Ping Duplicate (DUP!)

o_dogorshom · ‎09-05-2007

Hi,

I tried to ping an ethernet interface in router in another site and I got the following:

router# ping x.x.x.x

PING x.x.x.x (x.x.x.x): 56 data bytes

64 bytes from x.x.x.x: icmp_seq=0 ttl=254 time=10.352 ms

64 bytes from x.x.x.x: icmp_seq=0 ttl=253 time=10.878 ms (DUP!)

64 bytes from x.x.x.x: icmp_seq=1 ttl=254 time=10.314 ms

64 bytes from x.x.x.x: icmp_seq=1 ttl=253 time=10.876 ms (DUP!)

do you have any idea about the cause of this problem.

Regards,

lgijssel · ‎09-05-2007

Most likely, this means what it implies: the same ip address is configured in two places.

The ttl differs 1 hop but without knowing the topology this isn't of much help.

regards,

Leo

mheusing · ‎09-05-2007

Hi Leo,

How would the unicast ICMP Echo Request packet sent by the ping be received by two different hosts with the same IP?

One more question to the original poster: What IP address were you pinging? Could it be a broadcast address on a link?

Regards, Martin

o_dogorshom · ‎09-06-2007

Hi,

The IP address is not a broadcast, it is 10.0.0.1/25. Also there is no any other device has the same IP.

Regards,

lgijssel · ‎09-06-2007

In my opinion, this is very well possible. It could be something like a router-pair that was configured for HSRP but has wrongly been assigned the same interface IP.

Regards,

Leo

mheusing · ‎09-06-2007

Hi,

The problem with duplicate IPs is the MAC address. Depending on the ARP cache/CAM table of the sending device only one station would get the IP packet. So imho there is more to it than just a duplicate IP.

What is the ARP cache/CAM table in the 10.0.0.0/25 attached devices?

Regards, Martin

Damon Day · ‎08-10-2016

in my experience this happens with Wireless devices. We have seen it when there is another stronger radio/microwave near by in the LoS pathway that is sitting on or very near the same frequency as the AP. for example we have an AP sitting on a hilltop for our various departments to connect to. Verizon came in with a microwave shot off the same hill, supposed to use 6GHZ but didnt get their FCC licensing done in time so they just turned it up on 5.8Ghz... well as soon as they did I noticed my network go to crap. when i would ping the AP on the hill i would get 50-100 Dup! packets inside of 60 seconds of running a ping. not good. its like the microwave is "stealing" the packets and replying as well. so essentially my AP and their MW are both responding to my ping. its a huge mess, verizon says they should be @6 in 3 months... this is the only time I've ever seen this in my 20 years.

dchira · ‎12-08-2021

There are two options here:

a) two host in the network configured with same ip address;

b) check the IP address and make sure you are not pinging an SVI IP address ( IP address living on vlan interface, so to speak); in that care most likely all the host in that SVI might reply to your ping.

Here is an example: 10.10.10.192/ 27 is my subnet and SVI /VLAN interface IP address is 10.10.10.193/27.

This vlan is going across a 3 switches and is allowed to pass on all trunks

vlan 10 vlan 10 vlan 10

10.10.10.193/27 trunk 10.10.10.195/27 trunk 10.10.10.197/27

SW1 <<=================>>SW2<<=======================>>SW3

now I ping SVI subnet ip address

$ ping 10.10.10.192 -c 10

PING 10.10.10.192 (10.10.10.192): 56 data bytes

64 bytes from 10.10.10.193: icmp_seq=0 ttl=255 time=4.496 ms

64 bytes from 10.10.10.197: icmp_seq=0 ttl=255 time=4.522 ms (DUP!)

64 bytes from 10.10.10.195: icmp_seq=0 ttl=255 time=6.264 ms (DUP!)

64 bytes from 10.10.10.193: icmp_seq=1 ttl=255 time=1.058 ms

64 bytes from 10.10.10.195: icmp_seq=1 ttl=255 time=1.074 ms (DUP!)

64 bytes from 10.10.10.197: icmp_seq=1 ttl=255 time=1.079 ms (DUP!)

64 bytes from 10.10.10.193: icmp_seq=2 ttl=255 time=1.182 ms

64 bytes from 10.10.10.195: icmp_seq=2 ttl=255 time=1.207 ms (DUP!)

64 bytes from 10.10.10.197: icmp_seq=2 ttl=255 time=1.215 ms (DUP!)

64 bytes from 10.10.10.193: icmp_seq=3 ttl=255 time=1.240 ms

64 bytes from 10.10.10.197: icmp_seq=3 ttl=255 time=1.266 ms (DUP!)

64 bytes from 10.10.10.195: icmp_seq=3 ttl=255 time=1.274 ms (DUP!)

64 bytes from 10.10.10.193: icmp_seq=4 ttl=255 time=1.135 ms

64 bytes from 10.10.10.195: icmp_seq=4 ttl=255 time=1.159 ms (DUP!)

64 bytes from 10.10.10.197: icmp_seq=4 ttl=255 time=1.167 ms (DUP!)

64 bytes from 10.10.10.193: icmp_seq=5 ttl=255 time=1.204 ms

64 bytes from 10.10.10.197: icmp_seq=5 ttl=255 time=1.230 ms (DUP!)

64 bytes from 10.10.10.195: icmp_seq=5 ttl=255 time=1.239 ms (DUP!)

64 bytes from 10.10.10.193: icmp_seq=6 ttl=255 time=0.977 ms

64 bytes from 10.10.10.197: icmp_seq=6 ttl=255 time=0.993 ms (DUP!)

64 bytes from 10.10.10.195: icmp_seq=6 ttl=255 time=0.998 ms (DUP!)

64 bytes from 10.10.10.193: icmp_seq=7 ttl=255 time=1.097 ms

64 bytes from 10.10.10.197: icmp_seq=7 ttl=255 time=1.121 ms (DUP!)

64 bytes from 10.10.10.195: icmp_seq=7 ttl=255 time=1.129 ms (DUP!)

64 bytes from 10.10.10.197: icmp_seq=8 ttl=255 time=1.337 ms

64 bytes from 10.10.10.195: icmp_seq=8 ttl=255 time=1.361 ms (DUP!)

64 bytes from 10.10.10.193: icmp_seq=8 ttl=255 time=3.147 ms (DUP!)

64 bytes from 10.10.10.193: icmp_seq=9 ttl=255 time=1.299 ms

--- 10.10.10.192 ping statistics ---

10 packets transmitted, 10 packets received, +18 duplicates, 0.0% packet loss

round-trip min/avg/max/stddev = 0.977/1.660/6.264/1.278 ms

Amazingly all the active hosts in my subnet responds to my ping command and my ping is 100% succesfull

Conclusion:

1)check and make sure there is no duplicate IP address in the network

2) check and make sure you are not pinging you subnet IP address