===== Static NAT Configuration =====
Static NAT requires few configuration steps. Each static mapping between local and global addresses **must** be configured. Not unlike a static entry for every static IP address required. You must inform the router on which interfaces to use ''**NAT**''. Interface subcommands inform the router which interfaces are ''**inside**'' / ''**outside**''.
- ''**ip nat inside**'' command on an interface to specify inside.
- ''**ip nat outside**'' command on an interface to specify outside.
- ''**ip nat inside source static inside-local inside-global**'' from global config to configure the static mappings.
- inside local will be a LAN IP - inside global will be your public IP (an EXTRA public IP).
===== Port Address Translation =====
Create an access list to match a group of source addresses as needed -- why else would we overload?
R1(config-std-nacl)#permit 10.1.1.0 0.0.0.255
R1#sh access-lists
Standard IP access list NAT
10 permit 10.1.1.0, wildcard bits 0.0.0.255 (2 matches)
20 deny any
Then configure NAT to match against entries in the NAT list configured above. Specify ''**OVERLOAD**'' to enable PAT.
ip nat inside source list MY_LIST int fa0/0 OVERLOAD
===== Verify NAT =====
R1#sh ip nat statistics
Total active translations: 0 (0 static, 0 dynamic; 0 extended)
Outside interfaces:
FastEthernet0/0, Serial0/0
Inside interfaces:
FastEthernet0/1, Loopback0
Hits: 16 Misses: 2
CEF Translated packets: 18, CEF Punted packets: 0
Expired translations: 2
Dynamic mappings:
-- Inside Source
[Id: 2] access-list NAT interface FastEthernet0/0 refcount 0
Appl doors: 0
Normal doors: 0
Queued Packets: 0
R1#sh ip nat translations
Pro Inside global Inside local Outside local Outside global
icmp 2.2.2.1:1 10.1.1.1:1 2.2.2.2:1 2.2.2.2:1
icmp 2.2.2.1:11 10.1.1.3:11 2.2.2.2:11 2.2.2.2:11
==== Clear NAT Translations ====
Useful with dynamic NAT in the event you run out of dynamic addresses to translate to. Clearing translations will free up slots if the clearout timer isn't quick enough.
R1#clear ip nat translation *
===== Chapter Questions =====
==== One ====
**Examine the following show command output on a router configured for dynamic NAT:**
-- Inside Source
access-list 1 pool fred refcount 2288
pool fred: netmask 255.255.255.240
start 200.1.1.1 end 200.1.1.7
type generic, total addresses 7, allocated 7 (100%), misses 965
Users are complaining about not being able to reach the Internet. Which of the following is the most likely cause?
''**The NAT pool does not have enough entries to satisfy all requests.**''
The problem is not related to NAT, based on the information in the command output.
The command output does not supply enough information to identify the problem.
Standard ACL 1 cannot be used; an extended ACL must be used.
You answered this question correctly. ×
**Explanation:**
The last line mentions that the pool has seven addresses, with all seven allocated, with the misses counter close to 1000 - meaning that close to 1000 new flows were rejected because of insufficient space in the NAT pool.
==== Two ====
**Which of the following summarized subnets represent routes that could have been created for CIDR’s goal to reduce the size of Internet routing tables?**
* 200.1.1.0 255.255.255.0
* ''**200.1.0.0 255.255.0.0**''
* 10.1.0.0 255.255.0.0
* 10.0.0.0 255.255.255.0
You answered this question correctly. ×
**Explanation:**
CIDR’s original intent was to allow the summarization of multiple Class A, B, and C networks to reduce the size of Internet routing tables. Of the answers, only 200.1.0.0 255.255.0.0 summarizes multiple networks.
==== Three ====
**With static NAT, performing translation for inside addresses only, what causes NAT table entries to be created?**
* ''**Configuration using the ip nat inside source command**''
* The first packet from the inside network to the outside network
* Configuration using the ip nat outside source command
* The first packet from the outside network to the inside network
You answered this question correctly. ×
**Explanation:
**With static NAT, the entries are statically configured. Because the question mentions translation for inside addresses, the inside keyword is needed in the command.