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Defining an Overload Pool or an Overload Prefix

On the Services Router, you can configure an oversubscribed NAT pool to fall back on Network Address Port Translation (NAPT), also known as Port Address Translation (PAT). An overload NAPT pool provides additional NAT sessions when all the addresses in the source pool are in use. You can use one public address multiple times by assigning different port numbers to it.

Alternatively, for an oversubscribed NAT pool, you can configure an overload prefix to be used when the address pool is exhausted.

This example shows how to define an overload pool or an overload prefix. The terms used in the example are described in Table 89.

Note: An overload prefix is an alternative to an overload pool. Define either over-pool-term or over-prefix-term, not both.

Table 89: Sample Terms for Defining an Overload Pool or Prefix

Term

Purpose

over-pool-term

Dynamically translates the source address (10.10.10.0/24) to an address within the pool 121.0.1.2 through 121.0.1.20. After the addresses from the pool are used, the system uses the NAPT pool (pat-pool) 121.0.1.21 through 121.0.1.22 for address translation in combination with dynamically assigned ports by means of NAPT.

over-prefix-term

Dynamically translates the source address (10.10.10.0/24) to an address within the pool 121.0.1.2 through 121.0.1.20. After these addresses are used, the system uses the prefix 123.0.1.0/24.

To define an overload pool or prefix:

  1. Navigate to the top of the configuration hierarchy in either the J-Web or CLI configuration editor.
  2. Perform the configuration tasks described in Table 90.
  3. Apply the NAT configuration to an interface. See Applying NAT to an Interface.

Table 90: Defining an Overload Pool or Prefix

Task

J-Web Configuration Editor

CLI Configuration Editor

Navigate to the Nat level in the configuration hierarchy.
  1. In the J-Web interface, select Configuration>View and Edit>Edit Configuration.
  2. Next to Services, click Configure or Edit.
  3. Next to Nat, click Configure or Edit.

From the [edit] hierarchy level, enter

edit services nat

Define nat-pool and assign it an address range to be used for network address translation.
  1. Next to Pool, click Add new entry.
  2. In the Pool Name box, type nat-pool.
  3. Next to Address range, click Add new entry.
  4. In the High box, type 121.0.1.20.
  5. In the Low box, type 121.0.1.2
  6. Click OK twice.

Set the NAT pool name and the address range:

set pool nat-pool address-range high 121.0.1.20 low 121.0.1.2

Define pat-pool and assign it an address range to be used after addresses from nat-pool are fully used.

  1. On the Nat page, next to Pool, click Add new entry.
  2. In the Pool name box, type pat-pool.
  3. Next to Address range, click Add new entry.
  4. In the High box, type 121.0.1.22.
  5. In the Low box, type 121.0.1.21.
  6. Click OK.

Set the NAPT pool and address range:

set pool pat-pool address-range high 121.0.1.22 low 121.0.1.21

Specify the NAT port to be automatically assigned by the router.
  1. On the Pool page, next to Port, click Configure.
  2. From the Port choice list select Automatic.
  3. Click OK twice.

Set the NAT port to be assigned automatically:

set pool pat-pool port automatic

Define over-pool-rule and set its match direction.
  1. On the Nat page, next to Rule, click Add new entry.
  2. In the Rule name box, type over-pool-rule.
  3. From the Match direction list, select input.

Set the rule and its match direction:

set rule over-pool-rule match-direction input

Define one of the following terms for over-pool-rule:

  • For an overload pool—over-pool-term
  • For an overload prefix—over-perfix-term
  1. Next to Term, click Add new entry.
  2. In the Term name box, type the appropriate name:
    • over-pool-term
    • over-prefix-term

Set the appropriate term for the rule:

  • For an overload pool:

    set rule over-pool-rule term over-pool-term

  • For an overload prefix:

    set rule over-pool-rule term over-prefix-term

Define a match condition—the source address 10.10.10.0/24— for the term (over-pool-term or over-prefix-term).
  1. Next to From, click Configure.
  2. Next to Source address, click Add new entry.
  3. From the Address list, select Enter Specific Value.
  4. In the Prefix box, type 10.10.10.0/24.
  5. Click OK twice.

Set the match condition for the term, as appropriate:

  • For an overload pool:

    set rule over-pool-rule term over-pool-term from source-address 10.10.10.0/24

  • For an overload prefix:

    set rule over-pool-rule term over-prefix-term from source-address 10.10.10.0/24

Define an action for the term:

  • For over-pool-term, define a translation type, the source pool (nat-pool) and the overload pool (pat-pool).
  • For over-prefix-term, define a translation type, the source pool (nat-pool) and the overload prefix (123.0.1.0/24).
  1. Next to Then, click Configure.
  2. From the Designation list select Translated.
  3. Next to Translated, click Configure.
  4. From the Source translation type list, select dynamic.
  5. From the Source pool choice list, select Source pool.
  6. In the Source pool box, type nat-pool.
  7. From the Overload pool choice list, select the appropriate choice:
    • Overload pool
    • Overload prefix
  8. Do one of the following:
    • In the Overload pool box, type pat-pool.
    • In the Overload prefix box, type 123.0.1.0/24.
  9. Click OK.

Set the appropriate action for the term:

  • For an overload pool:

    set rule over-pool-rule term over-pool-term then translated translation-type source dynamic

    set rule over-pool-rule term over-pool-term then translated source-pool nat-pool

    set rule over-pool-rule term over-pool-term then translated overload-pool pat-pool

  • For an overload prefix:

    set rule over-pool-rule term over-prefix-term then translated translation-type source dynamic

    set rule over-pool-rule term over-prefix-term then translated source-pool nat-pool

    set rule over-pool-rule term over-prefix-term then translated overload-prefix 123.0.1.0/24

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