Hi Referring to Documentation/networking/netdevices.txt a) ndo->ndo_start_xmit if written "as is" will be thread safe? [Correct?] NETIF_F_LLTX is not set only then this is true. But dev_queue_xmit(skb) doesn't seem to take any lock, neither does dev_hard_start_xmit. Please let me know if i'm wrong and where is this lock taken before calling dev_queue_xmit/dev_hard_start_xmit. b) Why and when would I want to use rtnl_lock/unlock? Is it like registering multiple device simultaneously? c) ndo->ndo_start_xmit is supposed to start the transmission of the skb. However I've a doubt ---> Suppose that there's no room left for the incoming skb in the device buffer, so in that case it would be ideal to call netif_stop_queue. At this the the skb already with the ndo_start_xmit will not be retried again[Correct?] ----> Is ndo_start_xmit required to wait in this case? However if the above spin_lock in a) was taken then this would be a waste. So is it possible that this skb is "deffered" to whenever there's room and return NETDEV_TX_OK? But if we do this we are telling the application that it's packet was delivered so in case there was a timeout set by the application on a reply it would again send us the same packet. So instead of "deferring" is it good to "drop" ? -- ---P.K.S