Hi, This might be slightly off-topic altough it involves Linux, tap-device and ping.
For fun I'm implementing an IP-stack. To do so I open a tap-device and use read/write to obtain/send packets. I configured the interface with IFF_NO_PI to not to get flags/protocol header. At this point it can answer to ARP requests. If I use arping I see that it replies to requests. Also by verifying in wireshark of course. Now the problem is though, that ICMP doesn't work. When pinging, I see packets coming in and replies going out but for some reasons ping "doesn't see them". In wireshark everything looks fine: https://vps001.vanheusden.com/~folkert/myip2.pcap (and https://vps001.vanheusden.com/~folkert/myip.pcap ). but if I run ping with strace I see something peculiar: sendto(3, "\10\0&\354\0\0\0\1\303\3508_\0\0\0\0\10\370\r\0\0\0\0\0\20\21\22\23\24\25\26\27"..., 64, 0, {sa_family=AF_INET, sin_port=htons(0), sin_addr=inet_addr("192.168.3.2")}, 16) = 64 recvmsg(3, {msg_namelen=128}, 0) = -1 EAGAIN (Resource temporarily unavailable) As you see, the recvmsg (always!) fails with an EAGAIN. My question now is: how can I debug this? Or is this a common bug (in implementations of ip stacks)? Folkert van Heusden
