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47 votes

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

On a similar question here Luke Savage explained it perfectly: Traceroute is not a protocol itself, it is an application and the protocols used depends on the implementation your are using. Primarily ...
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23 votes
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Interpreting TTL in ping results

So needless to say, nobody on the planet knows how many nodes there are between here and there. I know how many nodes. There are exactly 16. The reason you get different responses is because ...
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  • 62.1k
23 votes
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Where is Ping's "round-trip time" stored in the IP header?

The round trip time is not actually stored anywhere. The sending host remembers the time it sends each ICMP Echo Request message, using ICMP's 16-bit identifier and sequence fields. When it gets the ...
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19 votes

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

To add to @naïveRSA's answer, if there's filtering/firewalling in the path one could also have the situation where an ICMP "echo reply" (ping) packet is blocked, but an ICMP "time exceeded" (tracert) ...
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  • 331
17 votes
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traceroute many hops with the same ip

That is a routing loop. The router with IP address 74.117.154.1 keeps sending your packets to another router (74.117.154.4), which keeps sending them back to 74.117.154.1. They keep doing this until ...
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  • 4,611
16 votes

PING port number?

I'd like to give you an additional answer especially to this part of the question: ... someone says ICMP uses Port 7 Port 7 (both TCP and UDP) is used for the "echo" service. If this service is ...
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14 votes
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Why can't I ping from one computer to another using L3 cisco 3550 switch?

You seem to be missing the ip routing command which enables L3 routing on the switch.
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14 votes
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What would happen to Ping if two PCs have same IP address with same Subnet Mask on same network?

Actually, the ping gets sent to a layer-2 address if they are on the same LAN. Assuming ethernet, the sending host may have a MAC address in its ARP cache, and the pings gets sent to the host with ...
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13 votes
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pinging broadcast address

Not all machines will answer a broadcast ping. (all broadcast -- 255.255.255.255, or subnet broadcast -- eg. x.x.x.255) Some see it as a "security feature", because one could spoof the origin to flood ...
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11 votes
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Ping a private IP address in another network

A PC in a private IP range can't be acccesed from the public internet. Devices in private range connecting to internet use a proxy or router/NAT device that replaces the local source IP for a single ...
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11 votes
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What happens with a ping when it enters a network? Is the router the one answering with a reply?

What happens with a ping when it enters a network? Does the router redirects it to one of the devices on the network, or it sends the reply itself? A router routes packets towards the destination. An ...
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10 votes
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dont fragment bit PING TOOL

Running "ping -M do -s 1490 example.com" says that the ICMP data size is 1490 bytes and fragmentation is not allowed. For this size of ICMP data, ICMP size (i.e., header + data) is 1498 bytes. Adding ...
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9 votes

What is first? ARP vs ICMP

Short Answer: The answer is that it depends. Longer Explanation: Naturally, when a device is sending out unicast IP traffic, it needs to add the layer 2 headers (including destination MAC address) to ...
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9 votes
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Difference between ping timed out and destination host unreachable

First we need to understand how packets are sent. When a host or router tries to send an IPv4 packet* it first looks up the destination in it's routing table. Based on the routing table it determines ...
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  • 11.6k
8 votes

I can ping but ports are closed

TCP port 7 ('echo') and ICMP echo request messages are two very different things. Ping uses ICMP echo messages, which (since it's ICMP) do not use TCP. So this has nothing to do with TCP ports being ...
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8 votes
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Strange router's MAC address from ICMP Echo Reply?

You are confused. What you claim is your router's MAC address is not your router's MAC address. The MAC address is in the range, 0000.0C07.ACxx, which is the MAC address range for HSRP. The 06 on the ...
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8 votes

Why ping with source address?

The biggest reason is that the return path from the destination back to you may depend on the source address. Often you want to test the network path in both directions. Furthermore things like ...
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  • 11.6k
8 votes

PING port number?

As others have already stated, in general pings are ICMP-based and have no ports. There is, however, such a thing as TCP Ping where, instead of the typical 3-way TCP handshake, only the first 2 steps ...
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8 votes
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does the DSL distance really add more latency

Twisted pair cable used for the local loop has a velocity factor of about .58 - each km of cable takes ca. 6 µs to travel, adding ca. 12 µs to latency. The rest of the Internet probably uses fiber ...
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8 votes

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

The usual ping command uses ECHO REQUEST and ECHO REPLY, as you've seen. It does indeed locally keep track of sent time and matches with the incoming reply to determine the round trip time. ...
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  • 15.9k
8 votes

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

Let's look at what happens, shall we? 8.8.8.8 makes a good example, because at least from my location, I can reach it both with traceroute and ping. First let's try ping 8.8.8.8 and watch what ...
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7 votes

How to trace outgoing interfaces?

I's not exactly the answer at your question, but that a simple (but limited) way to do (in certain case) what you want. I'm coping-post the option -R of ping man page: -R Record route. ...
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7 votes

Difference between ping timed out and destination host unreachable

The Request timed out. is while the destination MAC address is still in the source/router's ARP cache. The Reply from 192.168.2.120: Destination host unreachable. is after the destination MAC address ...
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  • 93k
7 votes
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Ping in the same subnet

On a directly connected layer-2 network/segment, IP communication works by encapsulating IP packets into layer-2 frames addressed to the destination's MAC. The source learns the destination's MAC ...
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7 votes
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Why I have higher ping to the VLAN interface than to other local interfaces

A "L3 switch" will perform the actual packet forwarding (both L2 and L3) using dedicated hardware, but exceptional cases like sending a ping reply or a time exceeded message are normally handled in ...
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7 votes
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Confusion about MTU

From reading on the web I understand that 28 bytes is reserved for ICMP so my actual MTU is 1472. No, the MTU is size of the payload of the data-link protocol. For ethernet, that is 1500. You are ...
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6 votes

If you can't ping an ip address this means nothing in regards to dns right?

You are correct in that if you ping an IP address you are not using DNS. If you are using a hostname instead of an IP address with ping, then you will be using DNS. However, just because you are ...
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6 votes
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Small variations in ping on a LAN

I'd say it looks normal. But I think you're doing this a bit wrong. Ping has one function only: probing, i.e. "Hello, are you there" - "Hello, yes I am here". While it shows you the latency between ...
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6 votes
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linux ping mtu and fragmentation

When a router should fragment but it receives the IP datagram with DF flag set, it sends ICMP (type should fragment but DF is set) to the source. Then the source adjust the MTU and it send again the ...
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