Technical basics
3.5 SNMP
SCALANCE W760/W720 to IEEE 802.11n Web Based Management
28
Configuration Manual, 11/2014, C79000-G8976-C350-03
To translate the internal into the global IP address, the NAT device maintains a translation
list. The address assignment is automatic. You configure the address assignment in "Layer 3
> NAT > Basic".
What is NAPT?
In "Network Address Port Translation" (NAPT) or "Port Address Translation" (PAT), several
internal source IP addresses are translated into the same external source IP address. To
identify the individual source nodes, the port of the source device is also stored in the
translation list of the NAT gateway and translated for the external address.
If several local clients send a query to the same external destination IP address over the
NAT gateway, the gateway enters its own external source IP address in the header of these
forwarded frames. Since the forwarded frames have the same global source IP address, the
NAT gateway assigns the frames to the clients using different port number.
Note
NAT/NAPT is possible only on layer 3 of the ISO/OSI reference model. To use the NAT
function, the networks must use the IP protocol.
When using the ISO protocol that operates at layer 2, it is not possible to use NAT.
If a client from the global network wants to use a service in the internal network, the
translation list for the static address assignment needs to be configured. You configure the
translation list for NAPT in "Layer 3 > NAT > NAPT".
3.5
SNMP
Introduction
With the aid of the Simple Network Management Protocol (SNMP), you monitor and control
network elements from a central station, for example routers or switches. SNMP controls the
communication between the monitored devices and the monitoring station.
Tasks of SNMP:
●
Monitoring of network components
●
Remote control and remote parameter assignment of network components
●
Error detection and error notification
In versions v1 and v2c, SNMP has no security mechanisms. Each user in the network can
access data and also change parameter assignments using suitable software.
For the simple control of access rights without security aspects, community strings are used.
The community string is transferred along with the query. If the community string is correct,
the SNMP agent responds and sends the requested data. If the community string is not
correct, the SNMP agent discards the query. Define different community strings for read and
write permissions. The community strings are transferred in plain text.
