Questions tagged [icmp]
For questions about the Internet Control Message protocol.
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Cannot ping interface although in same subnet? Why? Debug ip packet gives encapsulation error
I have the following setup:
From Laptop Mgmt2 (bottom right) I want to ping Se/0/0/0 on R1. I can only ping S0/0/0 on ISP router, which is in the same subnet.
If I enable debug ip packet on isp router ...
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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 ...
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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....
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ICMP codes in response to ICMP traffic, not UDP/TCP
I am trying to wrap my head around a concept and I am having some trouble. If I ping 8.8.8.8, 10.8.1.1 replies to me "Destination port unreachable".
Ping uses ICMP, so it does not have a '...
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ICMP error message's data for IP datagram with < 64 bits payload?
RFC792:
The internet header plus the first 64 bits of the original
datagram's data. This data is used by the host to match the
message to the appropriate process. If a higher level protocol
uses ...
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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, ...
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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.
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IP packet expired by TTL generate an ICMP response in any case?
Acording to Wikipedia IPv4 article for TTL header field:
An eight-bit time to live field limits a datagram's lifetime to
prevent network failure in the event of a routing loop. It is
specified in ...
CommunityBot
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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 ...
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If ICMP packet is lost then another ICMP could be generated?
Suppose there are two routers between Source and destination R1, R2 respectively. Suppose source sending packet to R1 and then R1 send to R2, but R2's buffer is full and discarded the packet and ...
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Actually ICMP message makes layer3 reliable?
We know that ICMP is connectionless because it does not require hosts to handshake before establishing a connection.
But when packets gets dropped in between route then respective router informs the ...
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PING port number?
Yesterday interviewer ask me what is port number for ping and which protocol ping use TCP/UDP.
After interview I search on internet and found different results someone says ICMP uses Port 7, someone ...
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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 (...
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What does a router do with a packet if it can't find the destination IP address in its routing table?
If a router receives an ARP request in which the destination hardware address is a broadcast address, and if the destination IP address is an address that the router cannot find in its routing table. ...
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How is traceroute Time to Live decremented?
By default, for Traceroute utility, the "time to live" value will be decremented by 1 each time packet passes through a router. However, is the "time to live" value also ...
CommunityBot
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Possible causes of ICMP Destination unreachble - Port unreachable
Are there any other causes, apart from the specific port to be reached being closed, that can lead to an ICMP Destination unreachable - Port unreachable message? What are possible reasons for this ...
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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 ...
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Is ICMP protocol widely used in real world?
Is the ICMP protocol generally used in real world networking configurations ?
If yes, what are some real world examples that make use of this protocol.
In addition, I see that the ICMP echo requests ...
CommunityBot
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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 ...
CommunityBot
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Permit ping and traceroute and deny all other services using an ACL
my topology is shown below:
I would like the networks that are connected to Hermes-Router to be accessible from all the other stations only when I use ping and traceroute. I tried to do this using an ...
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What is making switch CPU so busy that it's unable to respond with ICMP errors?
According to How to prioritize ICMP time exceeded packets my switch is dropping ICMP error replies because the CPU is apparently too busy.
It is a PowerConnect 7048 and it dropping anywhere between 5% ...
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How to prioritize ICMP time exceeded packets
According to why ICMP Time Exceeded packet takes longer ICMP Echo Reply, it is normal for ICMP time exceeded be treated as low priority and slowed down or even discarded. I'm observing this problem ...
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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 ...
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How to check cable without ping?
Is there any way to check if a network link is physically working, without using ping?
Recently bought a Power-Line-Communication device, and I wanted to test if it works. Before pinging the machines ...
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Static Routing - host to host ping does not work (MikroTik)? [closed]
I'm trying to do static routing using actual devices. Below is my setup:
The left router is a MikroTik RouterBoard hAP lite.
The right router is a MikroTik RouterBoard hAP ac.
I want to ping from ...
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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 ...
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Why does NAT keep track of each packet not just connections?
