pyswmap

This is a IETF Softwires Working Group MAP (MAP-E and MAP-T) Python module. It currently contains two classes:

• MapCalc: This class provides a set of medthods and attributes derived from the definition of a Base Mapping Rule(BMR).
• DmrCalc: This class provides a set of methods and attributes in support of a MAP-T Defualt Mapping Rule (DMR).

Using the MapCalc Class

Initial Steps

We create a new instance of class MapCalc and supply the BMR with the following values:

1. The IPv6 rule prefix: rulev6 (a string)
2. The IPv4 rule prefix: rulev4 (a string)
3. The PSID Offset: psidoffset (an integer) Note: In the absence of this value a default of 6 will be used
4. One of the two following values (both can be supplied if the resulting calculations is equivalent):

• The Sharing Ratio: ratio (an integer)

or

- The EA Length: ealen (an integer)

The code following code snippet demonstrates the creation of a new MapCalc object. The optional attributes have been included in this example but have been commented out. The psidoffset reflects the default value of 6 while the ealen has been set to reflect the caclulated value given a ratio of 64.

from pyswmap import MapCalc

m = pyswmap.MapCalc( rulev6='fd80::/48',
                     rulev4='24.50.100.0/24',
                     #psidoffset=6,
                     ratio=64,
                     #ealen=14,
                   )

This will result in the both calculated and validated class variables:

• m.rulev4: The IPv4 rule prefix used by a particular mapping rule.
• m.rulev6: The IPv6 rule prefix used by a particular mapping rule.
• m.rulev4mask: The number of bits in the IPv4 rule subnet mask.
• m.rulev6mask: The number of bits in the IPv6 rule subnet mask.
• m.ealen: The number of Embedded Address (EA) bits.
• m.ratio: The sharing ratio of # of users per IPv4 address. This is 2 to the power of bits in the PSID field.
• m.psidoffset: The PSID Offset value. Defined as the "A" field in the IETF MAP specification.
• m.portbits: The number of contiguous ports as defined by the "m bits" in the IETF MAP specification.
• m.psidbits: The length in bits of the PSID field. It is defined as the "k bits" in the IETF MAP specification.

Calculating Values Based on BMR

Given a Layer-4 Port Return the PSID Which Contains it

Supply arbitrary layer-4 port that is valid given PSID Offset to gen_psid method. This will return the following value:

• psid: The port-set ID which defines the algorithmically assigned ports unique to a particular MAP CE.

portvalue = 40000
psid = m.gen_psid(portvalue)

Determine the Originating IPv6 End-User Prefix and MAP Address

Supply an IPv4 address from IPv4 rule prefix and a unique PSID to get_mapce_addr and get_mapce_prefix methods and use them to calculate the following values:

• mapce: The MAP IPv6 address. This address is used to reach the MAP functions of a provisioned/configured MAP CE.
• pd: The end-user IPv6 prefix. Typically, but not exclusively DHCPv6 PD. Can also be assigned via SLAAC or configured manually.

In the example below we supply a valid IPv4 address from the IPv4 rule prefix (sharedv4) and a valid PSID value (psid) to allow us to obtain the mapce and pd values:

sharedv4 = '24.50.100.100'       # An address from the IPv4 rule prefix
psid = 4                         # A PSID integer value of 4
mapce = m.get_mapce_addr(sharedv4,psid)
pd = m.get_mapce_prefix(sharedv4,psid)
print(mapce)                   # Print the MAP IPv6 address
print(pd)                      # Print the end-user IPv6 prefix

Obtain the List of Ports Assigned to a Particular PSID

This method will return a Python list with a complete list of ports for the instance's psid attribute.

psid = 10                        # An example PSID value 
psidlist = m.port_list(psid)     # Obtain the set of ports for the PSID

Detailed definitions for all the variables discussed in this README are available in https://tools.ietf.org/html/draft-ietf-softwire-map.

Using the DmrCalc Class

Basic Example

We create a new instance of class DmrCalc and supply the DMR with the BR prefix:

from pyswmap import DmrCalc

brprefix = '2001:0db8:85a3::/64'       # The instance's BR prefix
ipv4addr  = '192.0.0.1'                # An arbitrary IPv4 address to embed
m = DmrCalc(brprefix)               
embedded = m.embed_6052addr(ipv4addr)  # An RFC6052 compliant IPv6 address

ACKNOWLEDGEMENTS

This code has been inspired or uses some parts of the following:

• Cisco MAP Simulation Tool

  http://map46.cisco.com

• Stateless NAT46 Linux kernel module implementation by Andrew Yourchenko

  https://github.com/ayourtch/nat46