Re: [CentOS] Centos 7 as gateway - UDP performance is busted/awful?
On Fri, 15 Aug 2014 09:19:29 -0400 David Both wrote: > I hope this helps. Nah, all the forwarding rules were in place. They all worked before I switched to centos7, and they all worked after I booted the fedora kernel. No sysctl or iptables changes were made when switching from centos to fedora kernel, yet the forwarding started working after booting fedora. I suspect if I backed up to the kernel centos 6.5 uses that would work as well. I betcha someone has a < that should be a <= somewhere in an MTU size check in the centos7 kernel :-). ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
Re: [CentOS] Centos 7 as gateway - UDP performance is busted/awful?
> It is much easier if you use ELRepo's kernel-ml > (http://elrepo.org/tiki/kernel-ml). Does look like a better long term solution, fedora was just a hack for testing :-). > > I guess it is time to make yet another bugzilla account > > and submit a bug... > > Yes, good idea. And here it is: http://bugs.centos.org/view.php?id=7505 ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
Re: [CentOS] Centos 7 as gateway - UDP performance is busted/awful?
I think I have my answer: The kernel is busted (or something isn't loaded that I need, but don't know about :-). I copied my Fedora 20 desktop 3.15.8-200.fc20.x86_64 kernel and /lib/module files to the centos7 KVM host, rebuilt grub.cfg, and rebooted into the 3.15.8-200 kernel, and with no other changes the UDP packet forwarding is now working perfectly. I guess it is time to make yet another bugzilla account and submit a bug... ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
Re: [CentOS] Centos 7 as gateway - UDP performance is busted/awful?
On Thu, 14 Aug 2014 14:09:44 -0500 Les Mikesell wrote: > Seems like a horrible thing to do, but does it fix it if you mount with > rsize=1500, wsize=1500 - or maybe 1484? I already tried that - no change :-). > Are you just bridging to the NIC interface? I don't see why that > would need to change the packets at all. What happens if you ping > with a large -s value through the bridge (host or external box to > guest)? There are two NICs. The one with the bridge is also running a subnet with the virtual machines and one real machine on the NIC. The other NIC is connected to the wider world of our local LAN where the NFS servers reside, so the host has to operate as a gateway for the traffic from the LAN to the virtual machine subnet. I did just try the ping experiment, and on the outer NFS server, if I try to ping the virtual machine with a big size, I get the error about the packet fragmentation: dino> ping -c 1 -s 1500 ubu14d04x PING ubu14d04x.ccur.kvm (192.168.118.52) from 10.134.30.46 : 1500(1528) bytes of data. >From godzilla (10.134.30.124) icmp_seq=1 Frag needed and DF set (mtu = 1500) But weirdly, I don't get that from every machine I try out here on the LAN, some can ping it just fine, others get the error. Whatever I discover just makes me more confused :-). ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
Re: [CentOS] Centos 7 as gateway - UDP performance is busted/awful?
On Thu, 14 Aug 2014 13:35:48 -0500 Les Mikesell wrote: > I thought NFS defaulted to writing 8192 blocks and let the network > stack fragment as needed I think it is those fragments I'm looking at in wireshark. I just did another experiment - If I mount the same NFS filesystem on the centos 7 host, and do the same "ls" command, it works perfectly and the wireshark trace shows the same 1516 capture length for the NFS readdir messages. Somehow it is just the idea of forwarding the UDP packets to the virtual machine that the host objects to. The exact same size packets destined for it to use directly have no problems. ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
Re: [CentOS] Centos 7 as gateway - UDP performance is busted/awful?
> If you look inside the ICMP packet in wireshark, it will tell you > who sent it and what MTU they said was acceptable. Well, I'm definitely drowning in network confusion here :-). Everyone's MTU is the default 1500, I checked all systems in the path. The wireshark display says 1516 in the Length column for the NFS packet that always shows up before the ICMP errors. If I expand the "IP V4" line in the packet, it says "Total Length: 1500" for that READDIRPLUS Reply which says 1516 for the capture length. It also has the "Don't fragment" flag set. It looks like the 16 byte extra is confusing it, but I have no idea why that is different than the IPv4 length info. ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
[CentOS] Centos 7 as gateway - UDP performance is busted/awful?
I just replaced a dead system disk on my KVM host that was running an ancient fedora 13. Since centos 7 was available, I decided to go with it to get some long term stability. The problem is that NFS mounts inside the virtual machines don't work for spit when talking to older NFS servers that must speak UDP. Is there something about UDP traffic that requires tweaks I don't know about for centos 7 to serve as a gateway machine? I've got the ip forwarding settings and other sysctl stuff that was set in the old fedora 13 system. I've got the bridges defined that same way as the old f13 system. I've got TCP stream connections working flawlessly, it is just the UDP traffic that seems to barf. Does this strike a familiar note with anyone? When I run wireshark on the KVM host machine, I see NFS packets retransmitting a lot and I also see ICMP messages about Destination Unreachable, Fragmentation Needed. (I don't know what any of it means though :-). This is an intel motherboard with these ethernets: 04:00.0 Ethernet controller: Intel Corporation 80003ES2LAN Gigabit Ethernet Controller (Copper) (rev 01) 04:00.1 Ethernet controller: Intel Corporation 80003ES2LAN Gigabit Ethernet Controller (Copper) (rev 01) ___ CentOS mailing list CentOS@centos.org http://lists.centos.org/mailman/listinfo/centos
