In fact, many inside
hosts could share the inside global IPv4 address by using many port numbers.
The router performs the following process when it overloads inside global addresses:
Step 1 The user at host 1.1.1.1 opens a connection to host B.
Step 2 The ?¬?rst packet that the router receives from host 1.1.1.1 causes the
router to check its NAT table.
1.1.1.2
Host B
9.6.7.3
1.1.1.1 1
SA
1.1.1.1
2
5
DA
1.1.1.1
3
SA
2.2.2.2
4
DA
2.2.2.2
4
DA
2.2.2.2
Inside
Outside Global
IPv4 Address:Port
Inside Global
IPv4 Address:Port
Inside Local
IPv4 Address:Port
Protocol
6.5.4.7:23
9.6.7.3:23
2.2.2.2:1723
2.2.2.2:1024
1.1.1.2:1723
1.1.1.1:1024
TCP
TCP
NAT Table
Internet
Host C
6.5.4.7
Scaling the Network with NAT and PAT 259
If no translation entry exists, the router determines that address 1.1.1.1 must be
translated and sets up a translation of inside local address 1.1.1.1 into a legal inside
global address. If overloading is enabled and another translation is active, the router
reuses the inside global address from that translation and saves enough information
to be able to translate back. This type of entry is called an extended entry.
Pages:
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390