Questions tagged [icmp]

For questions about the Internet Control Message protocol.

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Ping port number?

Yesterday an interviewer asked me what the port number for ping is and which protocol ping uses: TCP or UDP. After the interview, I searched on the Internet and found different results: someone says ...
Nishad Morey's user avatar
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28 votes
7 answers
25k views

Why can I traceroute to this IP address, but not ping?

I have an IP address and can traceroute to it, but I can not ping. You see, I can traceroute 43.24.226.50: dele-MBP:~ ll$ traceroute 43.24.226.50 traceroute to 43.24.226.50 (43.24.226.50), 64 hops ...
244boy's user avatar
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19 votes
2 answers
32k views

Traceroute - every packet has TTL == 1

I'm working on Wireshark lab-IP in Computer networking - A top down approach and I don't understand why every packet that normally expired has a TTL of 1. Here is my Wireshark capture file. https://...
ksp0422's user avatar
  • 193
18 votes
1 answer
3k views

Why do some common traceroute implementations default to using UDP probes?

I was recently troubleshooting a network connectivity meta-problem, in that I knew a given destination was reachable, but I was not able to demonstrate that with traceroute because the path went cold ...
neirbowj's user avatar
  • 869
11 votes
2 answers
57k views

Interpreting TTL in ping results

I work for a VoIP service provider and I am working an issue with a customer who has a cable internet connection that's throwing me for a loop. He has a single block, which we'll pretend is 70.141.15....
DTD's user avatar
  • 305
10 votes
3 answers
23k views

Traceroute Over TCP vs UDP

For what purpose would one wish to send traceroute over TCP rather than UDP? What advantages/disadvantages are there in doing so? I know that traceroute normally uses UDP ICMP "echo" packets while ...
THE DOCTOR's user avatar
9 votes
2 answers
3k views

Where is Ping's "round-trip time" stored in the IP header?

If we use ICMP's ping, we know the TTL and round-trip time are stored in the IP header. In the below IP header map we know TTL's location, but where is the round-trip time? Is it stored in Options?
aircraft's user avatar
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9 votes
5 answers
3k views

Why is the ICMP protocol considered to run at layer 3 on the Wikipedia page?

Why is the ICMP protocol considered to run at layer 3 on the Wikipedia page (same layer as IP) when the ICMP protocol data is a payload of the IP packet? This is the article on Wikipedia that states ...
yoyo_fun's user avatar
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9 votes
6 answers
98k views

Pinging broadcast address [closed]

I am using Linux. I read somewhere on the internet that pinging the address 255.255.255.255 will ping everyone in the network segment. And it will return every IP addresses in that subnet. But when I ...
ashok's user avatar
  • 595
8 votes
2 answers
63k views

Difference between ping timed out and destination host unreachable

I'm pinging from a Windows Box to a device that I rebooted. PS C:\Users\administrador> ping 192.168.2.10 Pinging 192.168.2.10 with 32 bytes of data: Control-C PS C:\Users\administrador> ping -...
Felipe Oliveira's user avatar
8 votes
2 answers
106k views

dont fragment bit PING TOOL

Actually my machine wwan0 MTU is 1500 ashokkrishna@ashokkrishna-Lenovo-B560:~$ ping -s 1490 example.com PING example.com (93.184.216.119) 1490(1518) bytes of data. 1498 bytes from 93.184.216.119: ...
ashok's user avatar
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8 votes
2 answers
3k views

Are ICMP Redirect messages really bad?

Due to potential for MITM attack, ICMP redirect messages should be blocked. However, the original purpose of the ICMP redirect message is to inform the host of a better router (or gateway). Then, is ...
baeharam's user avatar
  • 257
8 votes
2 answers
10k views

What are the SNMP MIBs for Cisco IPSLA ICMP echo

I have two ipsla operations set up: ipsla operation 10 type icmp echo source address 10.0.0.1 destination address 10.0.2 frequency 30 operation 11 type udp jitter tos 128 source ...
John Oxley's user avatar
7 votes
2 answers
6k views

What would happen to Ping if two PCs have same IP address with same Subnet Mask on same network?

If there are two PCs with same IP address on a LAN, what would happen if I ping that IP address from another PC on the same network and why?
Bhupendra Pandey's user avatar
7 votes
1 answer
300 views

How are ping times computed

I have been graphing ping (IPV4) responses times/vs packet size. I was expecting to see a discontinuity of around 2*MTU/BandWidth in response time around the MTU boundary (actually, around 1464 byte, ...
Alien Life Form's user avatar
6 votes
6 answers
35k views

Why doesn’t ICMP use port numbers?

