What happens when DNS returns multiple IPs for netnews.attbi.com?
Susan K
DNS returns multiple IP addresses for a name.
nslookup for netnews.attbi.com returns 4 IPs.
ping to each of these returns different round-trip
times and packet loss.
When I run my news reader using the server "netnews.attbi.com"
it seems to be selecting one of the slowest IPs identified by
nslookup.
I assume that some software is supposed to determine
which of the 4 IPs is the best, but I don't know how it
works or if it needs to be setup somehow. Is this program
called BIND/resolver? How does it work?
nslookup for www.yahoo.com returns 8 IPs.
I have a small home lan with unix/win boxes, and a
umax gateway/router for a cable modem. Maybe these multiple
IPs are just used with larger routers.
Mike
be registered as an Internet domain name. Multiple IP address are used to
give redundancy in the network, and to provide alternative paths for
information. Yahoo has 8 addresses simply because of the size of the site,
it runs several servers to allow many users access. Without multiple IP
addresses, the sheer volume of accesses to the site would shut it down if
only one IP address was used. Routers determine the best available path to
a given IP address.
Mike, MCSE
"Susan K" <jkk...@attbi.com> wrote in message
news:3C0EBD6A...@attbi.com...
Warren H.
> As a minimum, a domain name must have 2 registered IP addresses in order
to
> be registered as an Internet domain name. Multiple IP address are used to
> give redundancy in the network, and to provide alternative paths for
> information. Yahoo has 8 addresses simply because of the size of the
site,
> it runs several servers to allow many users access. Without multiple IP
> addresses, the sheer volume of accesses to the site would shut it down if
> only one IP address was used. Routers determine the best available path
to
> a given IP address.
>
> Mike, MCSE
Okay, if a registered Internet domain name needs a minimum of 2 IP
addresses, explain this:
==================
nslookup foodtv.com
Non-authoritative answer:
Name: foodtv.com
Address: 209.215.174.122
==================
Answer: Domain registration has nothing to do with DNS information.
Also, the number of IP addresses a site has is not an indication of the
number of servers they have. Multiple IP's could indicate multiple NIC's on
a single server, and a single IP could be a gateway to an array of servers.
Your comment about routers choosing the best route to a specific IP address
is correct, but it has nothing to do with the question asked. The question
asked is when a name resolves to more than one IP, what determines which IP
those packets are sent to, and that decision is made before the packet hits
any router.
So much for MCSE being a meaningful certification.
--
Warren H.
==========
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go outside now.
Ray Savage
>As a minimum, a domain name must have 2 registered IP addresses in order to
>be registered as an Internet domain name.
Hmmmm.......you sure you didn't mean to say that a domain must be
listed on 2 DNS servers to be registered?
Ray Savage
Encinitas CA
To reply via email, remove the "unspam." in the address shown.
Kimberly Murphy-Smith
MCSE: "Must Consult Someone Educated"
Kimberly Murphy-Smith -- kamu...@ix.netcom.com
http://members.aol.com/kimmurphy/
John Green
> I am just trying to figure out what happens when
> DNS returns multiple IP addresses for a name.
>
> nslookup for netnews.attbi.com returns 4 IPs.
> ping to each of these returns different round-trip
> times and packet loss.
>
> When I run my news reader using the server "netnews.attbi.com"
> it seems to be selecting one of the slowest IPs identified by
> nslookup.
>
> I assume that some software is supposed to determine
> which of the 4 IPs is the best, but I don't know how it
> works or if it needs to be setup somehow. Is this program
> called BIND/resolver? How does it work?
<snip>
It's really up to the application software to handle multiple IP
addresses for a single host. Microsoft's IE, for example, tries the
first IP address in the list. If that IP doesn't repond in the time out
period, it then tries the next one, and so on. Other programs handle
things differently. Some programs remember which IP addresses worked or
didn't and continue to use or ignore those addresses. Some, like
Netscape Navigator, will periodically retry the failing IP addresses to
see if they've come back online. Some programs don't support multiple IP
addresses and just use the first or last IP in the list.
