[AusNOG] Strange broadcast behaviour on linux 2.6.32 - riddle me this
Beeson, Ayden
ABeeson at csu.edu.au
Tue Apr 8 16:46:19 EST 2014
Yeah that definitely looks like a kernel bug or software bug with the network apps, check for an update, if you can't find one I would log a bug with centos / RHEL themselves and allow them to escalate it upstream, be prepared to provide a LOT of information though as part of the bug process :)
Thanks,
Ayden Beeson
From: AusNOG [mailto:ausnog-bounces at lists.ausnog.net] On Behalf Of Joshua D'Alton
Sent: Tuesday, 8 April 2014 2:12 PM
To: Shannon Gernyi
Cc: ausnog at lists.ausnog.net
Subject: Re: [AusNOG] Strange broadcast behaviour on linux 2.6.32 - riddle me this
Saw similar on an install of Centos 6.4, just figured it was the datacenters rolled version, as it went away when I booted into the OpenVZ kernel I installed on the server. Never saw it again after that.
On Tue, Apr 8, 2014 at 2:32 PM, Shannon Gernyi <shannon.gernyi at xsv.com.au<mailto:shannon.gernyi at xsv.com.au>> wrote:
Hey all,
I have a few boxen running CentOS 6.5 in a very vanilla install.
I ran into some weird behaviour that I couldn't get to the bottom of, and whilst a reboot "fixed" it, I'm not going to be able to sleep at night without asking the question, so riddle me this:
Box A is on a private network:
eth0 172.27.3.111/24<http://172.27.3.111/24>
I'm have a requirement to broadcast on eth0, however, the box isn't sending said broadcast packets to the ethernet broadcast mac - it's sending out ARP requests for 172.27.3.255 instead.
12:49:44.129501 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:49:45.129494 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:49:46.129494 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:49:48.132491 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:49:49.132488 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:49:50.132491 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:49:52.135503 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:49:53.135486 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:49:54.135513 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:49:56.139497 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:49:57.139491 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:49:58.139494 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:50:00.131503 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:50:01.131490 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:50:02.131495 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:50:04.134495 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:50:05.134487 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:50:06.134490 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:50:08.137499 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:50:09.137488 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
eth0 is definitely configured correctly regarding network/mask:
eth0 Link encap:Ethernet HWaddr REMOVED
inet addr:172.27.3.111 Bcast:172.27.3.255 Mask:255.255.255.0
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:227898706 errors:0 dropped:0 overruns:0 frame:0
TX packets:219816363 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:59578359175 (55.4 GiB) TX bytes:145429518480 (135.4 GiB)
Interrupt:245
arp output confirms the above dump:
arp -n
Address HWtype HWaddress Flags Mask Iface
172.27.3.255 (incomplete) eth0
And finally, manually adding the IP to the arp table with a destination of ethernet broadcast (ie, where the frames should be directed anyway) made things work:
arp -s 172.27.3.255 ff:ff:ff:ff:ff:ff
12:56:30.232505 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:56:31.232506 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:56:32.232496 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:56:34.235510 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:56:35.235505 ARP, Request who-has 172.27.3.255 tell 172.27.3.111, length 28
12:56:36.042743 IP 172.27.3.111.53957 > 172.27.3.255.ha-cluster: UDP, length 225
12:56:36.236321 IP 172.27.3.111.53957 > 172.27.3.255.ha-cluster: UDP, length 246
12:56:36.236353 IP 172.27.3.111.53957 > 172.27.3.255.ha-cluster: UDP, length 225
12:56:38.238098 IP 172.27.3.111.53957 > 172.27.3.255.ha-cluster: UDP, length 225
Now, I can't go back and debug further, but if anyone has seen this or similar behaviour before - please share possible explanations. It's doing my head in!
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