[Mailman-Users] Unknown user- what am I missing?

John W. Baxter jwblist at olympus.net
Wed Dec 1 17:35:18 CET 2004

On 12/1/2004 1:58, "Brad Knowles" <brad at stop.mail-abuse.org> wrote:

> The integer numbers between the host/domain name and "IN" is the
> "Time To Live", a.k.a., the TTL.  This basically says how long the
> nameserver should cache this information before it re-queries from
> the appropriate nameservers for gmail.com/google.com.  Note that the
> MX records shown have a low TTL of 2633 seconds (43 minutes and 53
> seconds), while the NS records have a higher TTL of 10750 seconds (2
> hours, 59 minutes, 10 seconds), and there are a wide range of TTLs
> for the various IP addresses.  Some domains choose to have low TTLs
> for their advertised MXes as a crude way of "load balancing" across a
> large number of machines.

Note that these TTLs are "local" in the sense that they reflect the time the
record has left to dwell in the cache of the name server that provided the
answer, which usually isn't the authoritative server for an active domain
(unless one never talks to gmail).  (Try doing several dig commands a few
minutes apart.)

For example, a dig I did on one of our servers showed shorter times for the
mail servers (I'm not including the whole result):
gsmtp171.google.com.    809     IN      A
gsmtp185.google.com.    809     IN      A
gsmtp57.google.com.     809     IN      A

(Just before sending this, the 809 times are down to 476.)


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