[OpenAFS] Re: tcp or udp?

Matt Benjamin matt@linuxbox.com
Wed, 01 Feb 2006 15:53:19 -0500

Adam Megacz wrote:
> My personal experience is that most places blocking UDP are also
> blocking TCP and forcing users to use an HTTP proxy for all internet
> access.  
> I'm actually interested in knowing about the prevalence of
> anything that falls in-between (NATted TCP but no UDP).  I know it's
> possible, of course; are there any network devices that do this by
> default, or is it usually the case that networks configured this way
> are setup this way deliberately?
Firewalls that permit only specific UDP traffic, eg, domain and ntp, 
would seem very common.
> I know it sounds like a hideous idea, but if AFS-over-TCP ever
> happens, I think tunnelling it inside HTTP would be a pretty useful
> hack.

> Given the way that most NATs work, it's actually possible to do
> something called "unreliable TCP".  I've never seen this mentioned
> before, but I can't be the first person to think of it.  The idea is
> that you "speak TCP" but always ACK all packets periodically,
> regardless of whether or not you got them -- the NAT can't tell the
> difference.  So you get UDP-type performance with TCP-type
> compatability.  With many NATs you wouldn't even need to bother with
> the ACKs at all.
>   - a
Google finds a lot of references to "unreliable TCP--"unreliable. TCP" 
and "unreliable, TCP" seem especially frequent.

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Matt Benjamin

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