Extensible Authentication Protocol - EAP

* Extension to PPP
* Authentication Framework , not a Specific Authentication Mechanism
* Desired Authentication Method can be Negotiated  like EAP-TTLS, EAP-MD5, EAP-TLS,EAP-PSK
* In 80.11 it is used to negotiate Secure PMK (Pairwise Master key )

TTLS -Tunneled Transport Layer Security
PSK- Pre Shared Key

Codes :
EAP                                          Radius
1--Request                              1--Access Request
2--Success                              2--Access Accept
3--Response                           3--Access Reject
4--Failure                               4--Accounting Request
                                              5--Accounting Response

Authentication in Wimax System

Protocols  Stack :

  

Any real problem faced

I face a problem wehre RAw Socket was in promniiscous mode and lietening to all intefaces  though it was intended to listen on one Inteface .
// creation of raw socket 

 read_sockfd = socket( AF_PACKET , SOCK_RAW, htons(ETH_P_ALL)) ;
This stmt was success but not solving purpose
setsockopt(read_sockfd , SOL_SOCKET , SO_BINDTODEVICE , BIND_DEV , devlen+1 )


Solution
    struct sockaddr_ll sa
    int interfaceId =-1;
    struct ifreq ifr;

    memset(&sa, 0, sizeof(sa));
    strncpy(ifr.ifr_name,BIND_DEV, devlen+1);
    sa.sll_family = AF_PACKET;
// get interface index
    interfaceId = ioctl(read_sockfd ,SIOCGIFINDEX,&ifr);
    sa.sll_protocol = htons(ETH_P_ALL);
    sa.sll_ifindex =ifr.ifr_ifindex 
   bind( g_frame_read_sockfd , (struct sockaddr*) &sa, sizeof(sa));

Thing is we have to explicitly bind raw socket to socket address structure(with proper interface index )
Man page clearly says
By default all packets of the specified protocol type are passed  to  a    packet  socket.    To  only  get  packets    from  a specific interface use  bind(2) specifying an address in  a  struct  sockaddr_ll  to  bind  the
 packet    socket     to  an  interface.  Only  the    sll_protocol  and  the  sll_ifindex address fields are used for purposes of binding.

------------------------------------------
 tcpdump  -d   vlan and ip  
tcpdump -dd vlan and \(ip or arp \)
tcpdump -d ether src 00:80:42:1B:1D:94 and vlan and \(ip or arp \)
tcpdump -d not ether src 00:80:42:1B:1D:94 and vlan and \(ip or arp \)

Compiling Shared Libraries .so

Need to compile Library in Position independent code 

When the object files are generated, we have no idea where in memory they will be inserted in a program that will use them. Many different programs may use the same library, and each load it into a different memory in address. Thus, we need that all jump calls ("goto", in assembly speak) and subroutine calls will use relative addresses, and not absolute addresses. Thus, we need to use a compiler flag that will cause this type of code to be generated

gcc -fPIC -c util_file.c

gcc -fPIC -c util_net.c

gcc -fPIC -c util_math.c

gcc -shared libutil.so util_file.o util_net.o util_math.o

Why is this Required ??

dlopen()  --Thing is inspite of Loading library at begining . 

From program we can specify when to Load and unload a Library 

and what to use. 

dlopen returns a handler on success 

lib_handle = dlopen("/full/path/to/library", RTLD_LAZY); 

 
RTLD_LAZY  -- Lazy aproach --defining whether all 
symbols refered to by the library need to be checked immediately or When used 

dlopen() UNLOAD


Reference:
http://tldp.org/HOWTO/Program-Library-HOWTO/shared-libraries.html

Random C question

Q How to write Multi line MACRO ???  

#define MUL_LINE_MACRO(x)    do{  x=123; } while (0)
 http://c-faq.com/cpp/multistmt.html

Dont put ; after Macro let user put it  MUL_LINE_MACRO(x);

This is required as 

if in code macro is used in if else  condition like;

if (cond )

    MUL_LINE_MACRO(x);

else

   some ;

and macro also has an  ";"  then complilation fails 

if (cond )

      do{  x=123; } while (0);

  ; // this will cause compilation failure

else

   some ;

How to do Multicast and Broadcast ? Is it possible for both TCP and UDP

Multicast can not happen on TCP it works only in UDP or RAW socket.
Same applies to Broadcast also .

TCP sockets are always Unicast.

A reliable multicast protocol, like PGM(Pragmatic General Multicast ), adds the ability for receivers to detect lost and/or out-of-order messages and take corrective action (similar in principle to TCP), resulting in a gap-free, in-order message stream.

http://tldp.org/HOWTO/Multicast-HOWTO-6.html

Can two application Listen on same port

No. Only one process can bind to a port on an address at any one time. You can bind two processes to the same port number, but on different IP addresses Different NIC , hence different ports.

For UDP (Multicasts), multiple applications can subscribe to the same port.
With multicast sockets more than one application can bind to a port as long as SO_REUSEADDR is set in each socket's options.
We can  accomplish this by writing a "master" process, which accepts and processes all connections, then hands them off to your two applications who need to listen on the same port. This is the approach that Web servers and such take, since many processes need to listen to 80.