What You Need To Know - ZyXEL Communications NR2101 User Manual

8.1.2 What You Need to Know

Inside/Outside
Inside/outside denotes where a host is located relative to the NR2101, for example, the computers of
your subscribers are the inside hosts, while the web servers on the Internet are the outside hosts.
Global/Local
Global/local denotes the IP address of a host in a packet as the packet traverses a router, for example,
the local address refers to the IP address of a host when the packet is in the local network, while the
global address refers to the IP address of the host when the same packet is traveling in the WAN side.
NAT
In the simplest form, NAT changes the source IP address in a packet received from a subscriber (the
inside local address) to another (the inside global address) before forwarding the packet to the WAN
side. When the response comes back, NAT translates the destination address (the inside global address)
back to the inside local address before forwarding it to the original inside host.
NAT Types
This section discusses the following NAT types that are implemented on the NR2101.
• Full Cone: In full cone NAT, the NAT router maps all outgoing packets from an internal IP address and
port to a single IP address and port on the external network. The NAT router also maps packets
coming to that external IP address and port to the internal IP address and port.
• Address Restricted or Restricted Cone: As in full cone NAT, a restricted cone NAT router maps all
outgoing packets from an internal IP address and port to a single IP address and port on the external
network. The difference from full cone NAT is in how the restricted cone NAT router handles packets
coming in from the external network.
• Port Restricted: Port restricted cone NAT maps all outgoing packets from an internal IP address and
port to a single IP address and port on the external network.
• Symmetric: The full, restricted and port restricted cone NAT types use the same mapping for an
outgoing packet's source address regardless of the destination IP address and port. In symmetric NAT,
the mapping of an outgoing packet's source address to a source address in another network is
different for each different destination IP address and port.
Chapter 8 NAT
NR2101 User's Guide
75