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5. IPv4 API Description

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Chema García edited this page Jan 11, 2016 · 2 revisions

Data structures

Structure to identify an IPv4 flow:

/* @brief Struct to generate the flow key **/
typedef struct
{
	/// source IP address
	unsigned int source;
	/// destination IP address
	unsigned int destination;
	/// Transport layer protocol
	unsigned char protocol;
	/// Identification
	unsigned short id;
} ntoh_ipv4_tuple4_t, *pntoh_ipv4_tuple4_t;

Structure to store an IPv4 fragment:

/** @brief Struct to store the information of each fragment */
typedef struct _ipv4_fragment_
{
	/// pointer to the next fragment
	struct _ipv4_fragment_ *next;
	/// fragment offset
	unsigned int offset;
	/// fragment data length
	unsigned int len;
	/// fragment data
	unsigned char *data;
} ntoh_ipv4_fragment_t , *pntoh_ipv4_fragment_t;

Structure to store all information of an IPv4 flow:

/** @brief Struct to store the information of each IPv4 flow */
typedef struct
{
	/// flow identification data
	ntoh_ipv4_tuple4_t ident;
	/// flow key
	ntoh_ipv4_key_t key;
	/// fragments list
	pntoh_ipv4_fragment_t fragments;
	/// total amount of received data
	size_t meat;
	/// total amount of expected data
	size_t total;
	/// final fragment received?
	struct ip *final_iphdr;
	/// user defined function to receive defragmented packets
	void *function;
	/// last activity
	struct timeval last_activ;
	/// user-defined data
	void *udata;
	ntoh_lock_t lock;
} ntoh_ipv4_flow_t, *pntoh_ipv4_flow_t;

Structure to store all information needed for an IPv4 session:

/** @brief Structure to store global parameters */
typedef struct _ipv4_session_
{
	struct _ipv4_session_ *next;

	/// max. number of IP flows
	sem_t max_flows;
	sem_t max_fragments;
	/// hash table to store IP flows
	pipv4_flows_table_t flows;
	/// connection tables related
	pthread_t tID;
	ntoh_lock_t lock;
}ntoh_ipv4_session_t , *pntoh_ipv4_session_t ;

Functions

Function to initialize IPv4 defragmentation

void ntoh_ipv4_init ( void );

Function to flush all IPv4 sessions and release all resources

void ntoh_ipv4_exit ( void );

Function to create a new session:

pntoh_ipv4_session_t ntoh_ipv4_new_session ( unsigned int max_flows , unsigned long max_mem , unsigned int *error );
  • max_flows: Max. number of allowed flows in this session
  • max_mem: Max. amount of memory to be used to store fragments
  • *error: Returned error code

This function returns a pointer to the new session, or NULL on error.

Function to resize an existing session:

int ntoh_ipv4_resize_session ( pntoh_ipv4_session_t session , size_t size );
  • session: Pointer to the IPv4 session to be resized
  • size: New size

This function returns NTOH_OK on success and the error code when it fails.

Function to free a session:

void ntoh_ipv4_free_session ( pntoh_ipv4_session_t session );
  • session: Session pointer to be released

Function to create a new flow:

pntoh_ipv4_flow_t ntoh_ipv4_new_flow ( pntoh_ipv4_session_t session , pntoh_ipv4_tuple4_t tuple4 , pipv4_dfcallback_t function , void *udata , unsigned int *error);
  • session: IPv4 session
  • tuple4: Tuple4 identifying the flow
  • function: User defined callback function to receive the defragmented datagrams of this flow
  • udata: User data linked to this flow
  • *error: Returned error code

This function returns a pointer to the new created IPv4 flow, or NULL on error.

Function to find an IPv4 flow:

pntoh_ipv4_flow_t ntoh_ipv4_find_flow ( pntoh_ipv4_session_t session , pntoh_ipv4_tuple4_t tuple4 );
  • session: IPv4 session
  • tuple4: Tuple4 structure identifying the flow

This function returns a pointer to the flow if it was found, or NULL if it was not found.

Function to free an IPv4 flow:

void ntoh_ipv4_free_flow ( pntoh_ipv4_session_t session , pntoh_ipv4_flow_t flow , unsigned short reason );
  • session: IPv4 session
  • flow: Flow to be free'd
  • reason: Value to be sent to the user-defined callback function

Function to add a fragment to a given IPv4 flow:

int ntoh_ipv4_add_fragment ( pntoh_ipv4_session_t session , pntoh_ipv4_flow_t flow , struct ip *iphdr );
  • session: IPv4 session
  • flow: IPv4 flow where the new fragment will be added
  • iphdr: IPv4 header

This function returns NTOH_OK on success and the error code on failure.

Function to get the number of stored IPv4 flows in a session:

unsigned int ntoh_ipv4_count_flows ( pntoh_ipv4_session_t session );
  • session: IPv4 session

This function returns the number of IPv4 flows stored in the given session.

Function to get the size of the IPv4 stream table (max allowed flows):

unsigned int *ntoh_ipv4_get_size ( pntoh_ipv4_session_t session );
  • session: IPv4 session

This function returns the size of the IPv4 sessions table.

Function to get the tuple4:

unsigned int ntoh_ipv4_get_tuple4 ( struct ip *ip , pntoh_ipv4_tuple4_t tuple );
  • ip: IPv4 Header
  • tuple: Pointer to the output tuple4 struct

This function returns NTOH_OK on success and the error code on failure.

Data types and macros

Macro to check if an IPv4 datagram is part of a fragmented datagram:

#define NTOH_IPV4_IS_FRAGMENT(off)			( ( (8*(ntohs(off) & 0x1FFF)) > 0 || (ntohs(off) & 0x2000) ) && !(ntohs(off) & 0x4000) )
  • off: IPv4 header field (iphdr->ip_off)

Typedef defining the user defined callback function:

typedef void(*pipv4_dfcallback_t) ( pntoh_ipv4_flow_t flow , pntoh_ipv4_tuple4_t tuple4, unsigned char* data, size_t len, unsigned short reason);
  • flow: IPv4 flow where the defragmented datagrams of the sent datagram where stored
  • tuple4: Tuple4 identifying the flow
  • data: Defragmented datagram
  • len: Total length of the defragmented datagram (IPv4 header + payload)
  • reason: Why the datagram is sent?

Unlike TCP reassembly, IPv4 defragmentation only store the information of the sender.

Possible values for "reason" parameter:

  • NTOH_REASON_DEFRAGMENTED_DATAGRAM
  • NTOH_REASON_TIMEDOUT_FRAGMENTS

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