed, run it. Sdr needs multicast, so if it
displays sessions, then multicast is working.
Assuming you're connected to VLAN 8 at NCAR, run the
Video Furnace. Even if it says "Unable to authorize
station", leave it running, as it's probably sucking a
multicast stream. With Video Furnace running, gazelle showed:
gazelle$ netstat -g
IPv6/IPv4 Group Memberships
Interface RefCnt Group
--------------- ------ ---------------------
lo 1 ALL-SYSTEMS.MCAST.NET
eth0 1 233.0.103.53
eth0 1 ALL-SYSTEMS.MCAST.NET
vmnet8 1 ALL-SYSTEMS.MCAST.NET
vmnet1 1 ALL-SYSTEMS.MCAST.NET
lo 1 ip6-allnodes
eth0 1 ff02::1:ff5e:6694%3221213520
eth0 1 ip6-allnodes
vmnet8 1 ff02::1:ffc0:8%3221213520
vmnet8 1 ip6-allnodes
vmnet1 1 ff02::1:ffc0:1%3221213520
vmnet1 1 ip6-allnodes
gazelle$
Which shows that gazelle thinks it's a member of group 233.0.103.53.
With Video Furnace running, mlra showed:
mlra#show ip igmp groups vlan 8
IGMP Connected Group Membership
Group Address Interface Uptime Expires Last Reporter
239.255.255.254 Vlan8 6w6d 00:02:08 128.117.8.125
239.255.255.253 Vlan8 6w6d 00:02:13 128.117.11.192
239.255.255.250 Vlan8 6w6d 00:02:13 128.117.11.74
224.2.127.255 Vlan8 4w6d 00:02:06 128.117.11.60
224.2.127.254 Vlan8 4w6d 00:02:12 128.117.11.60
233.45.17.171 Vlan8 06:13:58 00:02:04 128.117.11.67
224.101.101.101 Vlan8 4w1d 00:02:07 128.117.8.111
235.80.68.83 Vlan8 6w6d 00:02:12 128.117.8.126
233.0.103.53 Vlan8 01:57:38 00:02:03 128.117.10.161
224.1.0.38 Vlan8 1d17h 00:02:09 128.117.10.160
224.0.1.40 Vlan8 03:06:55 00:02:08 128.117.11.25
224.0.1.60 Vlan8 6w6d 00:02:13 128.117.10.88
224.1.0.1 Vlan8 03:06:57 00:02:06 128.117.11.25
224.0.1.1 Vlan8 1d22h 00:02:10 128.117.9.51
239.7.7.0 Vlan8 4w6d 00:02:12 128.117.11.60
224.0.1.24 Vlan8 6w6d 00:02:12 128.117.8.126
mlra#
As you can see, my laptop at 128.117.10.161 is a member of
multicast group 233.0.103.53. At the time, this was what mlrb
showed:
mlrb#show ip mroute 233.0.103.53 128.117.10.161
IP Multicast Routing Table
Flags: D - Dense, S - Sparse, s - SSM Group, C - Connected, L - Local,
P - Pruned, R - RP-bit set, F - Register flag, T - SPT-bit set,
J - Join SPT, M - MSDP created entry, X - Proxy Join Timer Running
A - Advertised via MSDP, U - URD, I - Received Source Specific Host
Report
Outgoing interface flags: H - Hardware switched
Timers: Uptime/Expires
Interface state: Interface, Next-Hop or VCD, State/Mode
(*, 233.0.103.53), 02:38:47/00:02:59, RP 128.117.243.9, flags: SJC
Incoming interface: Vlan303, RPF nbr 128.117.243.73, Partial-SC
Outgoing interface list:
Vlan8, Forward/Sparse-Dense, 00:30:52/00:02:56, H
mlrb#
This shows a multicast stream going out Vlan8. When I stopped
the Video Furnace application and waited a minute, the
"Outgoing interface list" changed to "Null". So my
laptop was doing multicast. Of course, I wasn't
actually seeing CSPAN, because the Video Furnace
application says "Unable to authorize station", but the
Video Furnace seems to have been doing multicast anyway.
On a Windows box, download the Internet2 Detective application
from
detective.internet2.edu/. This application will listen
for multicast beacons that are regularly broadcast by Internet2
servers. See the docs at the website.
Pete Siemsen
Last modified: Thu Jul 14 10:50:37 MDT 2005