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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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linux ping incorrect source ip

I have a Linux box handling routing for my network. Here are some relevant configurations (public IP Addresses masked to 192.0.0.x): IP configuration: [root@gw ~]# ip addr 1: lo: mtu 65536 qdisc noqueue state UNKNOWN group…
fdmillion
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Cannot ping through one of the network interfaces

Setup ubuntu linux VM ( virtual-box) is configured with two interfaces, eth0 and eth1. eth0 is on a bridged network and directly connected to external network. eth1 is on "nat network", which is also connected to external network. Problem Unable…
Nambi
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How can I test an ICMP Re-direct message?

I want to test whether my linux machine is actually accepting ICMP re-direct message and updating the entry in routing table.This is what i have done so far to achieve the same. Simulated a ICMP redirect message with 0,1,2,3 code from ostinato…
Renold Singh
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pfsense: all interfaces up, but all non default gateways down

I am seeing some strange behavior in pfSense 2.0.3 in which all of my WAN interfaces are up according to the Interfaces screen, yet all but the default gateway are shown as "Offline" in gateway groups. My default gateway works just fine. My first…
tacos_tacos_tacos
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How to properly interpet the results of tracert, in particular the second to last hop before a timeout

I am troubleshooting a wireless internet connection that is continuously dropping. The isp says the radio signal is good so it must by my cisco asa 5505. I don't believe them... For discussion assume the following: Remote site public ip is…
James Moore
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How can I tell if a host is bridged and acting as a router

I would like to scan my DMZ for hosts that are bridged between subnets and have routing enabled. Since I have everything from VMWare servers, to load balancers on the DMZ I'm unsure if every host is configured correctly. What IP, ICMP, or SNMP…
makerofthings7
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How does the ping command differentiate between its ICMP responses and anothers?

If I have two shells open each pinging the same host, how do the two shells differentiate between the ICMP responses coming back for each shell?
Peter
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Port Knocking and TCP/IP within the OSI model

I have read that Port Knocking can be subject to false negative (type II error) due to the optimization techniques of TCP/IP. A correct port knock given by the client may be read as incorrect by the server. Is this avoidable by using only UDP and/or…
jtrip
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How to disable ICMP redirect packets in Cisco IOS?

I'm studying a "good practices" document for Cisco IOS, and one of its controls tells me to disable ICMP Redirect packets in the router. Sounds reasonable. So I go test it in Cisco Packet Tracker (a nifty little network emulator program). In my…
JCCyC
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Ping command is not accepted if firewall is on at remote system

I am using ping command to know whether remote machine is on or not. But problem is that ping command (ICMP Packect) is not accepted at remote machine if firewall is on and it assumed that remote machine is off because ping status returns false. Is…
Ashish
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seeing remote MTUs of 250 and 68. is this ever valid?

I'm seeing an ICMP storm from a mobile phone netblocks belonging to "TELEFONICA MOVILES". Periodically we will get upwards of 5 million in a few seconds, all something like this: 08:12:05.740781 IP (tos 0x0, ttl 112, id 40224, offset 0, flags…
cjp
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How to check who blocks ICMP during MTU path negotiation?

I am getting MTU problems with connections to my web host provider. The issue is that I am behind ppoe with MTU size set to 1492 which preventing me from using 'scp'. Once changing MTU from 1492 to 1500 the scp works fine however most of other…
bogumbiker
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Ping to IP address returned Destination Unreachable for a different IP address... huh?

This was totally an isolated incident, but I performed this command: ping 192.168.1.134 and got this result [image]: Pinging 192.168.1.134 with 32 bytes of data: Reply from 192.168.1.133: Destination host unreachable. Reply from 192.168.1.134:…
Hafthor
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How to identify PID of process that is generating lots of ICMP ping requests?

I have a box that is generating lots of outgoing ICMP requests. I am able to see a few happening every second with tcpdump -nni ens192 icmp. However, I don't have anyway of tracing these back to the PID that is causing them. Any thoughts?
srowley
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Is there any way to scan host or network for icmp tunnel server?

I am looking for a tool that would be able to scan hosts for working on them iсmp tunnel server. For example ptunnel. I want to check hosts for which there is a lot of suspicion outgoing pings from my network. I want to make this check automatically…
Slipeer
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