[SOLVED] how to understand the following output of traceroute

jcwkyl · 07-11-2010, 07:17 PM

My IP: 10.60.56.90/24
My default gateway: 10.60.56.254
I run traceroute command and get the following output:

Code:

[root@jcwkyl ~]# traceroute www.jlu.edu.cn
traceroute to www.jlu.edu.cn (202.198.16.80), 30 hops max, 40 byte packets
 1  10.60.27.254 (10.60.27.254)  0.481 ms  0.551 ms  0.688 ms
 2  192.168.1.121 (192.168.1.121)  0.837 ms  0.998 ms  1.159 ms
 3  192.168.1.134 (192.168.1.134)  1.001 ms  1.257 ms  1.508 ms
 4  ws16-80.jlu.edu.cn (202.198.16.80)  0.234 ms !X  0.225 ms !X  0.249 ms !X

I know how traceroute works, hence my questions are:
1. My default gateway is 10.60.56.254, but the output shows that the first hop router is 10.60.27.254, does it means that my default gateway does not route packets? Please explain to me.
2. Is it possible to get the rough topology of the network from the output?

Thanks very much!

troop · 07-11-2010, 09:12 PM

1. No. Your router is invisible for traceroute (router use 'mangle' table to adjust the TTL. This means 10.60.56.254 forward the first probe to the next upstream router.)
2. yes

jcwkyl · 07-12-2010, 02:50 AM

Could you tell me what is the benefit of hiding the 10.60.56.254 from the traceroute ?

acid_kewpie · 07-12-2010, 03:33 AM

I wouldn't say that the router is necessarily invisible, why would it be assumed to be? It is possible that it's reporting it's IP address from a different interface though. Is that IP on the router? You've told us just about nothing about the architecture you're using so it's hard to make any actual comments.