Hola. Estoy intentando hacer DNAT con Debian. El SNAT funciona perfectamente . Después de leerme el How
to e instalar el rc.firewall-iptables que viene en ese documento Os hago un esquema de cómo está la red Router ADSL -à
192.168.0.1/255.255.255.240 Linux --> Eth0 à
192.168.0.2/255.255.255.240 GW 192.168.0.1 à Eth1
à
192.168.1.1/255.255.255.240 Red local à 192.168.1.X /
255.255.255.240 Todos los equipos en la red local acceden a Internet sin
problemas. Ahora lo que necesito es redireccionar los puertos que
antes tenía redireccionados al router redireccionarlos a los equipos de la red
192.168.1.X Como el 46138 (VNC) por ejemplo que estaba redireccionado
al 192.168.0.14 , que ahora pasa a ser 192.168.1.14 Este equipo navega perfectamente pero creo que el DNAT no
funciona. La prueba que yo hago es intentar desde la red 192.168.0.x
con un pc con red 192.168.0.x intentar acceder con un cliente VNC a 192.168.0.2:46138.
Entiendo que si el DNAT se hiciera correctamente me pediría la clave de acesso
al VNC. (Lo hace si esa máquina la cambio a la red 192.168.0.x tanto desde la
red local como desde Internet, el router redirecciona correctamente a ese
puerto) De hecho si hago un dmesg me sale esto IN=eth0 OUT=eth1 SRC="" DST=192.168.1.14
LEN=52 TOS=0x00 PREC=0x00 TTL=63 ID=47736 DF PROTO=TCP SPT=12154 DPT=46138
WINDOW=65535 RES=0x00 SYN URGP=0 Os pego el script que uso , indicando las líneas que he
añadido para hacer DNAT . Está al final del todo la línea que hace DNAT. ---Inicio---- #!/bin/sh # # rc.firewall-iptables FWVER=0.76 # # Initial SIMPLE IP Masquerade test
for 2.6 / 2.4 kernels # using IPTABLES. # # Once IP Masquerading has been
tested, with this simple # ruleset, it is highly recommended
to use a stronger # IPTABLES ruleset either given later
in this HOWTO or # from another reputable resource. # # # # Log: # 0.76 - Added comments on why the default
policy is ACCEPT # 0.75 - Added more kernel modules to the
comments section # 0.74 - the ruleset now uses modprobe vs.
insmod # 0.73 - REJECT is not a legal policy yet;
back to DROP # 0.72 - Changed the default block behavior
to REJECT not DROP # 0.71 - Added clarification that PPPoE users
need to use # "ppp0" instead of
"eth0" for their external interface # 0.70 - Added commented option for IRC nat
module # - Added additional use of environment
variables # - Added additional formatting # 0.63 - Added support for the IRC IPTABLES
module # 0.62 - Fixed a typo on the MASQ enable line
that used eth0 # instead of $EXTIF # 0.61 - Changed the firewall to use
variables for the internal # and external interfaces. # 0.60 - 0.50 had a mistake where the ruleset
had a rule to DROP # all forwarded packets but it didn't
have a rule to ACCEPT # any packets to be forwarded either # - Load the ip_nat_ftp and
ip_conntrack_ftp modules by default # 0.50 - Initial draft # echo -e "\n\nLoading simple
rc.firewall-iptables version $FWVER..\n" # The location of the iptables and kernel module
programs # # If your Linux distribution came with a copy of
iptables, # most likely all the programs will be located in
/sbin. If # you manually compiled iptables, the default
location will # be in /usr/local/sbin # # ** Please use the "whereis iptables"
command to figure out # ** where your copy is and change the path below
to reflect # ** your setup # IPTABLES=/sbin/iptables #IPTABLES=/usr/local/sbin/iptables DEPMOD=/sbin/depmod MODPROBE=/sbin/modprobe #Setting the EXTERNAL and INTERNAL interfaces for
the network # # Each IP Masquerade network needs to have at
least one # external and one internal network. The external
network # is where the natting will occur and the internal
network # should preferably be addressed with a RFC1918
private address # scheme. # # For this example, "eth0" is external
