Hi, I have a following very simple network topology:
CISCO1921[Gi0/0] <-> [eno3]svr Gi0/0 in Cisco 1921 ISR has 10.66.66.2/24 configured and eno3 in Linux server has 10.66.66.1/24 configured. RTT on this link is 10ms: svr$ ping -qc 100 -I 10.66.66.1 10.66.66.2 PING 10.66.66.2 (10.66.66.2) from 10.66.66.1 : 56(84) bytes of data. --- 10.66.66.2 ping statistics --- 100 packets transmitted, 100 received, 0% packet loss, time 99098ms rtt min/avg/max/mdev = 10.317/10.411/11.089/0.199 ms svr$ However, when I ping from the Cisco 1921 router, then some results are less than 10ms: CISCO1921#ping ip 10.66.66.1 source 10.66.66.2 Type escape sequence to abort. Sending 5, 100-byte ICMP Echos to 10.66.66.1, timeout is 2 seconds: Packet sent with a source address of 10.66.66.2 !!!!! Success rate is 100 percent (5/5), round-trip min/avg/max = 8/9/12 ms CISCO1921# The same behavior seems to be present when using IP SLA "icmp-echo" probes: https://i.imgur.com/Uu5uHAh.png ..or CISCO-PING-MIB: https://i.imgur.com/gG5L310.png On both graphs I have plotted 21600 results. For comparison, I replaced Cisco 1921 router with Juniper MX series router like this: Juniper-MX[ge-3/3/9] <-> [eno3]svr ge-3/3/9 in Juniper MX series router has 10.66.66.2/24 configured and eno3 in Linux server has 10.66.66.1/24 configured. When I execute the "ping 10.66.66.1 source 10.66.66.2 count 1000 rapid" command in Juniper router, then the summary of the results is following: --- 10.66.66.1 ping statistics --- 1000 packets transmitted, 1000 packets received, 0% packet loss round-trip min/avg/max/stddev = 10.333/11.315/54.519/4.506 ms As expected, all the results are >10ms. Maybe someone (from Cisco) can explain how Cisco IOS handles the ICMP "echo reply" messages? thanks, Martin _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
