Hello List, Due to a problem with CentOS 5 and one of our firewalls I am having to disable tcp window scaling to stop network connections grinding to a halt. I am also trying to Kickstart CentOS 5 machines through the firewall so need to disable window scaling at install time. I have added to the kickstart file %pre echo 0 > /proc/sys/net/ipv4/tcp_window_scaling But the install still hangs while transferring the stage2.img Should the above %pre work or do I need to do something else to disable window scaling during the install. In case anyone's interested CentOS 5 is the first time we have suffered this problem both CentOS 3&4 worked without issue. Thanks Dean
On Thu, May 10, 2007 at 06:34:54PM +0100, Plant, Dean wrote:> Hello List, > > Due to a problem with CentOS 5 and one of our firewalls I am having to > disable tcp window scaling to stop network connections grinding to a > halt. I am also trying to Kickstart CentOS 5 machines through the > firewall so need to disable window scaling at install time. > > I have added to the kickstart file > > %pre > echo 0 > /proc/sys/net/ipv4/tcp_window_scaling > > But the install still hangs while transferring the stage2.img > > Should the above %pre work or do I need to do something else to disable > window scaling during the install. > > In case anyone's interested CentOS 5 is the first time we have suffered > this problem both CentOS 3&4 worked without issue.Weird issue. Haven't seen anyone else have it (at least on this list). Can you switch over to your shell console when the hang happens and examine the value of tcp_window_scaling to see if maybe it gets reset somehow? I believe %pre should work.... Ray
Ray Van Dolson wrote:> On Thu, May 10, 2007 at 06:34:54PM +0100, Plant, Dean wrote: >> Hello List, >> >> Due to a problem with CentOS 5 and one of our firewalls I am having >> to disable tcp window scaling to stop network connections grinding >> to a halt. I am also trying to Kickstart CentOS 5 machines through >> the firewall so need to disable window scaling at install time. >> >> I have added to the kickstart file >> >> %pre >> echo 0 > /proc/sys/net/ipv4/tcp_window_scaling >> >> But the install still hangs while transferring the stage2.img >> >> Should the above %pre work or do I need to do something else to >> disable window scaling during the install. >> >> In case anyone's interested CentOS 5 is the first time we have >> suffered this problem both CentOS 3&4 worked without issue. > > Weird issue. Haven't seen anyone else have it (at least on this > list). > > Can you switch over to your shell console when the hang happens and > examine the value of tcp_window_scaling to see if maybe it gets reset > somehow? I believe %pre should work.... >Weird... Tell me about it, I spent a lot of time head scratching trying to figure out why network connections would just mysteriously hang. Eventually found reference to a problem with tcp_window_scaling and firewalls and after disabling tcp_window_scaling on my test CentOS 5 box, everything started working. The install does not get far enough for the shell console to be available, it hangs at the transferring stage2.img. Dean
Ray Van Dolson wrote:> On Thu, May 10, 2007 at 07:04:51PM +0100, Plant, Dean wrote: >> Weird... Tell me about it, I spent a lot of time head scratching >> trying to figure out why network connections would just mysteriously >> hang. Eventually found reference to a problem with >> tcp_window_scaling and firewalls and after disabling >> tcp_window_scaling on my test CentOS 5 box, everything started >> working. >> >> The install does not get far enough for the shell console to be >> available, it hangs at the transferring stage2.img. >> > > Ah, probably before %pre even has run (?) Well you could rebuild the > kernel on the install CD to disable window scaling by default. :) Ok, > not a particularly useful option... maybe someone else will have a > suggestion. > > In HP-UX you can pass kernel parameters at boot-time, I wonder if > anything similar could be done? Probably not. > > Have you captured a tcpdump of what happens when the "freeze" occurs > with an intermediary system? Maybe a setting could be changed on your > switch? Although I would doubt the switch would be a factor. Are > your packets going through an intermediary router? > > I plan to do some network installs of CentOS 5 soon, will be > interesting to see if this issue occurs. >I don't think this is a issue with CentOS/RHEL. The kickstart in this instance is passing through a firewall appliance, which I think is Open/FreeBSD based and we now believe is breaking tcp window scaling. It seems that CentOS3&4 was unaffected by this but with v5 network connections hang after transferring about 500k. On a network that does not pass through this firewall v5 works as expected. Dean