ROUND ROBIN and antivirus server

[Kevin Darcy]

I'd guess something on your relay servers, e.g. nscd or the MTA itself, 
is caching the DNS result. There's nothing in BIND you can do to fix 
this. You'd need to find what is doing the caching, and turn off that 
behavior, if possible.

                                                                         
                                          - Kevin

Clade wrote:

>Hi
>
>I work at an ISP. Currently all emails coming from the internet are
>first passing through two relay servers. These relay servers employ
>smart host to relay emails to an antivirus server after which they are
>directed to our mail server to be delivered to our clients' malboxes.
>I have now implemented a second antivirus servers. In order to test
>its performance, I have removed all all of our domains, except for one
>particular domain, from being relayed from one of our relay servers. I
>have changed the sendmail.cf file of the relay server which is
>receieving emails for just one domain to round robin between the two
>antivirus servers. I performed the necessary changes in the zone file
>for this particular domain
>
>xxx  IN   60    A     yyyy.yyyy.yyyy.yyyy
>xxx  IN   60    A     zzzz.zzzz.zzzz.zzzz
>
>I also set mailertable for this domain to point to xxx.
>
>Last week I implemented this setup for testing. HOwever, I noticed
>that round robin was not occurring as I had wanted it to. All emails
>were being passed on to one of the antivirus servers for a long time
>(say almost two hours). AFter then, the emails were being sent to
>either the same server and or to the other antivirus server. I had not
>desired such a behaviour. I had wanted the relay server to stay
>swutching between one antivirus server and the other. Am I doing
>anything wrong
>
>This morning, I removed the network connection to this new antivirus
>server (at a time when all emails were being sent to it) just to
>verify whether emails starting being sent to the other antivirus
>server. They did not. They wer just queued on the server.
>
>Is there some way how I can implement a ROUND-ROBIN method where
>emails are being sent cyclically from one server to another or to just
>one server if the other server becomes faulty? From my implementation,
>it appears as if the relay server is caching one ip and keeping it
>until it expires (even though I set a TTL of 60s as you can see from
>my configuration above). Then, when the TTL is expiring, the ip is
>searched for again and cached.
>
>Can someone please help?
>
>Thank you in advance for any help or hints that you will be able to
>give me. They are much appreciated.
>
>
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