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sajal
Asked: 2009-07-13 05:31:19 +0800 CST

ping -f shows problems but regular ping doesn't

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I have a strange issue, hosting at Softlayer Washington data center.

Test from an EC2 instance to my server at Softlayer :-

[root@EC2-box ~]# ping -f -c 100 MY-SL-BOX
PING MY-SL-BOX (MY-SL-BOX) 56(84) bytes of data.
..................................................
--- MY-SL-BOX ping statistics ---
100 packets transmitted, 50 received, 50% packet loss, time 743ms
rtt min/avg/max/mdev = 2.464/2.906/3.606/0.220 ms, ipg/ewma 7.505/2.927 ms
[root@EC2-box ~]#

Test from an EC2 instance to www.softlayer.com (or any other website):-

[root@EC2-box ~]# ping -f -c 100 www.softlayer.com
PING www.softlayer.com (66.228.118.51) 56(84) bytes of data.

--- www.softlayer.com ping statistics ---
100 packets transmitted, 100 received, 0% packet loss, time 1168ms
rtt min/avg/max/mdev = 35.143/35.485/36.216/0.211 ms, pipe 4, ipg/ewma 11.804/35.518 ms
[root@EC2-box ~]#

Test from my server at softlayer to EC2 instance :-

[root@MY-SL-BOX ~]# ping -f -c 100 7EC2-box
PING 7EC2-box (7EC2-box) 56(84) bytes of data.
.................................................
--- 7EC2-box ping statistics ---
100 packets transmitted, 51 received, 49% packet loss, time 866ms
rtt min/avg/max/mdev = 2.067/2.378/2.679/0.131 ms, ipg/ewma 8.756/2.414 ms

Test from my server at softlayer to www.softlayer.com instance :-

[root@MY-SL-BOX ~]# ping -f -c 100 www.softlayer.com
PING www.softlayer.com (66.228.118.51) 56(84) bytes of data.
....................................................
--- www.softlayer.com ping statistics ---
100 packets transmitted, 48 received, 52% packet loss, time 1424ms
rtt min/avg/max/mdev = 33.677/34.041/34.693/0.240 ms, pipe 4, ipg/ewma 14.386/34.083 ms

Note.. in all the above cases, when I don't use the "-f" option, there is no packet loss at all. 7EC2-box and MY-SL-BOX are real IPs. I masked them to post here.

If I do a traceroute to any other IP from my server, and even ping -f the first node shown there, it shows a 50% packet loss, and no loss without "-f".

I spoke to the support, and they said that since there is no problem without the "-f" there is no issue here.

Are they right?

It's odd that the "ping -f" from any external network to any site shows no loss but only to mine.

I've been searching for an hour now, would be very grateful if someone can point me to some detailed instructions for testing packet loss.

linux networking ping icmp

3 Answers

  1. Best Answer

    Some machines (hosts, firewalls or routers) will, if they allow ICMP transit at all, throttle ICMP ping requests/responses to avoid performance (CPU or network) being impaired by excessive ping activity. Using -f without setting a reasonable interval (see -i parameter to ping) is discouraged in most environments as it can be disruptive (in effect -f -c 100 sends 100 ping requests back to back with no gap between them). Whilst you might use -f as a parameter (always with conservative -c and/or -i parameters) on your own network most other network administrators won't want you doing it on theirs.

    • 8

  2. I would perhaps suggest using Nmap to do a packet trace might give you an idea of where the packets are getting lost.

    http://nmap.org/book/output-formats-commandline-flags.html#output-formats-ex-packettrace

    Another idea have you tried doing it while specifying an interval to slow it down a bit

    ping -f -i 0.5 google.co.uk

    if you don't get such a massive amount of packet loss with that could indicate a firewall or something blocking it.

    • 2

  3. Yeah I would try removing the -f flood option. Most likely that a firewall is not happy. Do you get good pings in both directions normally? What's the trace route say for each?

    • 0