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Questions tagged [icmp]

ICMP is the Internet Control Message Protocol. It is used for diagnostic purposes, for querying information, and for transmitting network-level error messages. ICMPv6, the version for IPv6, is also used for configuring nodes on the link.

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ICMP “TTL expired in transit” and “Fragmentation required” messages when forwarding is disabled

I have a server with IPv4 forwarding(routing) disabled: # sysctl net.ipv4.ip_forward net.ipv4.ip_forward = 0 # Is there a circumstance where such server sends out ICMP 11/0(TTL expired in transit) ...
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Tunneling TCP via ICMP slowness

There is: Server "A" Server "B" I have root permission on both. They can ONLY ping each other. I installed ptunnel on both. On Server "A", I tried to: ptunnel -p SERVER-B-IP -lp 6969 -da SERVER-...
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How to view ICMP Redirect Logs

I have read on multiple sources that there is are logs for rejected ICMP redirect messages, one of them being "Understanding Linux Network Internals: Guided Tour to Networking on Linux" By Christian ...
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Should I remove ICMP Protocol from firewall rules base on security concern?

As you can see from the screenshot of GCP firewall rule page, should I remove ICMP Protocol from firewall rules base on security concern? Will it lower the chance of being attacked? I'm using CentOS ...
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How come one can successfully ping 127.0.0.2 on Linux?

On a FreeBSD system with a loopback network interface … % ifconfig lo0 lo0 link up loopback drv_running running multicast nd6 performnud auto_linklocal no_radr link rxcsum ...
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Does the `drop` zone (and the `block` zone) allow all ICMP packets?

$ rpm -q firewalld firewalld-0.6.3-1.fc29.noarch $ cd /usr/lib/firewalld/zones/ $ cat drop.xml <?xml version="1.0" encoding="utf-8"?> <zone target="DROP"> <short>Drop</short> ...
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92 views

It is possible to traceroute without touching ICMP?

I often run into a situation where I want to traceroute an IP without root or NET_RAW cap in Linux. I have attempted to send a UDP packet with a small TTL but no ttl error is emitted at all. It seems ...
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267 views

How to Disable Ping ( TCP ) in Linux all the time? [closed]

I want to disable ping response all the time. I use the following command for disable ICMP ping iptables -A INPUT -p icmp --icmp-type echo-request -j DROP what should I do for disable TCP ping ?
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19 views

Exclude interface when send ICMP ping

for build small linux application I need to check the internet connectivity of the system. But my box have multiple network interfaces with interfaced for backup internet connection. I need to do some ...
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1answer
255 views

How to check whether kernel received MLD query or not?

On the Internet I found this command netstat -p icmp6 -s which can dump how many MLD queries received by the kernel. But I have Busybox for my system and because of this I'm unable to run netstat ...
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mtu 9000 issues only on tcp and not icmp possible?

I have a connection between two datacenters and rsync between them stalls often. I think it is related to the mtu 9000 (I actualy set it to 8900 because of some possible vlan use) I have the ...
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What Linux process is responsible for responding to pings?

I have a Linux based process controller that occasionally locks up to the point where you can't ping it (i.e. I can ping it, then it becomes no longer pingable without any modifications to network ...
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1answer
63 views

I have disabled all rules in firewall, but still can tracert from LAN

I have disabled all positive rules in firewall on my pfSense box, and I can't browse Web, but I still can tracert 10.10.0.251 from LAN machine and receive 3 hops from my ISP (behind the router). ...
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775 views

tcpdump -i any doesn't work on FreeBSD

How to listen all interfaces on FreeBSD with tcpdump > tcpdump -i any tcpdump: any: No such device exists (BIOCSETIF failed: Device not configured) (I would like to listen ICMP)
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2k views

UDP port unreachable although process is listening

I am experimenting with communication over UDP port 6666 (the goal is setting up a listener for netconsole, but that's not really relevant here). On the listening side, nc -luv 6666. On the sending ...
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14k views

How to Disable Ping Response ( ICMP echo ) in Linux all the time?

