Thread: Strange Linux Networking issue:

  1. #1
    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
    Join Date
    Aug 2006

    Strange Linux Networking issue:

    On an embedded system we send an IP address via the kernel command line. This IP address is arbitrary and is there to set a default IP address. These command line parameters are:
    We use an interfaces file that is called by ifup/down. The interfaces file has the following:
    # Configure Loopback
    auto lo eth0
    iface lo inet loopback
    # DHCP on the first ethernet device
    #iface eth0 inet dhcp
    iface eth1 inet dhcp
    # Static interface for the first ethernet interface, comment out the
    # above and uncomment this
    iface eth0 inet static
    Now, here is a shot of ifconfig eth0
    eth0      Link encap:Ethernet  HWaddr 00:60:0C:01:A8:89
              inet addr:  Bcast:  Mask:
              UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
              RX packets:400 errors:0 dropped:0 overruns:0 frame:0
              TX packets:45 errors:0 dropped:0 overruns:0 carrier:0
              collisions:0 txqueuelen:1000
              RX bytes:39171 (38.2 KiB)  TX bytes:4074 (3.9 KiB)
              Interrupt:194 Base address:0x8300 DMA chan:8
    Here is a shot of route -n:
    Kernel IP routing table
    Destination     Gateway         Genmask         Flags Metric Ref    Use Iface   U     0      0        0 eth0   U     0      0        0 eth0       U     0      0        0 lo         UG    0      0        0 eth0
    You may note that BOTH the command line parameter and the interfaces file are used on this network adapter. The really odd thing is that I can ping the device from EITHER network (on my development station I set an IP alias of and I could ping, telnet, and do whatever I wanted with that IP address.

    So, my question is WHAT IS GOING ON HERE???? I have searched the /sys and /proc directories attempting to find the stale information about the IP addresses and can find nothing. I find what I think is the MAC address under /sys but cannot locate anything else.

    My goal is to make it so the interfaces file trumps the command line settings but I don't even understand why/how this is doing this. I didn't even know it was possible to bind two IP addresses to the same interface (not an alias, the SAME interface).

    Any ideas?

  2. #2
    {Jaxom,Imriel,Liam}'s Dad Kennedy's Avatar
    Join Date
    Aug 2006
    I still don't know what the deal is (this seems completely against the kernel binding protocols) but I am able to remove the unwanted IP address without dropping the whole connection. I found that I can execute the command:

    ip address del dev eth0

    and I'll instantly only have as the network address.

    How funky is that!

  3. #3
    Registered User
    Join Date
    Jul 2010
    Can you ping both networks from the same device at the same time? That would be odd.

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