Python script support for ESM

The system provides a Python object for input GTPv1-C packet alc.gtp1c. The alc.gtp1c packet has following attributes to represent the GTPv1-C header fields as displayed in GTPv1-C header fields .

The following is a list of alc.gtp1c functions:

• alc.gtp1c.drop()

  The system drops the resulting packet.

• alc.gtp1c.getIEList()

  The system returns a tuple of ie-type, each element represent one IE instance in the packet.

• alc.gtp1c.get(ie_type)

  The system returns a tuple of str, each str is the IE data of specified ie_type instances. If the specified IE does not exist, then return (); if the IE length=0, then return ‟” for this IE instance.

• alc.gtp1c.set(ie_type, ie_tuple)

  This function removes all instances of ie_type and insert a list of new IE instances. Each element in ie_tuple is a string, represent one instance of IE to be inserted. For each inserted IE instance, the type is ie_type. System uses the TV format for type<128 and TLV format for type>=128.

• alc.gtp1c.clear(ie_type)

  This function removes all existing instances of ie_type.

The system provides a Python object for input GTPv2-C packet: alc.gtp2c.

Shown in GTPv2-C API , the alc.gtp2c packet has following attributes to represent the GTPv2-C header fields:

The following is a list of alc.gtp2c functions:

• alc.gtp2c.drop()

  The system drops the resulting packet.

• alc.gtp2c.getIEList()

  The system returns a tuple of 2-element tuple (ie-type, ie-instance). Each 2-element tuple represent one IE instance in the packet. For example: a packet with the following IEs:

  • type:2, instance: 1

  • type:2, instance: 1

  • type:74, instance: 0

    The system returns ((2,1),(2,1),(74,0))

  • alc.gtp2c.get(ie_type, instance_id)

    The system returns a tuple of str. Each str is the IE data of specified (ie-type, instance-id). If the IE is a grouped IE, then the str is also the content of whole grouped IE. If the specified (ie_type, instance_id) does not exist, then return (); if the IE length=0, then return ‟” for this IE instance.

  • alc.gtp2c.set(ie_type, instance_id, ie_tuple)

    This function removes all instances of (ie_type, instance_id) and inserts a list of new IE instances. Each element in an ie_tuple is a string, represent one instance of IE to be inserted. For each inserted IE instance, the type is ie_type, the instance is instance_id.

  • alc.gtp2c.clear(ie_type, instance_id)

    This function removes all existing instances of (ie_type, instance-id).

  • alc.gtp2c.str_to_groupedIE (parent_ie_str)

    Parses the parent_ie_str and return a tuple of embedded IEs. Parent_ie_str is a string of data field of parent IE; each element of returned tuple is a tuple of (ie_type, ie_instance, ie_data), which represent one embedded IE. For example, with the following code:

    • ie_str = alc.gtp2c.get(93,0)[0]

    • ie_tuple = alc.gtp2c.str_to_groupedIE(ie_str)

    The above code parses the first instance of the bearer context with an instance=0. Assume the bearer context looks like that shown in Bearer context example:

    

    Then, the ie_tuple is

    ((5,0,’\x05’),(87,5’\x9f\xfe\x50\x02\x25\x0a\xbe\xac\xfe’),(80,0,’\x04\x08\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00’))

    An exception is raised if the system cannot parse the parent_ie_str into a ie_tuple.

  • alc.gtp2c.groupedIE_to_str(grouped_ie_tuple)

    Converts the grouped_ie_tuple into a str and return the str (see the description of alc.gtp2c.str_to_groupedIE for the format grouped_ie_tuple). An exception is raised if the conversion fails. The following is an example:

    • ie_str = alc.gtp2c.get(93,0)[0]
    • ie_tuple = alc.gtp2c.str_to_groupedIE(ie_str)
    • fteid = list(ie_tuple[1])
    • fteid[1]=0
    • ie_str = alc.gtp2c.groupdedIE_to_str((ie_tuple[0],tuple(ftied),ie_tuple[2]))
    • alc.gtp2c.set(93,0,(ie_str,))

    With the previous example packet, the code changes the instance of the embedded F-TEID to 0.

