21
votes
Accepted
Why ICMP is different that TCP and UDP?
ICMP is a control protocol, meaning that it designed to not carry application data, but rather information about the status of the network itself. The best known example of ICMP in practice is the ...
- 787
16
votes
Accepted
ICMP packet with TCP?
According to the ICMP message type (3 "Destination Unreachable"), these are not monitoring but error packets (which is the most common use of ICMP). They do not use TCP, but they were caused ...
- 416k
14
votes
How ping a server which has ICMP blocked
I use Nping, which is packaged with Nmap. It queries a port of your choosing, for example port 80, and if the port is open, it will receive a response. For example:
nping --tcp microsoft.com
- 5,819
8
votes
Accepted
Why is 32bytes the default ping size? Is it okay to use less?
Ethernet has a minimum frame size of 64 bytes. If you try to send less than that, your system will pad it to 64 bytes anyway, if it's being sent on Ethernet. Ping already sends close to minimum-sized ...
- 101k
7
votes
Accepted
how to test ntp servers as real servers that responding without using ping test
An ntp server can be tested by asking it for the date using the
ntpdate command.
For example:
ntpdate -q pool.ntp.org
The parameter -q is for query only, don't set the clock.
The command will return ...
- 445k
6
votes
Win10 allow incoming ICMPv6 - firewall is behaving weirdly
For others that ran into the same issue described above. ICMPv6 echo requests are code 128, not 8 as they are in ICMPv4. That needs to be reflected in the rule.
netsh advfirewall firewall add rule ...
- 61
4
votes
Why ICMP is different that TCP and UDP?
The primary difference is that TCP and UDP are for transferring application data (i.e. whatever the app desires), whereas ICMP is a "control" protocol that transfers information about other protocols.
4
votes
Linux Virtual machine can't ping Google, while Host can do it
As a workaround (or arguably a fix), disable any network offloading settings on the physical NIC on the host.
Open Control Panel, System, Device Manager
Expand "Network Adapters"
Double-click on your ...
- 27.4k
3
votes
SSH and PWNAT for SSH Connection Between Two Separate NATs
Yes. Suppose your network looks like this:
You want to SSH from A to B. You have sshd running on B; it is listening on on tcp://127.0.0.1:22.
B$ pwnat -s 0.0.0.0 2022 127.0.0.1:22
pwnat on B is now ...
- 523
3
votes
Accepted
How can Ping not use a transport protocol?
When one says "Ping", they refer to ICMP ping, as that is what the original ping is. ICMP actually works on a lower level than the UDP & TCP transport protocols and does not use ports[1]:...
- 4,480
3
votes
Accepted
Do Linux (4.15.0-130) and Windows (10) treat ICMP differently?
It's not the same traceroute. Linux traceroute actually sends UDP probes by default, instead of ICMP Echo as Windows would. Use sudo traceroute --icmp to get something closer to Windows. (Try out mtr ...
- 416k
3
votes
Detect ICMP requests on a Windows 10 System
Unfortunately it does not work with netstat, since ICMP doesn't depend on a port
No; it's because the ICMP handler does not use a regular socket, but is built into the IP stack. But if you had a ...
- 416k
2
votes
Accepted
Why ping/latency lower in-game than command prompt?
Most games are fairly inaccurate at determining ping from in-game. Many games don't measure ping at all, but rather game traffic latency, i.e. time taken for an actual game action to complete.
OS ...
- 6,581
2
votes
Accepted
Is ICMP port unreachable error generated by both TCP and UDP?
Destination unreachable is generated by the host or its inbound
gateway to inform the client that the destination is unreachable for
some reason. A Destination Unreachable message may be generated ...
- 8,636
2
votes
Accepted
icmpping in Zabbix, one item multiple server
That is not possible - it's not how Zabbix operates. You must have an item per host.
What you can do, is template that item. That allows you to configure it once, then apply that configuration to all ...
- 353
2
votes
Why does ICMP Echo Request and Echo Reply packets contain a Data portion?
The data portion is mandatory in reply packets, if there is a data portion in the request packet. The answering system must send a reply containing exactly the same data portion. The RFC792 does not ...
- 968
2
votes
Accepted
Required ICMP types for IPSec tunnel?
Most Time Exceeded messages are from someone running traceroute. Aside from that it could indicate a few relatively rare things, like you have a routing loop, or you have a machine with a too-low ...
- 101k
2
votes
TCP application setting Don't Fragment (DF) Bit
You're describing an algorithm called "Path MTU Discovery". It's a default feature of all modern OS networking stacks (so it's generally the TCP/IP stack that does this, not the apps) and it ...
- 101k
2
votes
Why does the 2nd ARP request wait until the pings are over to show up?
This appears to be what Bruce Hartpence calls a “Return ARP.” As described in this excerpt from Packet Guide to Core Network Protocols.
The conversation shown in Figure 4-12 illustrates another ...
- 11.5k
2
votes
Accepted
Ping from VMware guest machine to the Ethernet interface of the Host machine
These two addresses are on differing network segments, so messages cannot cross over.
You can specify for the virtual machine the Network Adapter as NAT or Bridged
so it participates in the same ...
- 445k
2
votes
Only allow pinging in one direction
For those who need an answer:
On both routers I matched ICMP type 0 (echo reply) to rule:
add action=accept chain=forward dst-address=192.168.100.17 protocol=icmp \
src-address=192.168.11.252
...
- 33
2
votes
Accepted
Allow VRRP on firewall
No, VRRP is not part of ICMP, nor vice versa – it's a standalone protocol with its own packet format.
However, although it runs on top of IP, VRRP does not use a transport protocol and does not have "...
- 416k
2
votes
Accepted
Does Windows Firewall block ICMP Timestamp Request (Type 13) by default?
Windows Firewall blocks everything by default. The full processing order is documented on TechNet, but for simplicity, you can think of it as "1) handle all 'deny' rules, 2) handle all 'allow' rules, ...
- 416k
2
votes
Traceroute/tracert fails to receive hops return information
There are at least two possible cases here:
One: If you are behind a NAT (specifically what the standards call NAPT, or what proprietary Cisco-ese calls "PAT") gateway, and none of the hops ...
- 101k
2
votes
Spectrum Router not allowing ICMP Echo Requests
Users outside of your home LAN shouldn't be trying to ping the non-routable private IP address of a server on your LAN. If they need to ping you, the only publicly accessible address they can ping is ...
- 101k
2
votes
Spectrum Router not allowing ICMP Echo Requests
This is pretty much a standard feature of a firewall router. More specifically it is a feature of any kind of firewall.
If you want this machine to be accessible you have two options.
In your router ...
- 88k
2
votes
Detect ICMP requests on a Windows 10 System
A free tool that can detect ICMP probes is
Wireshark.
Once you choose the network adapter and start capturing,
you may set the Display filter to ICMP.
Here is an example for detecting ping localhost:
- 445k
1
vote
Accepted
Only allow pinging in one direction
Both 'ping' requests and responses are ICMP. So one rule allows the request and another allows the response, in either direction.
You can match individual ICMP packet types using icmp-options=Type[:...
- 416k
1
vote
Forwarding ICMP over a server without redirects
You need to prevent BOTH the server and the router from SENDING icmp redirects to the source host.
If it is a cisco router, "no ip redirects" will do that.
On the server, depends on your linux ...
Only top scored, non community-wiki answers of a minimum length are eligible