Two A records

[Joseph S D Yao]

On Mon, Apr 30, 2001 at 05:14:31PM -0400, Jennifer wrote:
> Is it possible to have two A records for one host? (not really one host,
> they would point to two different interfaces on the firewall.)

You can certainly have two "A" records:

fwall		A	1.2.3.4
fwall		A	1.2.3.5

but (a) some name servers will round-robin these, (b) some won't, (c)
this will not help an application which gets one of these that happens
not to be working at the time.

You need a combination of things to have this be an effective redundant
or high-availability solution.  Going out, you may want to have a box
that decides which line to use based on load and whether the line is
working.  Coming in, router protocols like BGP might help.

If you expect one line to go down, you might want to have short TTLs on
these and get rid of whichever one is failing.

Also, to help you do maintenance and trouble-shooting, you should also
have unique names for these, and use the unique names in your reverse
DNS zone files.

fwall		A	1.2.3.4
fwall		A	1.2.3.5
fwall-A		A	1.2.3.4
fwall-B		A	1.2.3.5

-- 
Joe Yao				jsdy at cospo.osis.gov - Joseph S. D. Yao
OSIS/COSPO Computer Support					EMT-B
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