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Questions tagged [icmp]

For questions about the Internet Control Message protocol.

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1 answer
27 views

Missing ICMP identifier equivalent in ARP protocol and desired arping behavior

Running simultaneously more arping on the same interface and the destination IP address all clients get the responses due missing ICMP identifier equivalent. First, am I correct that there is no ICMP ...
-1 votes
1 answer
64 views

Why MLS2 Doesn't Get ICMP Packet To Where It Should?

This is a Packet Tracer lab from Kieth Barker's website with minor modifications. It is intended to exhibit how can we get to the network 10.10.0.0/24 access to the Web Server 23.1.2.2/24 Using NAT. ...
0 votes
1 answer
81 views

In wireshark, why following a TCP or UDP stream does not remove ICMP packets?

In Wireshark, when I follow a TCP or UDP stream using right click -> Follow -> UDP Stream, if there are some ICMP packets from same endpoints, wireshark will keep them in the stream. Why? Since ...
0 votes
1 answer
82 views

Change source and destination adresses from a valid captured ping to create a valid ping with different source and destination

I want to create traffic in my network, especially I want to send a repetitive ping to the device with the IP 192.168.3.146 from my traffic generator (IP 192.168.3.100) (see scematic) For the creation ...
0 votes
2 answers
82 views

Do destination hosts decrement the TTL?

I was trying to understand more about traceroute when I stumbled upon this site and I have a question about this diagram: As you can see in the diagram, the destination host S1 receives a packet ...
0 votes
1 answer
107 views

In a trace route, do routers that do not respond still forward the packets?

In traceroute, The sender expects a reply within a specified number of seconds. If a packet is not acknowledged within the expected interval, an asterisk is displayed. Pasting here the example trace ...
80 votes
5 answers
523k views

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 ...
1 vote
1 answer
80 views

The TTL and packet drop [duplicate]

I would just like to verify one thing. When a router receives a packet with a TTL of 1, the router can still process and accept it if its destined for itself, correct? Because for example, eBGP ...
0 votes
1 answer
74 views

BGP configuration multi-hop ping not working

I'm learning bgp and studying on a simple lab I'm unable to ping a loop0 two hops away while the loop0 on the nex-hop router is reachable Topology is simple R3-R1-R2, from R2 i'm able to ping loop0 on ...
0 votes
1 answer
1k views

Why am I not capturing any ICMP packets on wireshark?

I am doing a lab where we are meant to ping an address and use wireshark to capture ICMP packets when we ping that address. WHen I run the wireshark capture with the ICMP filter on and ping my address,...
0 votes
0 answers
52 views

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 ...
9 votes
6 answers
101k 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 ...
11 votes
2 answers
59k 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....
1 vote
1 answer
471 views

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 '...
0 votes
1 answer
134 views

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 ...
7 votes
1 answer
305 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, ...
6 votes
2 answers
3k 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.
0 votes
2 answers
453 views

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 ...
3 votes
2 answers
4k 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 ...
0 votes
2 answers
121 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 ...
0 votes
1 answer
38 views

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 ...
3 votes
1 answer
65 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 (...
0 votes
2 answers
1k views

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. ...
0 votes
2 answers
516 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 ...
1 vote
1 answer
3k 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 ...
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 ...
1 vote
1 answer
147 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 ...
2 votes
2 answers
2k 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 ...
0 votes
2 answers
5k views

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 ...
0 votes
0 answers
121 views

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% ...
1 vote
1 answer
724 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 ...
9 votes
5 answers
4k 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 ...
0 votes
2 answers
248 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 ...
0 votes
1 answer
1k 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 ...
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 ...
0 votes
2 answers
656 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? ...
2 votes
3 answers
206 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)?
2 votes
2 answers
227 views

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 ...
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?
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 ...
1 vote
2 answers
457 views

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 ...
2 votes
1 answer
1k 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 ...
1 vote
2 answers
92 views

ICMP distinguish error messages

Can a Internet Control Message Protocol when an error is sent can it tell which datagram that made the error?
0 votes
2 answers
3k views

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 ...
0 votes
1 answer
79 views

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 ...
-1 votes
3 answers
6k views

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 ...
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 ...
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?
2 votes
6 answers
128k views

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....
0 votes
2 answers
84 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.