Skrevet av Emne: Linux: NAT slowness/instability  (Lest 2197 ganger)

ATC

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Linux: NAT slowness/instability
« på: 27. ſeptember 2008, 18:24 pm »
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  • After introducing a NAT router in the network, separating servers and clients, several odd problems appeared:

    - Web browsing sometimes appeared to hang, large images would usually fail.

    - FTP browsing would work OK but large file transfers would slow down and usually fail.

    - SMB exhibited weird behaviour, like shares suddenly becoming unavailable, read errors and frequent lock-ups.



    ATC

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    [Solved] Linux: NAT slowness/instability
    « Svar #1 på: 27. ſeptember 2008, 18:24 pm »
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  • After going through all the usual troubleshooting of possible firewall problems, we noticed something unusual about the ifconfig output on one of the interfaces:

    eth2      Link encap:Ethernet  HWaddr 00:05:5D:10:52:BC  
              inet addr:#.#.#.#  Bcast:85.95.37.255  Mask:255.255.255.0
              BROADCAST MULTICAST  MTU:1500  Metric:1
              RX packets:4397856 errors:0 dropped:732 overruns:0 frame:0
              TX packets:3597942 errors:0 dropped:0 overruns:0 carrier:3589674
              collisions:0 txqueuelen:1000
              RX bytes:3756826843 (3582.7 Mb)  TX bytes:437463838 (417.1 Mb)
              Interrupt:9 Base address:0xcc00


    The "carrier" value should normally be 0 or very close to 0. The number would increase by about 1-5 per second during low traffic, high traffic would increment the counter by several hundred per second.

    A google for the actual meaning of this value showed nothing, but the name and context suggests some kind of transmission problem. Replacing the cable and trying a different switch port did not have any effect.

    We finally replaced the network card, and the problem was solved.