78 lines
2.8 KiB
Plaintext
78 lines
2.8 KiB
Plaintext
Configuring NAT on your network.
|
|
================================
|
|
|
|
To start setting up NAT, we need to define which is your "internal" interface
|
|
and which is your "external" interface. The "internal" interface is the
|
|
network adapter connected to the network with private IP addresses which
|
|
you need to change for communicating on the Internet. The "external"
|
|
interface is configured with a valid internet address.
|
|
|
|
For example, your internal interface might have an IP# of 10.1.1.1 and be
|
|
connected to your ethernet, whilst your external interface might be a PPP
|
|
connection with an IP number of 204.51.62.176.
|
|
|
|
Thus your network might look like this:
|
|
|
|
<Internal Network>
|
|
[pc] [pc]
|
|
| |
|
|
+-+---------+------+
|
|
|
|
|
[firewall]
|
|
|
|
|
|
|
|
Internet
|
|
<External Network>
|
|
|
|
|
|
Writing the map-rule.
|
|
---------------------
|
|
When you're connected to the Internet, you will either have a block of IP
|
|
addresses assigned to you, maybe several different blocks, or you use a
|
|
single IP address, i.e. with dialup PPP. If you have a block of addresses
|
|
assigned, these can be used to create either a 1:1 mapping (if you have
|
|
only a few internal IP addresses) or N:1 mappings, where groups of internal
|
|
addresses map to a single IP address and unless you have enough Internet
|
|
addresses for a 1:1 mapping, you will want to do "portmapping" for TCP and
|
|
UDP port numbers.
|
|
|
|
For an N:1 situation, you might have:
|
|
|
|
map ppp0 10.1.0.0/16 -> 209.23.1.5/32 portmap tcp/udp 10000:40000
|
|
map ppp0 10.1.0.0/16 -> 209.23.1.5/32 portmap
|
|
|
|
where if you had 16 addresses available, you could do:
|
|
|
|
map ppp0 10.1.0.0/16 -> 209.23.1.0/28 portmap tcp/udp 10000:40000
|
|
map ppp0 10.1.0.0/16 -> 209.23.1.0/28 portmap
|
|
|
|
Or if you wanted to allocate subnets to each IP#, you might do:
|
|
|
|
map ppp0 10.1.1.0/24 -> 209.23.1.2/32 portmap tcp/udp 10000:40000
|
|
map ppp0 10.1.2.0/24 -> 209.23.1.3/32 portmap tcp/udp 10000:40000
|
|
map ppp0 10.1.3.0/24 -> 209.23.1.4/32 portmap tcp/udp 10000:40000
|
|
map ppp0 10.1.1.0/24 -> 209.23.1.2/32 portmap
|
|
map ppp0 10.1.2.0/24 -> 209.23.1.3/32 portmap
|
|
map ppp0 10.1.3.0/24 -> 209.23.1.4/32 portmap
|
|
|
|
*** NOTE: NAT rules are used on a first-match basis only!
|
|
|
|
|
|
Filtering with NAT.
|
|
-------------------
|
|
IP Filter will always translate addresses in a packet _BEFORE_ it checks its
|
|
access list for inbound packets and translates addresses _AFTER_ it has
|
|
checked the access control lists for outbound packets.
|
|
|
|
For example (using the above NAT rules), if you wanted to prevent all hosts
|
|
in the 10.1.2.0/24 subnet from using NAT, you might use the following rule
|
|
with ipf:
|
|
|
|
block out on ppp0 from 10.1.2.0/24 to any
|
|
block in on ppp0 from any to 10.1.2.0/24
|
|
|
|
and use these with ipnat:
|
|
|
|
map ppp0 10.1.0.0/16 -> 209.23.1.0/28 portmap tcp/udp 10000:40000
|
|
map ppp0 10.1.0.0/16 -> 209.23.1.0/28 portmap
|