Querying libiptc HOWTO
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# 12. Functions to modify firewalling rules and statistics

For those of you who are a little brave, libiptc has a group of functions to directly modify the firewalling rules and statistics (use of iptables is really the safest way).

These functions are not covered by this HOWTO and I will limit myself to presenting improved information taken from `libiptc.h` and the Linux netfilter Hacking HOWTO by Rusty Russell.

## 12.1. iptc_commit

Name: iptc_commit

Usage: Makes the actual changes.

Prototype: int iptc_commit(iptc_handle_t *handle)

Description: The tables that you change are not written back until the iptc_commit() function is called. This means it is possible for two library users operating on the same chain to race each other; locking would be required to prevent this, and it is not currently done. There is no race with counters, however; counters are added back in to the kernel in such a way that counter increments between the reading and writing of the table still show up in the new table. To protect the status of the system you must commit your changes.

Parameters: handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.2. iptc_insert_entry

Name: iptc_insert_entry

Usage: Insert a new rule in a chain.

Prototype: int iptc_insert_entry(const ipt_chainlabel chain, const struct ipt_entry *e, unsigned int rulenum, iptc_handle_t *handle)

Description: This function insert a rule defined in structure type ipt_entry in chain chain into position defined by integer value rulenum. Rule numbers start at 1 for the first rule.

Parameters: chain is a char pointer to the name of the chain to be modified; e is a pointer to a structure of type ipt_entry that contains information about the rule to be inserted. The programmer must fill the fields of this structure with values required to define his or her rule before passing the pointer as parameter to the function. rulenum is an integer value defined the position in the chain of rules where the new rule will be inserted. Rule numbers start at 1 for the first rule. handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.3. iptc_replace_entry

Name: iptc_replace_entry

Usage: Replace an old rule in a chain with a new one.

Prototype: int iptc_replace_entry(const ipt_chainlabel chain, const struct ipt_entry *e, unsigned int rulenum, iptc_handle_t *handle)

Description: This function replace the entry rule in chain chain positioned at rulenum with the rule defined in structure type ipt_entry. Rule numbers start at 1 for the first rule.

Parameters: chain is a char pointer to the name of the chain to be modified; e is a pointer to a structure of type ipt_entry that contains information about the rule to be inserted. The programmer must fill the fields of this structure with values required to define his or her rule before passing the pointer as parameter to the function. rulenum is an integer value defined the position in the chain of rules where the old rule will be replaced by the new one. Rule numbers start at 1 for the first rule. handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.4. iptc_append_entry

Name: iptc_append_entry

Usage: Append a new rule in a chain.

Prototype: int iptc_append_entry(const ipt_chainlabel chain, const struct ipt_entry *e, iptc_handle_t *handle)

Description: This function append a rule defined in structure type ipt_entry in chain chain (equivalent to insert with rulenum = length of chain).

Parameters: chain is a char pointer to the name of the chain to be modified; e is a pointer to a structure of type ipt_entry that contains information about the rule to be appended. The programmer must fill the fields of this structure with values required to define his or her rule before passing the pointer as parameter to the function. handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.5. iptc_delete_num_entry

Name: iptc_delete_num_entry

Usage: Delete a rule in a chain.

Prototype: int iptc_delete_num_entry(const ipt_chainlabel chain, unsigned int rulenum, iptc_handle_t *handle)

Description: This function delete the entry rule in chain chain positioned at rulenum. Rule numbers start at 1 for the first rule.

Parameters: chain is a char pointer to the name of the chain to be modified; rulenum is an integer value defined the position in the chain of rules where the rule will be deleted. handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.6. iptc_flush_entries

Name: iptc_flush_entries

Usage: Empty a chain.

Prototype: int iptc_flush_entries(const ipt_chainlabel chain, iptc_handle_t *handle)

Description: This function flushes the rule entries in the given chain (ie. empties chain).

Parameters: chain is a char pointer to the name of the chain to be flushed; handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.7. iptc_zero_entries

Name: iptc_zero_entries

Usage: Zeroes the chain counters.

Prototype: int iptc_zero_entries(const ipt_chainlabel chain, iptc_handle_t *handle)

Description: This function zeroes the counters in the given chain.

Parameters: chain is a char pointer to the name of the chain which counters will be zero; handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.8. iptc_create_chain

Name: iptc_create_chain

Usage: Create a new chain.

Prototype: int iptc_create_chain(const ipt_chainlabel chain, iptc_handle_t *handle)

Description: This function create a new chain in the table.

Parameters: chain is a char pointer to the name of the chain to be created; handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.9. iptc_delete_chain

Name: iptc_delete_chain

Usage: Delete a chain.

Prototype: int iptc_delete_chain(const ipt_chainlabel chain, iptc_handle_t *handle)

Description: This function delete the chain identified by the char pointer chain in the table.

Parameters: chain is a char pointer to the name of the chain to be deleted; handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.10. iptc_rename_chain

Name: iptc_rename_chain

Usage: Rename a chain.

Prototype: int iptc_rename_chain(const ipt_chainlabel oldname, const ipt_chainlabel newname, iptc_handle_t *handle)

Description: This function rename the chain identified by the char pointer oldname to a new name newname in the table.

Parameters: oldname is a char pointer to the name of the chain to be renamed, newname is the new name; handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.11. iptc_set_policy

Name: iptc_set_policy

Usage: Set the policy in a built-in chain.

Prototype: int iptc_set_policy(const ipt_chainlabel chain, const ipt_chainlabel policy, struct ipt_counters *counters, iptc_handle_t *handle)

Description: This function set the policy in chain chain to the value represented by the char pointer policy. If you want to set at the same time the counters of the chain, fill those values in a structure of type ipt_counters and pass a pointer to it as parameter counters. Be careful: the chain must be a built-in chain.

Parameters: chain is a char pointer to the name of the chain to be modified; policy is a char pointer to the name of the policy to be set. counters is a pointer to an ipt_counters structure to be used to set the counters of the chain. handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.12. iptc_zero_counter

Name: iptc_zero_counter

Usage: Zero counters of a rule in a chain.

Prototype: int iptc_zero_counter(const ipt_chainlabel chain, unsigned int rulenum, iptc_handle_t *handle)

Description: This function zero packet and byte counters of the entry rule in chain chain positioned at rulenum. Rule numbers start at 1 for the first rule.

Parameters: chain is a char pointer to the name of the chain to be modified; rulenum is an integer value defined the position in the chain of rules of the rule which counters will be zero. handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

## 12.13. iptc_set_counter

Name: iptc_set_counter

Usage: Set counters of a rule in a chain.

Prototype: int iptc_set_counter(const ipt_chainlabel chain, unsigned int rulenum, struct ipt_counters *counters, iptc_handle_t *handle)

Description: This function set packet and byte counters of the entry rule in chain chain positioned at rulenum with values passed in a type structure ipt_counters. Rule numbers start at 1 for the first rule.

Parameters: chain is a char pointer to the name of the chain to be modified; rulenum is an integer value defined the position in the chain of rules of the rule which counters will be set. counters is a pointer to an ipt_counters structure to be used to set the counters of the rule; the programmer must fill the fields of this structure with values to be set. handle is a pointer to a structure of type iptc_handle_t that was obtained by a previous call to iptc_init.

Returns: Returns integer value 1 (true) if successful; returns integer value 0 (false) if fails. In this case errno is set to the error number generated. Use iptc_strerror to get a meaningful information about the problem. If errno == 0, it means there was a version error (ie. upgrade libiptc).

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