Appendix B: Network IP Topology
CS-5200
Inter-Tel
®
5000 Installation Manual – Issue 2.4, May 2008 Page B-15
6. For the “internal” IP endpoints (those in the internal network with private addresses), set
the NAT address type
Native, and configure the IP endpoints to communicate with the
Inter-Tel CS-5200 (private) internal address, 192.168.1.2. Incorrect configuration may
result in an undesirable effect called tromboning (also known as “hairpinning”). Not all
firewalls support tromboning, so avoid this configuration, if possible. The following
diagram illustrates tromboning.
Internet
Office Firewall/NAT
Public IP: 208.13.17.33
Private IP: 192.168.1.1
Site A
(Private Addresses )
IP Endpoint
(Private Address)
Inter -Tel CS-5x00
192.168.1.2
(Private Address)
IP Endpoint
(Private Address)
Home Office LAN
Home Office
Router (for
example,
Linksys)
Accessing the outside “NATed”
address from inside the firewall is
referred to as “tromboning .” Some
firewalls do not support tromboning .
IP Endpoint
(Private Address)
If the internal endpoint
communicates with the NATed
address instead of the native
address , “tromboning” takes
place.
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