I want to disable ping response all the time on my Ubuntu operating system, the following commands work but these are just until the system reboots: Ping off: echo "1" > /proc/sys/net/ipv4/...
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Reading MLDv2 queries using an IPv6 socket

I have mrd6 installed on my raspberry pi. It registers with a local interface (tun0) and periodically transmits MLDv2 queries over it. According to [RFC3810], MLDv2 message types are a subset of ...
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No buffer space available - ICMP

I'm trying to set up a Heartbeat client on a linux machine (CentOS Linux release 7.3.1611) which is sending ICMP echo requests to roughly 1300 hosts. However, in future this number will be higher. The ...
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1k views

Network Interface VLAN static addressing

I have been trying to configure the static IP addresses with Ubuntu 16.04 Dabian version. The network as follows in the graph I have been failing to ICMP (ping echoing) between the Client and the ...
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118 views

What is ICMP reply for all-zero host-bit IPv4 address?

We all know that the first address of any sub-net is network identifier and it can't be assigned to any hosts. For example in network 10.1.1.4/30, the address 10.1.1.4 is network identifier. If ...
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How to DROP icmp requests with firewalld?

How to DROP icmp requests with firewalld? An equivalent example instead using iptables would be: $ iptables -A INPUT --protocol icmp --in-interface enp0s8 -j DROP The above produces the desired ...
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964 views

How to configure iptables ICMP rules on a router?

I'm trying to configure iptables rules on a router that allows ICMP (PMTU-D, ping, traceroute, etc.) to function. GOALS: 1) Allow all ICMP outbound traffic initiated from the router and internal ...
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446 views

How to make Linux stop sending IPv6 ICMP redirects?

In case of IPv4 we have net.ipv4.conf.all.send_redirects flag, but it's not available for IPv6. Is there anything better than this? ip6tables -A OUTPUT -p icmpv6 --icmpv6-type redirect -j DROP For ...
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1answer
814 views

MTU (IPv4) tests in Linux

I noticed I have several networks with all ICMP messages blocked at the firewall level, except for ICMP echo and reply. I know that there is a need at least ICMP messages type 3 in IPv4 have to be ...
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981 views

How to disable ICMP timestamp on AIX - not using firewall

On AIX 6/7 how can we disable this function? I cannot see any in "man no". Installing firewall just because of this is not really an option.
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131 views

Only ping fail output should get visible

Is there a possibility for getting only the error output when running the ping command? Its very tricky to understand if we have n number of server monitoring. icmp_seq will obviously show the drop ...
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187 views

iptables REJECT with delay

Simulating an unreachable host: iptables -I OUTPUT -d 192.168.1.42 -j REJECT And then ping 192.168.1.42. It rejects immediately, so the terminal is flooded with Destination Port Unreachable. How to ...
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1answer
2k views

Forward ICMP Ping Packets to Interface

I've got a script that listens for ICMP ping packets (containing data payload) and while this works if you run it from command line, it doesn't work in a Docker container because ICMP ping packets are ...
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1answer
1k views

ICMP - Destination unreachable (Port unreachable)

I have two Ethernet-wired connected devices. I gave to both of them address from same sub-network. As result I can see second device in arp-table of the first. $ arp -a ? (128.247.77.90) at 10:60:4b:...
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Can two android devices in different network(3g) comunicate themselves with ssh connection?

I have two rooted android devices with different isp (I use different 3g connection for them) and created a double ssh connection (I can with a public ip server) communicating both to this server (I ...
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504 views

iptables REJECT icmp-admin-prohibited

The iptables man page says: Using icmp-admin-prohibited with kernels that do not support it will result in a plain DROP instead of REJECT I have been unsuccessful at finding out at which kernel ...
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7k views

How to accept ICMP redirects?

tcpdump showed me there are some ICMP-redirect in my network (KVM virtual-machines, bridged network). I decided to take a closer look on them and how my system behaves and how it looks. I found it ...
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504 views

Subnet routing problem

In my LAN I have an openwrt router configured with IP 10.0.0.1. It is the default gateway (and dhcp server) in my LAN 10.0.0.0/24. Now I have a new network, say 10.9.0.0/24 used by virtual machines. ...
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21k views