Be aware that the alc.gtp2c.str_to_groupedIE (parent_ie_str) and alc.gtp2c.groupedIE_to_str(grouped_ie_tuple) do not check whether the input parameter is a grouped IE. The user should verify that the input parameter is a grouped IE before using these two functions.

The following changes have been made to Python for it to run on an embedded system:

• No files or sockets can be opened from inside Python scripts.

• No system calls can be made from inside Python scripts nor is the posix package available.

• The maximum recursion depth is fixed to twenty.

• The total amount of dynamic memory available for Python itself and Python scripts (excluding the Python cache) is capped at 8 Mb for 32-bit SR OS and 16 Mb for 64-bit SR OS on a CPM.

• The size of the Python script source file should be less than 60 kb.

Consider using script us5.py which sets the subscriber ID (sub_ident) based on the circuit-id in the DHCP message.

Configure the URL to this script in a sub-ident-policy as follows:

---------------------------------------------- 
    sub-ident-policy "DSLAM" create
        description "Parse circuit IDs from different DSLAMs" 
        primary

            script-url "ftp://198.51.100.0/py/us5.py" 
            no shutdown
        exit
    exit
----------------------------------------------

And attach this sub-ident-policy to the sub-sla-mgmt from a SAP:

A:dut-A>config>service>vpls>sap# info
---------------------------------------------- 
    dhcp
        description "client side 
        lease-populate 50

        no shutdown 
    exit
    anti-spoof ip-mac
    sub-sla-mgmt
        sub-ident-policy "DSLAM" 
        no shutdown
    exit
----------------------------------------------

Verbose debug output is sent to debug-trace on compile errors, execution errors, execution output and the exported result variables.

A:dut-A>config>subscr-mgmt>sub-ident-pol>primary# script-url "ftp://xxx.xxx.xx.xx/py/
parsefail1.py"
A:dut-A>config>subscr-mgmt>sub-ident-pol>primary# no shutdown

1 2006/07/30 01:17:33.14 UTC MINOR: DEBUG #2001 - Python Compile Error
"Python Compile Error: parsefail1.py
    File "ftp://xxx.xxx.xx.xx/py/parsefail1.py", line 2 def invalid_function():
        ^
IndentationError: expected an indented block
"

A:dut-A>config>subscr-mgmt>sub-ident-pol>primary# script-url "ftp://xxx.xxx.xx.xx/py/
dump.py"

2 2006/07/30 01:24:55.50 UTC MINOR: DEBUG #2001 - Python Output
"Python Output: dump.py htype   = 0
hlen    = 0 hops    = 0 flags   = 0
ciaddr  = '0.0.0.0' yiaddr  = '0.0.0.0' siaddr  = '0.0.0.0' giaddr  = '0.0.0.0' chaddr  = ''
sname   = ''
file    = ''
options = '5\x01\x056\x04\n\x01\x07\n3\x04\x00\x00\x00\xb4\x01\x04\xff\xff\xff
\x00\x1c\x04\n\x02\x02\xffR\x0f\x01\rdut-A|1|1/1/1\xff' "

3 2006/07/30 01:24:55.50 UTC MINOR: DEBUG #2001 - Python Result
"Python Result: dump.py
"

A:dut-A>config>subscr-mgmt>sub-ident-pol>primary# script-url "ftp://xxx.xxx.xx.xx/py/end- less.py"

4 2006/07/30 01:30:17.27 UTC MINOR: DEBUG #2001 - Python Output
"Python Output: endless.py
"

