The main difference is that the address of the site in the web browser will change in URL forwarding but not in frame forwarding. We can illustrate the difference with an example of a forwarding rule to redirect your www.your-old-domain.co.uk to your www.your-new-domain.com.
- URL forwarding: any visitor will see www.your-old-domain.co.uk change to www.your-new-domain.com in the address bar of their browser.
- Frame forwarding: any visitor will still see www.your-old-domain.co.uk in the address bar of their browser.
If you are conscious of search engine rankings we'd recommend avoiding frame forwarding as it can impact how your site is listed in search engines. It is possible to partially compensate for this by adding the meta data from website to your frame forward in the Maintenance section of the Domains Centre.