Rubin Shrestha
Rubin Shrestha
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Network on Linux refuses to get IPv6 address from DHCP and extremely low bandwidth

by |Published

TL;DR;

  • Linux (Debian, Debian Testing, Fedora, Ubuntu Server) refuses to obtain the defined IPv6 address but does obtain the correct IPv4

  • Network extremely slow

  • All of this was working 100% fine, literally two days ago with my previously installed Debian Testing

  • Other computers connected to the same network, work perfectly

The full story

For a while I was running Debian Testing on my server (L1) at home. But I thought that going to Debian Stable would be a good idea.

So initially, with that Debian Testing everything worked well.

Then I installed Debian Stable, Ubuntu Server, Fedora Server and….Debian Testing again.

And for, ANY of those distributions I have the same exact problem.

  1. The network is extremely slow, when I should have 1Gbit/s symmetric

  2. The obtained IPv6 address is NOT the one I set in my router (typical internet box) (Box)

But here’s the kicker, the cable I use to connect L1 to Box, I unplugged it, and connected it to my windows computer (W1). And, in that case -> no problem, Windows obtains the right IPv6 address that I defined for it in Box.

Also when the cable is connected between L1 and Box, I do obtain the correct IPv4 address!

So now, I am EXTREMELY confused.

Technical information

Network interface:

Ethernet controller: Realtek Semiconductor Co., Ltd. RTL8111/8168/8211/8411 PCI Express Gigabit Ethernet Controller (rev 15)

Network on Linux

2: enp4s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:e0:24:75:02:f4 brd ff:ff:ff:ff:ff:ff
    altname enx00e0247502f4
    inet 192.168.1.42/24 brd 192.168.1.255 scope global dynamic noprefixroute enp4s0
       valid_lft 85788sec preferred_lft 85788sec
    inet6 2a02:842a:ccc0:a601:f2f8:ccb7:878b:a2f5/128 scope global dynamic noprefixroute 
       valid_lft 85789sec preferred_lft 85789sec
    inet6 2a02:842a:ccc0:a601:b1c3:b702:772a:2e06/64 scope global dynamic noprefixroute 
       valid_lft 604459sec preferred_lft 604459sec
    inet6 fe80::de52:17af:312e:13e2/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

That address right there 2a02:842a:ccc0:a601:f2f8:ccb7:878b:a2f5 is absolutely not the one I defined in my DHCP.

Negotiated throughput

 sudo ethtool enp4s0
[sudo] password for mrjay: 
Settings for enp4s0:
    Supported ports: [ TP    MII ]
    Supported link modes:   10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
                            1000baseT/Full
    Supported pause frame use: Symmetric Receive-only
    Supports auto-negotiation: Yes
    Supported FEC modes: Not reported
    Advertised link modes:  10baseT/Half 10baseT/Full
                            100baseT/Half 100baseT/Full
                            1000baseT/Full
    Advertised pause frame use: Symmetric Receive-only
    Advertised auto-negotiation: Yes
    Advertised FEC modes: Not reported
    Link partner advertised link modes:  10baseT/Half 10baseT/Full
                                         100baseT/Half 100baseT/Full
                                         1000baseT/Full
    Link partner advertised pause frame use: Symmetric
    Link partner advertised auto-negotiation: Yes
    Link partner advertised FEC modes: Not reported
    Speed: 1000Mb/s
    Duplex: Full
    Auto-negotiation: on
    master-slave cfg: preferred slave
    master-slave status: slave
    Port: Twisted Pair
    PHYAD: 0
    Transceiver: external
    MDI-X: Unknown
    Supports Wake-on: pumbg
    Wake-on: d
    Link detected: yes

Kernel Modules


lsmod | grep r8
r8169                 143360  0
mdio_devres            12288  1 r8169
libphy                188416  3 r8169,mdio_devres,realtek
mdio_bus               69632  3 r8169,libphy,realtek

I have tried A LOT of things: networkd, NetworkManager.

Literally installed other distribs of Linux.

This, I can’t show here, but literally THROUGH THE SAME NETWORK, if I use WiFi, the connection is at normal speed. But with the cable, I am below 500 KB/s

I have tried disabling IPv4 just to see if maybe it was this causing the issue -> nope, it just broke my access to internet. I tried a lot of different

  • Could this be a driver thing? On ALL distribs? It seems that the r8169 is not super good…but it was literally working a few days ago on my Debian Testing!!

  • Did my own Box blacklisted me somehow?

  • Could it be that the network card itself (the device) on my motherboard got damaged somehow? but still works to an extent?

I think I’m gonna install windows on this machine, just to see if the results are the same. If I have the courage to do that -> I’ll come here to update this post.

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