clue for the clueless please

This is a Microsoft Passport / Hotmail access question, so if these are
alien to you, please move on...

Before anyone has a go at me, I have looked on their web site(s) and cannot
find any policies or pointers that are outside "forgotten password" land

We have turned up a new customer for BGP multihoming with a new IP block
from RIPE (217.71.224/20) and in testing we are having problems getting to
certain sites. Normally I would attribute this to no reverse DNS (yet), but
for Hotmail it is getting weird.

The reverse DNS issue is in hand and is awaiting DNS servers to be up etc.

The Hotmail issues (and maybe some other sites we have not yet got to)
appear to be IP block related. Do "they" do some sort of geographical
redirection or filtering based on IP block or AS number ? Testing from
another IP (OK, the nearend point-to-point address on one of the routers)
which also does not have reverse DNS but is in an older IP block, in a
different AS works fine.

The problem is the redirection from authentication -> mailbox. It just
hangs. Tested with multiple browsers (lynx included :wink: and all the same.

And pointers would be greatly appreciated.

What does telnet to port 80 reveal?

If you can get short queries back (E.g. HEAD / HTTP1/0) but not longer
queries it sounds like a PMTUD problem. Does the new customer have Frame
Relay or any other links with MTUs less than 1500?

Windows sets the DF bit on outbound packets, and I believe Microsoft
filter PMTUD ICMP packets.

Sounds almost certainly like an MTU problem. Try, if that fails
then it's pretty much definite. Microsoft are a bit silly for setting the
DF bit on outbound packets, firewalls at web hosting facilities that block
all ICMP are even more silly. Why on earth Microsoft, who must know about this
problem, block ICMP on their kit I don't know...

Most if not all dialup has an MTU of 1500.

Fixed - yep MTU on the E1 link was the problem.

Thanks Ryan, and all the other who tried in private e-mail.


Re the dialup mtu, 1500 is indeed the norm for ppp. I have a couple old
school slip friends, whose mtu is lower. They are confused.