CHAP

The system provides the following Python objects to inspect and in certain cases, modify the corresponding protocol packet or message:

alc.pppoe: PPPoE packet
alc.ppp: LCP/IPCP/IPv6CP packet
alc.pap: PAP message
alc.chap: CHAP message

The `alc.pppoe` object

Note

In addition to PPPoE packets, alc.pppoe is also available when the Python script is triggered by packets encapsulated in PPPoE, such as LCP, PAP, or CHAP.

Attributes

The object exposes the header fields as attributes on the object.

Attributes defined on alc.pppoe object
Attribute	Access	Type	Format
dest_mac	ro	str	“xx:xx:xx:xx:xx:xx”
src_mac	ro	str	“xx:xx:xx:xx:xx:xx”
port_id	ro	str	“1/2/3”
vlan_tag	ro	int
ver	ro	int
type	ro	int
code	ro	int
session_id	ro	int
len	ro	int

Methods

alc.pppoe.drop(): Drops the packet.

alc.pppoe.getTagList()

Retrieves a tuple that includes tag-type of existing PPPoE tags in the packet.

The order of the element in the tuple is the same as the order of the tags in the packet.
If there are multiple instances of the same tag, the tag appears multiple times in the resulting tuple.

Returns: tuple of tag-types
Raises: RuntimeError – when called on a PPPoE packet that does not accept tags.

alc.pppoe.get(type, /)

Retrieves all instances of a specific tag-type.

Parameters: type (int) – tag type
Returns: tuple of bytes where each element is the value (as a bytestring) of a single instance. An empty tuple is returned when the tag is not present.
Raises: RuntimeError – when called on a PPPoE packet that does not accept tags.

alc.pppoe.set(type, values, /)

Deletes existing tags of the specified type and inserts new tags with the specified type and values.

Parameters

type (int) – tag type
values – tuple of bytes, each element is the value of a separate tag (the length is deduced from this value)

Raises

RuntimeError – when called on a PPPoE packet that does not accept tags.

alc.pppoe.clear(type, /)

Removes all tags of specified type.

Parameters: type (int) – tag type
Raises: RuntimeError – when called on a PPPoE packet that does not accept tags.

alc.pppoe.getPPP()

Retrieves an object of type alc.Ppp which represents the LCP, IPCP or IP6CP packet encapsulated inside the PPPoE packet.

Returns: alc.Ppp object
Raises: RuntimeError – when called on a PPPoE packet without embedded PPP packet.

Note

Modifying the object returned by this function does not alter the PPPoE packet.

alc.pppoe.getPAP()

Retrieves an object of type alc.Pap which represents the embedded PPP packet.

Returns: alc.Pap object
Raises: RuntimeError – when called on a PPPoE packet without embedded PAP packet.

Note

Modifying the object returned by this function does not alter the PPPoE packet. For the changes to take effect, alc.pppoe.setPAP() must be called with the modified PAP packet as its argument.

alc.pppoe.setPAP(pap, /)

Replaces the existing PAP packet.

Parameters: pap (alc.Pap) – new PAP packet
Raises: RuntimeError – when called on a PPPoE packet without embedded PAP packet.

alc.pppoe.getCHAP()

Retrieves an object of type alc.Chap which represents the embedded CHAP packet.

Returns: alc.Ppp object
Raises: RuntimeError – when called on a PPPoE packet without embedded CHAP packet.

Note

Modifying the object returned by this function does not alter the PPPoE packet. For the changes to take effect, alc.pppoe.setCHAP() must be called with the modified CHAP packet as its argument.

alc.pppoe.setCHAP(chap, /)

Replaces the existing CHAP packet.

Parameters: chap (alc.Chap) – new CHAP packet
Raises: RuntimeError – when called on a PPPoE packet without embedded CHAP packet.

The `alc.Ppp` class

The object returned from calling alc.pppoe.getPPP() is of type alc.Ppp. This object can be inspected.

class alc.Ppp(bytes, /)

Creates a new object representing a PPP packet.

Parameters: bytes (bytes) – the bytes representation of the complete PPP packet, including the header.

Attributes

The object exposes the header fields as attributes on the object.

Attributes defined on alc.Ppp objects
Attribute	Access	Type
protocol	ro	int
code	ro	int
id	ro	int
len	ro	int

Methods

alc.Ppp.getOptionList()

Retrieves a tuple of all PPP options that are present in the packet.

The order of the options is the same as they appear in the packet.
Each instance of the option is reflected in the tuple.

Returns: tuple of option-types

alc.Ppp.get()

Retrieves the values of a specific PPP option.

