On 24 May 2017, at 10:17, William Gathoye wrote:
In this use case, you make the assumption that my gateway is actually
the first one to respond, this is why you select only the first answer
using -c1. But as you can see below, if I remove that argument,
several
routers are answering to me (seems sensible to me), how can I be sure
my
gateway is actually the first device that answers?
You cannot. It’s all about latency and where your time goes. Switch
buffers, distance, NICs, input paths, CPU loads, .. lots of things can
change the timing of a packet.
PING6(56=40+8+8 bytes) fe80::ff:fec2:e61d%vtnet0 --> ff02::2%vtnet0
16 bytes from fe80::268a:7ff:fe91:e970%vtnet0, icmp_seq=0 hlim=64
time=0.292 ms
16 bytes from fe80::268a:7ff:fe91:ea98%vtnet0, icmp_seq=0 hlim=64
time=0.355 ms(DUP!)
16 bytes from fe80::2ff:ffff:feff:fffd%vtnet0, icmp_seq=0 hlim=64
time=2.970 ms(DUP!)
16 bytes from fe80::2ff:ffff:feff:fffe%vtnet0, icmp_seq=0 hlim=64
time=5.964 ms(DUP!)
16 bytes from fe80::268a:7ff:fe91:e970%vtnet0, icmp_seq=1 hlim=64
time=0.314 ms
16 bytes from fe80::268a:7ff:fe91:ea98%vtnet0, icmp_seq=1 hlim=64
time=0.389 ms(DUP!)
16 bytes from fe80::2ff:ffff:feff:fffd%vtnet0, icmp_seq=1 hlim=64
time=3.222 ms(DUP!)
16 bytes from fe80::2ff:ffff:feff:fffe%vtnet0, icmp_seq=1 hlim=64
time=6.382 ms(DUP!)
How can I understand the "DUP!" statement here? I assume these are due
because we are using multicast here end the ICMP reply are echoes to
each others? Right?
The DUP! here in case is indeed as you get 4 replies for each request
you are sending out. It’s not “each other”, it’s one request to
the multicast address, 4 unicast replies to you.
/bz
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