and "eth1" is internal" # # # NOTE: If this doesnt EXACTLY fit your
configuration, you must # change the EXTIF or INTIF variables
above. For example: # # If you are a PPPoE or analog modem
user: # # EXTIF="ppp0" # # EXTIF="eth0" INTIF="eth1" MAC="192.168.1.14" # 46138 echo " External Interface: $EXTIF" echo " Internal Interface: $INTIF" #====================================================================== #== No editing beyond this line is required for
initial MASQ testing == echo -en " loading modules: " # Need to verify that all modules have all required
dependencies # echo " - Verifying that all kernel modules
are ok" $DEPMOD -a # With the new IPTABLES code, the core MASQ
functionality is now either # modular or compiled into the kernel. This HOWTO
shows ALL IPTABLES # options as MODULES. If your kernel is compiled
correctly, there is # NO need to load the kernel modules manually. # # NOTE: The following items are listed ONLY for
informational reasons. # There is no reason to manual load these
modules unless your # kernel is either mis-configured or you
intentionally disabled # the kernel module autoloader. # # Upon the commands of starting up IP Masq on the
server, the # following kernel modules will be automatically
loaded: # # NOTE: Only load the IP MASQ modules you need. All
current IP MASQ # modules are shown below but are commented
out from loading. #
=============================================================== echo
"----------------------------------------------------------------------" #Load the main body of the IPTABLES module -
"iptable" # - Loaded automatically when the
"iptables" command is invoked # # - Loaded manually to clean up kernel
auto-loading timing issues # echo -en "ip_tables, " $MODPROBE ip_tables #Load the IPTABLES filtering module -
"iptable_filter" # - Loaded automatically when filter policies are
activated #Load the stateful connection tracking framework -
"ip_conntrack" # # The conntrack module in itself does nothing
without other specific # conntrack modules being loaded afterwards such as
the "ip_conntrack_ftp" # module # # - This module is loaded automatically when MASQ
functionality is # enabled # # - Loaded manually to clean up kernel
auto-loading timing issues # echo -en "ip_conntrack, " $MODPROBE ip_conntrack #Load the FTP tracking mechanism for full FTP tracking # # Enabled by default -- insert a "#" on
the next line to deactivate # echo -en "ip_conntrack_ftp, " $MODPROBE ip_conntrack_ftp #Load the IRC tracking mechanism for full IRC
tracking # # Enabled by default -- insert a "#" on
the next line to deactivate # echo -en "ip_conntrack_irc, " $MODPROBE ip_conntrack_irc #Load the general IPTABLES NAT code -
"iptable_nat" # - Loaded automatically when MASQ functionality
is turned on # # - Loaded manually to clean up kernel
auto-loading timing issues # echo -en "iptable_nat, " $MODPROBE iptable_nat #Loads the FTP NAT functionality into the core
IPTABLES code # Required to support non-PASV FTP. # # Enabled by default -- insert a "#" on
the next line to deactivate # echo -en "ip_nat_ftp, " $MODPROBE ip_nat_ftp #Loads the IRC NAT functionality into the core
IPTABLES code # Required to support NAT of IRC DCC requests # # Disabled by default -- remove the "#"
on the next line to activate # #echo -e "ip_nat_irc" #$MODPROBE ip_nat_irc echo "----------------------------------------------------------------------" # Just to be complete, here is a partial list of
some of the other # IPTABLES kernel modules and their function. Please
note that most # of these modules (the ipt ones) are automatically
loaded by the # master kernel module for proper operation and
don't need to be # manually loaded. #
-------------------------------------------------------------------- # # ip_nat_snmp_basic - this module allows for