5 2006/07/30 01:30:17.27 UTC MINOR: DEBUG #2001 - Python Error
"Python Error: endless.py
Traceback (most recent call last):
File "ftp://xxx.xxx.xx.xx/py/endless.py", line 2, in ? FatalError: script interrupted (timeout)
"

dump.py from alc import dhcp

def print_field(key, value):
print '%-8s = %r' % (key, value)

def ipaddr2a(ipaddr):
return '%d.%d.%d.%d' % (
(ipaddr & 0xFF000000) >> 24, (ipaddr & 0x00FF0000) >> 16, (ipaddr & 0x0000FF00) >> 8, (ipaddr & 0x000000FF))

print_field('htype',   dhcp.htype) print_field('hlen',    dhcp.hlen) print_field('hops',    dhcp.hops) print_field('flags',   dhcp.flags) print_field('ciaddr',  ipaddr2a(dhcp.ciaddr)) print_field('yiaddr',  ipaddr2a(dhcp.yiaddr)) print_field('siaddr',  ipaddr2a(dhcp.siaddr)) print_field('giaddr',  ipaddr2a(dhcp.giaddr)) print_field('chaddr',  dhcp.chaddr) print_field('sname',   dhcp.sname) print_field('file',    dhcp.file) print_field('options', str(dhcp.options))

This section provides examples to show how the script can be used in the context of Enhanced Subscriber Management.

'%' operator

While %f is supported, %g and %e are not supported.

Floating Point Arithmetic

The floating point arithmetic precision on the box is less than the precision required by the regression suites of Python.

1024.*1024.*1024. until five numbers after the point instead of seven and sqrt(9) equals to 3. for the first seven numbers after the point.

Using the round operator fixes these problems. For example, round(pow(2., 30)) equals round(1024.*1024.*1024.) and round(sqrt(9)) equals 3.

The following new Python objects, alc.radius, have the following methods:

• drop(): Drop the packet

• header(): Return the dictionary object that includes RADIUS header information

alc.radius also provides methods to manipulate radius attributes via alc.radius.attributes, which has the following methods:

• get(type): Return the first attribute with specified type as a string

• getTuple(type): The same as above but returns a tuple of strings

• getVSA(vendor, type): Return the first VSA as a string

• getVSATuple(vendor, type): The same as above but returns a tuple of strings

• getExt(type, ext-type): Return a string containing the value of the first Extended Type attribute (RFC 6929, Remote Authentication Dial In User Service (RADIUS) Protocol Extensions) matching the specified type and extended type

• getExtTuple(type, ext-type): Return a tuple of strings. For each occurrence of an Extended Type attribute (RFC 6929) matching the specified type and extended type, the attribute value is included as a string entry in the tuple

• getExtVSA(type, vendor, vendor-type): Return a string containing the value of the first Extended Vendor Specific attribute (RFC 6929) matching the specified type, vendor and vendor-type

• getExtVSATuple(type, vendor, vendor-type): Return a tuple of strings. For each occurrence of an Extended Vendor Specific attribute (RFC 6929) matching the specified type, vendor and vendor-type, the attribute value is included as a string entry in the tuple.

• getLongExtTuple(type, ext-type): Return a tuple of strings. For each occurrence of a Long Extended Type attribute (RFC 6929) matching the specified type and extended type, the attribute value is included as a string entry in the tuple. The value of all fragments of the same Long Extended Type attribute are concatenated in a single string entry.

• getLongExtVSATuple(type, vendor, vendor-type): Return a tuple of strings. For each occurrence of a Long Extended Vendor Specific attribute (RFC 6929) matching the specified type, vendor and vendor-type, the attribute value is included as a string entry in the tuple. The value of all fragments of the same Long Extended Vendor Specific attribute are concatenated in a single string entry.

• set(type, value): Set the specified attribute to the value. The value must be either a string or a tuple of strings.

• setVSA(vendor, type, value): Set the specified VSA to the value. The value must be either a string or a tuple of strings.

• setExt(type, ext-type, value): Set the specified Extended Type attribute value (RFC 6929). The value can be specified as a string (single attribute) or a tuple of strings (multiple attributes).

