Defining Address Pools

Before you can configure dynamic translation, create an address pool. An address pool is a group of IP addresses from which the NAT router obtains an address when dynamically creating a new translation. You can create address pools with either a single range or multiple, nonoverlapping ranges.

When you create a single range, you specify the starting and ending IP addresses for the range in the root ip nat pool command. However, when you create multiple, nonoverlapping ranges, you omit the optional starting and ending IP addresses in the root ip nat pool command; this launches the IP NAT Pool Configuration (config-ipnat-pool) mode.

The config-ipnat-pool mode uses an address command to specify a range of IP addresses. You can repeat this command to create multiple, nonoverlapping ranges.

When you create or edit address pools, keep the following in mind:

• Starting and ending IP addresses for the specified range are inclusive and must reside on the same subnet.
• Address ranges are verified against other ranges in the specified pool to exclude range overlaps. Additional verification occurs when the pool is associated with a translation rule and the router can determine whether the rule is inside or outside.
• You cannot change the network mask if configured ranges already exist.
• The network mask (or prefix length) is used to recognize host addresses that end in either all zeros or all ones. These addresses are reserved as broadcast addresses and are not allocated from an address pool, even if they are included in an address pool range.
• You cannot remove an address pool if the pool is part of a translation rule or if any of the ranges within the pool are still in use. You must issue the clear ip nat translation command to clear any ranges before you can remove the pool to which they apply.

address

• Use to specify a range of IP addresses in config-ipnat-pool mode; you can repeat the address command to create multiple ranges.
• Example

  host (config-ipnat-pool)#address 171.69.40.110 171.69.40.115

• Use the no version to remove the range for the current address pool.
• See address.

ip nat pool

• Use to create address pools.
• Example 1—Creating a single, continuous range

  host (config) #ip nat pool singlerange 171.69.40.1 171.69.40.100
  prefix-length 30

• Example 2—Creating multiple, discontinuous ranges

  host (config) #ip nat pool multiplerange prefix-length 30

  host (config-ipnat-pool)#address 171.69.40.110 171.69.40.112

  host (config-ipnat-pool)#address 171.69.40.118 171.69.40.120

  host (config-ipnat-pool)#exit

• Use the no version to remove the address range.
• See ip nat pool.

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