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-
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