In most enterprise networks, each router instances will have a default route that specifies the next hop for packets with a destination IP address that is not explicitly matched in the routing table. For most routing instances on the Internet, the BGP routing table has an entry for every possible IP route in the global routing table and this a default route is not needed.
Note that many companies build enterprise networks that are DFZ networks and use proxy servers or NAT Gateways 1 to provide strictly controlled access to the Internet. This is common for companies with an elevated security posture that ensure all external access traverses a controlled gateway. Its expensive and complex while provides high levels of control.
- In my experience, DFZ enterprise networks use firewalls as an extra layer of security because the source and the destination are not trusted. ↩