IP spoofing is a mechanism by which an IP packet is generated with invalid source IP address. Network Gateways cross verify the source IP address of an IP packet going outside.
In case of LTE network, PGW assigns IP addresses to UEs. PGW is aware about the IP addresses which have been assigned to UEs. When an uplink packet reaches at PGW from UE, PGW first verify whether source IP address is valid or not. If source IP address is valid than only PGW forwards IP packet towards external network. This way, PGW prevents IP spoofing in LTE network.
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