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NAT


Overview: 

How to setup NATing on a JunOS firewall. 

Outbound PAT (source nat): 

 

1: Zone To-From match: 

Define what the source and destination zones will be: 
set security nat source rule-set source-nat from zone inside
set security nat source rule-set source-nat to zone dmz
Where "inside" and "outside" are zones that are previously defined.  

2: rule #1 - do not match for internal routes

Create a rule that does not nat traffic that is staying internal
set security nat source rule-set source-nat rule nat-off match source-address 10.100.0.0/16
set security nat source rule-set source-nat rule nat-off match destination-address-name rfc3330
set security nat source rule-set source-nat rule nat-off then source-nat off
note that "rfc3330" would be a address book name that defines all non-routable IPs.  (see below for an example of this)

3: rule #2 - match everything else

Create a rule that matches any other traffic, and applys the nat to it.  
set security nat source rule-set source-nat rule patOut match source-address-name internalIp
set security nat source rule-set source-nat rule patOut then source-nat pool patIp1
Here "internalIP" would be another address book name that equated to the internal IPs behind the "inside" interface.  With this example it would be the same as "10.100.0.0/16".  

4: use this NAT IP for match: 

Define the IP that will be used for the PATting: 
set security nat source pool patIp1 address 1.1.1.100/32

3-4: rule #2 -match everything else and NAT to external interface: 

If you want the NAT to simply use the external interface for the NAT IP, then you can use the "interface" variable instead of defining a different IP for the NAT.  
set security nat source rule-set source-nat rule patOut match source-address-name internalIp
set security nat source rule-set source-nat rule patOut then source-nat interface

Inbound NAT (destination nat): 




Define the policy that will allow traffic to flow to the server from the outside: 
set security policies from-zone dmz1 to-zone prod3 policy webIn match source-address any
set security policies from-zone dmz1 to-zone prod3 policy webIn match destination-address web1
set security policies from-zone dmz1 to-zone prod3 policy webIn match application webIGV-8083
set security policies from-zone dmz1 to-zone prod3 policy webn match application junos-https
set security policies from-zone dmz1 to-zone prod3 policy webIn then permit
!
set security address-book global address web1 10.33.64.108/32


Define the VIP (and port it's listening on)
set security nat destination rule-set Public_VIPs rule web-in match destination-address 9.30.6.25/32
set security nat destination rule-set Public_VIPs rule web-in match destination-port 443
set security nat destination rule-set Public_VIPs rule web-in then destination-nat pool web_443

Define the Server (and port its listening on)
set security nat destination pool web_443 address 10.33.64.108/32
set security nat destination pool web_443 address port 443

And listen from the outside interface
set security nat destination rule-set Public_VIPs from zone dmz1



References: 

RFC3330 example: 

Just an easy way to define all non-routable IPs: 
set security address-book global address-set rfc3330 address this
set security address-book global address-set rfc3330 address 1918a
set security address-book global address-set rfc3330 address loopback
set security address-book global address-set rfc3330 address linklocal
set security address-book global address-set rfc3330 address 1918b
set security address-book global address-set rfc3330 address testnet
set security address-book global address-set rfc3330 address 6to4anycast
set security address-book global address-set rfc3330 address 1918c
set security address-book global address-set rfc3330 address benchmark
set security address-book global address-set rfc3330 address classd
set security address-book global address-set rfc3330 address classe

set security address-book global address this 0.0.0.0/8
set security address-book global address 1918a 10.0.0.0/8
set security address-book global address loopback 127.0.0.0/8
set security address-book global address linklocal 169.254.0.0/16
set security address-book global address 1918b 172.16.0.0/12
set security address-book global address testnet 192.0.2.0/24
set security address-book global address 6to4anycast 192.88.99.0/24
set security address-book global address 1918c 192.168.0.0/16
set security address-book global address benchmark 198.18.0.0/15
set security address-book global address classd 224.0.0.0/4
set security address-book global address classe 240.0.0.0/4

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