Re: Network suddenly stopped working

[Michael Lange <klappnase@freenet.de>]

Hi,
On Mon, 12 Jul 2021 13:32:48 +0300
Reco <recoverym4n@enotuniq.net> wrote:

(...)
> does not add up.
> 
> If, for some reason, an interface name had changed - you won't see
> "enp2s0" in the ifconfig output.

thanks for the clarification.

> 
> 
> > some sources I found suggest to look at
> > /etc/udev/rules.d/70-persistent-net.rules but there is nothing in that
> > file that is not commented out, so I guess that this mechanism may be
> > outdated.
> 
> It is outdated, and that file should not be present at all.

Ok, thanks.

(...)
> Troubleshooting steps:
> 
> 1) Obtain tcpdump unless it's installed already.
> 2) As root, run "tcpdump -pni any udp port 67 or udp port 68", and let
> it run for a while.
> 3) As root, run "dhclient enp2s0".
> 4) Wait for a minute or so, terminate both tcpdump and dhclient.
> 5) Post the output of steps 2 and 3, plain text preferred, add an output
> of "ip a" for a good measure please.

Ok, here is what I get:

# tcpdump -pni any udp port 67 or udp port 68
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on any, link-type LINUX_SLL (Linux cooked), capture size 262144 bytes
12:45:25.021291 IP 192.168.178.1.67 > 192.168.178.27.68: BOOTP/DHCP, Reply, length 548
12:45:40.099508 IP 192.168.178.1.67 > 192.168.178.27.68: BOOTP/DHCP, Reply, length 548
12:45:59.837396 IP 192.168.178.1.67 > 192.168.178.27.68: BOOTP/DHCP, Reply, length 548
12:45:59.839837 IP 192.168.178.1.67 > 192.168.178.27.68: BOOTP/DHCP, Reply, length 548
12:46:04.723115 IP 192.168.178.1.67 > 192.168.178.27.68: BOOTP/DHCP, Reply, length 548
12:46:04.725104 IP 192.168.178.1.67 > 192.168.178.27.68: BOOTP/DHCP, Reply, length 548
12:46:42.878014 IP 192.168.178.1.67 > 192.168.178.27.68: BOOTP/DHCP, Reply, length 548
12:47:00.290058 IP 192.168.178.1.67 > 192.168.178.27.68: BOOTP/DHCP, Reply, length 548
12:47:23.566465 IP 192.168.178.1.67 > 192.168.178.27.68: BOOTP/DHCP, Reply, length 548
12:47:55.826397 IP 192.168.178.1.67 > 192.168.178.27.68: BOOTP/DHCP, Reply, length 548
^C
10 packets captured
10 packets received by filter
0 packets dropped by kernel

# dhclient enp2s0
RTNETLINK answers: File exists

(this command always returns immediately; when I enter it a new entry to
the tcpdump output is added)

# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp2s0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 50:e5:49:d8:51:94 brd ff:ff:ff:ff:ff:ff
    inet 192.168.178.27/24 brd 192.168.178.255 scope global dynamic enp2s0
       valid_lft 863861sec preferred_lft 863861sec
    inet6 fe80::52e5:49ff:fed8:5194/64 scope link 
       valid_lft forever preferred_lft forever

Does that tell something?

Regards

Michael