Strange TCP connection behavior 2.0 RC2 (+3)

Steven Bellovin smb at
Wed Jun 29 14:25:28 UTC 2011

On Jun 29, 2011, at 8:59 49AM, Ryan Malayter wrote:

> On Jun 28, 3:35 pm, Cameron Byrne < at> wrote:
>> AFAIK, Verizon and all the other 4 largest mobile networks in the USA
>> have transparent TCP proxies in place.
> Do you have a reference for that information?  Neither AT&T nor Sprint
> seem to have transparent *HTTP* proxies according to
> I would have thought that
> would be the first and most important optimization a mobile carrier
> could make. I used to see "mobile-optimized" images and HTTP
> compression for sites that weren't using it at the origin on Verizon's
> 3G network a few years ago, so Verizon clearly had some form of HTTP
> proxy in effect.
> Aside from that, how would one check for a transparent *TCP* proxy? By
> looking at IP or TCP option fingerprints at the receiver? Or comparing
> TCP ACK RTT versus ICMP ping RTT?
Or see what bandwidth is like if you use IPsec or the like.

		--Steve Bellovin,

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