Do ping requests put a load on a server?

Question

I have a lot of clients (around 4000). Each client pings my server every 2 seconds. Can these ping requests put a load on the server and slow it down?

How can I monitor this load? Now the server response slowly but the processor is almost idle and the free memory is ok. I'm running Apache on Ubuntu.

Answer 1

Yes, they can. A ping request does not put much CPU load on, but it certainly takes up bandwidth and a nominal amount of CPU.

If you want to monitor this, you might use either tcpdump or wireshark, or perhaps set up a firewall rule and monitor the number of packets it matches.

Answer 2

Assuming you mean a UDP/ICMP ping just to see if the host is alive, 4000 hosts probably isn't much load and is fairly easy to calculate. CPU and memory wise, ping is handled by you're kernel, and should be optimized to not take much resources. So, you need to look at network resources. The most critical point will be if you have a half-duplex link, because all of you're hosts are chatty, you'll cause alot of collisions and retransmissions (and dropped pings). If the links are all full duplex, let's calculate the actual amount of bandwidth required at the server.

• 4000 client @2 seconds
• Each ping is 72 bytes on the wire (32 bytes data + 8 bytes ICMP header + 20 bytes IP header + 14 bytes Ethernet). * You might have some additional overhead if you use vlan tagging, or UDP based pings
• If we can assume the pings are randomly distributed, we would have 2000 pings per second @ 72 bytes = 144000 bytes
• Multiple by 8 to get Bps = 1,152,000 bps or about 1.1Mbps.
• On a 100Mbps Lan, this would be about 1.1% utilization just for the pings.

If this is a lan environment, I'd say this is basically no load at all, if it's going across a T1 then it's an immense amount of load. So you should basically run the same calculation on which network links may also be a bottle neck.

Lastly, if you're not using ICMP pings to check the host, but have an application level ping, you will have all the overhead of what protocol you are using, and the ping will need to go all the way up the protocol stack, and you're application needs to respond. Again, this could be a very minimal load, or it could be immense, depending on the implementation details and the network speed. If the host is idle, I doubt this is a problem for you.

Answer 3

The other problem apart from bandwidth is the CPU. If a ping is directed up to the CPU for processing, thousands of these can cause a load on any CPU. It's worth monitoring - but as you said yours is almost idle so it's probably going to be able to cope. Worth keeping in mind though.

Depending on the clients, ping packets can be different sizes - their payload could be just "aaaaaaaaa" but some may be "thequickbrownfoxjumpedoverthelazydog" - which is obviously further bandwidth requirements again.