Nokia M1112 Administrator's Manual
Also see for M1112: User manual
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M1112 Administrator Manual Copyright Nokia Networks Oy C33907001SE_002-8self-learning bridge supporting up to 1024 MAC addresses. Bridgingis done between the Ethernet 10Base-T interface and each ATM VCCinterface. Optionally, the bridging between the VCCs can be disabled.2.2.4 Network Address Port TranslationM1112 supports Network Address Port Translation (NAPT) forTCP/IP, UDP/IP and ICMP/IP protocols. When NAPT is used, a singleIP address is allocated to a VCC which leads to the public IP network.The Ethernet subnet has private IP addressing and is not visible to theVCC. NAPT translates the IP source address and source port numberdynamically to the VCC IP address and port number. Similarly,packets coming from the VCC are mapped back to the originaldestination addresses. NAPT allows up to hundreds of hosts to share asingle VCC IP address to the public network. The principle of NetworkAddress Port Translation is presented in Figure 2-4.NAPT router192.168.1.254195.112.12.161src:192.168.1.112:1228dst:194.112.11.111:80src:194.112.11.111:80dst:192.168.1.112:1228src:195.112.12.161:50001dst:194.112.11.111:80src:194.112.11.111:80dst:195.112.12.161:50001Home network (LAN) Internet (WAN)Figure 2-4 Principle of Network Address Port TranslationNAPT may restrict the operation of some IP applications. NAPT alsooperates as a simple IP firewall because translation is only allowedwhen the first packet is transmitted from the LAN. This means that theNAPT table entry is created only when a packet is sent from the homenetwork to the Internet. With server support capability, the user canadd static entries to the NAPT table allowing the translation always inboth directions. This capability is used to add servers (HTTP, NNTP,and FTP), which are visible to the public IP network via the VCC, onthe LAN subnet.NAPT supports most IP-based protocols. Because NAPT operates onthe IP and transport layer, the application that includes IP address andport within the payload will not work properly through NAPT. In manycases, these applications can be passed through the NAPT using |
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