Hardware-address filtering
How can we send packets to just
one node on our ‘anchor’ cluster?
Privacy, please!
• Our ‘nic.c’ device-driver transmits all of its
packets to every node on the segment -and it receives every packet sent out by
any of the other nodes on that segment!
• Is this what we really want to happen?
anchor16
anchor01
anchor02
anchor03
anchor04
anchor05
anchor06
anchor07
…
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
Transmit
FIFO
Receive
buffer
filtering
engine
Receive
FIFO
Network Interface Controller
Host memory
to/from
LAN
Our new ‘nicf.c’ module
• This device-driver combines the ‘write()’
and ‘read()’ methods from our charactermode device-driver ‘nic.c’, 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:
Find the destination’s node-name on the command-line
Search our ‘ethers’ file for a line with that node’s name
Convert that node’s MAC-address from ascii to numeric
Open the ‘/dev/nic’ device-file
Call our driver’s ‘ioctl()’ method to setup packets’ destination
Write our application’s test-message to the ‘/dev/nic’ device-file
Print a message confirming this destination and bytes written
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:
#include <stdio.h> // for fopen(), fgets(), puts()
#include <string.h> // for strstr()
int main( int argc, char *argv[ ] )
{
if ( argc == 1 ) exit(1);
// command-line argument is absent
FILE
*fd = fopen( “ethers”, “ro” );
if ( fd == NULL ) exit(1);
// file not present in current directory
char
line[ 80 ];
while ( fgets( line, 80, fd ) ) if ( strstr( line, argv[1] ) puts( line );
/* additional processing goes here */
}
‘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
unsigned char
dst[ 6 ];
// storage for 6-byte MAC-address
// loop converts colon-formatted hex-string to array of numbers
for (int i = 0; i < 6; i++) dst[ i ] = strtol( line+3*i, NULL, 16 );
Our ‘ioctl()’ function
• Our ‘nicf.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
// open the network interface controller’s device-file
int
fp = open( “/dev/nic”, O_RDWR );
if ( fp < 0 ) { perror( “/dev/nic” ); exit(1); }
// setup packet-destination to be used when transmittting
if ( ioctl( fp, 1, dst ) < 0 ) { perror( “ioctl” ); exit(1); }
ID-number for the ioctl-request
Driver’s ‘ioctl()’ function
char mac[ 6 ];
char dst [ 6 ];
// packet source-address gets filled in by ‘module_init()’
// packet destination-address gets filled in by our ‘ioctl()’
int my_ioctl( struct inode *, struct file*, unsigned int cmd, unsigned long address )
{
unsigned char
*addr = (unsigned char *)address;
switch ( cmd )
{
case 0:
case 1:
// get the driver’s ethernet-packet destination-address
if ( copy_to_user( addr, dst, 6 ) ) return –EFAULT;
return 0; //SUCCESS
// set the driver’s ethernet-packet destination-address
if ( copy_from_user( dst, addr, 6 ) ) return –EFAULT;
return 0; //SUCCESS
}
return –EINVAL;
}
// the requested command is not implemented
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:
31
26
22
15
8
4
3 2 1 0
RCTL 0001 0100 0100 0000 1000 0010 0000 0110
(0x0100)
DPF (Discard Pause Frames)
FLEXBUF
SECRC (Strip Ethernet CRC)
RDMTS (Rx-Desc Min Thresh Size)
BAM (Broadcast Accept Mode)
MPE (Multicast Promiscuous Enable)
UPE (Unicast Promiscuous Enable)
SBP (Store Bad Packets)
EN (Enable receive engine)
Is 00:00:00:00:00:00 legal?
• If you comment out all the lines of code in
our ‘sendto.cpp’ application that precede
the ‘open()’ statement, then our driver’s
‘dstn[ 6 ]’ array will remain all zeros, and
hence packets will be sent with a ‘zero’
destination-address (normally not legal)
• EXERCISE: Try this out and see if your
test-message gets received any nodes
Receive-filter Array
quadword (64-bits)
The NIC’s own unique
hardware-address
gets programmed into
this initial array-entry
during initialization
Other addresses may
be added later by
driver software
‘valid’-bit (1=yes, 0=no)
0x5400
1
Filter-address 0
0
Filter-address 1
0x5408
0
Filter-address 2
0x5410
0
Filter-address 3
0x5418
0
Filter-address 4
0x5420
0
Filter-address 5
0x5428
0
Filter-address 6
0x5430
0
Filter-address 7
0x5438
…
In-class exercise #1
• Apply your knowledge of the Intel 82573L
‘Receive-filter Array’ to add the quadword
0x8000000000000000 at offset 0x5408 in
the NIC’s i/o-memory space
• Then test your modified ‘sendto.cpp’ code
to see if you can ‘receive’ a packet which
has ‘zero’ as its destination MAC-address
Multicast MAC-addresses
• Recall that there is a multicast IP-address
(namely 224.0.0.1) which all the systems
on a local subnet are expected to listen to
• The corresponding hardware multicast
address would be: 01:00:5E:00:00:01
• Does our ‘nicf.c’ device-driver allow a nic
to ‘hear’ messages sent to this address?
In-class exercise #2
• Add the quadword 0x80000100005E0001
to your nic’s ‘Receive-filter Array’ at offset
0x5410 in its i/o-memory space, and then
modify the initialization the ‘dst[ 6 ]’ array
in your ‘sendto.cpp’ application, like this:
unsigned char dst[ 6 ] = { 0x01, 0x00, 0x5E, 0x00, 0x00, 0x01 };
• Is your nic now able to receive a packet
sent to this hardware ‘multicast’ address?