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[SOLVED] Unstable LAN wired connection

Linux Kernel, Network, and Services configuration.
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andoru
Posts: 272
Joined: 2014-03-14 16:59

Re: Unstable LAN wired connection

#21 Post by andoru »

Three more things I've tried:

Restored the BIOS settings to factory defaults.
Disabled IPv6 using this article: https://techrepublic.com/article/how-to ... -on-linux/ (which actually didn't do anything)
Disabled IPv6 from within Network Manager (Edit Connections -> (selected the troublesome connection) -> IPv6 Settings -> Selected "Ignore" from the first drop-down menu

All three of those didn't fix the issue...

shep
Posts: 423
Joined: 2011-03-15 15:22

Re: Unstable LAN wired connection

#22 Post by shep »

Some routers reserve DHCP addresses for clients w/ static IP's and will renew the clients "Static" connection.

When you test the dropped connection by pinging, it is helpful to ping both http://www.google.com and one of Googles DNS servers:
IPV4 8.8.8.8
IPV6 2001:4860:4860::8888
https://developers.google.com/speed/pub ... docs/using

If pinging http://www.google.com fails and 8.8.8.8 works then you have a problem with DNS resolution. Others have reported DNS isssues with IPV6
https://community.spiceworks.com/topic/ ... -with-ipv6

This was my problem with an LEDE flashed router
https://forum.lede-project.org/t/lan-st ... en/2648/20

andoru
Posts: 272
Joined: 2014-03-14 16:59

Re: Unstable LAN wired connection

#23 Post by andoru »

It's not that the pinging doesn't work at all, it's that there are a lot of dropped packets (30%-70%), even when pinging to the router, and on some domains/IPs, it takes over 200ms to send a packet.
Before disabling IPv6 in Network-Manager, I would occasionally get "Network is unreachable" errors while pinging, and when looking at the connection info in NM, the IPv4 addresses wouldn't show up.

DNS resolution, AFAIK, works fine, as I have pinged domain names (debian.org) and it has connected (I don't think you can ping something unless the client knows the IP address, whether or not it has to get it through DNS lookup, or you provide the IP)

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4D696B65
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Re: Unstable LAN wired connection

#24 Post by 4D696B65 »

shep wrote:I'll mention that your problem could be in router rather than your client.
Agreed, I have an isp supplied router/modem that needs to be rebooted once or twice a week or I get 40% packet loss.

andoru
Posts: 272
Joined: 2014-03-14 16:59

Re: Unstable LAN wired connection

#25 Post by andoru »

I've previously tried rebooting the router, and that didn't solve anything either... ugh. :evil:
I'd hate to send back this machine, only for them to return it back to me, saying there's nothing wrong with the NIC and asking me to pay for shipping...

p.H
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Re: Unstable LAN wired connection

#26 Post by p.H »

Segfault wrote: I never said (MAC and PCI ID) have same purpose. You said it would be nice to have first 3 bytes to see the manufacturer.
No, I did not say that. I do not care about the manufacturer. Most often the OUI identifies the system manufacturer (HP), not the ethernet controller manufacturer (Intel). Big deal.

FWIW, I just wanted to check that the special bits in the MAC address first byte (unicast/multicast and global/local) were correctly set to 0. Sometimes the MAC address stored in the system NVAM is invalid, or the driver incorrectly reads it, resulting in an invalid MAC address being used, which can cause all kinds of trouble.
andoru wrote:Here's the first three bytes of the address: 3c:d9:2b
So the first two bits are 0. Good.
Segfault wrote:I'm going to read up on IPv6 now.
Check Stateless Address Autoconfiguration (SLAAC), EUI-64 and IPv6 Privacy Extensions.
andoru wrote:Let me know what you want me to look for, and what commands to use.
Use dmesg to print the kernel log buffer.
Look for messages containing the driver name (e1000e), the interface name (eno1), or the PCI bus ID (00:19.0).
andoru wrote:It's weird how it doesn't mention any dropped packets or errors/failures, as I went through a lot of dropped packets and connection timeouts during the session.
How then did you see there were dropped packets ? With ifconfig or ip -s link ?
andoru wrote:DNS resolution, AFAIK, works fine, as I have pinged domain names
You ping an IP address, not a domain name. The destination of an IP packet is an IP address, not a domain name.

A few thoughts.
- There can be variants of a same ethernet controller, and the driver may not work equally with all variants. The situation of Realtek RTL8168 and the kernel driver r8169 comes into mind. However Intel ethernet controllers and drivers have a better status.
- Did you try to disable offload optimizations with ethtool ?
- Did you check the power supply voltages ? An insufficient or flaky voltage could cause erratic behaviour. I think about the +5V stand-by voltage (5VSB) which supplies the ethernet interface for wake-on-LAN. This output is always on even when the system is shut down, so it can wear out faster.
- There can be incompatibilities due to border cases between two ethernet devices. I once used a computer whose ethernet port did not work on one specific wall plug, while it worked on other plugs and other computers worked on this plug. Did you test the computer on another switch port, another switch, another network... ?

andoru
Posts: 272
Joined: 2014-03-14 16:59

Re: Unstable LAN wired connection

#27 Post by andoru »

p.H wrote: How then did you see there were dropped packets ? With ifconfig or ip -s link ?
While pinging the router, and a few domains.
p.H wrote:You ping an IP address, not a domain name. The destination of an IP packet is an IP address, not a domain name.
I know that. What I meant to say was that in order to get the (server) IP address of a domain, the ping tool has to do a DNS look up.
p.H wrote:A few thoughts.
- There can be variants of a same ethernet controller, and the driver may not work equally with all variants. The situation of Realtek RTL8168 and the kernel driver r8169 comes into mind. However Intel ethernet controllers and drivers have a better status.
- Did you try to disable offload optimizations with ethtool ?
- Did you check the power supply voltages ? An insufficient or flaky voltage could cause erratic behaviour. I think about the +5V stand-by voltage (5VSB) which supplies the ethernet interface for wake-on-LAN. This output is always on even when the system is shut down, so it can wear out faster.
- There can be incompatibilities due to border cases between two ethernet devices. I once used a computer whose ethernet port did not work on one specific wall plug, while it worked on other plugs and other computers worked on this plug. Did you test the computer on another switch port, another switch, another network... ?
The last one has finally elucidated why the connection was unstable: it was the cable. I took the machine to the other room where the router is, and used a shorter cable to connect, and it worked flawlessly. It seems that for whatever reason, this NIC doesn't want to play nice with the cable I was using...
I've also read somewhere that somebody had a similar issue with a similar Intel NIC. The user in question said they bought a CAT6 cable, so I guess I'll be doing that now.
Thank you everyone for the help!

andoru
Posts: 272
Joined: 2014-03-14 16:59

Re: [SOLVED] Unstable LAN wired connection

#28 Post by andoru »

Just to give an update, I replaced the previous Cat 5e cable with a Cat 6a S/FTP cable, and it now works a treat!
I thought I'd write this update in case anyone else faces the same problem as I did.

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