multiple ip addresses

  • Thread starter Thread starter OS
  • Start date Start date
O

OS

Hi,

I want to set up multiple DNS entries to resolve a single name to multiple
IP addresses. Could you tell me what a browser would do if it got multiple
results for a DNS query, and would this provide fault tolerance?

Thank You

Oliver
 
In
OS said:
Hi,

I want to set up multiple DNS entries to resolve a single name to
multiple IP addresses. Could you tell me what a browser would do if
it got multiple results for a DNS query, and would this provide fault
tolerance?
Thank You

Oliver
Click to expand...

If you create multiple IPs for a single name, you will be using Round Robin.
Round Robin rotates the list of possible IPs for each query. The client will
take the one off the top of the list. You can verify that byusing nslookup.
Keep hitting up-arrow and re-run the query. You will see it rotate the
respones.

It will also use subnet mask priortization. DNS will look at the querying
client's IP address. If there is a subnet match, it will offer the record
that matches the subnet. If there are more than one IP, then subnet mask
priortization and Round Robin kicks in where it will offer all possible
records as a list. For each query coming in, it will rotate the list.

If there is no subnet match, all records are offered and rotated for each
query.


--
Regards,
Ace

If this post is viewed at a non-Microsoft community website, and you were to
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Ace Fekay, MCSE 2003 & 2000, MCSA 2003 & 2000, MCSE+I, MCT, MVP
Microsoft Windows MVP - Windows Server - Directory Services
Infinite Diversities in Infinite Combinations.
=================================
 
Oh that is interesting...

So where does the DNS server obtain the subnet masks and why? Is it to
specific networks can use certain servers for beter perfomance?

Oliver

"Ace Fekay [MVP]"
 
In
OS said:
Oh that is interesting...

So where does the DNS server obtain the subnet masks and why? Is it to
specific networks can use certain servers for beter perfomance?

Oliver
Click to expand...

It's not that the DNS server 'obtains" the mask, but rather provides the
best answer that it believe best matches the possible subnet of the querying
client (I believe it's based on class).

You can use this a number of ways. I've seen in some cases where a DC has
multiple NICs (not recommended anyway) and if a client on the inside network
queries for the GC, for example, DNS will provide the client with the
internal IP. If there are multiple subnets internally, the querying client's
ip assumed subnet will not match any of the records and will offer both,
rotating the responses. If the client gets the outside NIC's IP then it may
not be able to connect.

When designing your multi IPs, just keep in mind how it works in order to
design it properly.

Ace
 
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