Firewall is showed in port no 7 and Google search is also showed in port no 7 so I am confused about how exactly ICMP use the port number. Regards, Bhushan
Bhushan Wankhede's user avatar
6 votes
2 answers
1k views

IP Traceroute RFC 1393

Is RFC 1393 implemented by real routers in practice? Are there any tools that generate traceroutes using it?
Knio's user avatar
  • 163
6 votes
2 answers
9k views

USE of ICMP echo request in DHCP

In RFC2131 (page 12) it's been mentioned that The server should use whatever information is available in the configuration information repository to choose an address to reuse. For example, ...
dillip_beta's user avatar
6 votes
3 answers
12k views

When is 'Timestamp' and 'Timestamp Reply' are used in ICMP protocol?

I started the packet capture in my laptop through Wireshark application. Now through cmd, I pinged some server (say, www.google.com). And i stopped packet capture and analysed the packets being ...
Deepak's user avatar
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6 votes
2 answers
2k views

Why can I ping IP addresses from 127.0.0.1 to 127.255.255.254?

I thought that the loopback IP address of my machine is 127.0.0.1. I do not understand why am I able to ping IP addresses until 127.255.255.254.
yoyo_fun's user avatar
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6 votes
2 answers
18k views

Ethernet padding

I'm using Wireshark for my project. I sent a ping over to Google.com and Wireshark said that the length was 57 bytes(when I received the reply it was 60 bytes long and it contained 6 bits of padding. ...
user35754's user avatar
6 votes
1 answer
795 views

IPv6 replacement for ICMP timestamp

Does any standard IPv6 protocol has anything analogous to an ICMP timestamp message?
cnst's user avatar
  • 417
5 votes
2 answers
411 views

Why there are ip(ip) and domain(ip) 's difference and multi rows records in the traceroute?

In the traceroute command: $ traceroute 104.43.54.2 traceroute to 104.43.54.2 (104.43.54.2), 64 hops max, 52 byte packets 1 10.10.10.1 (10.10.10.1) 4.852 ms 4.623 ms 1.588 ms 2 100.64.0.1 (100....
fanhualuojin154873's user avatar
5 votes
3 answers
5k views

Does a router send frames or packets?

Perhaps it's a novice question, but does a router send/receive frames? When I read about this subject, it seems that routers decapsulate the frame on arrival, and encapsulate the packet in a frame in ...
Smbbo's user avatar
  • 51
5 votes
2 answers
5k views

Calculating checksum for ICMPv6

Referring http://www.faqs.org/rfcs/rfc1071.html, I try to deduce the c code for calculating the checksum for ICMPv6. But check with the checksum parse by wireshark, I find that the answer got from my ...
Anakin Tung's user avatar
4 votes
1 answer
19k views

What is first? ARP vs ICMP

I want to know what is first after STP. There are just three devices, switch and two hosts. A switch is not configurated and two hosts have each IP by static. Of course, two hosts are connected to ...
user17426's user avatar
4 votes
1 answer
225 views

Features of ICMP

I'm taking a Network class and learned ICMP, but I cannot understand the reason why below arguments are applied. ICMP message is not generated on header checksum errors If a datagram carrying an ICMP ...
baeharam's user avatar
  • 257
4 votes
2 answers
22k views

How to find out TCP/UDP latency of your network? [closed]

Many people often suggest you to use ping command to find out your network latency. But it is false and a myth you often find in articles on Internet. ICMP ping was never designed to find out latency ...
defalt's user avatar
  • 400
4 votes
3 answers
5k views

Telnet - "Destination unreachable" response

I'm looking to implement, what I feel, is Telnet security when it comes to unwanted hosts initiating a Telnet connection to one of my devices. I can lock down a specific subnet or only allow a range ...
BabyPython's user avatar
4 votes
1 answer
7k views

ICMP type 3 code 1 and 7, what is the diference?

What exactly is the difference between ICMP type 3 code 1 and code 7 messages? By reading their descriptions they seem to be used for the same purpose. I am trying to understand when a router will ...
user5469's user avatar
  • 158
3 votes
2 answers
2k views

Strange router's MAC address from ICMP Echo Reply?

Using Wireshark to capture ICMP packets (Windows) using ping to google.com, I can see the source-MACAddr of the ICMP Echo replies is not the same as the MAC address of my direct router (which is the ...
David Tran's user avatar
3 votes
1 answer
461 views

ICMP response to source IP when the payload of IP packet is not ICMP?

