Дорожная карта для Cisco Cisco Packet Data Gateway (PDG)
Network Address Translation Overview
NAT Feature Overview ▀
Cisco ASR 5000 Series Product Overview ▄
OL-22937-01
NAT Port-chunk Allocation and Deallocation
This section describes the Port-chunk Allocation and Deallocation feature for many-to-one NAT.
NAT Port-chunk Allocation
Subscribers sharing a NAT IP address are allocated NAT ports in chunks. The ports in a port-chunk are always used for
the subscriber to whom that port-chunk is allocated irrespective of the protocol.
the subscriber to whom that port-chunk is allocated irrespective of the protocol.
Whenever a NAT IP address gets allocated to a subscriber, the first port-chunk gets allocated along with the NAT IP
address. Thus, for not-on-demand pools, the first port-chunk gets allocated during call setup, and for on-demand pools
during data flow.
address. Thus, for not-on-demand pools, the first port-chunk gets allocated during call setup, and for on-demand pools
during data flow.
A subscriber‘s TCP and UDP data traffic is NATed with ports chosen in a random fashion from the port-chunk allocated
to that subscriber. For other protocol traffic, the first available port is allocated. When all the ports in a port-chunk are in
use, a free port-chunk is requested for. A new port-chunk is only allocated if the ―Maximum Port-chunks Per User‖ limit
is not reached.
to that subscriber. For other protocol traffic, the first available port is allocated. When all the ports in a port-chunk are in
use, a free port-chunk is requested for. A new port-chunk is only allocated if the ―Maximum Port-chunks Per User‖ limit
is not reached.
NAT Port-chunk Deallocation
A port-chunk gets deallocated in the following cases:
―NAT Binding Timer‖ expiry
Subscriber session disconnect
NAT Binding Timer
When all flows using ports from a particular port-chunk get timed out/cleared, the port-chunk gets freed. When the last
port of that port-chunk gets freed, the NAT Binding Timer starts counting. Before the NAT Binding Timer expires, if
any new flows come up, ports are reallocated from the port-chunk, and the timer gets cancelled. The port-chunk cannot
be deallocated as long as there are active flows using that port-chunk. But, if no new flows come and the NAT Binding
Timer expires, the port-chunk gets deallocated.
port of that port-chunk gets freed, the NAT Binding Timer starts counting. Before the NAT Binding Timer expires, if
any new flows come up, ports are reallocated from the port-chunk, and the timer gets cancelled. The port-chunk cannot
be deallocated as long as there are active flows using that port-chunk. But, if no new flows come and the NAT Binding
Timer expires, the port-chunk gets deallocated.
In case of not-on-demand pools, the additional port-chunks that were allocated on demand will be deallocated based on
the NAT binding timeout. However, the last port-chunk will not be deallocated even after the Binding Timer expires.
This last port-chunk will only be deallocated when the NAT IP address is deallocated from the subscriber.
the NAT binding timeout. However, the last port-chunk will not be deallocated even after the Binding Timer expires.
This last port-chunk will only be deallocated when the NAT IP address is deallocated from the subscriber.
In case of on-demand pools, the port-chunks are deallocated based on the NAT binding timeout. When the last port-
chunk gets freed, the NAT IP address also gets deallocated from the subscriber.
chunk gets freed, the NAT IP address also gets deallocated from the subscriber.
It is ensured that a port-chunk is associated with the subscriber as long as a valid NAT IP address is allocated to the
subscriber.
subscriber.
Subscriber Session Disconnect