Cable modem users could get static IPs soon.

[Anthony de Boer]

D. Hugh Redelmeier wrote:
> | From: Lennart Sorensen <lsorense-1wCw9BSqJbv44Nm34jS7GywD8/FfD2ys at public.gmane.org>
> | But it might use your other ISPs IP block in this case.  Could happen
> | right?
> 
> I wonder.  I think that the cable plant routes internally on IP
> address so an IP address supplied by a different ISP might be
> problematic.

Several years ago, when I was in the ISP business, the IANA/IETF Best
Current Practices document said (inter alia) that we should filter so
that customers could send packets from their assigned addresses only. 
This prevents compromised machines from taking part in DDoS games that
involve sending packets forged as if coming from the victim's address.

It turns out most ISPs didn't do this filtering, and we had a merry game
of debugging with a customer who turned out to have two upstreams and was
wondering why they could only use both sets of addresses if they
default-routed through the other ISP.

Bottom line is that a proper multi-homing solution ensures that packets
from you that use the address assigned to you from whichever ISP actually
go out on that same ISP's link.  Playing fast and loose shouldn't work,
or may stop working at some future point.

-- 
Anthony de Boer
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