Switching ISP to Comcast

We are switching from at&t to Comcast ISP.  When we switch what to I need to keep in mind?  What pitfalls should I be aware of?.  

The basics
We host our own website
Our domains are registered though a separate service (not through our ISP)
All traffic comes in to a router then a Firewall then to our network
Email filtering is hosted by a separate service, we use exchange 2010 once we receive it

Thank you in advance
John
John HausknechtITAsked:
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Paul MacDonaldDirector, Information SystemsCommented:
Make sure they help you port your IP addresses, especially if you don't own them outright.  Aside from that, it should be straightforward.
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btanExec ConsultantCommented:
See this list
http://www.netcorps.org/kb/office-tech/isp-cutover-checklist
http://www.hilltopconsultants.com/component/k2/item/90-considerations-when-changing-isps.html

Make a complete list of what you have now, exactly, and what the IP addresses are used for and re-directed to.

Determine what needs to be migrated over, and then add the new elements you will need. Match these up without IP addresses to make sure you order enough keeping in mind that you will probably get a subnet which will actually control the number of addresses you receive.

Plan your firewall(s) and IP address uses out exactly and match all to the old and the new.

Make sure all are live before you make the DNS changes. Verify all IP address uses by testing using the IP. Plan out your DNS records and get your internal DNS/advertised DNS listing ready to post.

Those should be done last making sure all IP Address/Name resolution is exactly as needed.

Change the DNS and wait for it to replicate, then test again and make sure all is well before shutting down the old.

If possible, do not cancel your current ISP until your new ISP is in place and active.  If feasible for your budget, consider using two ISP's and a firewall that allows for automatic failover and load balancing.  It is always a good idea to have a Backup Internet Connection.

Bear in mind that since you are not changing locations, you may need to put in static routes during the testing phase to bypass the default gateway arrangements.

Communicate often with the management of your business to set expectations.  When done properly, there should be no downtime, as long as you plan your ISP change carefully.
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