4 Start-up CPU 03
Page 24 of 38 HI 800 479 E Rev. 1.00
Parameter Description
ARP Aging Time [s]
A processor or COM module stores the MAC addresses of the
communication partners in a MAC/IP address assignment table
(ARP cache).
If in a period of 1x...2x ARP Aging Time ...
- ... messages of the communication are received, the MAC
address remains stored in the ARP cache.
- ... no messages of the communication partner are received,
the MAC address is erased from the ARP cache.
The typical value for the ARP Aging Time in a local network
ranges from 5...300 s.
The user cannot read the contents of the ARP cache.
If routers or gateways are used, the user must adjust (increase)
the ARP Aging Time due to the additional time required for two-
way transmission.
If the ARP Aging Time is too low, the processor or the COM
module deletes the MAC address of the communication partner
from the ARP cache and the communication is either delayed or
breaks down entirely. For an efficient performance, the ARP
aging time value must be less than the receive timeout set for
the protocols in use.
Range of values: 1...3600 s
Default value: 60 s
MAC Learning Learning behavior of the ARP cache
Conservative: MAC addresses of stored ARP entries are not
overwritten by received messages
Tolerant: MAC addresses of stored ARP entries are
overwritten by received messages
Default setting: Conservative
IP Forwarding
Allow a processor module to operate as router and to forward
data packets to other network nodes.
Default setting: Deactivated
ICMP Mode
Message types of Internet Control Message Protocol (ICMP)
supported by the processor module:
No ICMP Responses
Echo Response
Host Unreachable
All Implemented ICMP Responses
Default setting: Echo Response
Table 16: Configuration Parameters of the CPU and COM, Module Tab
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