Q. about dropped packets

English Network/Internet
1

Hello guys,

if i call ifconfig, i see:


linux131:/var/log # ifconfig eth0
eth0      Link encap:Ethernet  Hardware Adresse 80:EE:73:28:21:F3  
          inet Adresse:192.168.0.13  Bcast:192.168.0.255  Maske:255.255.255.0
          UP BROADCAST RUNNING  MTU:1500  Metric:1
          RX packets:38806 errors:0 dropped:12345 overruns:0 frame:0
          TX packets:30128 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 Sendewarteschlangenlänge:1000 
          RX bytes:40079134 (38.2 Mb)  TX bytes:3355248 (3.1 Mb)

RX dropped:12345

Who dropped the incomming packets and why?
NIC is intel 82579V, 1Gbit
Cableing is very fine.

What about :


linux131:/var/log # sysctl -a | egrep -i '(rmem|wmem|tcp_mem)'
net.core.rmem_default = 212992
net.core.rmem_max = 212992
net.core.wmem_default = 212992
net.core.wmem_max = 212992
net.ipv4.tcp_mem = 758217       1010958 1516434
net.ipv4.tcp_rmem = 4096        87380   6291456
net.ipv4.tcp_wmem = 4096        16384   4194304
net.ipv4.udp_rmem_min = 4096
net.ipv4.udp_wmem_min = 4096

Does the kernel drop the packets cause they’re coming to fast and i have to set these values higher?

If i run ‘systemctl isolate rescue.target’ and start the network with ‘service network start’ i have also dropped packets.
So, it cannot be a service like sshd or samba.

This is in all versions since kernel 3.x

Best regards

2

I wouldn’t be too concerned with dropped packets unless you experience noticeable network latency. Your network might be setup with several machines and in a Workgroup for example which uses broadcasts to communicate and self-manage machines instead of setting up a Domain typically with some designated authenticator, DHCP and DNS (possibly also a NBNS) so instead of broadcasts your machines would be using directed connections.

The reason why broadcasts cause dropped packets is that a broadcast is sent to all machines on the network segment when the machine doesn’t know how to find a specific machine (again, because your network isn’t setup with a central directory of all machines like DNS or a NBNS). Only one machine will acknowledge as the intended target, all other machines on the network will drop the packets.

If you’re curious about the content and maybe confirm most if not all the dropped packets are broadcasts, you can install Wireshark to view a packet capture.

TSU

3

To add to what Tsu is saying, rx_dropped now includes things like Unintended/Broken VLAN tags, IPv6 if your system doesn’t support it and protocols that are unrecognised.

So it can be caused by those mentioned above by him and these as well.

4

And not to forget, as someone told me last night:

  • the old ipx causes dropped packets
  • old netbeui/netbios causes dropped packets

I should not change the target/servers config, i should changes the source computers
to avoid dropped packets.
NIC is Intel 82579V or Relatek 8169, newer drivers from Intel (3.0.4) causes less
dropped packets

Best regards.