On Tue, Aug 26, 2008 at 02:40:37AM +0200, Denys Vlasenko wrote: > On Tuesday 26 August 2008 02:00, Doug Graham wrote: > > However, in my tests between these two processors, there's a datasize > > range from 65494 through 65507 where the ping fails quietly (gets no > > What happens with sizes > 65507?
I get this: % ./busybox ping -s 65508 192.168.0.2 PING 192.168.0.2 (192.168.0.2): 65508 data bytes ping: sendto: Message too long I haven't done the math, but I take this to mean that the maximum size of an IP datagram has been exceeded. I get a similar error on my rh desktop using its installed (iputils) ping: % ping -s 65508 47.128.20.74 WARNING: packet size 65508 is too large. Maximum is 65507 PING 47.128.20.74 (47.128.20.74) 65508(65536) bytes of data. ping: local error: Message too long, mtu=1500 ping: local error: Message too long, mtu=1500 I think the math does work out. 65508 + 8 byte ICMP header + 20 byte IP header = 65536 which is larger than the maximum IP datagram size of 64k - 1. > > response) without issuing any error message. I was going to suggest > > a further patch to limit the maxium packet size to MAXPACKET (already > > defined in ping.c but never used for anything), but then I realized that > > this symptom probably really does demonstrate a quirk somewhere in the > > networking stack on the destination machine. > > Are you saying that you verified that there genuinely were no reply packets > (say, with tcpdump), or do you just guess? Yes, I did verify this with tcpdump. Also verified that the "netstat -s" stats on the destination machine look quite odd. The destination machine got and reassembled the packet without error, but didn't recognize it as an ICMP packet and didn't send a reply. This destination machine is running a 3rd party protocol stack, so I think we've found a bug to report to the vendor. Busybox's ping works fine with sizes in this range when the destination is a standard desktop machine, so whatever is going on, it's not a busybox problem. --Doug. _______________________________________________ busybox mailing list [email protected] http://busybox.net/cgi-bin/mailman/listinfo/busybox