Let us say I create a valid packet (contains telnet request) with TTL value less than the TTL value required to reach the destination IP. Will the computer that receive the IP packet with TTL=1 (...
Ron Vince's user avatar
  • 927
3 votes
1 answer
793 views

ICMP packet with correct mac address but wrong ip address

I was wondering what would happen if you send an ICMP request with the correct mac address but the wrong ip on a local network. Would the request reach the computer with the correct mac address since ...
user1313324's user avatar
3 votes
2 answers
874 views

Cisco 2600 IOS ICMP packets viewing

Does anyone know how to view ICMP packets (ping), if possible, traversing through a Cisco 2600 router, that is, how to use the console connection to the router (the usual for configuration) to display ...
shirowww's user avatar
  • 147
3 votes
1 answer
492 views

ICMP redirect message

As I understand ICMP redirect message is sent to host to "shorten" the routing path of the packet . If i have the example here and the path from host in network 1 to network 3 is equal using both R2 ...
saeed hardan's user avatar
3 votes
2 answers
7k views

Difference of tracert and pathping

What is the difference between tracert and pathping command? Thanks
J. Doe's user avatar
  • 55
3 votes
1 answer
2k views

What Does ICMP Code 9 Mean For a Type 8 Packet?

I am currently doing an assignment that requires us to generate ICMP packet with various types and codes. I have consulted the RFCs as well as various other place. Many of the types and codes I get ...
Danny K's user avatar
  • 43
3 votes
1 answer
61 views

How to handle IPv6 Extension Header Options with action = 01

RFC 8200 section 4.2 states that if a node does not recognize an option type, that node must do some action depending on the 2 higher order bits of the option type. When the higher order bits are 01, ...
ghanan94's user avatar
3 votes
2 answers
517 views

How to handle ICMP-in-IPv6 or ICMPv6-in-IPv4?

Since ICMP and ICMPv6 have different IP protocol numbers, it's technically possible for an IPv4 host to receive an ICMPv6 packet or for an IPv6 host to receive an ICMP packet. Is the host's behavior ...
joshlf's user avatar
  • 327
3 votes
2 answers
3k views

Is DHCP in the application layer or the network layer?

Tanenbaum's Computer Networks says: 5.6 THE NETWORK LAYER IN THE INTERNET ... 5.6.4 Internet Control Protocols In addition to IP, which is used for data transfer, the Internet has several companion ...
Tim's user avatar
  • 1,545
3 votes
1 answer
64 views

Should Bit Errors Cause Loss Proportional To PDU Size?

Should I expect random (or even regularly-occurring) bit errors to cause corrupted/dropped PDUs (packets) proportionate to the PDU size ? Troubleshooting high (0.01% to 0.1%) packet loss over a short (...
robut's user avatar
  • 243
3 votes
2 answers
1k views

OSPF can't ping other network segments

I'm trying to setup a very simple OSPF network with Vyatta. From the best of my knowledge they let all traffic in by default, and I haven't set any firewall rules. The vyatta instances are launched as ...
Muff's user avatar
  • 183
3 votes
1 answer
2k views

ICMP Redirects uncovers routing issues

So our newly configured servers have uncovered some switch configuration issues. In /etc/sysctl.conf we have the following: net.ipv4.conf.all.send_redirects = 0 # CIS 4.1.2 net....
TheTemplateBlog's user avatar
3 votes
1 answer
3k views

How do I permit only specific types of ICMP unreachable packets to be sent out from a Cisco IOS router? [closed]

I have a Cisco IOS router and want to permit only types of ICMP packets to be sent (type 8, code 0 and type 3, code 4). I tried putting an outbound ACL on the interface connecting to the Internet, but ...
slantalpha's user avatar
2 votes
3 answers
201 views

ping server vs. connecting to server

Networking newb here. Under what circumstances could you fail to ping a remote server with the ping command, but still be able to connect to it via other means (as long as it was still TCP/IP)?
Alexander Mills's user avatar
2 votes
2 answers
1k views

Confusion about MTU

I am studying about IP fragmentation and MTU. What I know is MTU is the property of Physical medium, as in the amount of data it can process without having to fragment the data. The default MTU on ...
Techievent.in's user avatar
2 votes
2 answers
3k views

NAT Translation Table Port Number

I had a practice question about a NAT-enabled router with outside address 24.34.112.235 and inside network 192.168.1/24 and three inside hosts .1, .2 and .3. The three hosts all open two connections ...
Ludwigthestud's user avatar
2 votes
1 answer
2k views

Default Gateway Best Practice

Recently I was troubleshooting a firewall issue on one of my servers and noticed that there was a LOT of ICMP redirect traffic being rejected (as it should be). But this got me thinking why I was ...
Caynadian's user avatar
  • 123
2 votes
1 answer
1k views

ICMP "echo request" handling on routers running Cisco IOS-XR

I am aware that ICMP "echo request" messages addressed to router are handled in process switching in case or routers running IOS. However, what about Cisco ASR9K routers running IOS-XR? Is the ...
Martin's user avatar
  • 1,227
2 votes
2 answers
1k views

How exactly does Path-MTU Blackhole Detection work?

I'm currently trying to understand how the Path-MTU Blackhole Detection really works. From what I understand: You send rather big packets, starting at like 1460 Bytes (TCP example) and wait for ...
Gereon99's user avatar
  • 123