• setExtVSA(type, vendor, vendor-type, value): Set the specified Extended Vendor Specific attribute value (RFC 6929). The value can be specified as a string (single attribute) or a tuple of strings (multiple attributes).

• setLongExt(type, ext-type, value): Set the specified Long Extended Type attribute value (RFC 6929). The value can be specified as a string (single attribute) or a tuple of strings (multiple attributes). When the string value length is too long to fit in a single attribute (more than 251 octets), then the value field is fragmented across multiple attributes. The M-bit (more) is set in all but the last fragment.

• setLongExtVSA(type, vendor, vendor-type, value): Set the specified Long Extended Vendor Specific attribute value (RFC 6929). The value can be specified as a string (single attribute) or a tuple of strings (multiple attributes). When the string value length is too long to fit in a single attribute (more than 246 octets), then the value field is fragmented across multiple attributes. The M-bit (more) is set in all but the last fragment.

• clear(type): Remove the specified attribute

• clearVSA(vendor, type): Remove the specified VSA

• clearExt(type, ext-type): Remove all Extended Type or Long Extended Type attributes (RFC 6929) matching the specified type and extended type

• clearExtVSA(type, vendor, vendor-type): Remove all Extended Vendor Specific or Long Extended Vendor Specific attributes (RFC 6929) matching the specified type, vendor and vendor-type

• isSet(type): Return True if the specified attribute exists, False otherwise

• isVSASet(vendor, type): Return True if the specified VSA exists, False otherwise

• isExtSet(type, ext-type): Return True if an Extended Type or Long Extended Type attribute (RFC 6929) matching the specified type and extended type is present. Else return False

• isExtVSASet(type, vendor, vendor-type): Return True if an Extended Vendor Specific or Long Extended Vendor Specific attribute (RFC 6929) matching the specified type, vendor and vendor-type is present. Else return False.

Extended attribute type, Long Extended attribute type, and Extended Vendor Specific data type are specified in RFC 6929 RADIUS Protocol Extensions.

Both the RADIUS client and RADIUS server must support RFC 6929 RADIUS Protocol Extensions to successfully use the Extended and Long Extended attribute types and the Extended Vendor Specific data type. Therefore, it is recommended to check the RADIUS servers for RFC 6929 support and upgrade if needed. As shown in RADIUS Python: interworking with RADIUS server with no RFC 6929 support, RADIUS Python can be used as a workaround to interwork with a RADIUS server that does not support these extensions. Use the general purpose [26-6527-242] Alc-Radius-Py VSA of type ‟octets” for this purpose.

From alc import radius

#1. Get the value of an existing Attribute

Username=radius.attributes.get(1)

#2. Modify an existing attribute

radius.attributes.set(1, 'Tom')

#3. Remove an existing attribute

radius.attributes.clear(1)

#4. Add a new attribute

radius.attributes.set(126,”WIFI-operator”) 

The RADIUS API in Python policy uses the same API of the radius-script-policy.

• The system provides a Python object for input DHCPv4 packet: alc.dhcpv4.

• alc.dhcpv4 has following attributes to represent the DHCPv4 header fields:

  alc.dhcpv4 attributes displays alc.dhcpv4 attributes.

  Table 4. alc.dhcpv4 attributes

  Class attributes	DHCPv4 header field	Access
  alc.dhcpv4.pkt_len	Integer Total length of original DHCPv4 packet (UDP/IP header excluded, including pad option) in bytes	read
  alc.dhcpv4.pkt_netlen	Integer Total length of original DHCPv4 packet (UDP/IP header excluded, pad option in the ‟options” field excluded) in bytes	read
  alc.dhcpv4.op	op	read
  alc.dhcpv4.htype	htype	read/write
  alc.dhcpv4.hlen	hlen	read/write
  alc.dhcpv4.hops	hops	read/write
  alc.dhcpv4.xid	xid	read
  alc.dhcpv4.secs	secs	read/write
  alc.dhcpv4.flags	flags	read/write
  alc.dhcpv4.ciaddr	ciaddr	read/write
  alc.dhcpv4.yiaddr	yiaddr	read/write
  alc.dhcpv4.siaddr	siaddr	read/write
  alc.dhcpv4.giaddr	giaddr	read/write
  alc.dhcpv4.chaddr	chaddr	read/write
  alc.dhcpv4.sname	sname	read/write
  alc.dhcpv4.file	file	read/write

