Skip to main content
Share Your Experience: Take the 2024 Developer Survey
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 ...
grawity_u1686's user avatar
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 ...
Spiff's user avatar
  • 105k
8 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 ...
harrymc's user avatar
  • 484k
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 ...
duux's user avatar
  • 61
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 ...
grawity_u1686's user avatar
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 ...
Snowball's user avatar
  • 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]:...
Fanatique's user avatar
  • 4,648
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 ...
grawity_u1686's user avatar
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 ...
Richlv's user avatar
  • 363
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 ...
Jonas Köritz's user avatar
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 ...
Spiff's user avatar
  • 105k
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 ...
Spiff's user avatar
  • 105k
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 ...
Appleoddity's user avatar
  • 11.8k
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 ...
harrymc's user avatar
  • 484k
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 ...
Alex's user avatar
  • 33
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 ...
Mokubai's user avatar
  • 93.1k
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 ...
Spiff's user avatar
  • 105k
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, ...
grawity_u1686's user avatar
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 "...
grawity_u1686's user avatar
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 ...
Spiff's user avatar
  • 105k
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:
harrymc's user avatar
  • 484k
1 vote
Accepted

Windows ping to Any IP including 127.0.0.1 hangs, but internet works

Interestingly enough, I had this happen to me when I was working on a VPN client problem in windows 8.1. The vpn app crashed while doing a transfer, also IKEv2. pings failed, with strange DHCP ...
Tim_Stewart's user avatar
  • 5,989
1 vote

Why can't I ping a computer in same network?

If none of the other replies in the linked posts help you, try looking into this: link Whenever you first connect to a network on Windows, you get a popup asking you if you want to detect for other ...
Endor's user avatar
  • 21
1 vote

Why can't I ping a computer in same network?

Your WiFi router may have a Wireless Isolation option enabled, which prohibits communication between wireless clients, described here in detail: https://www.howtogeek.com/179089/lock-down-your-wi-fi-...
Beli's user avatar
  • 409
1 vote
Accepted

IPv6 ping only possible when target machine pings back

With link-local IPv6 addresses you always need to specify the interface. The reason is that the same address block (prefix) is used on every network: The address fe80::21c:1cff:fe00:3de3 is only ...
harrymc's user avatar
  • 484k
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[:...
grawity_u1686's user avatar
1 vote

What is the purpose of using a large ping packet?

A bad router, even wired, can fail on large pings and succeed on small ones, until restarted, so it can be used for debugging issues like this one Packet loss may be a result of a bad connection, and ...
Jonathan's user avatar
  • 1,772
1 vote

Can the maximum ping size of 65500 bytes can be increased?

the max size is 65507 which is 65535 (max ip length) - 20 (ip hdr) - 8 (icmp/ping hdr) = 65507. Windows OS blocks max size at 65500 but in Linux you can ping up to the real limit
ido goldschmidt's user avatar
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 ...
Steve Faulkner's user avatar

Only top scored, non community-wiki answers of a minimum length are eligible