Geo boundaries
Geo boundaries limit select DNS responses to clients within certain geographic boundaries. Clients outside those boundaries may be given a fallback response or no response at all.
Boundary determinations on the internet are necessarily imprecise. As such, they are always best effort. Nonetheless, boundaries can be quite useful for guiding a majority of users to the preferred destination.
Start by configuring one or more boundary routing definitions at Routing -> Boundaries -> Add Geo Location.
Name: a name for this boundary
Locations: one or more Geo location names (space separated)
; Configured boundary:
Name : Americas
Locations: nam sam
Next, assign your boundaries to host records.
; Configured host:
www.your-domain.com A 192.0.2.1 Boundary=Americas
www.your-domain.com A 198.51.100.1 Boundary=(not set)
With the above configuration, users in North America (nam) and South America (sam) will be routed to 192.0.2.1. Everyone else will be routed to 198.51.100.1, which is the fallback record.
When a fallback isn’t needed
Under most circumstances, a fallback record is required. If your configuration doesn’t benefit from a fallback record, you can use a dummy record of 0.0.0.0 (A) or ::0 (AAAA).
www.your-domain.com A 192.0.2.1 Boundary=Americas
www.your-domain.com A 0.0.0.0 Boundary=(not set)
Only rarely can fallback records be skipped without negative consequences. Most of the time this will be in combination with IP boundaries, not Geo boundaries. See notes at the bottom or contact us to discuss your sitation further.
Multiple matches
When a user’s location matches 2 or more boundaries simultaneously, all matching records are returned. For example:
www.your-domain.com A 192.0.2.1 Boundary=Americas [nam sam]
www.your-domain.com A 192.0.2.2 Boundary=Americas [nam sam]
www.your-domain.com A 192.0.2.3 Boundary=USA [us]
www.your-domain.com A 198.51.100.1 Boundary=(not set)
In this case, users in the USA will receive the first 3 records while users in Canada would receive just the first 2.
DNS caching without a fallback
Some DNS resolvers do not scope their cache for “no response” answers. Using boundaries without a fallback deliberately returns “no response”, which can then trigger odd results. If the host records are intended to be queried using broadly available DNS resolvers, it is strongly recommended to add a dummy fallback record (eg: www.your-domain.com A 0.0.0.0 Boundary=(not set)). On the other hand, if the boundary is used to constrain access to a known and limited set of resolvers (eg: a corporate office), then no dummy fallback record is required.
Technical details and Combinations
Boundaries may be assigned to A, AAAA, and ALIAS host record types.
IP and Geo boundary routing are processed together. A client that matches both an IP boundary and a Geo boundary will see both records. A fallback record is only used if neither an IP boundary nor a Geo boundary match.
IP and Geo boundaries are processed before Geo-closest.