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Questions tagged [icmp]

For questions about the Internet Control Message protocol.

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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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2 answers
38 views

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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3 votes
1 answer
52 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 (...
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2 answers
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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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2 answers
117 views

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 ...
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1 vote
1 answer
98 views

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 ...
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1 answer
483 views

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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2 votes
2 answers
259 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 ...
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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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1 answer
123 views

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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1 answer
267 views

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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2 answers
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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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2 votes
1 answer
286 views

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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2 answers
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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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1 answer
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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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2 answers
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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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-1 votes
3 answers
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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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2 votes
2 answers
514 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 ...
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2 answers
208 views

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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2 answers
45 views

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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1 answer
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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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2 answers
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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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1 vote
0 answers
375 views

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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2 answers
88 views

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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1 vote
3 answers
393 views

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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4 answers
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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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2 answers
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While sniffing with Wireshark, i get lot of ICMP packets in my loop back interface with the word "CKAAAA.." in it, why is this happening? [closed]

So i have a parrot VM, and i tried to use wireshark on the lo interface of it just for fun, now I'm seeing loads of ICMP packets, which seems to be Netbios inside(not sure why is Wireshark naming the ...
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28 votes
7 answers
18k 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 ...
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1 vote
2 answers
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How does packet tracing deterministically work?

If a packet can take any route, how can you iteratively figure out the path from you to a host? From what I can tell, packet tracing works on the basis that packet_i takes a the route: route(...
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3 votes
1 answer
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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, ...
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2 votes
2 answers
281 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 ...
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2 votes
1 answer
1k views

Virtual IP failover issue with vmware exsi ip based hashing

We are deploying HA database cluster on exsi which based on virtual IP concept for failover. if One node fail reserved VIP will be assigned to another node we have two exsi nodes and two virtual ...
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1 vote
1 answer
2k views

How to use ICMP to send message

I was trying to send ICMP package with Payload/Message on server_A to server_B(10.1.1.5) as following: ping -p 12345 10.1.1.5. but when I use Tcpdump to capture the ICMP package from server_A, I ...
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2 votes
0 answers
1k views

Point to Point ICMP Ping Loss between Juniper MX routers

I am facing problem with regard to 1 x 10G link (which is actually configured as an aggregated Ethernet (ae) i.e ae link contains only single 10G link. This ae link is connected between 2 x Juniper ...
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1 vote
0 answers
3k views

Modifying linux ping icmp payload [closed]

On analyzing ping request and reply from a windows system to Linux. It was observed that the windows ping request payload was "abcdefghijklmnopqrstuvwabcdefghi" with size 32 bytes Could this ...
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5 votes
3 answers
3k 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 ...
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2 votes
2 answers
2k 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 ...
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2 votes
3 answers
2k views

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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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 ...
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1 vote
3 answers
121 views

Whether the traceroute command only can check "to" path, can not check "back" path?

How to detect the router path of traffic? I use the ipip.net for ICMP traffic: I want to check the out path and back path. such as I have A address 60.248.41.135 and B address 103.248.41.135. ...
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4 votes
1 answer
195 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 ...
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5 votes
2 answers
396 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....
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9 votes
2 answers
2k 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?
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0 votes
2 answers
403 views

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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1 vote
2 answers
508 views

CRC done by ICMP?

Is cyclic redundancy check (CRC) done by Internet Control Message Protocol(ICMP)? How can Time to live (TTL) help for this?
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1 vote
1 answer
233 views

How do ICMP packets travel in a networks?

Questions: I'd like to know how ICMP packets travel in a network? Are they encapsulated within IP datagram? The RFC 792 doesn't explicitly states the layer of ICMP. Are ICMP messages sent using a ...
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5 votes
6 answers
23k 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
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3 votes
1 answer
2k 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 ...
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6 votes
3 answers
8k 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 ...
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