User's Manual

Configuration Guide of XGS-5240-Series
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protocol widely used in computer network management. SNMP is an evolving protocol. SNMP
v1 [RFC1157] is the first version of SNMP which is adapted by vast numbers of manufacturers
for its simplicity and easy implementation; SNMP v2c is an enhanced version of SNMP v1,
which supports layered network management; SNMP v3 strengthens the security by adding
USM (User-based Security Mode) and VACM (View-based Access Control Model).
SNMP protocol provides a simple way of exchange network management information
between two points in the network. SNMP employs a polling mechanism of message query,
and transmits messages through UDP (a connectionless transport layer protocol). Therefore it
is well supported by the existing computer networks.
SNMP protocol employs a station-agent mode. There are two parts in this structure: NMS
(Network Management Station) and Agent. NMS is the workstation on which SNMP client
program is running. It is the core on the SNMP network management. Agent is the server
software runs on the devices which need to be managed. NMS manages all the managed
objects through Agents. The switch supports Agent function.
The communication between NMS and Agent functions in Client/Server mode by
exchanging standard messages. NMS sends request and the Agent responds. There are
seven types of SNMP message:
 Get-Request
 Get-Response
 Get-Next-Request
 Get-Bulk-Request
 Set-Request
 Trap
 Inform-Request
NMS sends queries to the Agent with Get-Request, Get-Next-Request, Get-Bulk-Request
and Set-Request messages; and the Agent, upon receiving the requests, replies with
Get-Response message. On some special situations, like network device ports are on
Up/Down status or the network topology changes, Agents can send Trap messages to NMS to
inform the abnormal events. Besides, NMS can also be set to alert to some abnormal events
by enabling RMON function. When alert events are triggered, Agents will send Trap messages
or log the event according to the settings. Inform-Request is mainly used for inter-NMS
communication in the layered network management.
USM ensures the transfer security by well-designed encryption and authentication. USM
encrypts the messages according to the user typed password. This mechanism ensures that
the messages can’t be viewed on transmission. And USM authentication ensures that the
messages can’t be changed on transmission. USM employs DES-CBC cryptography. And
HMAC-MD5 and HMAC-SHA are used for authentication.
VACM is used to classify the users’ access permission. It puts the users with the same