Starting last night we have the vast majority of our hosts showing as down, all services are showing as up. I can ping the hosts from the cli. I have run the latest update and rebooted, no change. Where should i look next?
Answer:
Check which plugin you're using to check hosts. I've noticed that check_ping sometimes doesn't work but check_icmp does.
Hosts down , can ping them from the CLI
Re: Hosts down , can ping them from the CLI
it has to do with arp table
The Address Resolution Protocol (ARP) handles the mapping between an Internet Protocol (IP) address and a Media Access Control (MAC) address. Linux stores all such mappings in a local system cache called an ARP table.
Since it maps IP to MAC addresses, ARP works with IPv4 between layers 2 and 3 of the Open Systems Interconnection (OSI) model. Critically, the Network Discovery Protocol (NDP) replaces ARP for IPv6.
In addition to handling the mappings, ARP also allows the discovery of hosts on the network via requests. In fact, we can leverage ARP as a layer 2 ping via the arping command.
arpa -a
ping xx.xx.xx.xx
arpe -a
The Address Resolution Protocol (ARP) handles the mapping between an Internet Protocol (IP) address and a Media Access Control (MAC) address. Linux stores all such mappings in a local system cache called an ARP table.
Since it maps IP to MAC addresses, ARP works with IPv4 between layers 2 and 3 of the Open Systems Interconnection (OSI) model. Critically, the Network Discovery Protocol (NDP) replaces ARP for IPv6.
In addition to handling the mappings, ARP also allows the discovery of hosts on the network via requests. In fact, we can leverage ARP as a layer 2 ping via the arping command.
arpa -a
ping xx.xx.xx.xx
arpe -a