Hi David
Thanks a lot for your answer!
4. (my main question!): The reason given by the ISP to expose
the router is totaly weird, because the IP range for
_outgoing_ ADSL-connections is irrelevant for router remote
administration, which is performed in the opposite direction
and need's only one IP, p.ex. the one of the target router.
Uh, no. Any TCP connection needs both source and target addresses.
Oh yes, I know this - but maybe my question was not clear, or I have another
basic misunderstanding?
I used severel IPs (as target, not as source) to telnet the router, all of
them where, _at_the_time_ I used them, in use by a ISP customer which is
located in the same building and visiting my website. All these IPs I tried
are within the ISPs IP pool used for their customers (most of them ADSL and
non in the same building I think).
So, I thought:
- the IP (the router was reachable at) belonged to a PC somehow _within_ their
network
- there is no need for the ISP to use their _own_ IPs (as source IP) when
remote administering (but maybe this provides a basic restriction of source
IPs?)
- why must the router be reachable _at_ (not from) some hundreds IP adresses
(of their IP pool)?
What the ISP said is: We've considered only allowing telnet
connections to this box from specific source addresses (assigned
to those who should be able to administer the router).
yes, I understand this; but the customer the IPs where assigned to is neither
allowed nor capable to administer the router. I suppose none of their
customers should aminister it
We haven't restricted access to only those sources yet;
they even don't plan to do so.
it's entirely possible
that the administrators need the option to access it from wherever
they are on the Internet *today*, and that changes, either because
they travel and/or they get an address via DHCP or other dynamic
mechanism.
ok, clear.
So, independent from within what range those IPs at the moment of remote
administration are: Is it common practice to admin a router by telnet from
outside, exposing plain text password? Why not use ssh somehow? Is there no
danger that anybody brute forces the router password and can disable
internet access for all the ISPs customers?
[...]
You are an expert, and I really hope not annoying you with
bullshit... and if so, I really apologize, and I won't do more postings to
this subject.
thanks again
J.
P.S. Shouldn't I have post this answer to the list?
