Chapter 16: Dynamic Routing Protocols
STANDARD Revision 1.0
C4® CMTS Release 8.3 User Guide
© 2016 ARRIS Enterprises LLC. All Rights Reserved.
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Encrypted Packets
Message Digest 5 (MD5) authentication allows a System Administrator to encrypt RIPv2 packets based on an interface-
specific key. This key is used to generate an MD5 hash which is appended to all outgoing RIP packets originating from the
C4/c CMTS.
Routers that receive these encrypted RIPv2 packets must have the same key associated with the incoming interface. The
key is used to verify the MD5 of each encrypted packet.
Similarly, all RIPv2 packets that are received by the C4/c CMTS interfaces for which MD5 is enabled must have the key
associated with that interface applied to all RIPv2 packets. These encrypted packets allow the C4/c CMTS to communicate
securely with other routers in the network.
Invalid Encryption
If a router or host attempts to provide the C4/c CMTS with RIP information and it does not have the correct MD5 hash, the
packet is dropped and an error message is logged.
Time-of-Day
The RIP protocol requires a sequence number to increase monotonically based on the time-of-day. This key is used to
generate an MD5 hash over the entire RIP message plus the concatenated plain-text key which is appended to all outgoing
RIP packets originating from the C4/c CMTS.
Any out-of-sequence number violates the monotonic sequence rule and the packet will be discarded. The C4/c CMTS uses
its system time as the MD5 message sequence number. As a result, exercise caution when changing the system time to an
earlier time.
If the C4/c CMTS is running RIPv2 with MD5 authentication and the system time is changed to an earlier time,
communication with peer routes cease until either the system time reaches it previous point, or all the RIP routes age out
of the routing tables on the C4/c CMTS.
Time-Out Limit
RIP routes sent by the C4/c CMTS to adjacent peer routers age out (time-out) five minutes after the last authenticated RIP
message was received.
