[RESOLVED] CentOS 6 - Problems with Multicast

Issues related to configuring your network
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jvdimas
Posts: 3
Joined: 2011/12/01 01:01:39

[RESOLVED] CentOS 6 - Problems with Multicast

Post by jvdimas » 2011/12/01 01:16:43

Hi All,

I have a server with two network interfaces, eth0 and eth1. I need to subscribe to and then receive packets from a multicast group on eth1.

Until recently the server was running Ubuntu 10.04 which had no problems receiving the multicast data. For a number of reasons I needed to make the switch to CentOS. I installed CentOS on the original server and there were no changes made to routers or network structure. However, I now can't receive the multicast packets and I can't figure out what's going on. I've tried everything I can think of and am open to all suggestions.

ifconfig:
[quote]
eth0 Link encap:Ethernet HWaddr 00:15:17:4A:99:A2
inet addr:x.x.x.x Bcast:10.255.255.255 Mask:255.255.255.0
inet6 addr: xxxx::xxxx::xxxx::xxxx:xxxx/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:27654 errors:0 dropped:0 overruns:0 frame:0
TX packets:11900 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:23427898 (22.3 MiB) TX bytes:1328983 (1.2 MiB)
Interrupt:16 Memory:fdac0000-fdae0000

eth1 Link encap:Ethernet HWaddr 00:15:17:4A:99:A3
inet addr:y.y.y.y Bcast:10.145.60.255 Mask:255.255.255.0
inet6 addr: yyyy::yyyy::yyyy::yyyy::yyyy/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:3679 errors:0 dropped:0 overruns:0 frame:0
TX packets:971 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:338804 (330.8 KiB) TX bytes:1359289 (1.2 MiB)
Interrupt:17 Memory:fda80000-fdaa0000

lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:24 errors:0 dropped:0 overruns:0 frame:0
TX packets:24 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:7266 (7.0 KiB) TX bytes:7266 (7.0 KiB)
[/quote]

netstat -rn
[quote]
Destination Gateway Genmask Flags MSS Window irtt Iface
y.y.y.0 * 255.255.255.0 U 0 0 0 eth1
z.z.z.0 y.y.y.1 255.255.255.0 UG 0 0 0 eth1
x.x.x.0 * 255.255.255.0 U 0 0 0 eth0
link-local * 255.255.0.0 U 0 0 0 eth0
link-local * 255.255.0.0 U 0 0 0 eth1
224.0.0.0 * 240.0.0.0 U 0 0 0 eth1
default x.x.x.1 0.0.0.0 UG 0 0 0 eth0
[/quote]

After starting the application I want to subscribe to multicast on through netstat -gn I see that the kernel thinks I'm registered to receive packets from the IP address I want. In addition, I've used tcpdump to see that the IGMP packets are sent. However, I then get nothing. I've verified that other people on the local network are receiving multicast packets from the same servers I want to connect to. (These are other datacenter customers so I can't directly talk to them to see what they've done.)

Any ideas here? I've updated to the CR repo and tried downgrading IGMP to v2. Is there some reason the default behavior would be different in CentOS vs Ubuntu on something as fundamental as this? Any further places I should be configuring?

Appreciate the help

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vonskippy
Posts: 839
Joined: 2006/12/30 03:00:04
Location: Western Slope Colorado

[RESOLVED] CentOS 6 - Problems with Multicast

Post by vonskippy » 2011/12/01 04:33:27

Are you sure the Network Interfaces are up? Can you ping IP's in your LAN, can you ping IP's external your router?

Is IPTABLES running? If so, try disabling that and see if you can get IGMP packets

jvdimas
Posts: 3
Joined: 2011/12/01 01:01:39

Re: CentOS 6 - Problems with Multicast

Post by jvdimas » 2011/12/01 05:06:49

I'm positive the network interface eth1 is up. I can ping the gateway and connect to other servers over the interface including those outside of my subnet. (But no multicast connections work.)

iptables was running, but shutting it down did not change anything in regards to IGMP and multicast. I hadn't thought of looking into if the local firewall was messing things up.

I did notice that I'm now sending IGMP v2 membership join requests, but I'm unsure of when this change happened. (I had forced version 2 earlier but /proc/sys/net/ipv4/conf/eth1/force_igmp_version is now set at 0, the "auto" value.) It may have happened when I added the CR package and updated. I'm now running kernel version 2.6.32-131.17.1.el6.x86_64.

Thanks for the suggestions.

the_nev
Posts: 1
Joined: 2011/12/22 16:28:53

Re: CentOS 6 - Problems with Multicast

Post by the_nev » 2011/12/22 16:37:18

We had a similar issue, seems like reverse port forwarding behavour has changed in EL6

https://www.redhat.com/archives/rhelv6-list/2011-January/msg00080.html

[code]
echo 2 > /proc/sys/net/ipv4/conf/eth0/rp_filter
echo 2 > /proc/sys/net/ipv4/conf/eth1/rp_filter
echo 2 > /proc/sys/net/ipv4/conf/eth2/rp_filter
[/code]
also modify /etc/sysctl.conf

# Controls source route verification (previously 1)
net.ipv4.conf.default.rp_filter = 2


Thanks,

Mike

jvdimas
Posts: 3
Joined: 2011/12/01 01:01:39

[Solved] CentOS 6 - Problems with Multicast

Post by jvdimas » 2012/01/12 05:35:31

[quote]
the_nev wrote:
We had a similar issue, seems like reverse port forwarding behavour has changed in EL6

https://www.redhat.com/archives/rhelv6-list/2011-January/msg00080.html

[code]
echo 2 > /proc/sys/net/ipv4/conf/eth0/rp_filter
echo 2 > /proc/sys/net/ipv4/conf/eth1/rp_filter
echo 2 > /proc/sys/net/ipv4/conf/eth2/rp_filter
[/code]
also modify /etc/sysctl.conf

# Controls source route verification (previously 1)
net.ipv4.conf.default.rp_filter = 2


Thanks,

Mike[/quote]

I just came here to post that I had resolved the problem by...doing exactly this. I should have checked back sooner! Thanks for the help everyone.

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AlanBartlett
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Re: [RESOLVED] CentOS 6 - Problems with Multicast

Post by AlanBartlett » 2012/01/12 19:43:17

Thank you for reporting back.

For posterity (and on your behalf) this thread is now marked [RESOLVED].

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