Hardware-addressfiltering.pptVIP

Hardware-address filtering How can we send packets to just one node on our ‘anchor’ cluster? Privacy, please! Our ‘xmit1000.c’ driver transmits all of its packets to every node on our LAN, and our ‘recv1000.c’ driver receives all of the packets transmitted by any of the nodes! Is this what we really want to happen? Receive address filtering Nowadays any network interface controller has a “filtering” capability which allows any packet NOT to be received by nodes that the packet’s sender didn’t intend it to go to Our new ‘nic.c’ module This device-driver combines the ‘write()’ and ‘read()’ methods from our ‘xmit1000.c’ and ‘recv1000.c’ modules, but it adds an ‘ioctl()’ method that lets applications setup any ethernet-packet’s destination-address, as is illustrated in our companion program (named ‘sendto.cpp’) which finds a node’s hardware-address in our ‘ethers’ database The ‘sendto’ algorithm Here are the steps which our ‘sendto.cpp’ demo-program performs: Notes on library functions Use ‘fopen()’ to open the ‘ethers’ textfile, so you can use the ‘fgets()’ function to read in its contents one-line-at-a-time: ‘ascii-to-numeric’ Use ‘strstr( string, substring )’ to find line in ‘ethers’ file with name of specified node Use ‘strtol( string, NULL, 16 )’ to convert a hexadecimal digit-string to a numeric value Our ‘ioctl()’ function Our ‘nic.c’ driver implements an ‘ioctl()’ service allowing a user-program to setup the network hardware-address that will be used in the destination-field of any packet that the driver’s ‘write()’ function transmits Driver’s ‘ioctl()’ function Change in ‘write()’ Our device-driver’s ‘write()’ method needs only a tiny change in order to make use of the user-supplied destination-address: Change in ‘init()’ To prevent reception of ethernet packets whose destination-address doesn’t match our device’s address, we need to alter the way we program our nic’s RCTL register: A change in memory-usage Is 00:00:00:00:00:00 legal? If you comment out all