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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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iptables can't block timestamp request with CentOS

I am setting up firewall with iptables on my host. I want to disable timestamp ICMP request, but it's wired, I only allows type 8 (echo-request) comes into host, but event still, I can get timestamp from my host 64 bytes from xxxxxxxxx: icmp_seq=2…
Fang-Pen Lin
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Arp tries on various *nix based systems

Does anyone know what determines the amount of arp tries a router will make? I have different behaviors with two devices, if I try to traceroute to a non-existent host on a subnet that belongs to an interface on the router, a Linux box will try to…
salparadise
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What firewall changes could cause a drastic increase in spam?

I created some iptables rules, basically allowing incoming traffic from TCP/UDP Ports 80,53(for the bind server), 22, and blocking everything else incoming however I forgot to allow the ICMP protocol through the filter. This resulted in expected…
BuckFilledPlatypus
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No transmission via IP

I'm using netstat on Win XP to check protocol transmission details for TCP, IP, and ICMP. There is transmission only in TCP. No transmission in ICMP is understandable since it's for errors and I assume that there were none, but why is there no…
Richard
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Timeout for echo request for public IP

Following situation: When I request an echo reply of my public IP from my local network I get an ICMP timeout; on the other hand, making an echo request on my public IP from a machine from the internet (connected via ssh) returns an echo reply. How…
Kenny Meyer
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ICMP - TTL - Trace Route

I asked this question at Stack Overflow and then thought this may be the better place to ask. Given the following situation: PC --- |aa RTR1 bb| --- |aa RTR2 bb| --- |aa RTR3 bb| etc Each of the |aa rtr bb| is meant to be a router with two ports aa…
dbasnett
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Route an incoming ICMP packet to a different interface/process

I have an interface enp4s0 with several IPs. I get ICMP packets (type 8, echo request) from external device to my device on enp4s0. I'm trying to route only packets sent to 192.168.1.90 into another interface on the same device. On that interface…
hudac
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Why is it not possible to establish a connection between these servers?

I have the problem that my two servers (master, worker) can not connect to each other. However, connections outside e.g. "google.com" are possible. I have already tried to allow all ICMP connections, which are otherwise forbidden in the prerouting.…
Jerome Wolff
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Wierd firewalld block after recent update, Centos Stream 9, blocks icmp replies as invalid state

I am running Centos Stream 9 on VMware. I recently used dnf update and now there is a weird problem that some ping-replies are stopped by the firewalld. If I stop the firewall, ping works ok. The problem presents itself like this: I ping from the…
Teemu Sa
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How to identify application that is generating ICMP echo requests on Windows 10?

My company security team has informed me that my workstation is pinging some "blacklisted" IP addresses. The enterprise security tool reporting this information sits in place of the usual Windows firewall, but it seems it is unable to tell which…
Gordon Mckeown
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Ping issues with Windows Server 2008 R2 with mail server!

For some reason I can ping all servers in my network except for the mail server and the mail server can ping all servers except the windows server 2008 R2. The firewall has been disabled and still it doesn't respond. The weird part is that every…
S. M.
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Local devices aren't reachable via VPN

I have a VPN configured on a router (router model is bintec be.ip plus). VPN Connections are successfully established by the clients using IKEv2 (router is reachable via DynDNS). Router's local ip address is 192.168.73.1. One of the local device's…
Abid
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ICMP/Ping works even after adding iptables drop rule

We have an application which will configure network interface as well as iptables rules based on user configuration. Please find the iptables rules after configuring with the application Even after adding this rule we can able to ping 10.10.10.10…
Gilson PJ
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Forwarding packets using multiple servers

I have a IP block from RIR. I'm using two providers for make anycast to "some" IPs. I will call this as A and B. I want forward to other provider when that IP not at that location. I'm using two Ubuntu servers to BGP announce and forwarding packets,…
Hoto Cocoa
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when router sends ICMP protocol error message how does it set it's own TTL?

when using (traceroute -q 1 serverAddress), we know that it starts with TTL(Time to Live) = 1. when it goes through router, the router decrements TTL by 1. If TTL becomes 0 at that router, it sends back ICMP error TTL exceeded message. Now, tell me…
David Roonie
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