The affiliate link structures are changing in the Google Affiliate Network as they complete the migration of affiliate operations to Google systems.
Currently, there is a mix of legacy and new generation links available, but eventually all links will migrate to the gan.doubleclick.net url and any legacy links will redirect to the new domain.
The new link structure is like the following:
http://gan.doubleclick.net/gan click?lid=410000000XXXXXXXX&pubid=210000000XXXXXXXX
See the Google Affiliate Network help section for how to build a redirect link.
More details on the Google Affiliate Network at http://www.google.com/ads/affiliatenetwork/.