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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

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Linux equivalent of "no ICMP Unreachable" and "no ICMP Mask Reply"?

I have a Linux machine that is being used as a router. It has quagga installed and has ip forwarding enabled. It's forming an OSPF adjacency with a 3925 Cisco router. I'm being asked to ensure that this Linux machine (running Redhat 6.8) will not…
dutsnekcirf
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What should be the behavior after also dropping outgoing destination-unreachable packets?

On system A I'm using ip6tables and I'm DROPing INPUT packets coming from system B through IPv6. As expected, when system B uses ping6 to system A, it sees destination unreachable. However, when on system A I also DROP OUTPUT…
Adelin
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ICMP maximum delay between echo request and reply sustained by a router NAT

I was trying to slow down network on my server (arch linux vm) with netem sudo tc qdisc add dev eth0 root netem delay 1600ms With 1600ms delay client doesn't receive the echo reply packet though the packet is generated from the serverside. However…
user59088
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Is icmp ping a reliable way to monitor host up/down in EC2?

We use icmp ping to determine host up/down status from icinga2 in our AWS EC2 environment. This works well, but we have had a handful of issues where host will fail ping but its services are still ok. My colleague is under the impression that…
Michael Martinez
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Printer stops pinging after 3 minutes from IPSEC remote side. Continues from local side

I have a very strange issue that I have come across twice now. It is making me go cross-eyed. We have two sites, one runs our server infrastructure and the other hosts end-users. There is an IPSEC tunnel established between StrongSWAN and Cisco ASA…
user1955162
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tcpdump host unreachables for specific host

I'm trying to rule out some issues and needing to capture all ICMP messages except echo/echo reply. However the issue I'm struggling to find a way around is I only want these involving a particular host. The filter I've been trying is tcpdump icmp…
Cameron Moody
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Split ping RoundTripTime

Data obtained from ping: is it round trip or one way? shows that the data of a ping measures both directions together. Is there any way to split this information in time-to-destination and time-back?
M K
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Slave interface receiving packets but not bond. Why?

I have 2 network interfaces with mac aa:aa:aa:aa:aa:aa and bb:bb:bb:bb:bb:bb When i bind them the bond gets the mac aa:aa:aa:aa:aa. I make a configuration where i make sure all the replies of icmp requests leaving the bond reaches the bond ip at…
Raunak
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icmp redirect how to check if it works

I have seen on the internet many tips to disable icmp redirects. What I would like to know is how to properly check on windows and linux if it actually works? I have managed to spoof a fake icmp redirect packet with scapy on linux, i can see that…
uQuad
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Windows Firewall log shows insane amount of ICMP SEND/RECEIVE requests. Normal?

I was checking my Windows Firewall logs after receiving a website notice that my connection was banned for sending too many requests, and noticed the following entries: 2017-05-18 03:39:23 ALLOW ICMP 127.0.0.1 127.0.0.1 - - 0 - - - - 8 0 -…
script'n'code
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Centos7 disable IP Redirect sending on IPSec VPN Server

When using StrongSwan as an IPSEC S2S VPN Gateway, ICMP redirects are being sent to machines behind the right side. I have added the following lines to…
Sam Alsalem
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Slave smokeping on xen VM shows substantial packet loss

I am using a Xen VM instance as a smokeping host. Recently I added a second XEN VM (on different iron, about 200 Km away) with smokeping in slave configuration. This is - again - a Xen VM, with a similar configuration to its master. While the…
Alien Life Form
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Linux server icmp security

I have a Linux router, it is connecting to internet via pppoe with dynamic IP and I would like it NOT to respond to ping (or any other kind of icmp) from outside (internet), BUT I would like that ping (and all icmp, like traceroute, tcptraceroute,…
THESorcerer
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Why would a host block ICMP echo (ping response) yet it allows me to connect to it?

Is there a security reason for that?
Matka
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How to use icmptx?

In Trusty (Ubuntu 14.04, both sides) I want to create an ICMP tunnel. I don't know how to set IP's. I searched and read some documents like this and this but I couldn't figure out what exactly I should do and in what server. Is real IP (internet…
hamidi
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