All attributes, except alc.dhcpv4.pkt_len and alc.dhcpv4.pkt_netlen, are string with value of the actual bytes in the header.

The following is a list all functions of alc.dhcpv4:

• alc.dhcpv4.drop()

• alc.dhcpv4. getOptionList()

• alc.dhcpv4.pad(min_size=300)

• alc.dhcpv4. get(op_code)

• alc.dhcpv4. set(op_code,valTuple)

• alc.dhcpv4. clear(op_code)

• alc.dhcpv4.get_relayagent() / alc.dhcpv4.set_relayagent(D4OL)

• alc.dhcpv4.get_vendorspecific() / alc.dhcpv4.set_vendorspecific (D4OL)

DHCPv4 allows using sname and file fields to store options. However all DHCPv4 functions only operates with the ‟options” field. If a customer wants to manipulate options in the sname/file field, they need to do the parsing work in the script. (extended string.tlvxy method could help here)

• alc.dhcpv4. drop(): The system drops the result packet

• alc.dhcpv4. getOptionList(): Returns a tuple that includes the option-code of the existing top level DHCPv4 options in the packet.

  • The order of the element in the tuple is as same as the options that appear in the packet.

  • If there are multiple instances of the same option, then each instance is one element in the tuple.

  • Pad option(0) is excluded.

  • End option(255) is included

  • Example: A DHCP discovery packet with msg-type/lease-time/request-addr/parameter-request-list/agent-info/end returns (53,51,50,55,82,255)

• alc.dhcpv4.pad(min_size=300): This function pads the resulting DHCPv4 packet to the specified min_size with pad option(0) after executing the whole script. Padding is not added if the result packet is already >=min_size. The default value of min_size is 300. Although not defined in DHCPv4 RFC, many DHCPv4 implementation has a minimal length requirement of 300 bytes. So this function could pad the result packet to the specified min_size.

• alc.dhcpv4. get(op_code): Returns a tuple that includes all instances of the specified top level option as a string. The value of this string is the exact bytes of the option as it appears in packet(excludes option-code and option-len).

  • If the specified option does not exist, then the function returns ()

  • If the instance of the specified option does not have the value (len=0 or does not have len and value part), then the function returns ‟” for that instance in the tuple.

  • Example: There is an address lease time option(51) in the packet, with value 60, then alc.dhcpv4.get(51) should return: (‛\x00\x00\x00\x3c’,)

• alc.dhcpv4. set(op-code,valTuple): This function removes all the existing instances of specified top level option and insert a list of new options. Each element in valTuple is a string, representing one instance of the new option to be inserted; For each new option, the option-code is specified in op-code. The option-len is the length of the element. The rest of option is the element itself.

  Example: To insert an address lease time option(51) in the packet, with the value 60; use alc.dhcpv4.set(51, (‛\x00\x00\x00\x3c’,))

• alc.dhcpv4. clear(op-code): This function removes all the existing instances of specified top level option.

• Although alc.dhcpv4.get() and alc.dhcpv4.set() provide a generic way to manipulate DHCPv4 top level options, but some DHCPv4 options have a complex/hierarchical structure like option82 and option43. To provide a friendly access to these kinds of options, the system provides the following options’ specific functions:

  • alc.dhcpv4.get_relayagent() / alc.dhcpv4.set_relayagent(D4OL)

  • alc.dhcpv4.get_vendorspecific() / alc.dhcpv4.set_vendorspecific (D4OL)

  All alc.dhcpv4.get_XXX() returns a data structure:‟D4OL” (DHCPv4 Option List)

  • D4OL is a list. Each element in the list represents an instance of that option. For example, if there are 3 option82 in the ‟options” field of packet, then get_relayagent() returns a list of 3 elements. Each element represents one instance of the option in the packet.

