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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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When connecting from one subnet to another through a WireGuard VPN, why TCP requires NAT on both sides but ICMP works without NAT?

I encountered this issue today with the following setup: [Cloud Server] --> [Cloud Gateway Server] <- WireGuard -> [Home Router] <-- [Home Device] I have source NAT on my router. My home devices can SSH into my cloud server. I have no NAT on my…
Minsheng Liu
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UFW Weird ICMP log record - Pinging is blocked

In the log records below I have replace my eth MAC address with ETH_MAC_ADDRESS the IP of my server with MY_SERVER_IP and other IPs with STRANGE_IP plus a number to distingue. Jan 29 15:11:48 cld kernel: [140229.731612] [UFW BLOCK] IN=eth0 OUT=…
fat_mike
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iptables and SNAT spoofing

So we are working with iptables at class and I've been testing some rules in the NAT table. As far as I know SNAT changes the IP source of a packet to which the rule dictates but what I tested does not seem to work every time. I added this rule:…
Deketh
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How do I limit ping (ICMP) responses on a debian 10 server?

I have a VPS with debian 10 installed, primarily used for website hosting. when I issue a ping to the server from a remote machine, I am able to and receive responses for packet sizes up to around 64Kb using -s 65507 flag. using sudo also enables me…
pulsar
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Whitelist ICMP traffic with iptables

I'm configuring iptables, for an Ubuntu Server VPS. It runs sshd, and various Dockerised web apps. It is not a router, and is not part of a complicated network. After researching the topic, I decided to respect ICMP. However, I'm using a whitelist,…
lonix
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ICMP types commands on CMD?

To use ICMP type 8 we write : >ping IP@. I was wondering what commands would allow me to use other types of ICMP like type 13?
medilies
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How do I do traceroute/tracepath without any admin privileges?

Basically, I need to "trace a packet from my computer to the host" to diagnose a network issue and I do not need any fancy additional functionality. Redirect me to the right place if this is not the place for this question, but I need to do…
Sacha T Red
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Manually sent ICMP redirect packets

I'm trying to sent a ICMP redirect to my router to add a new route, as I can not configure it from the portal, and have no access to it though telnet/ssh. The scenario is the next. LAN network 192.168.1.0/24 New network 102.168.2.0/24 If I setup all…
erdn
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Default gateway and ARP confusion

I have the following configuration (I'd post a pic but not enough rep for more than 2): PC1 (10.0.2.10/24) and PC2 (10.0.2.137/29) are connected to a hub, which is connected to a router on interface FastEthernet0/1 (10.0.2.138/24). I ran two tests…
Gerk
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Any protocol used by TRACEROUTE ? ICMP or UDP

Any protocol used by TRACEROUTE : ICMP or UDP or IP ? Or use them all : Encapsulation ?
Karim Michel
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Why can I not ping my host behind the firewall? Cisco asa 5505

Can anyone please help me to figure out, what in my configuration of the Cisco asa 5505 is wrong or missing? I have multiple host behind my firewall. These hosts run different websites on port 80. I can ping the server from one to another, but I am…
Banks
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firewalld causing nmap to return host seems down

I've two machines, server1 and server2. On server2, I stop firewalld. [root@server2 ~]# systemctl stop firewalld From server1, nmap returns Host is up. [root@server1 ~]$ nmap -sn server2 Starting Nmap 6.40 ( http://nmap.org ) at 2020-09-02 11:27…
JeremyCanfield
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How can I stop Linux from sending ICMP "Destination Unreachable" responses?

I have a Linux system which has a number of services disabled (for example, telnet). When a telnet client attempts a connection, the system responds with an ICMP "Destination Unreachable". Is there a way, short of modifying the Linux network…
Dave
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Firewall rules does not apply to pfsense hosted machine

I am using pfsense as my home firewall and configured multi-wan setup. In addition, I have installed package 'Telegraf ' package for exporting my pfsense stats into InfluxDB, also in 'Telegraf' configuration I have enabled 'Ping Monitor' for 4…
JavaMachine
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How to manage PING replies?

How can I manage, for example, my Ubuntu mashine so it doesn't (or does) respond to PING(ICMP ECHO_REQUEST - type 8) requests? Normally almost all computers in a LAN network responds to ping with an ICMP ECHO_REPLY, but how to turn it off? How to…
Jonathan Gurebo
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