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Communicating with the SNMP Engine

The SNMP engine performs the following tasks for SNMPv3:

Sends and receives messages.
Prepares messages and extracts data from messages.
Authenticates, encrypts, and decrypts messages.
Determines whether access to a managed task is allowed.

Each SNMP engine has an SnmpEngine ID, a hexadecimal number 15 octets long. Table 19 shows the structure of the SnmpEngine ID.

Table 19: SnmpEngineID Structure Object

Octet Assignment	Description
1 – 4	E-series router SNMP management private enterprise number
5	Indicates that octets 6–15 contain information determined by the E-series router
6 – 11	The MAC address for the device
12 – 15	The 32-bit (4 octet) router index (or routerUID)

Request protocol data units (PDUs) for the SNMP engine must contain the corresponding contextEngine ID and contextName for the SNMP engine. When the system receives a PDU, it examines the contextEngine ID and contextName, and forwards the request to the corresponding virtual router.

The contextEngine ID is the same as the SnmpEngine ID.
The contextName is an internally derived ASCII string associated with the router. It has the format routerN, where N is a number (with no leading zeros) in the range 1–16777215, corresponding to the least significant 24 bits of the 32-bit router index (or router UID). You can obtain the contextName for a specific router through the Juniper-ROUTER-MIB from the juniRouterContextName object in the juniRouterTable, which is indexed by the 32-bit router index (juniRouterIndex).

The following table shows examples of the E-series router SNMP engine objects that are associated with the default virtual router.

Object	Value
SnmpEngineID	0x80:00:13:0a:05:00:90:1a:00:04:6c:80:00:00:01
contextEngineID	0x80:00:13:0a:05:00:90:1a:00:04:6c:80:00:00:01
contextName	router1

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