AM79C987 datasheet(29/30 Pages) AMD

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Am79C987

IMR+/HIMIB Security Features

APPENDIX A

The Am79C981 Integrated Multiport Repeater Plus

(IMR+) and the Am79C987 Hardware Implemented

Management Information Base (HIMIB) Ethernet re-

peater chip-set is capable of providing physical network

security features. AMD will only make these features

available to customers who are under an IMR+/HIMIB

security non disclosure agreement (NDA). A description

of the security feature is summarized below. For more

information, contact your local AMD sales office to gen-

erate an IMR+/HIMIB security NDA.

Security Features Summary

The HIMIB incorporates a feature to allow the destina-

tion address (DA) field of a received packet to be com-

pared with the known MAC address connected to each

port. The MAC address for each port is contained in the

HIMIB Last Source Address (LSA) register, which can

be programmed by the user or it will be “learnt” by the

HIMIB device. On receipt of a packet on one port, all

other ports have the contents of the LSA register com-

pared with the DA field of the received frame. If there is a

match on any port, the frame is repeated to that port

normally. For those ports which have the security fea-

ture enabled and do not have a DA/LSA match, the

repeated bit stream of the packet will be corrupted (fre-

quently termed “eavesdrop protection”), and the port will

transmit an alternating pattern of 1 and 0 following the

18th (approximate) bit of the Source Address field. This

feature can be enabled/disabled on a port by port basis

using a mask located in the HIMIB Port Control Regis-

ters. Any port with the security feature disabled (using

the field in the Port Controls Registers) will repeat the

packet normally. Note that multicast and broadcast

packets are transmitted to all ports unmodified, regard-

less of the enable/disable state of the security function.

Ports that are connected to single stations can be se-

cured by enabling the eavesdrop protection function

and enabling the Last Source Address Change Inter-

rupt. This prevents unauthorized eavesdropping by sta-

tions on the LAN who are not directly addressed by the

sourcing node, hence the learning of valid source ad-

dresses and “snooping” on data is virtually impossible.

In addition, this allows the management software to de-

tect and possibly disable the port in real time if the HIMIB

indicates via the hardware interrupt line that the Source

Address has changed.

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