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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 ...
naïveRSA's user avatar
  • 760
23 votes
Accepted

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 ...
jonathanjo's user avatar
  • 16.3k
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) ...
Arjan's user avatar
  • 331
18 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 ...
Martin Rosenau's user avatar
11 votes
Accepted

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 ...
jcbermu's user avatar
  • 4,497
11 votes
Accepted

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 ...
Zac67's user avatar
  • 84.9k
9 votes
Accepted

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 ...
Peter Green's user avatar
  • 13.3k
9 votes

Ethernet padding

IEEE 802.3 describes structure of Ethernet frames. As it says the minimum frame length is 64 bytes. Every frame less than 64 bytes should be padded with 0 before transmitted on the Ethernet link. This ...
SuB's user avatar
  • 308
9 votes
Accepted

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 ...
Zac67's user avatar
  • 84.9k
9 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 ...
Phil Frost's user avatar
8 votes
Accepted

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 ...
Ron Maupin's user avatar
  • 99.8k
8 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 ...
Ron Maupin's user avatar
  • 99.8k
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 ...
Peter Green's user avatar
  • 13.3k
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 ...
Jesse P.'s user avatar
  • 4,690
8 votes
Accepted

Why can I ping IP addresses from 127.0.0.1 to 127.255.255.254?

The entire address block 127.0.0.0/8 is the block of loopback addresses for a host. There are RFCs that explain this. The goes back at least as far as RFC 990, ASSIGNED NUMBERS: The class A network ...
Ron Maupin's user avatar
  • 99.8k
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. ...
jonathanjo's user avatar
  • 16.3k
7 votes
Accepted

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 ...
Zac67's user avatar
  • 84.9k
7 votes
Accepted

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 ...
Peter Green's user avatar
  • 13.3k
7 votes
Accepted

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 ...
Ron Maupin's user avatar
  • 99.8k
6 votes

Multiple NICs, only eth0 can ping

You have all your interfaces in the same subnet. That is not going to work. Your computer can't figure out which interface to use to send to each host because it believes they are reachable from any ...
Ron Trunk's user avatar
  • 67.7k
6 votes

Why can't two hosts (in two different logical networks) connected to each other through cross-over cable communicate?

A host knows if the destination address is on a different network (the same way that you do, by masking the host and destination addresses with the host mask). If the destination is on the same ...
Ron Maupin's user avatar
  • 99.8k
6 votes
Accepted

Understanding hubs and switches

If I connect 3 computers to the same hub, and use PC1 to ping PC2, then all the 3 computers will receive the ping? PC2 and PC3 receive the echo request, and PC1 and PC3 receive the echo reply. A ...
Zac67's user avatar
  • 84.9k
6 votes

What happens with a ping when it enters a network? Is the router the one answering with a reply?

It's the host which is addressed in the outgoing ECHO REQUEST packet which is responsible for answering. As far as the routers in between are concerned, this is just like any other IP packet, and ...
jonathanjo's user avatar
  • 16.3k
6 votes
Accepted

Cisco, Router can communicate; hosts cannot

For NAT to work, you must specify a standard access list to identify the traffic that should be NATted. You reference the access list (source list 1) correctly, but you have not created the access ...
RobinG's user avatar
  • 1,969
5 votes
Accepted

How are ping times computed

I'm not sure why you would think fragmentation would double the time. If a router fragments a packet, it sends both fragments sequentially. The host on the other end will get the fragments, reassemble ...
Ron Maupin's user avatar
  • 99.8k
5 votes

Multiple NICs, only eth0 can ping

If You need all nodes to work in one subnet and one L2 broadcast domain, add bridge interface, enable rstp on it, assign IP on bridge interface and add physical interfaces to bridge. /etc/sysconfig/...
mmv-ru's user avatar
  • 774
5 votes

Is ping in the application layer?

I'll start with the oft-repeated caveat (at least by me, anyway) that things don't fit neatly into the OSI model. "Ping" is the name of an application that generates ICMP echo request packets and ...
Ron Trunk's user avatar
  • 67.7k

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