DNS delegation

[Shivkumar]

Can someone explain delegation with reference to DNS on Unix with regard to Network LoadBalancer ?

Regards,
Shiv

[Arunvijai_4 · Accepted solution]

Hi Shiv,

What is Reverse Delegation?
The Domain Name System (DNS) is a globally distributed Internet service. It provides name-to-number (forward) and number-to-name (reverse) translations, using defined client-server and server-server protocols. The DNS is a public service - any Internet user is freely able to query the DNS system for forward or reverse translations.

Reverse DNS delegations allow applications to map to a domain name from an IP address. Reverse delegation is achieved by use of the special domain names in-addr.arpa (IPv4) and ip6.arpa (IPv6).

-Arun

[Steven E. Protter]

Shalom Shiv,

A network load balance takes DNS name requests to the same Domain name host and splits them between multiple hosts.

I look up shalom.investmenttool.com and I get sometimes you get 192.168.0.10

Sometimes you get 192.168.0.20


The allocation can be via round robin or other allocation methods. Round robin's problem is if one of the IP addresses is down the allocatoin fials.

Network load balancers are pretty common and some are smart enough to not route traffic to dead hosts.

If I have confused you ask for clarification.

SEP

[A. Clay Stephenson]

If I understand your question, about the only load balancing that DNS allows is "round-robin". The idea is that you create multiple entries for the same hostname but with different IP addresses. DNS then cycles through all the identical hostnames on a round-robin basis. The idea is that the 1st time a request comes in for "superman" an IP address of "10.1.2.1" might be given, next time it gets "10.1.2.2"
, then "10.1.2.99", and so on until all the entries are used and then it starts over. If combined with Dynamic DNS so that servers that are down can be detected, it gives one a means to create a highly available pool of servers that are known to the outside worlf as "superman".

[Geoff Wild]

Do you mean in the sense of delegated sub domains?

How that works is, say you are primary for yourdoamin.com, but your comapny has an office in say the uk.

Their namespace is say uk.yourdamain.com - and they want to be primary for it.

In your named.conf, add something like:

// here are our child domains

zone "uk.yourdomain.com" in {
type forward;
forward only;
forwarders { ip.of.uk.server; ip.of.uk2.server; };
};


Rgds...Geoff

[Arunvijai_4]

Hi Shiv,

Some links on this topic

http://www.ripe.net/rs/reverse/
http://www.zytrax.com/books/dns/ch3/

-Arun

[Florian Heigl (new acc)]

Hi,

a few years I have ebayed myself a bunch of load balancers for toying around with.

Those are essentially the HP SA9200 models.

The driving force for using such a solution is to achieve higher availabilty than round robin DNS (as already described) offers.

For example, You have four D/R sites spread all over the world because Your service levels are hard to meet.

Let's say
SiteA == Somewhere in US
SiteB == Somewhere else in US
SiteC == Somewhere in Europe
SiteD == At a Internet Hub in Panama

At one of the US and Europe sites there's a subsidiary of Your company with a load-balanced server farm, the other two sites are just single high-end servers.

The delegation comes in now:

At each site You also set up a global load distributor, which is just a high performance dns server.
it does:
- check the availability of all sites
- check the proximity of the accessing client
- check all other distributors availabilty

while ns1.yoursite.com would refer to *your* local nameserver, www.yoursite.com would be delegated to the distributors (either by listing all their IPs or by pointing it to an anycast network)

when a client now requests www.yoursite.com, the request will safely end up at one of these distributors, which will go through the above checks and in the end return the most suitable web server (or load balancer) for the client.

There a lot of little knobs with these setups, but in the end You gain a maximum of availability with no SPOF in Your hands.

The remaining points are:
- root dns server failure
- internet failure

while i.e. a failure of europe (i.e. when CERN comes up with 1KG of antimatter and a power failure at the same time) would not interfere with Your website availabilty.