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Ping to the remote subnet fails, but traceroute gives the same IP in all 30 lines

Hello.

 

I got a complaint that some users in Prague are unable to access subnet 22.246.0.0/18 in Joburg. 

 

Trace from a Prague WAN router to one of the Joburg host ends after 4 hops:

 

PG#traceroute 22.246.224.12

1 10.254.16.65 0 msec 12 msec 4 msec
2 10.254.16.61 [AS 65000] 26 msec 30 msec 24 msec
3 10.254.16.62 [AS 65000] 26 msec 24 msec 26 msec
4 10.252.4.126 [AS 64805] 26 msec 24 msec 26 msec
5 * *

 

10.252.4.126 is a router located somewhere in France. I logged in to that router and issued the same traceroute command and got this:

 

FR# traceroute 22.246.224.12
traceroute to 22.246.224.12 (22.246.224.12), 30 hops max, 40 byte packets
1 10.252.5.52 (10.252.5.52) (AS 64770) 1.492 ms 1.099 ms 1.095 ms
2 10.252.5.52 (10.252.5.52) (AS 64770) 0.923 ms 0.761 ms 0.877 ms
3 10.252.5.52 (10.252.5.52) (AS 64770) 1.725 ms 0.946 ms 1.173 ms
4 10.252.5.52 (10.252.5.52) (AS 64770) 1.203 ms 0.976 ms 1.186 ms
5 10.252.5.52 (10.252.5.52) (AS 64770) 1.782 ms 1.546 ms 1.053 ms
6 10.252.5.52 (10.252.5.52) (AS 64770) 1.24 ms 1.209 ms 1.226 ms
7 10.252.5.52 (10.252.5.52) (AS 64770) 2.087 ms 2.273 ms 1.466 ms
8 10.252.5.52 (10.252.5.52) (AS 64770) 10.878 ms 1.421 ms 1.48 ms
9 10.252.5.52 (10.252.5.52) (AS 64770) 1.604 ms 1.776 ms 1.725 ms
10 10.252.5.52 (10.252.5.52) (AS 64770) 1.846 ms 1.522 ms 1.733 ms
11 10.252.5.52 (10.252.5.52) (AS 64770) 3.51 ms 2.37 ms 2.696 ms
12 10.252.5.52 (10.252.5.52) (AS 64770) 2.495 ms 3.176 ms 1.965 ms
13 10.252.5.52 (10.252.5.52) (AS 64770) 3.238 ms 3.281 ms 3.613 ms
14 10.252.5.52 (10.252.5.52) (AS 64770) 2.716 ms 2.396 ms 3.16 ms
15 10.252.5.52 (10.252.5.52) (AS 64770) 4.235 ms 2.419 ms 3.748 ms
16 10.252.5.52 (10.252.5.52) (AS 64770) 4.361 ms 4.241 ms 2.442 ms
17 10.252.5.52 (10.252.5.52) (AS 64770) 2.674 ms 34.388 ms 4.665 ms
18 10.252.5.52 (10.252.5.52) (AS 64770) 3.813 ms 4.386 ms 2.647 ms
19 10.252.5.52 (10.252.5.52) (AS 64770) 5.342 ms 4.833 ms 3.184 ms
20 10.252.5.52 (10.252.5.52) (AS 64770) 3.01 ms 4.886 ms 4.812 ms
21 10.252.5.52 (10.252.5.52) (AS 64770) 5.47 ms 3.964 ms 3.566 ms
22 10.252.5.52 (10.252.5.52) (AS 64770) 4.835 ms 12.711 ms 5.413 ms
23 10.252.5.52 (10.252.5.52) (AS 64770) 4.082 ms 3.776 ms 5.58 ms
24 10.252.5.52 (10.252.5.52) (AS 64770) 5.864 ms 5.841 ms 3.415 ms
25 10.252.5.52 (10.252.5.52) (AS 64770) 5.355 ms 5.035 ms 6.436 ms
26 10.252.5.52 (10.252.5.52) (AS 64770) 3.931 ms 4.537 ms 9.516 ms
27 10.252.5.52 (10.252.5.52) (AS 64770) 6.383 ms 5.961 ms 3.939 ms
28 10.252.5.52 (10.252.5.52) (AS 64770) 3.978 ms 5.564 ms 5.319 ms
29 10.252.5.52 (10.252.5.52) (AS 64770) 6.32 ms 4.54 ms 6.724 ms
30 10.252.5.52 (10.252.5.52) (AS 64770) 5.011 ms 3.992 ms 6.668 ms

 

10.252.5.52 is IP address of the interface directly attached to FR router.

 

What is this? A routing loop or what?  But the route does exist for the subnet on that France router:

 

SLGMANML201# sh ip route 22.246.224.12
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
'%<string>' in via output denotes VRF <string>

22.246.224.0/22, ubest/mbest: 1/0
*via 10.252.5.76, [20/175], 4d03h, bgp-64770, external, tag 64515

 

 

And the destination IP does not respond to pings neither from Prague nor France:

 

FR# ping 22.246.224.12
PING 22.246.224.12 (22.246.224.12): 56 data bytes
Request 0 timed out
Request 1 timed out
Request 2 timed out
Request 3 timed out
Request 4 timed out

 

So my question is - why traceroute command gives me 30 hops with the same IP address? Shouldn't it fail just as the ping fails? 

 

Thank you.

 

1 REPLY 1
VIP Advisor

Re: Ping to the remote subnet fails, but traceroute gives the same IP in all 30 lines

Hi

Can you verify if there’re some global nat with that IP in FR router?

Thanks
Francesco
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