ICMP : Port unreachable error even if port is open

I am testing my Debian Server with some Nmap port Scanning. My Debian is a Virtual Machine running on a bridged connection. Classic port scanning using TCP SYN request works fine and detects port 80 ...
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614 views

How to get different types of ICMP

I have a task on which I have spent a lot of time. I am not fluent in Linux, but I can manage basic things. The task is to gather different types of ICMP packets. I can harvest them by tcpdump (which ...
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How to disable IPv6 ping response in Linux without firewall

How can I disable IPv6 ping responses in Linux without using the IPv6 firewall? This question covers how to do this using the IPv6 firewall via iptables, but I'm using an embedded system that doesn't ...
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1answer
165 views

IPV6 ND router advert Malformed packet

Am trying to simulate IPv6 ND router Advertisement packet in openvswitch for one of my projects, but the formed packet is malformed(analyzed it in wireshark). Following is the packet dump I created, ...
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1answer
504 views

Some ICMP-Reply messages don't arrive in User Space in recent Kernels

I'm moving an application from 2.6.23 (yes, it's ancient; that's why we are moving) to 3.18LTS. The application monitors multiple network links to the same target with ping packets. The different ...
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1answer
352 views

Drop all ICMP packets?

Is it ok for me to drop all types of ICMP packets? I.e. iptables -I INPUT -p icmp -j DROP. Everything except one service seems to work. I already stopped this service. To be specific I functioned as ...
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Why is a Linux Tun interface not returning ICMPv6 Echo replies?

I wrote a program which connects to a TUN interface and replies to ICMPv6 Echo Requests. Even though I can successfully observe the echoes and replies with tcpdump on the TUN interface, it appears ...
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3k views

firewalld zones and ICMP Packets

How are the zones in firewalld configured with respect to ICMP packets? Do they act differently for interfaces and sources? 1. How firewalld filter ICMP packets? I would assume the main zones act as ...
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Undesired ICMP Destionation Unreachable Message

I am running CentOS with a 2.6.38 kernel. The Linux box has an IP of 10.0.0.10 assigned to eth0, which is the only network adapter on the box. I have created a program that fake an additional IP 10.0....
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104 views

icmp limited in many network spaces?

I wrote small script do show example usage of ip netns on unused class size C (here changed into 192.168.10) #!/bin/sh network=192.168.10 for id in `seq 0 127`; do ip netns del test-$id; done; ...
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1answer
874 views

Linux as a router: Sending ICMPv4 messages “net unreachable” and “host unreachable”

I want routers based on GNU/Linux to sent at least those ICMPv4 messages: net unreachable, host unreachable. Especially the host unrechable message is important to me: If a router resides in the same ...
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1answer
935 views

Observing ping replies under DNAT

I'm confused while trying to understand the DNAT mechanism under below circumstance. My understanding: DNAT = Destination Network Address Translation: Functionality which translates the destination ...
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832 views

Is there an ICMP echo request service?

Often, in applications that I develop, I like to include a network status indicator for various devices on the network. The easiest way to monitor these devices is by pinging them. But ICMP echoes are ...
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4answers
1k views

Delay when iptables icmp rules take effect

I have setup my iptables to disable all incoming connection, i.e. :INPUT DROP [0:65535] When the iptables has been started, I run the following command to enable ping: /usr/sbin/iptables -A INPUT -...
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1answer
5k views

Curious about strange ICMP type 3 code 10 traffic to my IP address

My firewall (iptables) logs some strange ICMP type 3 code 10 traffic that I am curious to understand (specifically how or if this could be an exploit of some sort). Type 3 = Destination ...
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1answer
882 views

ICMP timestamp requests

Is there a way to disable ICMP timestamp requests without using iptables on our RedHat 5 and 6 servers? We are not using iptables because we use a hardware-based firewall. Is there any setting (say,...
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1answer
710 views

How to log incoming icmp traffic?

I am watching my ip6table and observing an icmp packet arriving and getting dropped at the rate of 1 per second. I am trying to find out what that message is about. I tried using tcpdump (it is ...