Without DHCPv4, the fixed-wireless RG can only get an IPv4 address during initial attach using NAS SM (session management) procedures. As part of NAS signaling, the BNG acting as a fixed-wireless gateway allocates an IPv4 address and returns it in a PDN address allocation (PAA) IE in the GTP session creation response.
If an RG requires IPv4 address allocation using DHCPv4 instead of address allocation during initial attach using NAS signaling, then it can signal a PCO "deferred address allocation" (value 0x000b) in GTP session setup. If this PCO is present in GTP setup request, then the BNG does not allocate an IPv4 address during GTP session setup. The GTP setup completes with IPv4 address of 0.0.0.0 returned in a PAA to the RG. The BNG only allocates and assign an IPv4 address using subsequent DHCPv4 from the RG, which is received over the GTP-u tunnel (S1-U interface) on the BNG.
If PCO ‟allocation via NAS” (value 0x000a) is present in a GTP setup request, then the IPv4 address is allocated during GTP setup and returned in a GTP session creation response.
If neither PCO is present, then by default, anIPv4 address is allocated on the GTP setup, and returned in the GTP session creation response. This can be overridden using the skip-gtp-ipv4-alloc CLI command. In this case, no IPv4 address is allocated during GTP setup and is only allocated using a subsequent DHCPv4 exchange.
The skip-gtp-ipv4-alloc configuration is a per-APN configuration. This can be
overridden on a per-subscriber basis using a RADIUS VSA
(Alc-Gtp-Skip-Ipv4-Alloc-Override).