traceroute not displaying default gateway and home router IP address

Question

I am confused as to why traceroute on mac os does not display the IP address of my home router.

My traceroute to www.google.com looks like this

1  182.55.226.3 (182.55.226.3)  11.116 ms  13.576 ms  14.185 ms
2  183.90.44.217 (183.90.44.217)  8.347 ms  5.254 ms  7.229 ms
3  183.90.44.201 (183.90.44.201)  7.215 ms  5.495 ms  7.216 ms
4  203.117.35.193 (203.117.35.193)  7.693 ms
   203.117.35.105 (203.117.35.105)  9.191 ms
   203.117.35.221 (203.117.35.221)  7.427 ms
5  203.117.34.81 (203.117.34.81)  7.399 ms  7.444 ms
   203.117.34.85 (203.117.34.85)  9.939 ms
6  203.117.37.22 (203.117.37.22)  14.190 ms
   203.117.36.38 (203.117.36.38)  7.944 ms
   203.117.37.22 (203.117.37.22)  12.577 ms
7  72.14.198.156 (72.14.198.156)  9.226 ms
   72.14.196.189 (72.14.196.189)  12.200 ms  7.388 ms
8  108.170.240.242 (108.170.240.242)  5.872 ms * *
9  216.239.57.50 (216.239.57.50)  14.198 ms
   72.14.234.96 (72.14.234.96)  8.626 ms
   216.239.57.50 (216.239.57.50)  10.731 ms
10 72.14.239.65 (72.14.239.65)  10.027 ms
   64.233.175.215 (64.233.175.215)  12.213 ms
   72.14.233.43 (72.14.233.43)  28.103 ms
11  * * 216.239.35.168 (216.239.35.168)  16.768 ms
12  64.233.175.215 (64.233.175.215)  11.001 ms *

Since traceroute displays routers that the packet passes through to visit the google.com servers, why is my first router not the home router( 192.168.0.1 ) which receives the packet. Instead 182.55.226.3 seems to come from one of the routers in my country. Should traceroute display the private or public IP address of my home router. The first hop's IP address does not match my router's external IP address either.

Traceroute to my router's WAN IP address gives exactly one hop. When i try traceroute to 182.55.226.3 however, the result is something like this.

traceroute to 182.55.226.3 (182.55.226.3), 64 hops max, 52 byte packets
1  * * *
2  * * *
3  * * *
4  * * *
5  * * *
6  * * *
7  * * *
8  * * *
9  * * *
10  * * *
11  * * *
12  * * *

Solution

why is my first router not the home router( 192.168.0.1 ) which receives the packet.

How traceroute works? It sends a ping packets with different TTL (time-to-live) property value. In common case each router decrements TTL, and routes this packet to the next hop, if its value is more than 0, or, if it became zero, it drops ping and sends "TTL expired" packet backward. So traceroute sends packet with TTL=1 and receives "TTL expired" from the closest node in a trace (and expracts its IP), then it sends a packet with TTL=2 and receives "TTL expired" from second node in trace ... and so on until the pong returns.

In common any router decreases TTL by 1. But it can decrease it by 2, 3 or more (meaning this trace is very expensive), or do not alter it (self-hide), or ever increase it (allow long-way traces).

It seems that your router do not alter TTL. So when TRACEROUTE sends a packet with TTL=1, router simply routes it without TTL change. The next hop decrements it, the result is 0, it sends "TTL expired"... and the first node in trace is 182.55.226.3 (is it your router's WAN interface's default gateway?), not your router (192.168.0.1).

Comments

[Akina]

traceroute to 182.55.226.3 Does your output copypast mean you do not reach the trace destination?

[calveeen]

I dont think it reach the destination. It cuts off after 64 hops. I am able to ping the IP addresss though.

[Jon Freed]

My traceroute also did not display my router when I was using "Perimeter 81".

[calveeen]

hmm i checked my router's external IP address via websites that show you such as whatsmyrouterip.com and ip4.me. The external ip address does not match with 182.55.226.3

[dirkt]

The websites will show where the http requests originate from. If your ISP does http caching, or does carrier-grade NAT, this will not be the external IP address of your router. That's why I wrote "if your router has a webinterface ...".

[davidgo]

@dirkt this answer seems wrong - I'm not sure that a router would mangle the packet it returns to report the external interface. More likely it is hiding itself by not decrementing the ttl.

[calveeen]

are you referring to my router's external IP address that the world sees? My router's WAN IP address is not 182.55.226.3. Calling traceroute to 182.55.226.3 gives multiple hops. But all the replies are * * *, while calling traceroute to my router's WAN IP address is exactly one hop.

[calveeen]

traceroute to my router's WAN IP address gives exactly one hop while tracerouting to 182.55.226.3 gives multiple hops all of which are * * *

[Akina]

@calveeen are you referring to my router's external IP address that the world sees? No. IP address of the interface and default gateway of this interface are 2 different addresses (excluding some special types of the connection).

[dirkt]

Assuming however you acquired your routers WAN IP address is correct (the webinterface will show the correct address, websites won't necessarily), multiple *** hops to the first normal traceroute address means your ISP is doing funny things in its internal network. So yes, 182.55.226.3 is indeed a router of your ISP, and it will be difficult to find out what your ISP really does. If you have root access to your home router you can at least try to investigate what's happening on this box.