ZyXEL Communications VMG1312-B Series, Руководство пользователя

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Chapter 11 Network Address Translation (NAT)
VMG1312-B Series User’s Guide
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Not e t hat inside/ out side refers t o t he locat ion of a host , while global/ local refers t o t he I P address
of a host used in a packet . Thus, an inside local address ( I LA) is t he I P address of an inside host in
a packet when t he packet is st ill in t he local net work, while an inside global address ( I GA) is t he I P
address of t he sam e inside host when t he packet is on t he WAN side. The following t able
sum m arizes t his inform at ion.
NAT never changes t he I P address ( eit her local or global) of an out side host .
11.8.2 What NAT Does
I n t he sim plest form , NAT changes t he source I P address in a packet received from a subscriber
( t he inside local address) t o anot her ( t he inside global address) before forwarding t he packet t o t he
WAN side. When t he response com es back, NAT t ranslat es t he dest inat ion address ( t he inside
global address) back t o t he inside local address before forwarding it t o t he original inside host . Not e
t hat t he I P address ( eit her local or global) of an out side host is never changed.
The global I P addresses for t he inside host s can be eit her st at ic or dynam ically assigned by t he I SP.
I n addit ion, you can designat e servers, for exam ple, a web server and a t elnet server, on your local
net work and m ake t hem accessible t o t he out side world. I f you do not define any servers ( for Many-
t o- One and Many- t o- Many Overload m apping) , NAT offers t he addit ional benefit of firewall
prot ect ion. Wit h no servers defined, your Device filt ers out all incom ing inquiries, t hus prevent ing
int ruders from probing your net w ork. For m ore inform at ion on I P address t ranslat ion, refer t o
RFC
1631 , The I P Net work Address Translat or ( NAT) .
Table 61 NAT Definit ions
ITEM DESCRIPTION
I nside This refers t o t he host on t he LAN.
Out side This refers t o t he host on t he WAN.
Local This refers t o t he packet address ( source or dest inat ion) as t he packet t ravels on t he
LAN.
Global This refers t o t he packet address ( source or dest inat ion) as t he packet t ravels on t he
WAN.