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Re: Alternative to BGP-4 for multihoming?
- From: Gary E. Miller
- Date: Tue Mar 14 15:55:46 2000
On Tue, 14 Mar 2000, Joe Loiacono wrote:
> >Checking the path to my DNS servers tells you NOTHING about the
> >path to my hosts.
> Right. But your situation is not the one being looked at, as you don't have
> geograpically distributed web servers.
But of course I DO (and that is a different question again... :-)
> I believe for that situation 3DNS,
> et. al., can work. Once the client's DNS request has worked its way over to
> the primary DNS for the distributed web-servers, 3DNS has each of the other
> 3DNS boxes (located adjacent to the other distributed servers) ping the
> *clients* primary DNS. 3DNS then returns the URL for the web-server whose
> 3DNS machine is 'closest' (fewest hops) to the clients DNS machine. Thus,
> for example, clients in Asia can get to a server in Asia.
> I think that's the gist of it, if not the specifics...
Let us take a client example. I manage a DNS with clients (users)
in Singapore, California, New York and UK. DNS servers in Singapore
and California and mirrored Web servers in Singapore in California.
The DNS servers in Singapore do forward, and reverse for all zones
in use (except ISP roaming) AND cacheing for ALL hosts in use. All
hosts worldwide use our in house master DNS servers and not the local
ISP servers. This allows the users to get DNS access for
hostnames that are behind our firewalls on private addresses. It also
allows inhouse tech support to more easily troubleshoot PCs remotely. I
have seen this setup in use by many companies with firewalls.
All laptops given to employees are shipped preset to use the 2
main corporate DNS servers for their DNS cacheing servers.
Now let us say that a user (client) in UK connects to one of our corporate
DNS cacheing server in Singapore or California. That DNS server
connects to the 3DNS in New York. Now how does the 3DNS in New York
decide the nearest web server to UK by checking DNS servers in California
And I sure hope that HOP count is not used, Singapore has a mixture
of very fast and very slow links to foreign countries so hop count is
a useless measure of "closeness".
Now it gets worse. Our users in Singapore take their laptops home
but still use the DNS cacheing from the office servers. At home they
are on a local ISP network that connects to the US by a very
different path! Some ISPs in Singapore connect directly from Singapore
to LA, some directly to Palo Alto and some to Japan and then Seattle.
When our user goes home all that changes about his configuration is
his IP address and reverse DNS. But his connectivity to the US
is totally changed.
Some ISPs connect directly to Malaysia and some need to go to LA and back.
Picking the server based on DNS could add a second of extra round trip
I have a few other clients with totally different configurations that
also break the 3DNS, but that is another discussion...
Gary E. Miller Rellim 20340 Empire Ave, Suite E-3, Bend, OR 97701
firstname.lastname@example.org Tel:+1(541)382-8588 Fax: +1(541)382-8676