
5-25
Cisco PIX Firewall and VPN Configuration Guide
78-15033-01
Chapter 5 Configuring Application Inspection (Fixup)
Voice Over IP
This command statement causes the PIX Firewall to allow a new connection on port 5060 from an
outside phone if a UDP connection already exists from that phone to an inside phone. A call can be
placed on hold for the time specified in the timeout interval for SIP. You can increase this interval as
necessary with the timeout command.
Providing IP Address Privacy
Achieving IP address privacy requires the ability to retain outside IP addresses embedded in inbound SIP
packets for all transactions. With the exception of REGISTER, you can hide phone IP addresses from
one another by invoking ip-address privacy.
The REGISTER message and the response to REGISTER message will be exempt from this operation
since this message is exchanged between the phone and the proxy.
Your can turn on this feature by using the [no] sip ip-address-privacy command.
Note By default this command is turned off.
When the above command is turned on, SIP fixup will retain outside IP addresses in the SIP header and
SDP data of inbound SIP packets.
Here is an example of enabled IP address privacy:
INVITE sip:bob@Proxy SIP/2.0
Via: SIP/2.0/UDP A:5060 ===============> A':patport#
From: terry@A =========================> terry@A'
To: robin@Proxy
Call-ID:
Contact:terry@A =======================> terry@A'
SDP
o=A ==================================> A'
c=IN IP4 A ===========================> A'
m=port# ==============================> patport# (if applicable)
When the Proxy sends the INVITE to B:
INVITE sip:bob@Proxy SIP/2.0
Via: SIP/2.0/UDP A':5060 ===========>Has to remain as A':patport#
From: terry@A' =====================>Has to remain as A'
To: robin@Proxy
Call-ID:
Contact:terry@A' ===================>Has to remain as A'
SDP
o=A' =============================>Has to remain as A'
c=IN IP4 A' =======================>Has to remain as A'
m=patport#
If there is a requirement to hide phone ip addresses connected on the same PIX interface from each other
and eliminate the direct P2P communication between the phones, this feature should be enabled. SIP
ip-address-privacy managed with fixup sip, controls traffic (SIP) and voice (RTP/RTCP) traffic flow by
creating pin holes for voice traffic. Using this feature eliminates direct point-to-point communication
between phones.
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