When transferring domains to another registrar, to avoid any downtime the things to consider are:
- Will the web hosting account or server change too:
If so, then you'll need to upload all of your content and data there so both match and the new hosting will transparently pick up from your old hosting.
- Who's DNS servers are you using:
Major registrars provide DNS service for free for their customers, and if you don't specify custom DNS servers during registration or sometime afterwards, then likely you're using their DNS servers. If you're not changing your web hosting, then the DNS records should be transferred to the new register. To confirm this, check with their support team.
If you're using custom DNS servers or a third-party DNS service, then nothing will change as neither registrar is involved in that case.
If you created custom nameservers (often referred to as "Vanity Nameservers") with your registrar (e.g.,
ns2.yourdomain.com) using their DNS service, then these would map to their IP addresses. This will likely present a problem during the transfer.
In this case, you must create the custom nameservers with the new registrar's DNS service so they point to their IP's instead.
You can view the nameservers and which registrar they correspond to for your domain here: Internic's WHOIS
First look up the hosts for your domain name by doing a
Domain search there. Look at the results it returns for
Name Server. Typically this looks like:
ns1.domain.com If your domain doesn't appear in this, then you're likely not using custom nameservers. If it does, then look at the
Registrar field. If this corresponds to your old registrar, then you will need to update the IP addresses of your custom name servers to the IP addresses of your new registrar.
In this case, I recommend contacting the new registrar for assistance in creating custom nameservers, or review their FAQ's and knowledge-base. It's vital that you have this updated or visitors may not be able to reach your site. For an example of this, please see this question and my answer and comments there: Only I can access my hosted website!
If you follow the above, then if there are any changes to your DNS records, the new information should propagate within 24-72 hours. If you're changing web hosts, then leave the old one up for at least a week or more just to be on the safe-side, so that visitors will be directed to either web host containing the same content. Websites with frequently changing data may want to plan to mirror the two accounts/servers so both are current during the transfer (advanced).