The longest prefix matching (LPM) table of GK blocks does not accept a default route (i.e. a route for the prefix of length zero) because it uses DPDK's LPM implementation, which doesn't accept a prefix of length zero.

Given that Gatekeeper servers are expected to be BGP speaker, this may not be an issue at all, but someone may find a deployment scenario in which default routes are necessary. Thus, until this deployment scenario becomes known, this issue has very low priority.

A solution is patching DPDK to support zero-length prefixes.