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Re: can't reach internet

Subject: Re: can't reach internet
From: Smoot Carl-Mitchell
Date: Mon, 13 Aug 2007 10:14:17 -0700
On Mon, 2007-08-13 at 09:14 -0700, NoOp wrote:

> I'd also recommend that you check and set your MTU to match your router.
> Here are a few helpful links:

I had the same TCP Window scaling problem with a hotel network.  You can
turn off window scaling negotiation by
setting /proc/sys/net/ipv4/tcp_window_scaling = 0.

I think this problem occurs when a NAT proxy is unable to negotiate
window scaling and gets confused. In most cases window scaling is a good
thing, so it should be toggled off only when it is absolutely necessary.

Normally, the symptoms are large packets (close to the MTU size) are not
received correctly.  That is why a telnet some-site 80 will appear to
work.  But try doing a:

GET /

after a telent some-site 80
and see if the Web page response comes back correctly (or at all).

I generally saw this problem with SSH.  I could login in to a remote
machine fine, but when I tried a long directory listing, the connection
would appear to hang.  A tcpdump of the TCP stream would show the SSH
client issuing TCP ACK segments with no response from the remote server.
-- 
Smoot Carl-Mitchell
System/Network Architect
email: smoot@xxxxxxx
cell: +1 602 421 9005
home: +1 480 922 7313

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