Multicast questions

sabre2 · 02-28-2010, 04:23 PM

I am attempting to get multicast running on a couple of RHEL 5.4 test boxes. I have gone through the How-To at TLDP. I added a route

Code:

route add -net 224.0.0.0 netmask 240.0.0.0 dev eth0

I added the following to /usr/lib/syslinux/com32/include/netinet/in.h

Code:

struct ip_mreq
{
        struct in_addr imr_multiaddr;   /* IP multicast address of group */
        struct in_addr imr_interface;   /* local IP address of interface */
};

Is that all that needs to be done for a app running on these machines to use multicast?

Is there a way I can test that multicast is functioning on these machines? Because if I issue the following neither of these 2 machines respond.

Code:

ping -t 1 -c 2 224.0.0.1

Thanks in advance.

rigor · 02-28-2010, 09:03 PM

Please post the output from each of these commands:

ifconfig eth0

netstat -rn

netstat -gn

sabre2 · 03-01-2010, 06:51 AM

ifconfig eth0:

Code:

eth0      Link encap:Ethernet  HWaddr 00:0C:29:E4:17:ED
          inet addr:10.0.1.239  Bcast:10.0.3.255  Mask:255.255.252.0
          inet6 addr: fe80::20c:29ff:fee4:17ed/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:10158706 errors:0 dropped:0 overruns:0 frame:0
          TX packets:3454869 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:1836111445 (1.7 GiB)  TX bytes:740462745 (706.1 MiB)
          Base address:0x2000 Memory:d8920000-d8940000

netstat -rn:

Code:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
10.0.0.0        0.0.0.0         255.255.252.0   U         0 0          0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth0
224.0.0.0       0.0.0.0         240.0.0.0       U         0 0          0 eth0
0.0.0.0         10.0.1.254      0.0.0.0         UG        0 0          0 eth0

netstat -gn:

Code:

IPv6/IPv4 Group Memberships
Interface       RefCnt Group
--------------- ------ ---------------------
lo              1      224.0.0.1
eth0            2      230.0.0.1
eth0            1      224.0.0.251
eth0            1      224.0.0.1
lo              1      ff02::1
eth0            1      ff02::fb
eth0            1      ff02::1:ffe4:17ed
eth0            1      ff02::1

Thanks for your help

rigor · 03-01-2010, 12:07 PM

Sorry, I wasn't quite sure from what perspective you were doing things.

I was attempting to make sure that the interfaces are active, have
viable configurations, are multi-cast enabled, that the routing is
applicable, and that each machine is a member of the same multi-cast
group.

For that, you need to run those three commands on each machine.

Can the two machines communicate if you don't try to use multi-cast?
For example, can you ping each machine from the other? Are they
directly connected to each other, or connected through other
hardware? If there's other hardware, what is that hardware?
Is there a firewall between the machines? Are there any iptables
or ipchains rules on either machine, or something between them,
that could be causing a problem?

sabre2 · 03-01-2010, 03:39 PM

HI kakaka,

sorry for the delay, I didn't get a notice this was updated

To answer your questions.
Yes they can see each other outside of multicast ping, ssh, nfs, etc. The only thing between them is a switch.

Is there a way outside of my ping that I can test multicast?

here are the outputs from machine 2.

ifconfig eth0:

Code:

eth0      Link encap:Ethernet  HWaddr 00:0C:29:A2:99:8B
          inet addr:10.0.1.240  Bcast:10.0.3.255  Mask:255.255.252.0
          inet6 addr: fe80::20c:29ff:fea2:998b/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:2085158 errors:0 dropped:0 overruns:0 frame:0
          TX packets:892007 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:212875526 (203.0 MiB)  TX bytes:109545134 (104.4 MiB)
          Base address:0x2000 Memory:d8920000-d8940000

netstat -rn:

Code:

