I have did a simple program to open a tun interface.

My program will generate a simple ICMP ECHO request datagram and writes to the tun device. However, the Linux network stack does not generate the corresponding ICMP ECHO reply. I have checked with both ethereal and tcpdump. No packet is dropped and the checksums and fields are correct. The firewall is off.

My question is, will

1. the Linux network stack generate ICMP replies, or
2. at least process ICMP ECHO request , or
3. we need to enable some options

if it is a tun interface?

Thanks.