Mailscanner filter server to my Mail store " I just canna do it c aptain! "

[Youn Gonzales]

Disadvantages of DNS based load balancing:
In many cases spammers target a particular ip address.

Spammer A may connect and send 10,000 spam messages to mx1, while Spammer B
connects to mx2 and sends only 500, then Spammer C connects to mx1 and sends
10,000 messages, while Spammer D connects to mx2 and sends only 500, etc.

Spammer A uses caching DNS, Spammer B does not

I tried it using 3 different servers. One server would always get hammered
and the other two only received a minimal load.

Advantages of hardware based load balancing:
Hardware load balancing devices can keep track of how much traffic is going
to each server and dynamically balance the traffic, DNS load balancing
cannot.

Hardware load balancing can detect server outages and dynamically balance
the traffic across the remaining servers, DNS load balancing typically
cannot.

Hardware load balancing can allow you to increase or decrease the number of
servers in the "server farm" on the fly and adjust the traffic dynamically.

Harware load balancing can allow you to use weighting systems so that you
can have some really fast servers that handle more of the load and some
slower servers that only handle a smaller portion of the load.

The only drawback I can see from hardware load balancing would be if your
mail servers are in different locations - ie a spooling server on a
redundant network segment. I know that some load balancing systems require
the devices to be on the same network segment. In that case, if your mail is
so critical that it requires off-site spooling servers, I would configure
load balanced servers at each location.

Youn Gonzales
System Administrator
Comptia A+, Network+, INET+,
Cisco CCNA/CCDA Certified Technician
Microsoft Certified Professional

"sabbe dhamma anatta"


----- Original Message -----
From: "Antony Stone" <Antony at SOFT-SOLUTIONS.CO.UK>
To: <MAILSCANNER at JISCMAIL.AC.UK>
Sent: Wednesday, August 27, 2003 2:08 PM
Subject: Re: Mailscanner filter server to my Mail store " I just canna do it
c aptain! "


> On Wednesday 27 August 2003 7:24 pm, Youn Gonzales wrote:
>
> > Load balancing via DNS does not work very well at all.
>
> Oh?   I thought round-robin DNS made sure that each client request coming
in
> to a DNS server got the addresses records in a different order, and
clients
> try to contact the first one they're given (unless it's uncontactable, in
> which case they try the second, etc).
>
> In what way does this system not work very well?   I've heard it
recommended
> several times for different services - mail, web, ftp - and as far as I
know
> that wasn't just because it's simple to set up.
>
> I'm interested to know if there's some reason why this scheme results in a
> noticeably more unbalanced load on the servers than can be achieved with
> network hardware on an incoming link (which can only be used, of course,
if
> all the servers are on the same link at the same location, which in my
> opinion has its own drawbacks, which don't apply to round-robin DNS...)
>
> Regards,
>
> Antony.
>
> --
>
> You can spend the whole of your life trying to be popular,
> but at the end of the day the size of the crowd at your funeral
> will be largely dictated by the weather.
>
>  - Frank Skinner
>