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Questions tagged [icmp]

ICMP stands for Internet Control Message Protocol. It is primarily used by the operating systems of networked computers to send error messages indicating service status.

ICMP is not normally used by end-users or to send messages. It's main use is in diagnostics and checking that the network is functioning correctly.

ICMP is just one communications protocol on the web. Others include:

  • Transmission Control Protocol (TCP)
  • User Datagram Protocol (UDP)
  • Hypertext Transfer Protocol (HTTP)
  • Post Office Protocol (POP3)
  • File Transfer Protocol (FTP)
  • Internet Message Access Protocol (IMAP)

ICMP on Wikipedia

226 questions
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What is the best server or Ip address to use for prolonged testing?

I usually run uptime/latency tests against (and from) two servers that we own at different sites and until recently I've used the google dns servers as a control group. However, I've realized there is a potential problem with monitoring latency…
eldorel
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Iptables not allowing ICMP requests from remote machines

I've configured my linux router with the following iptables rules iptables --list-rules -P INPUT ACCEPT -P FORWARD ACCEPT -P OUTPUT ACCEPT -A FORWARD -i vmbr0 -o eth2 -j ACCEPT -A FORWARD -i vmbr0 -o eth1 -j ACCEPT -A FORWARD -i eth1 -o vmbr0 -m…
Prashanth Ellina
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Wireshark Display Filtered for Unreplied ICMP Echo Packets

Is there a wireshark display filter that will find ICMP echo requests that didn't have a reply?
Kyle Brandt
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What do the extra parts of the iptables ping log entry mean?

I'm dropping all ICMP type 8 packets on the INPUT chain and so now I'm seeing log entries as a Fabric script tries to contact another server, like this: kernel: INPUT DROP IN=eth0 OUT= SRC= DST= LEN=88 TOS=0x00 PREC=0xC0 TTL=50 ID=60964…
ghickman
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My computer is sending ICMP packets to arbitrary destinations

My computer is sending ICMP packets to arbitrary destinations. I can't understand the reason. Dump of one of the packet is : Internet Control Message Protocol Type: 3 (Destination unreachable) Code: 3 (Port unreachable) Checksum: 0x811b…
user58859
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sending ICMP request with Proxy

Is there any way for sending ICMP reguest with proxy (http proxy or Socks) ? if its possible please give me an example (by any language , perl , python , ...) . Thanks in Advance .
Jessica
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traceroute: sometimes routers don't respond and user sees timeouts

I'm an admin of small network and I'm investigating a problem my users complain about. The root of their complaints is traceroute: sometimes routers along the path simply don't respond to traceroute probes and users see timeouts (those *s in place…
ico
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ping: Warning: time of day goes back (-203647us), taking countermeasures

I'm getting the below weird warning message sometimes when pinging to 8.8.8.8 (Occurrence is very low). Any idea about the root cause? $ ping 8.8.8.8 PING 8.8.8.8 (8.8.8.8) 56(84) bytes of data. 64 bytes from 8.8.8.8: icmp_seq=1 ttl=111 time=256…
Harikrishnan
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ICMP "Port Unreachable" when sending email

Since several months I have sporadic problems when I send emails. With tcpdump I finally found out that I'm getting "Port unreachable" messages from what seems to be my email provider, according to the source IP. But my email provider says they…
bug.spencor
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Difference between icmp and icmpv6 for ip6tables?

I found the following lines in a firewall script on one of our Linux servers (kernel 5.x) ip6tables -A INPUT -p icmp -j ACCEPT ip6tables -A INPUT -p ipv6-icmp -j ACCEPT The two commands both run without error, but I'm confused about it. I can only…
iBug
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SmartOS can't ping any ip that resolves to failover ip

Our server is running SmartOS, we have 2 network cards one for internal use (10.x.x.x) and one external, i am able to ping any website / service except domains that resolve to our Failover IP (The IP just redirects to the pre-configured…
ChatN0ir
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How to allow responding to broadcast pings on Mikrotik RouterOS?

By default, most systems don't respond to broadcast ping requests. However, there exist ways to explicitly allow responding to broadcast ICMP requests on multiple systems, such as Linux. How can I enable responding to broadcast ping requests on…
TheNavigat
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DPM breaking network connectivity to itself

I'm backing up a specific folder in a VM (server 2016) with DPM (SC2016). Both have all the updates installed, latest patch versions. I noticed that after the initial replica, the backups have been failing to continue over the next few days. I…
user2629636
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Is RTT theoretically the same regardless of ping origination?

Let's say you send a ping from device 1 to device 2. The result would give you the RTT. Theoretically speaking (because many variables are realistically in play), would the RTT be the same by pinging device 1 from device 2?
Sterling Butters
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Layer 3 Device ICMP behavior and impact on tracert

Is it possible to configure a layer 3 device to set the TTL of all ICMP echo request packets to zero and not send out ICMP Time Exceeded message ? If so, wouldn't this make it impossible for tracert to finish for any path that got routed through it…
user1086516
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