DNS name resolution.

  • Thread starter Thread starter Ben Verhagen
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Ben Verhagen

This question is to find out how DNS name resolution is done.
Let's say i'm at my W2K-Pro client and I want to browse to
http://www.microsoft.com,

IPCONFIG:
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 10.0.0.20
Subnet Mask . . . . . . . . . . . : 255.0.0.0
Default Gateway . . . . . . . . . : 10.0.0.1
DHCP Server . . . . . . . . . . . : 10.0.0.1
DNS Servers . . . . . . . . . . . : 212.142.28.66


If you look at the two Microsoft links below, which steps are taken to
resolve the DNS name www.google.com?
http://www.microsoft.com/technet/tr...indows2000serv/reskit/tcpip/part2/tcpch05.asp
http://www.microsoft.com/technet/tr...indows2000serv/reskit/tcpip/part2/tcpch06.asp

A second question is, what will happen when I leave the WWW part out of the
DNS name: http://microsoft.com.
As far I believe, www is a node name. How will this effect the DNS
resolution?

Also, is there a simple (MS?) tool available were one can trace the DNS name
resolution?

Regards,

Ben.
 
In
Ben Verhagen said:
This question is to find out how DNS name resolution is done.
Let's say i'm at my W2K-Pro client and I want to browse to
http://www.microsoft.com,

IPCONFIG:
DHCP Enabled. . . . . . . . . . . : Yes
Autoconfiguration Enabled . . . . : Yes
IP Address. . . . . . . . . . . . : 10.0.0.20
Subnet Mask . . . . . . . . . . . : 255.0.0.0
Default Gateway . . . . . . . . . : 10.0.0.1
DHCP Server . . . . . . . . . . . : 10.0.0.1
DNS Servers . . . . . . . . . . . : 212.142.28.66


If you look at the two Microsoft links below, which steps are taken to
resolve the DNS name www.google.com?
http://www.microsoft.com/technet/tr...indows2000serv/reskit/tcpip/part2/tcpch05.asp
http://www.microsoft.com/technet/tr...indows2000serv/reskit/tcpip/part2/tcpch06.asp
Click to expand...
DNS resolution starts at the root zone which is a "." there are several
roots to go to but most common is the ICAAN root. you could also go to the
PACROOT or ORSC Root depending on your ISP the ORSC Root is probably the
largest there are literally hundreds of TLDs in the ORSC root from .1719 to
..zw.
The root has delegations to the gTLD DNS for "com" to the com gTLD DNS
servers have delegations to the content DNS servers for the second level
name. In this case it would be to the authoritative servers for google.com.
Those server have the resource records in the google.com zone for www, mail,
ftp or whatever the hostname is.
That being said when you type in www.google.com. chances are that there are
DNS servers in the path that will have that record cached so it may not have
to go to the root first.

A second question is, what will happen when I leave the WWW part out
of the DNS name: http://microsoft.com.
As far I believe, www is a node name. How will this effect the DNS
resolution?
Click to expand...
The www record in microsoft.com is an alias CNAME record which means it
resolves to a FQDN which must be resolved to get an IP address.
microsoft.com resolves to an "A" host record that has an IP address

Also, is there a simple (MS?) tool available were one can trace the
DNS name resolution?

Regards,

Ben.
Click to expand...
It is nslookup or dig with BIND
If you want to see resolution in action run nslookup -d2 for verbose output
 
When a query is first made it looks at your assigned DNS server
(212.142....) and ask for an A Record. If the DNS server does not have the
record and recursion is turned on at the server then it will go to a root
set of name servers to find out which name server is the authoritive name
server for that domain and query for the record to that server respectively.

www record is a alias or CNAME record. Again going off the above statement
when you make a query for google.com the DNS server should return only an A
record for that host (A record is just the plain ip address). However when
you make a query for www.google.com the DNS server will then return both an
A record for the host along with a CNAME record showing what domain is its
parent.

If on an XP or 2k box you can click start, run, type "cmd", type "nslookup".
Or follow this link: http://devbox.myplaceinspace.com/nettools/
 
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