BROCADE IP PRIMER

49F Link 50FPower11F 2F 3F 4F49F Link 50FPower11F 2F 3F 4F3232Console54Console54767698981110111013121312151415141716171619181918212021202322232225242524272627262928292831303130333233323534353437363736393839384140414043424342454445444746 484746 48BI4XGBI4XGBI24CBI24CBI24C16T X RX T X RX T X RX T X RXT X RX T X RX T X RX T X RX12BigIron RX-8NETWORKS7131819242530313637424348AC OK DC OK ALMEJECT SYS AC OK DC OK ALMEJECT SYS AC OK DC OK ALMEJECT SYS AC OK DC OK ALMBI4XGBI4XGBI24CBI24CBI24C16T X RX T X RX T X RX T X RXT X RX T X RX T X RX T X RX12BigIron RX-8NETWORKS7131819242530313637424348BI24CBI24CBI24CBI24CBI24CBI4XGBI4XGT X RX T X RX T X RX T X RXT X RX T X RX T X RX T X RXAC OK DC OK ALMEJECT SYS AC OK DC OK ALMEJECT SYS AC OK DC OK ALMEJECT SYS AC OK DC OK ALMBI24CBI24CBI24CBI24CBI24CBI4XGBI4XGT X RX T X RX T X RX T X RXT X RX T X RX T X RX T X RXEJECT SYSEJECT SYSNetwork Address Translation (NAT)This was completely arbitrary. I could just as easily have chosen “1.1.2.25” or“1.1.2.113.” For the functionality of NAT, it doesn't matter. Keeping the lastoctet the same is a good organizational tactic, but it won't always work in allsituations.But anyway, how does the router do this translation? Well, a router is a Layer 3device. It receives a packet bound for some destination (in this example, theInternet). If NAT is configured, the router will examine the IP header of thepacket. If the source address field in the IP packet header shows an IPaddress that needs to be translated, it simply overwrites the source field andputs the public address in it. Likewise, when the router receives an inboundpacket (from the Internet, in this example), it will examine the destination IPaddress in the IP header. If it matches the public address, the router will overwritethe destination address in the header with the private address.1.1.2.1/24INTERNET192.168.100.10/24192.168.100.1/24Source192.168.100.10Destination4.3.2.1Source1.1.2.10Destination4.3.2.14.3.2.11.1.2.1/24INTERNET192.168.100.10/24Destination192.168.100.10192.168.100.1/24Source4.3.2.1Destination1.1.2.10Source4.3.2.14.3.2.1The important thing to remember with NAT is that it's a one-to-one translation.One public IP address translates to one private IP address (and vice-versa).The term “NAT” is used very loosely these days. Keep reading to understandwhy I would say that.You can also configure a NAT pool. This is a group of public addresses. When aclient needs to have its address translated, the router will choose an addressout of the NAT pool (a range of public addresses). This allows several privateusers to be translated.Brocade IP Primer 63