Questions[ifconfig](server)

The problem

The ifconfig command shows more and more dropped packets in the RX section. So, there seem to be a problem to some packets arriving from the Internet to my server.

The questions

1. What kind of packets does this drop counter takes into account? Does it take all packets arriving, before reaching the iptables firewall, or after the packets have been accepted by iptables?

2. How to solve the situation so that the ipconfig drop packets counter stops to increase?

Useful troubleshooting infos

Since I don't know what my problem really is, feel free to ask me to complete this section if you think some other info would be needed.

ifconfig

eth0      Link encap:Ethernet  HWaddr 00:cc:cc:cc:cc:cc  
          inet adr:90.0.0.2  Bcast:90.0.0.255  Masque:255.255.255.0
          adr inet6: fe80::21c:c0ff:feb9:829c/64 Scope:Lien
          adr inet6: 2001:a100:1:bbbb::1/64 Scope:Global
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:113264620 errors:0 dropped:2523 overruns:0 frame:0
          TX packets:168526529 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 lg file transmission:1000 
          RX bytes:59171827564 (55.1 GiB)  TX bytes:223993117711 (208.6 GiB)

Note the "dropped:2523" in the RX section. This is the most important. This number is continuously increasing.

ip -4 route show

default via 90.0.0.254 dev eth0 
90.0.0.0/24 dev eth0  proto kernel  scope link  src 90.0.0.2

ip -6 route show

2001:a100:1:bbbb::1/64 dev eth0  proto kernel  metric 256 
fe80::/64 dev eth0  proto kernel  metric 256 
default via 2001:a100:1:bbff:ff:ff:ff:ff dev eth0  metric 1024

munin graph of plugin if_err_eth0_day

I'm sure this has been asked and answered before, but I wasn't able to find it, so hopefully this will at least link someone to the right place.

I want to find out my local interface and ip address used to reach a certain host. For instance, if I had 3 adapters connected to my box and they all three went to different networks, I'd like to know which of the three (specifically, its ip address) is used to reach my.local.intranet (in this case, it would be a vpn tunnel interface). I suspect this is a job for ifconfig or traceroute, but I haven't been able to find the correct switches.

I'm running OSX 10.7 (Darwin)

EDIT: For easy access, This is what I ended up writing to get the trick done:

ifconfig `route get <host> | grep "interface: " | sed "s/[^:]*: \(.*\)/\1/"` | grep "inet " | sed "s/.*inet \([0-9.]*\) .*/\1/"

Any improvements / optimizations are welcome.

I haven't found a really clear definition about what a 'carrier error' is within the context of the ifconfig output for a interface. I have been searching on Google and there really isn't a great definition, or list of issues that cause this.

I am assuming from the context, that this means something about the Ethernet signal is bad. I suspect something about the interconnecting cable, or the network interface/port is causing this problem?

I hardly ever see this counter changing, but a client contacted me this morning and mentioned network issues. The carrier counter is increasing by about 200 each second. They had recently made some modifications to the equipment connecting to the Linux box I manage. I would like to be able to give them some more specific details about what may be causing the problem, other then saying, something you changed is broke.

eth0      Link encap:Ethernet  HWaddr 00:1b:21:f3:ea:ae  
          inet addr:172.16.0.9  Bcast:172.16.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:13386121 errors:0 dropped:0 overruns:0 frame:0
          TX packets:21255715 errors:1701 dropped:0 overruns:0 carrier:1031707
          collisions:1313642 txqueuelen:1000 
          RX bytes:2467874046 (2.2 GiB)  TX bytes:3820141165 (3.5 GiB)

So what is it a 'carrier error', and what are the typical problems that cause it.

On CentOS I no longer have a ifcfg-eth0 configuration file (I deleted it). When I run system-configure-network it shows no interfaces that I can edit. How can I recreate the ifcfg-eth0 configuration file? (Like the CentOS installer does)

I can manually do a: ifconfig eth0 192.168.0.199 and then a ping 192.168.0.1. But that's not the proper way. How can I do it using the CentOS network scripts?

I prefer not to do this by hand as there are many hardlinks and confusing stuff. I am new to CentOS.

I'm seeing network problems with a (RHEL) node (packets dropped), which also seem to manifest themselves by a non-zero count of the 'error' and 'frame' fields in ifconfig output:

eth2      Link encap:Ethernet  HWaddr xx:xx:xx:xx:xx:xx  
          ...
          RX packets:277593775 errors:1049 dropped:0 overruns:0 frame:536

Is there a detailed description somewhere what the exact meaning of 'errors' and 'frame' is ?

EDIT: output of ethtool eth2:

Settings for eth2:
        Supported ports: [ TP ]
        Supported link modes:   10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/Full 
                                1000baseT/Full 
        Supports auto-negotiation: Yes
        Advertised link modes:  10baseT/Half 10baseT/Full 
                                100baseT/Half 100baseT/Full 
                                1000baseT/Full 
        Advertised auto-negotiation: Yes
        Speed: 1000Mb/s
        Duplex: Full
        Port: Twisted Pair
        PHYAD: 0
        Transceiver: internal
        Auto-negotiation: on
        Supports Wake-on: umbg
        Wake-on: d
        Current message level: 0x00000007 (7)
        Link detected: yes