Specifications

Table Of Contents
VMware, Inc. 175
Chapter 7 Networking
Windows Hosts
Systems!using!server!versions!of!Windows!2000!are!capable!of!forwarding!IP!packets!
that!are!not!addressed!to!them.!By!default,!however,!these!systems!come!with!IP!packet!
forwarding!disabled.!
If!you!find!packets!leaking!out!of!a!hostonly!network!on!a!Windows!2000!host!
computer,!check!to!see!whether
!forwarding!has!been!enabled!on!the!host!machine.!If!it!
is!enabled,!disable!it.!
Choose!Start!>!Programs!>!Administrative!Tools!>!Routing!and!Remote!Access.!An!
icon!on!the!left!is!labeled!with!the!host!name.!If!a!green!dot!appears!over!the!icon,!IP!
forwarding!is!turned!on.
!To!turn!it!off,!rightclick!the!icon!and!disable!Routing!and!
Remote!Access.!A!red!dot!appears,!indicating!that!IP!forwarding!is!disabled.!
Linux Hosts
If!you!find!packets!leaking!out!of!a!hostonly!network!on!a!Linux!host!computer,!check!
to!see!whether!forwarding!has!mistakenly!been!enabled!on!the!host!machine.!If!it!is!
enabled,!disable!it.!
For!many!Linux!systems,!disable!forwarding!by!writing!a!0!(zero)!to!the!special!file!
/proc/sys/net/ipv4/ip_forward
.!As!root,!enter!this!command:
echo 0 > /proc/sys/net/ipv4/ip_forward
Other!Linux!systems!have!a!system!configuration!option!that!you!can!set.!The!method!
depends!on!your!Linux!distribution.!You!can!use!a!control!panel,!specify!a!setting!at!the!
time!you!compile!your!kernel,!or!possibly!enter!a!specification!when!you!boot!your!
system.!
Consult!your!operating!system!documentation!for!details!on!the!method!to!use!
with!your!particular!distribution.!
Using Filtering
If!the!host!computer!has!multiple!network!adapters,!it!might!be!intentionally!
configured!to!do!IP!forwarding.!In!this!case,!you!do!not!want!to!disable!forwarding.!To!
avoid!packet!leakage,!you!must!enable!a!packet!filtering!facility!and!specify!that!
packets!from!the!hostonly!network!should!not!be!sent
!outside!the!host!computer.!
Consult!your!operating!system!documentation!for!details!on!how!to!configure!packet!
filtering.!
Leaks from a Virtual Machine
Virtual!machines!might!leak!packets,!as!well.!For!example,!if!you!use!dialup!
networking!support!in!a!virtual!machine!and!packet!forwarding!is!enabled,!hostonly!
network!traffic!might!leak!out!through!the!dialup!connection.