Specifications

Setting Up Secure SRST

Information About Setting Up Secure SRST

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Cisco IOS Survivable Remote Site Telephony Version 3.4 System Administrator Guide

Note The media is encrypted automatically once the phone and router certificates are exchanged and the TLS

connection is established with the SRST router.

Cisco IOS Credentials Server on Secure SRST Routers

Secure SRST introduces a credentials server that runs on a secure SRST router. When the client,

Cisco CallManager, requests a certificate through the TLS channel, the credentials server provides the

SRST router certificate to Cisco CallManager. Cisco CallManager inserts the SRST router certificate in

the Cisco IP phone configuration file and downloads the configuration files to the phones. The secure

Cisco IP phone uses the certificate to authenticate the SRST router during fallback operations. The

credentials service runs on default TCP port 2445.

Three Cisco IOS commands configure the credentials server in call-manager-fallback mode:

• credentials

• ip source-address (credentials)

• trustpoint (credentials)

Two Cisco IOS commands provide credential server debugging and verification capabilities:

• debug credentials

• show credentials

Establishment of Secure SRST to the Cisco IP Phone

Figure 5 and Table 9 show the interworking of the credentials server on the SRST router, Cisco

CallManager, and the Cisco IP phone, and describe the establishment of secure SRST to the Cisco IP

phone.

6. The TLS handshake occurs, certificates are exchanged, and mutual authentication and

registration occurs between the Cisco IP phone and the SRST router.

The SRST router sends its certificate, and the phone validates the certificate to the

certificate that it received from Cisco CallManager in Step 4.

The Cisco IP phone provides the SRST router the LSC or MIC, and the router

validates the LSC or MIC using the PEM format files that it was provided in Step 5.

Table 8 Overview of the Process of Secure SRST Authentication and Encryption (continued)

Process Steps Description or Detail