Please enable javscript for this test to work...
In this test your browser uploads a sizeable payload to our server, while your long TCP segments are being dropped. Our server will generate an ICMP message asking you to reduce the MTU to a laughingly small value.
ICMP is critical to a well functioning Internet connections, yet networks are often misconfigured. Broken ICMP (being an ICMP blackhole) can lead to serious issues:
perl -e "print 'packettoolongyaithuji6reeNab4XahChaeRah1diej4' x 180" > payload.bin curl -v -s http://icmpcheck.popcount.org/icmp --data @payload.binYou should see ICMP or ICMPv6 packet-too-big messages from the server:
$ sudo tcpdump -ni any icmp or icmp6 IP server > client: ICMP server unreachable - need to frag (mtu 905), length 136 IP6 server > client: ICMP6, packet too big, mtu 1285, length 136
Please enable javscript for this test to work...
In this test we send a large payload from the server, to your browser. Each TCP segment sent by the server will be fragmented into multiple IP packets.
A failure of this test means:
curl -v -s http://icmpcheck.popcount.org/frag -o /dev/nullYou should see fragmented IP packets:
$ sudo tcpdump -ni any '(ip[6] & (1<<5)) != 0 or (ip[7] != 0) or (ip[6] & ((1<<5)-1) != 0) or ip6[6] == 44' IP server.80 > client.36090: Flags [P.], seq ..., length 480: HTTP IP server > client: ip-proto-6 IP server > client: ip-proto-6 IP server > client: ip-proto-6 IP server > client: ip-proto-6 IP6 server > client: frag (0|512) 80 > 55660: Flags [.], seq ..., length 480: HTTP IP6 server > client: frag (512|512) IP6 server > client: frag (1024|221)