Specifications

Table Of Contents
VMware Server Virtual Machine Guide
192 VMware, Inc.
virtual!machines!to!a!DNS!server!that!is!known!by!the!host.!Responses!come!back!to!the!
NAT!device,!which!then!forwards!them!to!the!virtual!machines.
If!they!get!their!configuration!information!from!DHCP,!the!virtual!machines!on!the!
NAT!network!automatically!use!the!NAT!device!as!the!DNS!server.!
However,!the!
virtual!machines!can!be!statically!configured!to!use!another!DNS!server.
The!virtual!machines!in!the!private!NAT!network!are!not,!themselves,!accessible!via!
DNS.!If!you!want!the!virtual!machines!running!on!the!NAT!network!to!access! each!
other!by!DNS!names,!you!must!set!up!a!private!
DNS!server!connected!to!the!NAT!
network.
External Access from the NAT Network
In!general,!any!protocol!using!TCP!or!UDP!can!be!used!automatically!by!a!virtual!
machine!on!the!NAT!network!so!long!as!the!virtual!machine!initiates!the!network!
connection.!This!is!true!for!most!client!applications!such!as!Web!browsing,!Telnet,!
passivemode!FTP,!and!downloading!streaming!video.!Additional!protocol
!support!
has!been!built!into!the!NAT!device!to!allow!FTP!and!ICMP!echo!(ping)!to!work!
completely!transparently!through!the!NAT.
On!the!external!network!to!which!the!host!is!connected,!any!virtual!machine!on!the!
NAT!network!appears!to!be!the!host!itself,!because!its!network!traffic!uses!the
!host’s!IP!
address.!It!is!able!to!send!and!receive!data!using!TCP/IP!to!any!machine!that!is!
accessible!from!the!host.!
Before!any!such!communication!can!occur,!the!NAT!device!must!set!up!a!mapping!
between!the!virtual!machine’s!address!on!the!private!NAT!network!and!the!host’s!
network!
address!on!the!external!network.!
When!a!virtual!machine!initiates!a!network!connection!with!another!network!resource,!
this!mapping!is!created!automatically.!The!operation!is!perfectly!transparent!to!the!user!
of!the!virtual!machine!on!the!NAT!network.!No!additional!work!needs!to!be!done!to!let!
the!virtual!machine!access
!the!external!network.
The!same!cannot!be!said!for!network!connections!that!are!initiated!from!the!external!
network!to!a!virtual!machine!on!the!NAT!network.!
When!a!machine!on!the!external!network!attempts!to!initiate!a!connection!with!a!virtual!
machine!on!the!NAT!network,!it!cannot!reach!the!virtual
!machine!because!the!NAT!
device!does!not!forward!the!request.!Network!connections!that!are!initiated!from!
outside!the!NAT!network!are!not!transparent.!
However,!it!is!possible!to!configure!port!forwarding!manually!on!the!NAT!device!so!
network!traffic!destined!for!a!certain!port!can!still!be!forwarded!automatically!to!
a!