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Re: About the address allocation convention between ISPs

  • From: David Barak
  • Date: Wed Jun 04 15:05:26 2003

Dear Mr. Fei,

I surmise that hop 6 is the actual interface by seeing
gw-att.qwest.net <-- the fact that both qwest and att
appear in the same DNS lookup to me implies that qwest
intends that link to be the border.  hop 5 is the
ingress link to ATT's border router, and hop 7 is the
next qwest router upstream.

Generally the ISP who numbers the block provides the
DNS.  This breaks down, however, because there is no
single naming structure, and many providers don't do
reverse DNS for their infrastructure.

-David


--- Teng Fei <tfei@ipanema.ecs.umass.edu> wrote:
> Dear Mr. Barak,
> 
> Right, in your example, AS7018 and AS209 are both
> backbone ISPs and I
> guess they are peering at NY.   So if the addresses
> at both ends of
> the "real" inter-domain link were assigned with
> qwest's address, hop 6
> would be the inter-domain link.  But if the
> addresses were assigned with
> AT&T's address, hop 5 would be the inter-domain
> link.   DNS name
> seems would not help in this case.
> 
> And here is another question that confuses me. 
> Using your example.  If
> the link was as follows,
> 
> --+                                         
> +-----------+
>   |IP1(domainnameA) <------> IP2(domainnameB)|
> border rt |IP3(domainnameC)
> --+                                         
> +-----------+
> 
> If the router on the left(only half was drawn)
> physically belongs to att,
> and the router on the right physically belongs to
> qwest.  the Link between
> IP1 and IP2 is the inter-domain link.  IP1 and IP2
> should be a pair of /30
> addresses.   My question is how are the domain names
> of IP1 and IP2
> assigned?  If say IP1 and IP2 are both addresses
> from AT&T's address
> block, the for IP2, is it usually foo.att.com or
> foo.qwest.com?
> 
> Thank you very much!
> 
> Sincerely
> 
> Teng
> 
> On Tue, 3 Jun 2003, David Barak wrote:
> 
> > Many larger networks (with multiple
> interconnections
> > will split the chore, where the numbering reflects
> > exactly who is responsible for the physical
> circuit.
> >
> > So alas, there is no one "right" answer to your
> > question, unless you're going to try to put
> together a
> > table based on the naming conventions...
> >
> > for instance, probably hop "6" is the actual
> interface
> > between 7018 and 209 in NY according to this view.
> >
> >   5 gar4-p300.n54ny.ip.att.net (12.123.3.2) [AS
> 7018]
> > 4 msec 4 msec 4 msec
> >   6 att-gw.ny.qwest.net (192.205.32.170) [AS 7018]
> 4
> > msec 4 msec 4 msec
> >   7 jfk-core-03.inet.qwest.net (205.171.230.26)
> [AS
> > 209] 4 msec 4 msec 4 msec
> >
> > -David Barak
> >
> > --- Teng Fei <tfei@ipanema.ecs.umass.edu> wrote:
> > >
> > > Hello everyone,
> > >
> > > I have a question about the convention of
> address
> > > allocation between ISPs.
> > > If a smaller ISP tries to establish connection
> with
> > > its provider, does
> > > this small ISP configure one of the interface on
> its
> > > boarder router using
> > > an IP address obtained from the provider, or it
> is
> > > the other way around,
> > > that is, the provider uses one of the IP address
> > > belongs to the customer
> > > to configure the provider's boarder router?
> > >
> > > I have this question because I am trying to
> identify
> > > the link between two
> > > organizations from traceroute measurements.  
> How
> > > the addresses are
> > > allocated will affect the identification of the
> > > inter-domain link by
> > > exactly one hop.
> > >
> > > I am not sure if there is such a convention at
> all,
> > > or the address
> > > assignment is randomly decided according to the
> > > agreement between the
> > > customer and the provider?
> > >
> > > Since I know there are many seasoned network
> > > professionals on this mailing
> > > list, I think it might be a proper question to
> ask
> > > here.  Would anyone
> > > kindly be willing to share your experience? 
> Thank
> > > you very much!
> > >
> > > Sincerely
> > >
> > > Teng
> > >
> >
> >
> > =====
> > David Barak
> > -fully RFC 1925 compliant-
> >
> > __________________________________
> > Do you Yahoo!?
> > Yahoo! Calendar - Free online calendar with sync
> to Outlook(TM).
> > http://calendar.yahoo.com
> >
> 


=====
David Barak
-fully RFC 1925 compliant-

__________________________________
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