IP gateway, services, and routing

In many deployments, a BNG UPF acts as a direct IP gateway for sessions. The BNG CPF provides all the IP addresses and framed routes using the PFCP protocol. To assist with forwarding, the BNG CPF also signals the following information using the PFCP protocol:

• name of the preprovisioned IES or VPRN service in which forwarding must occur

• aggregate routes that the BNG UPF announces in routing protocols to attract traffic

  Note: The BNG CPF guarantees that no addresses from the aggregate routes are assigned to sessions on another BNG UPF. See the 7450 ESS, 7750 SR, 7950 XRS, and VSR Unicast Routing Protocols Guide for more information about route policies.

• IPv4 gateway address, which is typically a dedicated address within the aggregate route

• IPv6 gateway link-local address, only one of which is supported per VPRN or IES

The BNG UPF runs the appropriate routing protocols and responds to ARP/ND for the gateway addresses. For the purpose of exporting routes, the operator can distinguish all CUPS routes using the pfcp option for the configure policy-options policy-statement entry from origin command. Additionally, the operator can further distinguish routes using the following options for the protocol command in the same context:

• sub-mgmt option for session IP addresses and prefixes, as signaled in the UE IP Address IE in PFCP
• managed option for framed routes, as signaled in the Framed-Route IE in PFCP
  Note: When using the pd-as-framed-route option on the BNG CPF, an IPv6 PD prefix uses the managed option (instead of the sub-mgmt option) because the BNG UPF cannot distinguish the PD framed route from a regular framed route.
• direct option for all other routes, such as aggregate routes and gateway addresses