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(?) neighbour table overflow

From Berg Alexander

Answered By Heather Stern

hi,

i have the problem that i have a running terminal-server (booting over net via Root-NFS) system. now we want to add a second subnet to the server, and all should be okay in the config files. BOOTP is working, TFTP is working but the client is not able to mount the root-fs, with the error message "neighbour table overflow"... we also have changed the nfs-server, no luck...

bye

Alexander Berg

(!) [Heather] The message 'neighbor table overflow' is not about your NFS, it's at a lower layer than that.
It means that your arp cache is overflowing because your machine can't tell who is on its own subnet... its neighbors. Which usually means your localhost setup is broken (because lots of applications use networking internal to your machine - which is always on its own subnet, so those packets should never even escape the computer) or, far less commonly, that your netmask for your own external address is wrong.
Sadly, tftp and network booting are things I'm not so familiar with, so perhaps one amongst the rest of The Answer Gang can help tell you where to correct your terminals' localhost setup.
Because this happened when you're adding a new subnet, you may find a need to set up machines on both subnets with ethernet aliases. When properly set up then running ifconfig should result in something like this: 
eth0      Link encap:Ethernet  HWaddr so:me:he:xv:al:ue
          inet addr:192.168.129.15  Bcast:192.168.129.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:5939693 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5971444 errors:0 dropped:0 overruns:0 carrier:0
          collisions:8308 txqueuelen:100
          Interrupt:10 Base address:0xff00

eth0:1    Link encap:Ethernet  HWaddr di:ft:he:xv:al:ue
          inet addr:192.168.64.2  Bcast:192.168.64.255  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          Interrupt:10 Base address:0xff00

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:3924  Metric:1
          RX packets:320906 errors:0 dropped:0 overruns:0 frame:0
          TX packets:320906 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
Best of luck!

note, Alexander put antispam hooks in his address when mailing us, so he never saw his emailed response. We still hope this helps him and others with the dreaded Neighbour Overflow.

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Published in issue 65 of Linux Gazette April 2001
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