[sclug] Potential in-bound routing failure on BT: any thoughts welcomed

[Dickon Hood]

On Sun, Apr 07, 2013 at 20:47:41 +0100, Keith Edmunds wrote:
: On Sun, 7 Apr 2013 20:09:41 +0100, sclug at neilzone.co.uk said:
: > Before I try to escalate *again*, can anyone spot anything obvious I am
: > failing to check here? 

: Well, if you choose to use BT as your ISP... Seriously, I wouldn't. In my
: experience, the smaller ISPs are way, way better. I'm now with Andrews and
: Arnold, and would recommend them (they're not as expensive as I thought
: they would be, and they are good).

A&A are recommended, but their pricing isn't what you'd call transparent.
OTOH, they do IPv6.

: But you want to fix your problem. You say your router is showing an IP
: address of 100.x.x.x - is it 100, or 10? The latter is an RFC1918 address
: (http://tools.ietf.org/html/rfc1918), which is not routable over the
: Internet and would therefore imply CG-NAT. A quick Google for 'bt cg-nat'
: suggests that BT do use it in places (which only underlines the stupidity
: of BT, but I digress).

Without wishing to defend BT unduly, they almost certainly have no choice.
RIPE has been out of IPv4 space for some time now, and CGNAT is the only
way around this for the near-term.  Until the advent of IPv6 everywhere --
and there's little excuse for not having deployed it already -- you can
expect to see more and more of this problem cropping up.  In the
not-too-distant future, even the likes of A&A are going to have to do it.

: I suggest you ask BT if they are using CG-NAT. It's unlikely that you'll
: get a straight answer first time, though. I would also do a 'whois' on the
: IP address you have (the 100 one) to find out if it is a BT address. Then
: I would ping from another connection (work or, if you can't do that, PM me
: and I'll ping it) to see if it is routable from the Internet.

: That may help. What may help much more is changing ISPs.

For now.  IMHO, I suspect your best bet is to find an ISP that's handing
out guaranteed fixed IP addresses, and stick to it.  And one that does
IPv6, too, which rules out all of the big boys at present.


Dickon Hood
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