Nortel Networks WEB OS 212777 - Manual (Page 245)

Web OS 10.0 Application Guide
Chapter 10: Health Checking n 245
212777-A, February 2002
ARP Health Checks
Address Resolution Protocol (ARP) is the TCP/IP protocol that resides within the Internet
layer. ARP resolves a physical address from an IP address. ARP queries machines on the local
network for their physical addresses. ARP also maintains IP to physical address pairs in its
cache memory. In any IP communication, the ARP cache is consulted to see if the IP address of
the computer or the router is present in the ARP cache. Then the corresponding physical
address is used to send a packet.
In the switch, this features allows the user to health check the Intrusion Detection Server (IDS)
by sending an ARP query. The health check consists of the following sequence of actions:
1. Accessing the ARP table.
2. Looking for the session entry in the ARP table. If the entry exists in the table, that means
the real server is up, otherwise the health check has failed.
3. If the entry is present, then check the timestamp to find out if the last used time is greater
than the ARP health check interval. If it is, then delete the query, as this means that the
health check has failed.
4. Send another ARP request and repeat the above process until the timestamp shows the
last used time smaller than the ARP health check interval.
Configuring the Switch for ARP Health Checks
1. Select the SLB group from the health check menu.
2. Select the type of health check to use.
3. Enable ARP health checks for group 1.
4. Apply and save your configuration.
>> /cfg/slb/group 1
>> Real server group 1# health arp
>> Real server group 1# arp enable
>> Real server group 1# apply