I don't know that there's much you can do as far as setup, other than
perhaps setting timeout values. Applications selecting a non-optimal
server is a common problem when systems use multiple IP addresses for
load balancing or failover. More sophisticated systems use dedicated
load balancing and failover software in front of the servers to solve
that problem.
The Berkeley Internet Name Domain (BIND) is a specific implementation of
DNS, widely used on UNIX and UNIX-like systems. The resolver is included
with BIND. More info on BIND can be had from:
http://www.isc.org/products/BIND
--
John
Kenneth Porter
>I am just trying to figure out what happens when
>DNS returns multiple IP addresses for a name.
The BIND DNS server (used at most ISP's, and comes free with Linux) will
serve the addresses in "round robin" order. Each time you ask, it will
answer with the addresses "rotated" by one.
The default resolver action is just to use the first one from the list. (The
resolver is usually built into the OS (eg. Windows) and is the thing your
web browser or news client uses to ask questions of the DNS server.)
So try running your nslookup command several times. Each time you should get
back the 4 addresses in a different order. (Sometimes you'll get the same,
because lots of other people are asking, and if 3 others asked between your
two questions, the order would "wrap around" to the same order from your
first question.)
Feel free to ask if you have more questions about DNS.
Byers
>As a minimum, a domain name must have 2 registered IP addresses in order to
>be registered as an Internet domain name. Multiple IP address are used to
>give redundancy in the network, and to provide alternative paths for
>information. Yahoo has 8 addresses simply because of the size of the site,
>it runs several servers to allow many users access. Without multiple IP
>addresses, the sheer volume of accesses to the site would shut it down if
>only one IP address was used. Routers determine the best available path to
>a given IP address.
>
>Mike, MCSE
Somebody needs to get re certified! <G>
Kenneth Porter
>The Berkeley Internet Name Domain (BIND) is a specific implementation of
>DNS, widely used on UNIX and UNIX-like systems. The resolver is included
>with BIND.
Minor correction: *A* resolver is included with BIND. One also comes built
into Windows, and I think glibc has one built in. (Or does it use the
ISC/BIND resolver?) (The resolver is just a local hunk of code that apps use
to talk to DNS servers.)
Thomas Gilg
> Yahoo has 8 addresses simply because of the size of the site, it runs
> several servers to allow many users access. Without multiple IP
> addresses, the sheer volume of accesses to the site would shut it
> down if only one IP address was used.
Not really.
Any big web site will want to make sure that there are multiple
outside physical network paths to it. For example, hp.com can
be reached through 3 different addresses in the 192.6.*.* range
and 3 more in the 192.151.*.* range, the implication being that
you can reach hp.com by at least two very different physical
network paths.
Further, a single machine can be the receiver of multiple addresses,
and conversly, a load balancing router can take traffic intended
for one IP adddress and distribute it to many machines.
For some of the large web services I have worked on, we often
have 12 or more identically configured web servers that sit behind
one load balancer. Each http request that comes into the one IP
address on the WAN side of the load balancing router gets
randomly assigned to any of the 12+ web servers.
Thomas Gilg
to...@cv.hp.com
Mike Blackford
>
> As a minimum, a domain name must have 2 registered IP addresses in order to
> be registered as an Internet domain name. Multiple IP address are used to
> give redundancy in the network, and to provide alternative paths for
> information. Yahoo has 8 addresses simply because of the size of the site,
> it runs several servers to allow many users access. Without multiple IP
> addresses, the sheer volume of accesses to the site would shut it down if
> only one IP address was used. Routers determine the best available path to
> a given IP address.
>
> Mike, MCSE
<lol!> Incredible. Is it April 1st already?
--
"The liberty of a democracy is not safe if the people tolerate the
growth of private power to a point where it becomes stronger than their
democratic State itself. That, in its essence, is Fascism ó ownership
of government by an individual, by a group, or by any controlling
private power." óó Franklin Delano Roosevelt
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