This article explains why the predefined application `junos-ike` does not permit traffic on UDP port 4500.

This behavior is expected. The predefined application `junos-ike` is configured to allow only UDP port 500, while the predefined application `junos-ike-nat` is used for allowing traffic on UDP port 4500. Please see the differences between `junos-ike` and `junos-ike-nat` below:

Application `junos-ike`:

root@srx> show configuration groups junos-defaults applications application junos-ike 
protocol udp;
destination-port 500;

Application `junos-ike-nat`:

root@srx> show configuration groups junos-defaults applications application junos-ike-nat 
term t1 protocol udp destination-port 4500;