redirects: make sure one-to-one mapping is used for the port range #9
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The linux kernel provides NF_NAT_RANGE_PROTO_OFFSET flag (netfilter nf_nat_core.c for reference), to make sure that when port ranges are used, then if possible, one-to-one mapping is maintained between external port range and internal port range. But for that flag to be set, iptables extension libxt_DNAT.c requires that base port is also passed along with the port range. Therefore, make sure that if the conditions are right, then we also pass a base port to iptables. One such example where this behaviour is expected is TR-181 data model's Device.NAT.PortMapping. object's InternalPort attribute.
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The linux kernel provides NF_NAT_RANGE_PROTO_OFFSET flag (netfilter nf_nat_core.c for reference), to make sure that when port ranges are used, then if possible, one-to-one mapping is maintained between external port range and internal port range. But for that flag to be set, iptables extension libxt_DNAT.c requires that base port is also passed along with the port range. Therefore, make sure that if the conditions are right, then we also pass a base port to iptables. One such example where this behaviour is expected is TR-181 data model's Device.NAT.PortMapping. object's InternalPort attribute.