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Old 12-22-2006, 03:39 AM   #1
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NOOB - DNS latency on FC6 - seems to "hang" eth0 at random intervals? How to fix?

Hi guys

I have a problem with FC6 apparently as regards DNS queries. I've already disabled IPV6, but I get latencies of up to a minute when trying to do DNS lookups at random intervals. This times out most of my internet programs, interrupts any running downloads / uploads, and makes my system unavailable for minutes at a time on my LAN.

Strangest thing is that sometimes it works for up to half an hour or more straight, then suddenly for about a minute I have no access to the network.

My machine's ip is and my router is

Here's my /etc/sysconfig/network:



order hosts,bind
multi on


option timeout:1

modprobe.conf lines to remove IPV6 stack:

alias ipv6 off
alias net-pf-10 off


[root@StefanLinux ~]# ifconfig
eth0 Link encap:Ethernet HWaddr 00:16:E6:5D:F3:65
inet addr: Bcast: Mask:
RX packets:848 errors:0 dropped:0 overruns:0 frame:0
TX packets:856 errors:0 dropped:277 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:579256 (565.6 KiB) TX bytes:218654 (213.5 KiB)
Interrupt:177 Base address:0x9000

lo Link encap:Local Loopback
inet addr: Mask:
RX packets:113 errors:0 dropped:0 overruns:0 frame:0
TX packets:113 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:10977 (10.7 KiB) TX bytes:10977 (10.7 KiB)

I use FC6 under a custom kernel with CIFS filesystem support compiled in. My NIC is a

03:00.0 Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168B PCI Express Gigabit Ethernet controller (rev 01)

(according to lspci). I download a driver in a file called


from RealTek's website, compiled and installed this and is using it to interface to the NIC.

An interesting thing I noticed is that calling "route" in a terminal results in

[root@StefanLinux ~]# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface * U 0 0 0 eth0

(i. e. "route" does not return and freezez for up to a minute before finishing and showing the "gateway" line) while I am "hung" on DNS. If I am not, at that moment "hung" on DNS, it returns almost immediately:

[root@StefanLinux ~]# route
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface * U 0 0 0 eth0
default UG 0 0 0 eth0
[root@StefanLinux ~]#

However, running "route -n" at any time, returns immediately, regardless of whether I have a DNS "hang" at that moment or not:

[root@StefanLinux ~]# route -n
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface U 0 0 0 eth0 UG 0 0 0 eth0
[root@StefanLinux ~]#

The only way I have found to "un-hang" eth0 while this DNS thing is manifesting is by completely upping and downing the interface:

route del default
/sbin/ifconfig eth0 down

and then

/sbin/ifconfig eth0 netmask broadcast up

route add default gw netmask eth0

but I have to do the above over and over and over (up to five times a minute or more) to get a continuity in my box's LAN connection. And then it works only for a few seconds at most, before "hanging" again. Any people browsing pages over the LAN served by my FC6 box of course have extreme problems as, from a browser's perspective, it seems to lock up for minutes at a time on HTTP requests... I can't download large files, or upload large files, etc. etc. Distressing.

Anybody in here got a clue how I can get my FC6 machine NOT to apparently
make these minute-long DNS queries? The craziest thing is that now, if my
internet connection is off (I, for example, switch off the router) NOTHING
works on my FC6 machine as regards eth0. It can't even ping other
machines on my LAN, for which I most definitely NOT need a working router!

ANY idea as to how to fix this will certainly help a LOT!


Last edited by rylan76; 12-22-2006 at 03:50 AM.
Old 12-22-2006, 05:07 AM   #2
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