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I am not in charge of the network, but I have responsibility for the Email Server at my workplace. We outsource networking, and how it was set is like this:
Mail Server (192.168.0.2)
Internet Firewall (155.x.y.z)
Internal DNS Server (mail.example.com -> 192.168.0.2)
Public DNS (World) (mail.example.com -> 155.x.y.z)
If i ping 155.x.y.z from within my LAN 192.168.0.0/24, I do not get a reply. When I consulted my network team, they said that I was not able to access 155.x.y.z from within the 192.168.0.0/24.
Problem My users use laptops, when they come into the LAN, for a while they still have (mail.example.com -> 155.x.y.z) in their DNS cache, and thus cannot get any reply from the mail server.
The options I have used are using a shorter TTL, but it has not worked because some of it is being overridden.
How can I fix the above?
Pilling Fine
Posted 2016-07-07T12:28:58.447
Reputation: 133
1Windows? Flush the DNS cache
ipconfig /flushdns– DavidPostill – 2016-07-07T14:24:48.857@DavidPostill many executive users use this setup, day in day out. Hard to tell them to run a
cmddaily. – Pilling Fine – 2016-07-07T14:28:52.3871You can probably automate it ... – DavidPostill – 2016-07-07T14:30:07.423
Smart, maybe a windows service which they run when they come into the network...or even detects network change and runs itself, smart...make it an answer :D – Pilling Fine – 2016-07-07T14:34:56.747
Not enough meat for an answer. When you figure it out you can answer your own question :) – DavidPostill – 2016-07-07T14:36:53.580
Tell them that to fix the issue, they just need to reboot once; that'll clear the DNS cache. – Ƭᴇcʜιᴇ007 – 2016-07-07T14:48:37.723
The network design seems broken by design, it should be repaired. Workarounds are just that: Workarounds. Not solutions. – Daniel B – 2016-07-08T06:42:59.933