I have tried packet tracer and actual cisco routers and I find this weird: NAT uses different source ports, usually incrementally, for consecutive packets from the same connection. Why is that?
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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)?
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Traceroute probes
In traceroute, when a * is recieved, it could mean the router didn't reply due to various reasons- either the router is busy processing other packets or ICMP is blocked. I think few ISPs configure ...
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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?
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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 ...
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why ICMP Time Exceeded packet takes longer ICMP Echo Reply
I've noticed that when I use tracert a certain router(hop) always takes about 200ms to reply back, the rest reply's in 50ms, after digging into it with wireshark I've noticed that tracert uses normal ...
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IPv4 and UDP/TCP packets inside of ICMP packet?
A week ago, after opening wireshark, i was surprised by seing a storm of ICMP packets from different IP addresses. While deep analysing of thoses packets, i noticed that those ICMP packets contains ...
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ICMP distinguish error messages
Can a Internet Control Message Protocol when an error is sent can it tell which datagram that made the error?
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What's the Destination unreachable ICMP packet(ICMP payload the UDP) usage? [closed]
In my Mac(192.168.2.228), it will send ICMP packet to my house's router (192.168.2.1).
with the info Destination unreachable (Port unreachable)
and in the Wireshark packet detail panel, there ...
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When I send the ICMP packet with 4000B, but the IPv4 segment calculated 4008B
When I send the ICMP packet with data size as 4000B for testing the IP fragment.
ping 192.168.2.1 -c1 -s4000
and the Wireshark captured it,
Whether is is because of ICMP header? but we know ICMP ...
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Confusion about TTL when pinging
TTL value of a packet is supposed to decrease 1 at each router from 255 down to zero as follows:
But when I ping to 8.8.8.8 the TTL starts at 253 and doesn't change:
How can this be explained? Why ...
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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 ...
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IP Traceroute RFC 1393
Is RFC 1393 implemented by real routers in practice?
Are there any tools that generate traceroutes using it?
CommunityBot
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How Can I use "ping command" with source?
I can not use ping 'target' source 'interface'
ping 192.168.0.2 source lo0
% Invalid input detected at '^' marker.
It's possible if I use "ping"
R2#ping
Protocol [ip]: ip
Target IP address: 192....
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ICMP is a protocol working in the Network Layer. Why does it send few fields of the transport layer while reporting an error?
I was confused if ICMP is a network layer protocol why does it send transport layer fields in its error reporting messages.
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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 ...
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Broadcast ICMP and gratuitous ARP
When sending an ICMP broadcast, all nodes can respond. is it the case of the sender too?
If it's the case then:
Is it specified somewhere that the sender should respond with gratuitous ARP when the ...
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How computer "knows" how and what to respond to particulary ICMP messages
How a computer "knows" what to respond to particular ICMP messages?
As is known there are various ICMP messages that differ by type and / or code.
For example ICMP type 0 is "echo reply", type 13 /14 ...
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ICMP No Reply Found Issue [closed]
Currently working on a Go based NAT router and when translating ICMP traffic and am seeing some interesting behavior.
The clients request is forwarded to the server, the server keeps track of the ...
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Weird results when pinging
I'm learning IP addressing and routing basics, but I'm facing a problem which I cannot understand, so i have the following structure:
Well in this situation, a ping from 130.190.0.16 to 130.190.4.30 ...
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Estimate latency between two IP addresses
I would like to estimate what is the latency in sending a packet between two IP addresses.
Let's assume that I have two IP addresses: ip1 and ip2. I can easily ping both ip1 and ip2, and the ping ...
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Which first eight bytes of the IP datagram are included in ICMP message?
The definition of ICMP message says that it has a type, a code and the first 8 bytes of IP datagram causing error.
Question: Which first eight bytes of IP datagram are included in the ICMP datagram?
...
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Why ICMP Destination Port Unreachable error messeage is generated for unreliable UDP packets?
My doubt is why an icmp destination port unreachable error message generated for udp. Why we can't simply discard the udp packet if the destination port is not reachable by saying udp is connection-...
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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 -...
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