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LeoFlag for Australia

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ISP Change

We are going through changing our corporate ISP, new ISP has allocated new IPs and our vendor has configured it on our comms equipments, he has asked a question which I need more clarification on, he has requested that "the IP addressing of the servers in the DMZ and the DNS stuff needs to be changed before cutting over."

With DNS I have checked, only two HOST A records have Public IP address, rest of them are all local (Webmail as well), and to check IP addressing of servers, where should I check that?
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Mal Osborne
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This is only applicable if you have a DMZ, with servers in that are accessible to the outside world.

This MAY include a mail server, or a web server or DNS server. (or proxies).

For even moderately large corporations, it is quite possible that you have no DMZ or servers. It is common to outsource web services and email to a hosting provider these days.

Do you have externally accessible servers on this site?
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ASKER

We have Bluecoat for Proxy, PFsense for webmail....how can I find local IP address of DMZ?
A DMZ (De Militarised Zone) is a subnet on your internal network that is accessible from the outside world. This is best practice to prevent machines one your internal LAN from being exposed to the outside world.

Unless you have machines ON YOUR PREMISES that can be directly connected too by anonymous users on the internet, you probably have no DMZ.

Large organisations MAY have a mail server in their building, or a web server, or an FTP server. These machines are connected to by users from outside of your organisation.  

Is your email server on your premises, or is it on a server somewhere else?
Is your company web server on your premises, or is it on a server somewhere else?
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ASKER

Our Exchange server is on premises (Nutnanix) virtual server, all our servers are virtualized.
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masnrock
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With MX records for mail yes they are going through Mimecast, that have been updated.
Just confused about DMZ, how do I find local IP address for it to access and see whats on it?
So, Mimecast are filtering your email "in the cloud"?  

In that case, your MX record need not change; external senders will still send email for your domain to Mimecast's servers. Somehow, you need to tell Mimecast about your new IP address, when the ISP changes, so they know where to forward email.

Your on premises mail server may or may not be in a DMZ, in  either case it is the same thing, you need to let Mimecast know where to forward your email, after filtering.

Your mail server may send outgoing email directly, or it may send it to Mimecast for filtering as it goes out. In the former case, you will need to revise your SPF record, or outgoing mail will tend to look like spam.
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Mimecast has already been informed and taken care off.

Only puzzle left is DMZ, IPs of servers on DMZ....and any other information which might need updating.
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Do I have to do anything with servers IP addresses?
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Also I am not able to find DNS host name for our VPN connection which staff use to connect to work when they are outside.

Where else it could be?

thanks.
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Thanks I have informed them.
Can you guys please check your inbox :-)
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Thanks guys for your support, specifically Masnrock, internet has been cutover and its stable.