Chapter 36: Clock Synchronization Protocol
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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an authenticated NTP message are not encrypted and may be readily inspected; only the MD5 secure hash checksum is
encrypted using the shared secret.
NTPv4 provides for both symmetric key and public key server or peer authentication methods. However, the CER only
supports the symmetric key MD5 secure hash authentication method.
Use the following CLI command to install the symmetric key strings (aka shared secrets) into the local NTP authentication-
key database:
configure ntp authentication-key <int> md5 <word>
Where:
<int>
=
key identifier or ID, which must be an integer.
Range = 1-4,294,967,295 (2
32
-1)
<0>
=
no authentication.
<word>
=
authentication key, an ASCII string 1-16 characters long.
Any existing ASCII key string for the given key ID will be replaced when this command is executed. Use the no form of the
command to remove a key ID and its associated string.
On the CER, NTP authentication key strings may be 1 to 16 null-terminated 7-bit ASCII characters excluding ‘ ’ (space), ‘#’
(pound), ‘\t’ (tab), ‘\n’ (line feed), and ‘\0’ (null). Both the client and server must agree on an acceptable key ID and ASCII
key string pair.
The authentication-key database is indexed by key ID. It must not be shared with any other application in the CER. The NTP
symmetric key strings are associated with key identifiers used to organize a local database of NTP authentication key
strings. Note that the key identifier is also transmitted with the NTP messages so that the client and server can locate the
appropriate local key string that encrypts or decrypts the secure hash. Therefore, the client and server both have to agree
on a common key ID and a common key string for that key ID.
The CLI command configure ntp server uses the key <key-id> parameter to select the pre-defined ASCII key string from the
NTP authentication key database that is used when transmitting authenticated NTP messages between the client and the
target server.
Examples of command syntax:
configure ntp authentication-key 33 md5 KeyString1234567
configure ntp server 10.10.10.10 key 33
configure ntp authentication-key 55 md5 aShortKey
configure ntp no authentication-key 55