very slow network

Issues related to configuring your network
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weslowsk
Posts: 53
Joined: 2008/04/09 04:45:34
Location: Canada

very slow network

Post by weslowsk » 2017/07/16 19:35:36

I recently installed Centos 7.3 minimal on an old PC I have (about 10 years old) at home. I'm having some problems with networking, though.
It seems that all networking is slow through the wired ethernet connection in the PC.
I first thought that it was a yum issue because yum was timing out trying to connect to mirrors. I didn't think that all mirrors were slow, so I tried just using curl to download some large test files off of the internet and I got the same behaviour.
The behaviour I noticed when using curl is that the file will not start downloading for several seconds and then when it does, it doesn't stay at a constant speed and it frequently stops before resuming the dismal speed. By dismal, I mean anywhere from 0 to 25kbps. This is way less than what every other device on my network gets (10Mbps).
I've tried disabling ipv6 and changing the DNS server that the PC uses and neither change seems to make a difference.
Ping and DNS seems to work fine by the way.

The PC is inside my LAN and the router uses DHCP to assign IPs and DNS addresses. I have several other devices inside my network and they all work fine, so I don't think I have anything misconfigured on my router.

Since I have the minimal installation, I have limited tools at my disposal for debugging what the problem might be...I would normally get whatever tools I needed using yum but extremely slow updates through yum is just another symptom of the problem.

Any advice on what I can try to figure out my networking problem?

weslowsk
Posts: 53
Joined: 2008/04/09 04:45:34
Location: Canada

Re: very slow network

Post by weslowsk » 2017/07/17 04:40:50

After playing around with it, I found out that the reason I was getting slow speeds was because there was a conflict with duplex/speeds on the network.
By default, my NIC sets itself to speed 100 full duplex. But, for it work on my network, I need it to be speed 10. Once I changed that:

Code: Select all

ethtool -s enp0s25 speed 10 duplex full
I started getting normal speeds. The only thing left is to persist that change across restarts...I haven't been able to figure out how to do that.

According to some documentation I've read, this should be possible by adding:

Code: Select all

ETHTOOL_OPTS="autoneg off speed 10 duplex full"
to the /etc/sysconfig/network-scripts/ifcfg-enp0s25 file.
After restarting, it doesn't change the speed to 10.

Any ideas how I get my ethtool command to persist across restarts?

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