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.

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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 ...
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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 ...
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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 ...
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Windows Server 2008 machine only responds to PING from some machines

I have a colocated Windows Server 2008 machine that replies to PING from some machines but not others (not most machines). I'm not sure where to start to diagnose what the problem is. The server is ...
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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 ...
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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 .
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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 ...
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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 ...
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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 ...
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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: ...
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Why do some web servers not respond to icmp requests?

What is the purpose of blocking/dropping inbound ICMP traffic on a public web server? Is it common for it be blocked? I had to test if a server was accessible from various locations (tested on ...
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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 ...
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Why isn't ICMP routing with iptables nat routing

I'm using iptables on Ubuntu server to route a public IP to a private IP. I want to nat all traffic, including 80, 443 and ICMP. However, it appears that ICMP isn't routing. I have a steady ping ...
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How to make Windows honour an ICMP Connection Refused message after a TCP connection attempt

We have a tool which is used to manage a server process remotely over TCP. One of the tools features is to check if the server is running by attempting to connect to the server in a loop for a given ...
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Why not block ICMP?

I think I almost have my iptables setup complete on my CentOS 5.3 system. Here is my script... # Establish a clean slate iptables -P INPUT ACCEPT iptables -P FORWARD ACCEPT iptables -P OUTPUT ACCEPT ...
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Strange: why does linux respond to ping with ARP request after last ping reply?

I (and a colleague) have just noticed, and tested, that when a Linux machine is pinged, after the last ping it initiates a unicast ARP request to the machine that initiated the ICMP ping. When pinging ...
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Why is network stack ignoring icmp replies from non-default interface?

I have following situation: eth0 - default gateway ( ip: 172.28.183.100, gw: 172.28.183.1 ) eth0 - secondary network connection ( ip: 172.28.171.2, gw: 172.28.171.2). routing looks like this: ...
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Why block outbound ICMP?

This question is slightly related to "Why Block Port 22 Outbound?". I don't see how this can be a notable security risk.
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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 ...
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How do you allow ICMP Echo Requests on a Cisco ASA 55xx Router?

I'm very new to managing Cisco equipment, so bear with me. I'm configuring a Cisco ASA 5505 router for my office, and I am reasonably competent enough with the console to configure the basics -- our ...
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3answers
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ping -f shows problems but regular ping doesn't

I have a strange issue, hosting at Softlayer Washington data center. Test from an EC2 instance to my server at Softlayer :- [root@EC2-box ~]# ping -f -c 100 MY-SL-BOX PING MY-SL-BOX (MY-SL-BOX) ...
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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 ...
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Server with slow ping response

Two boxes with identical loads serving the same sites tend to slow down and stop responding to ping. The slow (or intermittent) ping causes our load balancer to think the servers are offline and ...