proper NATing of some # SNMP traffic # # iptable_mangle - this target allows for
packets to be # manipulated for things
like the TCPMSS # option, etc. # # -- # # ipt_mark - this target marks a given
packet for future action. # This automatically loads the
ipt_MARK module # # ipt_tcpmss - this target allows to
manipulate the TCP MSS # option for braindead remote
firewalls. # This automatically loads the
ipt_TCPMSS module # # ipt_limit - this target allows for
packets to be limited to # to many hits per sec/min/hr # # ipt_multiport - this match allows for targets
within a range # of port numbers vs. listing
each port individually # # ipt_state - this match allows to catch
packets with various # IP and TCP flags set/unset # # ipt_unclean - this match allows to catch
packets that have invalid # IP/TCP flags set # # iptable_filter - this module allows for
packets to be DROPped, # REJECTed, or LOGged. This
module automatically # loads the following modules: # # ipt_LOG - this target allows
for packets to be # logged # # ipt_REJECT - this target
DROPs the packet and returns # a configurable
ICMP packet back to the # sender. # echo -e " Done loading modules.\n" #CRITICAL: Enable IP forwarding since it is
disabled by default since # # Redhat Users: you may try changing the
options in # /etc/sysconfig/network from: # # FORWARD_IPV4=false # to # FORWARD_IPV4=true # echo " Enabling forwarding.." echo "1" >
/proc/sys/net/ipv4/ip_forward # Dynamic IP users: # # If you get your IP address dynamically from
SLIP, PPP, or DHCP, # enable this following option. This enables
dynamic-address hacking # which makes the life with Diald and similar programs
much easier. # #echo " Enabling DynamicAddr.." #echo "1" >
/proc/sys/net/ipv4/ip_dynaddr # Enable simple IP forwarding and Masquerading # # NOTE: In IPTABLES speak, IP Masquerading is a
form of SourceNAT or SNAT. # # NOTE #2: The following is an example for an
internal LAN address in the # 192.168.0.x network with a
255.255.255.0 or a "24" bit subnet mask # connecting to the Internet on external
interface "eth0". This # example will MASQ internal traffic out
to the Internet but not # allow non-initiated traffic into your
internal network. # # # ** Please change the above network
numbers, subnet mask, and your # *** Internet connection interface name to
match your setup # #Clearing any previous configuration # # Unless specified, the defaults for INPUT and
OUTPUT is ACCEPT # The default for FORWARD is DROP (REJECT is not
a valid policy) # # Isn't ACCEPT insecure? To some degree, YES,
but this is our testing # phase. Once we know that IPMASQ is working
well, I recommend you run # the rc.firewall-*-stronger rulesets which set
the defaults to DROP but # also include the critical additional rulesets
to still let you connect to # the IPMASQ server, etc. # echo " Clearing any existing rules and
setting default policy.." $IPTABLES -P INPUT ACCEPT $IPTABLES -F INPUT $IPTABLES -P OUTPUT ACCEPT $IPTABLES -F OUTPUT $IPTABLES -P FORWARD DROP $IPTABLES -F FORWARD $IPTABLES -t nat -F echo " FWD: Allow all connections OUT and
only existing and related ones IN" $IPTABLES -A FORWARD -i $EXTIF -o $INTIF -m state
--state ESTABLISHED,RELATED -j ACCEPT $IPTABLES -A FORWARD -i $INTIF -o $EXTIF -j ACCEPT $IPTABLES -A FORWARD -j LOG echo " Enabling SNAT (MASQUERADE)
functionality on $EXTIF" $IPTABLES -t nat -A POSTROUTING -o $EXTIF -j
MASQUERADE #A partir de aquí lo he añadido yo echo " Enabling DNAT functionality on
$EXTIF" iptables -t nat -A PREROUTING -p tcp --dport 46138
-i $EXTIF -j DNAT --to $MAC:46138 #Fin de la modificación respecto al script original echo -e "\nrc.firewall-iptables v$FWVER done.\n" ----Fin---- Atentamente, Jorge Giménez |