Kernel IP routing table
Destination     Gateway         Genmask         Flags   MSS Window  irtt Iface
10.0.0.0        0.0.0.0         255.255.252.0   U         0 0          0 eth0
169.254.0.0     0.0.0.0         255.255.0.0     U         0 0          0 eth0
224.0.0.0       0.0.0.0         240.0.0.0       U         0 0          0 eth0
0.0.0.0         10.0.1.254      0.0.0.0         UG        0 0          0 eth0

netstat -gn:

Code:

IPv6/IPv4 Group Memberships
Interface       RefCnt Group
--------------- ------ ---------------------
lo              1      224.0.0.1
eth0            2      230.0.0.1
eth0            1      224.0.0.251
eth0            1      224.0.0.1
lo              1      ff02::1
eth0            1      ff02::fb
eth0            1      ff02::1:ffa2:998b
eth0            1      ff02::1

Thanks again for your help,

rigor · 03-01-2010, 04:52 PM

Some devices ( switches, gateways, etc. ) are configuring by default to not allow anything through that doesn't have an IP address that is intended for a single host. Hopefully, each of these RHEL machines is the only machine on it's link to the switch. If so, then when you ping the multicast address, how does the behavior of the lights for those links on the switch, differ from the behavior when you ping the specific IP address of the other machine? Does it seem like the switch is receiving the ping for the multi-cast address? Does it seem like the switch is passing on the multi-cast ping to the link connected to the other machine? Also, you might try the ping of the multicast address, with a higher limit for the TTL, or none if the machines are currently isolated from the Internet.

sabre2 · 03-02-2010, 07:51 AM

When I issue a ping –t 1 –c 2 224.0.0.1 I get responses back from other devises, so I assume it’s not the switch.

I will check the link status when I ping a multi cast address.

So generally speaking is the only 2 things that need to be done is add the route and add what I have added to /usr/lib/syslinux/com32/include/netinet/in.h ?

rigor · 03-02-2010, 03:27 PM

I had hoped someone who knows RHEL specific multi-cast configuration would have helped out. I've been trying to help you trouble shoot multi-cast on a general basis because no one with RHEL specific knowledge has, so far. However, on the distro I'm using, I never had to do anything to any headers to get multi-cast working.

I just need to make sure that the interfaces are active, have viable configurations, are multi-cast enabled, that the routing is applicable, that each machine is a member of the same multi-cast group, that there are no iptables rules preventing communication, and that no active device between them is preventing communication. The output of the commands I asked you to run, seem to confirm that you've done that, apart from iptables. I thought you verbally confirmed that there are no iptables rules on the two machines that would prevent communication between them.

Since you got responses from other devices plural,it sounds like either your switch will forward multi-cast traffic, or it doesn't know the packets are multi-cast traffic. In fact, it sounds like you have multi-cast working if you got responses from more than one device for a single ping. So if the machine you want to respond, still isn't, it seems like it's some other problem. But if the switch does not know that it's multi-cast traffic, if you did the ping before everything was fully configured and other machines responded, the switch might have stopped sending packets to the devices that didn't response. If it's a type of switch you can configure, you could check the configuration, etc. If not, about the only further suggestion I have is, power the switch down for perhaps 10 or more seconds and try the ping again after you turn on the switch.

sabre2 · 03-02-2010, 04:25 PM

Awesome. Thanks, You have given me enough to forge ahead on.

Thanks again,

paccopp · 02-24-2012, 11:27 AM

Quote:

Originally Posted by sabre2

Awesome. Thanks, You have given me enough to forge ahead on.

Thanks again,

Ok I'm troubleshooting the same problem and I have run tcpdump on both machines and also connected them with a crossover cable.

Machines can see the multicast ping, but do not reply for whatever reason back.
Have you found out something more in your case?

jschiwal · 02-24-2012, 06:39 PM

You are adding to a 2 year old thread, so don't expect the same users to notice. Please repost your question in a new thread and incorporate the items from this thread that you have tried. I'm going to close this thread so people don't report your new thread as a duplicate.