Can we load balance traf[f]ic for CNAME records?
manishr78 at gmail.com
Fri Dec 14 09:14:51 UTC 2012
Ok - let me rephrase the question. I guess Charles got it right.
I understand that Mail Delivery load balance can be achieved by usingMX
priorities. My concern is not that, rather I am more worries about users
who will be using A record to configure their mail clients like IMAP or
POP. I am thinking on load balancing their since I want users to access the
both the ISPs to connect. I can have A/CNAME? record configured in my zone
with *lower TTL value say 180* so that if any of the link goes down I can
edit the zone and have the faulty entry removed which eventually would cost
me less downtime. That way I dont need to do any configuration at client
end since the A/CNAME record is gonna be the same.
That is why I was wondering if A or CNAME can be configured for two
different IP addresses which also holds MX Records and thus configure the
load balancing by that way?
On Fri, Dec 14, 2012 at 12:01 PM, Charles Swiger <cswiger at me.com> wrote:
> On Dec 13, 2012, at 9:27 PM, Manish Rane <manishr78 at gmail.com> wrote:
> > I m planning to add cname records to two A records to different IPs
> provided by two ISP. Can I loadbalance traffic then?
> Using CNAMES and load-balancing traffic isn't directly related. You can
> implement simple load-balancing by listing multiple A records for a name
> without using a CNAME at all, for example.
> > Like say i need to play with mail services and I have 2 ISPs.say ISP A
> and ISP B.
> > MX 10 mail.example.com 18.104.22.168 (from isp A)
> > Mx 20 mail01.example.com 22.214.171.124 (from isp B)
> > CNAME cas.example.com
> > mail.example.com 126.96.36.199
> > mail01.example.com 188.8.131.52
> > Now when users wil confugure their mail boxes they will use
> MX records are used to define a destination for SMTP mail delivery; SMTP
> uses MX records or falls back to A records in order to canonify the domain
> name portion; trying to use CNAMES to alter the canonical destination for a
> domain is a Bad Idea (tm).
> When you speak of users "configuring their mail boxes", you're probably
> referring to POP or IMAP clients, which could use a CNAME if you wanted.
> Mail reading (ie, POP/IMAP/etc) and mail delivery (ie, SMTP) are different
> protocols, and large sites almost invariably have separate pools of
> external MX, internal MX, and reader boxes.
> > Can I load balance the traffic for cas.example.com?
> Sure. But I suspect your real question involves something more
> complicated beyond the trivial round-robin behavior of multiple DNS
> records, such as load-balancing with session affinity, or liveness testing
> of destinations, or allocating traffic to the least busy destination, or
> geographic traffic management between multiple destinations (ie, data
> You can get somewhere with something like RFC-2391 LSNAT, for example, but
> there is a reason why folks pay for hardware load-balancing hardware and
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