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 ...
- 760
27
votes
Difference between unresponsive (*) and unreachable (!H) hosts in traceroute output
The answer by YLearn is correct but it is important to know more details.
* means that your machine received no response.
!H means that your machine received ICMP message "destination host ...
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) ...
- 331
11
votes
Accepted
Why there are ip(ip) and domain(ip) 's difference and multi rows records in the traceroute?
1) Traceroute may attempt to resolve the hop's domain name via DNS. As you didn't include any additional flags to explicitly enable this functionality, your traceroute application does so by default. ...
- 993
10
votes
Accepted
Traceroute UDP port question
To understand the mechanism, let's see it with an example:
I issue a traceroute to 44.12.44.1 from my PC
My PC sends 3 UDP datagrams to 44.12.44.1 with TLL=1 and port=33434
Inmediately sends 3 UDP ...
- 4,487
9
votes
Accepted
Slower hops in traceroute
Many routers prioritize routing packets over answering ICMP requests, they often have rate limits and queueing in place to reduce load on the router.
As a result, latency on intermittent hops can be ...
- 17k
9
votes
Accepted
Why traceroute is still Used?
Traceroute doesn't give inexact information, it performs tests in a specific way and give some results based on the response it receives (or do not receive).
You have to know how to interpret the ...
- 19.4k
9
votes
Accepted
difference between reverse, forwarding and return path on traceroute
You are "A", you are performing a Traceroute to "B"
First hop is A > R1. The response travels R1 > A. In this case, the RTT time is how long it took for the packet to get from A, to R1, and ...
- 14.8k
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 ...
- 311
8
votes
Accepted
Private IP inside internet?
Traceroute deliberately sends packets with low time-to-live values to make the routers between you and your destination send back ICMP TTL exceeded messages. The traceroute output is basically the ...
- 4,670
6
votes
Accepted
Why does ip routing not take an even remotely direct route?
The virtual world and physical world rarely line up. Just because machines are physically close, doesn't make them logically close. Traffic goes where routing entries, and interconnects take it.
Eons ...
- 31.5k
6
votes
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Whether the traceroute command only can check "to" path, can not check "back" path?
Traceroute, by its nature, only reports on the path towards the target, and very imperfectly too.
You need to run traceroute from both sides to see if your routes are asymmetric.
It has to be ...
- 16.1k
6
votes
Accepted
Is it possible to perform a Layer 2 (MAC address) traceroute?
But is there any way to do a traceroute that will show Layer 2 information?
Short answer: no.
Longer answer: traceroute exploits IP's TTL feature. There is no such concept in Ethernet, hence no ...
- 81.6k
5
votes
Accepted
Does traceroute show the IP address of the entry port? or exit port?
It is the address on the interface which responds back to with ICMP timeout. Which, by default, would be the interface closest to the source.
- 98.4k
5
votes
Tips on analyzing traceroute readings
Pretty much every post I see along these lines recommends the following document:
Practical Guide To (Correctly) Troubleshooting with Traceroute
Traceroute can you send you down the rabbit hole, ...
- 345
5
votes
Accepted
how to implement traceroute without using TTL?
In theory you could send a packet with IP option 7 set (record route). This would return the path the packet took to the destination.
In practice this option is not widely supported, which is ...
- 66.9k
5
votes
Accepted
how does Trace route packet work
traceroute works by sending ICMP echo requests or fake UDP datagrams towards the destination (probes), starting with TTL set to 1 and increasing one by one. On each router/hop on the way, the packet ...
- 81.6k
5
votes
Accepted
Why there is only one hop in the tracert?
As explained by Jens Link, usually a one-hop traceroute means the host is on the same network. Since in your case, it is higly unlikely, that means you probably have a proxy that respond in place of ...
- 19.4k
5
votes
How to traceroute in SDN Networks while traceroute is not working in SDN by default?
One of the points of SDN is that you build a virtual "network box" where all your switching, routing, NATing, etc happens and that looks like a single device from the outside, regardless of its ...
- 81.6k
4
votes
Accepted
Tips on analyzing traceroute readings
I highly recommend the Traceroute Guide posted by dareuja. There isn't a more complete single resource on interpreting the results (that I know of, at least).
Here are a few tips I've picked up over ...
- 14.8k
4
votes
Same hop appears 4 times on a traceroute
This is due to path MTU discovery.
As you can see the MTU for you first hop is 1300, while you computer expect 1500 by default.
So tracepath will send several packets to determine the correct MTU, ...
- 19.4k
4
votes
Why there are ip(ip) and domain(ip) 's difference and multi rows records in the traceroute?
1 - it is because your traceroute client is performing reverse DNS lookup. I.E. it asks to the DNS server which is the domain name associated with this IP address. In one case, there's no such reverse ...
- 19.4k
4
votes
Accepted
Are traceroute hop latency measurements relative to the previous hop or to the origin?
The return times in traceroute are always relative to the sending source. Due to different ICMP handling in the hops, some returns may be slower than subsequent ones that are actually more distant.
...
- 81.6k
4
votes
Accepted
Why there still need a parenthesis contains it again in traceroute logs?
1 - By default, traceroute try to perform a reverse DNS lookup and will output the DNS name followed by the IP address in parenthesis.
Many routers IP addresses don't have a PTR record, so the DNS ...
- 19.4k
4
votes
Is it possible to perform a Layer 2 (MAC address) traceroute?
Layer 2 information is stripped off and thrown away at every layer 3 ingress interface. A completely new layer 2 header is added on the outgoing interface. You're asking a router to do something ...
- 66.9k
3
votes
Accepted
Are ping-times directly related to location/distance?
Not really.
Yes there is certainly a correlation between ping time and distance. However there are many factors other than distance that can lead to a high ping. Congestion, crappy routing, Satellite ...
- 13k
3
votes
Accepted
Preventing a Cisco router from appearing in a traceroute
You don't block the icmp unreachables - which are sent by your router - but the inbound packets sent by the traceroute or other tool, that have a TTL (time to live) of 1.
See e.g. Cisco Guide to ...
- 2,638
3
votes
Windows implementation of traceroute (tracert)
Windows uses ICMP echoes for traceroute (tracert), while most *nix systems (including Cisco routers) use UDP.
Note: traceroute in Linux can use ICMP with the -I option.
- 66.9k
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