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Re: May be OT: Can ad blockers truncate POST data?

by ryantate (Friar)
on Feb 11, 2004 at 01:01 UTC ( #328093=note: print w/replies, xml ) Need Help??

in reply to May be OT: Can ad blockers truncate POST data?

This answer may be OT as well, but your post rang some bells.

I had a similar problem once. I couldn't submit large forms from home to a basic perl script of my own creation, but I could submit to the same script from work and elsewhere with no problem.

The issue turned out to be -- and I do not know much about networking so excuse my summary here -- an MTU (network maximum transmission unit) setting by my DSL provider, SBC/PacBell, at their upstream routers conflicting with the MTU used by Windows 2000 and my router. I think what was happening is when I submitted large-ish forms my computer/router was sending packets larger than SBC's MTU, which were promptly dropped on the floor, never reaching the server.

Setting my Linksys BEFSR41 V.2 4-port DSL Router/switch to fragment my packets (when neccesary) to fit into, as it turned out, 1460 (bytes?), fixed the issue. The router now breaks up large packets into smaller ones so they do not exceed SBC's MTU and get dropped on the floor.

The whole thing is documented in this usenet thread.

  • Comment on Re: May be OT: Can ad blockers truncate POST data?

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Re: Re: May be OT: Can ad blockers truncate POST data?
by Anneq (Vicar) on Feb 11, 2004 at 10:17 UTC
    The problem with MTU size that you had is not likely what is causing the OP's problem. He adds an extra dummy field to get trucated instead of the timestamp. Since this seems to work, then the actual size doesn't seem to matter. The end still gets scraped off. Anne
      The OP never said he actually observed that the padding is, in fact, truncated. Maybe you know more about networking than me: Is it not possible the padding pushes a packet over the local (Windows/router) MTU and the packet is then broken at a halfway point resulting in two pieces well under the local MTU and under the ISP MTU as well? -RT
        Good point, ryantate. I assumed, perhaps wrongly, that the new form was truncated as well. If the new document is NOT truncated, then, mismatched MTU size would be a possible place to try and eliminate the problem.


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