When you define a source pool, JUNOS software enables PAT by default. To disable PAT, you must specify no port translation when you are defining a source pool.
Before You Begin
For background information, read Source IP Address Translation Overview.
When using a source pool without PAT, JUNOS software performs source Network Address Translation for the IP address without performing PAT for the source port number. For applications that require that a particular source port number remain fixed, you must use source pool without PAT.
The source pool can contain multiple IP addresses, multiple IP address ranges, or both. For source pool without PAT, JUNOS software assigns one translated source address to the same host for all its concurrent sessions.
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Pool utilization for each source pool without PAT is computed. You can turn on pool utilization alarm by configuring alarm thresholds. An SNMP trap is triggered every time pool utilization rises above a threshold and goes below a threshold.