1-2
Cisco ASA Series CLI Configuration Guide
Chapter 1 Configuring the Cisco Phone Proxy
Information About the Cisco Phone Proxy
Figure 1-1
Phone Proxy Secure Deployment
The phone proxy supports a Cisco UCM cluster in mixed mode or nonsecure mode. Regardless of the
cluster mode, the remote phones that are capable of encryption are always forced to be in encrypted
mode. TLS (signaling) and SRTP (media) are always terminated on the ASA. The ASA can also perform
NAT, open pinholes for the media, and apply inspection policies for the SCCP and SIP protocols. In a
nonsecure cluster mode or a mixed mode where the phones are configured as nonsecure, the phone proxy
behaves in the following ways:
•
The TLS connections from the phones are terminated on the ASA and a TCP connection is initiated
to the Cisco UCM.
•
SRTP sent from external IP phones to the internal network IP phone via the ASA is converted to
RTP.
In a mixed mode cluster where the internal IP phones are configured as authenticated, the TLS
connection is not converted to TCP to the Cisco UCM but the SRTP is converted to RTP.
In a mixed mode cluster where the internal IP phone is configured as encrypted, the TLS connection
remains a TLS connection to the Cisco UCM and the SRTP from the remote phone remains SRTP to the
internal IP phone.
Since the main purpose of the phone proxy is to make the phone behave securely while making calls to
a nonsecure cluster, the phone proxy performs the following major functions:
•
Creates the certificate trust list (CTL) file, which is used to perform certificate based authentication
with remote phones.
•
Modifies the IP phone configuration file when it is requested via TFTP, changes security fields from
nonsecure to secure, and signs all files sent to the phone. These modifications secure remote phones
by forcing the phones to perform encrypted signaling and media.
•
Terminates TLS signaling from the phone and initiates TCP or TLS to Cisco UCM
•
Inserts itself into the media path by modifying the Skinny and SIP signaling messages.
•
Terminates SRTP and initiates RTP/SRTP to the called party.
271631
Internet
ASA
Internal
IP phone
IP
IP
Remote
IP phone
IP
Remote
IP phone
M
M
M
M
M
TLS/SRTP
TCP/RTP
Unencrypted signaling
Encrypted signaling
Un-trusted / Outside / Secured
Trusted / Inside / Un-Secured
Enterprise
Home Router
w/NAT
Home Router
w/NAT
Summary of Contents for 5505 - ASA Firewall Edition Bundle
Page 28: ...Glossary GL 24 Cisco ASA Series CLI Configuration Guide ...
Page 61: ...P A R T 1 Getting Started with the ASA ...
Page 62: ......
Page 219: ...P A R T 2 Configuring High Availability and Scalability ...
Page 220: ......
Page 403: ...P A R T 2 Configuring Interfaces ...
Page 404: ......
Page 499: ...P A R T 2 Configuring Basic Settings ...
Page 500: ......
Page 533: ...P A R T 2 Configuring Objects and Access Lists ...
Page 534: ......
Page 601: ...P A R T 2 Configuring IP Routing ...
Page 602: ......
Page 745: ...P A R T 2 Configuring Network Address Translation ...
Page 746: ......
Page 845: ...P A R T 2 Configuring AAA Servers and the Local Database ...
Page 846: ......
Page 981: ...P A R T 2 Configuring Access Control ...
Page 982: ......
Page 1061: ...P A R T 2 Configuring Service Policies Using the Modular Policy Framework ...
Page 1062: ......
Page 1093: ...P A R T 2 Configuring Application Inspection ...
Page 1094: ......
Page 1191: ...P A R T 2 Configuring Unified Communications ...
Page 1192: ......
Page 1333: ...P A R T 2 Configuring Connection Settings and QoS ...
Page 1334: ......
Page 1379: ...P A R T 2 Configuring Advanced Network Protection ...
Page 1380: ......
Page 1475: ...P A R T 2 Configuring Modules ...
Page 1476: ......
Page 1549: ...P A R T 2 Configuring VPN ...
Page 1550: ......
Page 1965: ...P A R T 2 Configuring Logging SNMP and Smart Call Home ...
Page 1966: ......
Page 2059: ...P A R T 2 System Administration ...
Page 2060: ......
Page 2098: ...1 8 Cisco ASA Series CLI Configuration Guide Chapter 1 Troubleshooting Viewing the Coredump ...
Page 2099: ...P A R T 2 Reference ...
Page 2100: ......