Parameters: type (int) – option-type
Returns: tuple of bytes, each element is the value of an instance of the specified option-type

The `alc.Pap` class

The object returned from calling alc.pppoe.getPAP() is of type alc.Pap. This object can be inspected and modified and can be passed to alc.pppoe.setPAP() to modify the active PPPoE packet.

Alternatively, new objects of this class can be created and used to set the embedded PAP packet.

class alc.Pap(bytes, /)

Creates a new object representing a PAP packet.

Parameters: bytes (bytes) – the bytes representation of the complete PAP packet, including the header.

Attributes

The object exposes the header fields as attributes on the object.

Attributes defined on alc.Pap objects
Attribute	Access	Type
code	ro	int
id	ro	int
len	ro	int

Methods

alc.Pap.getCred()

Retrieves the peer-id and password of an Authentication-Request packet.

Returns: (peer_id, password) tuple, both elements are bytes, possibly b’’ if the length is 0.
Raises: RuntimeError – when the packet is not an Authentication-Request

alc.Pap.setCred(value, /)

Set the peer-id and password on an Authentication-Request packet.

Parameters: value – (peer_id, password) tuple, both elements are bytes, b’’ is allowed for either element.
Raises: RuntimeError – when the packet is not an Authentication-Request

alc.Pap.getMsg()

Retrieves the contents of the packet.

Returns: contents as a bytestring
Raises: RuntimeError – when the packet is not an Authentication-Ack/Nak

alc.Pap.setMsg(value, /)

Sets the contents of the packet.

Parameters: value (bytes) – contents as a bytestring
Raises: RuntimeError – when the packet is not an Authentication-Ack/Nak

The `alc.Chap` class

The object returned from calling alc.pppoe.getCHAP() is of type alc.Chap. This object can be inspected and modified and can be passed to alc.pppoe.setCHAP() to modify the active PPPoE packet.

Alternatively, new objects of this class can be created and used to set the embedded CHAP packet.

class alc.Chap(bytes, /)

Creates a new object representing a CHAP packet.

Parameters: bytes (bytes) – the bytes representation of the complete CHAP packet, including the header.

Attributes

The object exposes the header fields as attributes on the object.

Attributes defined on alc.Chap objects
Attribute	Access	Type
code	ro	int
id	ro	int
len	ro	int

Methods

alc.Chap.getCred()

Retrieves the name and challenge/response from a challenge or response packet.

Returns: (name, value) tuple, both elements are bytes, where value is either the challenge or response depending on the code of the packet
Raises: RuntimeError – when the packet is not a challenge or response packet

alc.Chap.setCred(value, /)

Sets the name and challenge/response on a challenge/response packet.

Parameters: value – (name, value) tuple, both elements are bytes, where value is either the challenge or response depending on the code of the packet. b’’ is valid for either element.
Raises: RuntimeError – when the packet is not a challenge or response packet

alc.Chap.getMsg()

Retrieves the contents of the packet.

Returns: contents as a bytestring
Raises: RuntimeError – when the packet is not a success or failure packet.

alc.Chap.setMsg(value, /)

Sets the contents of the packet.

Parameters: value (bytes) – contents as a bytestring
Raises: RuntimeError – when the packet is not a success or failure packet.

Breaking changes

Class objects renamed

Warning

In Python 3, the classes alc.Ppp, alc.Pap, and alc.Chap follow the CapWords convention. In the Python 2 API, these are called alc.ppp, alc.pap, and alc.chap respectively (all lowercase).

New exceptions on alc.pppoe functions

Warning

When calling the functions alc.pppoe.getTagList(), alc.pppoe.get(), alc.pppoe.set(), alc.pppoe.clear() on a packet that is not in discovery state, an exception is raised. In the Python 2 implementation, None is returned.

The same is true when the functions getPPP, getPAP, and getCHAP are called on packets without a corresponding embedded packet.

New exceptions on alc.Pap functions

Warning

The functions alc.Pap.getCred(), alc.Pap.setCred(), alc.Pap.getMsg(), and alc.Pap.setMsg() raise an exception when called on a packet with the wrong code.

New exceptions on alc.Chap functions

Warning

The functions alc.Chap.getCred(), alc.Chap.setCred(), alc.Chap.getMsg(), and alc.Chap.setMsg() raise an exception when called on a packet with the wrong code.

PPPoE/PPP/PAP/CHAP

The alc.pppoe object

Attributes

Methods

The alc.Ppp class

Attributes

Methods

The alc.Pap class

Attributes

Methods

The alc.Chap class

Attributes

Methods

Breaking changes

Class objects renamed

New exceptions on alc.pppoe functions

New exceptions on alc.Pap functions

New exceptions on alc.Chap functions

The `alc.pppoe` object

The `alc.Ppp` class

The `alc.Pap` class

The `alc.Chap` class