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097-55501-01 Revision M – January 2009
TimeHub 5500 User’s Guide
77
Chapter 2 Engineering Ordering Information
NTP Server Card
Figure 2-15. Sample NTPv4 Packet
Setting Up TimeHub NTP for Authentication
Define the 16 keys
MKEYIDm is used to define up to 16 (m = 1 to 16) key IDs. The key ID value
range is currently 0 - 65534
For each key ID, the user defines a corresponding key MKEYVALUEm. The
value of each key is a string of 32 ASCII characters.
These 16 keys (key IDs and corresponding keys) are somehow distributed to all
trusted servers and clients
MKEYIDm is also used to pick the key ID used when the TimeHub NTP card is a
unicast server.
For server broadcast/multicast,
The same 16 keys defined above are used for broadcast/multicast
Up to four broadcast/multicast addresses can be defined per NTP card
For each broadcast/multicast address, BCMKEYm is used to choose one of the
16 key IDs.
For client (unicast):
Misc. header info (4 bytes)
Root Delay ( 4 bytes)
Root Dispersion (4 bytes)
Reference ID ( 4 bytes)
Timestamp ( 8 bytes)
Key ID (in the clear ) (4 bytes)
Message Digest (16 bytes)
Timestamp ( 8 bytes)
Timestamp ( 8 bytes)
Timestamp ( 8 bytes)
Optional
Extension Fields
Authenticator
Cryptosum is
calculated
over this field
48 bytes
(Unauthenticated
message length )
20 bytes
(authenticator
length)