  • Each element in D4OL is a dict (called dict as ‟D4O” in this example):

    The key of D4O is the sub-option- code. The value is a list of strings of sub-option-value of all instance of the sub-option.

  All alc.dhcpv4.set_XX(OPDL) accepts D4OL as the parameter. Remove all existing instances of the corresponding options and then insert the new options represented by specified D4OL.

Examples:

For a packet with an option82 like following

    Option: (82) Agent Information Option
        Length: 22
        Option (82) Suboption: (1) Agent Circuit ID
            Length: 8
            Agent Circuit ID: 4a616e737656e73
        Option 82 Suboption: (2) Agent Remote ID
            Length: 10
            Agent Remote ID 62617369632364617461

The option-data is (hex formatted) ‟01:08:4a:61:6e:73:73:65:6e:73:02:0a:62:61:73:69:63:23:64:61:74:61”

The following is an example script:

import alc

option82_list=alc.dhcpv4.get_relayagent()
#option82_list will be [{1:['\x4a\x61\x6e:73\x73\x65\x6e\x73',],2:['\x62\x61\x73\x69\x63\x23\x64\x61\x74\x61',]},]
Option82_list[0][2][0]='basic#video' #change remote-id to 'basic#video'
alc.dhcpv4.set_relayagent(option82_list)#update the option82

• The system provides a Python object for input DHCPv6 packet: alc.dhcpv6

• alc.dhcpv6 has following attributes to represent the DHCPv6 header fields:

  DHCPv6 header fields displays DHCPv6 header fields.

  Table 5. DHCPv6 header fields

  Class attributes	DHCPv6 header field	Client/server msg	Relay msg	Access
  alc.dhcpv6.pkt_len	Integer, Total length of original DHCPv4 packet(UDP/IP header excluded) in bytes	✓	✓	Read
  alc.dhcpv6.msg_type	msg-type	✓	✓	Read
  alc.dhcpv6.transaction_id	transaction-id	✓		Read
  alc.dhcpv6.hop_count	hop-count		✓	read/write
  alc.dhcpv6.link_addr	link-address		✓	read/write
  alc.dhcpv6.peer_addr	peer-address		✓	read/write

All header fields (as the attribute of alc.dhcpv6 class) are strings (except pkt_len) with exact bytes as it appears in the packet.

If the attribute does not exist in the specified msg-type, for example if the link_attr does not exist in client/server message(C/S msg), then its value should be None.

• The following is a list of all functions in the class:

  • alc.dhcpv6.drop()

  • alc.dhcpv6. getOptionList()

  • alc.dhcpv6. get(op-code)

  • alc.dhcpv6. set(op-code,valTuple)

  • alc.dhcpv6. clear(op-code)

  • alc.dhcpv6.get_iana() / alc.dhcpv6.set_iana(OPDL)

  • alc.dhcpv6.get_iata() / alc.dhcpv6.set_iata(OPDL)

  • alc.dhcpv6.get_vendoropts() / alc.dhcpv6.set_vendoropts(OPDL)

  • alc.dhcpv6.get_iapd() / alc.dhcpv6.set_iapd(OPDL)

  • alc.dhcpv6.get_relaymsg()

  • alc.dhcpv6.set_relaymsg(packet)

• alc.dhcpv6. drop(): The system drops the resulting packet.

• alc.dhcpv6. getOptionList(): Returns a tuple that includes the option-code of the existing top level DHCPv6 options in the packet. The order of the element in the tuple is as same as the options appear in the packet. If there are multiple instances of same option, then each instance is one element in the tuple. For example:

  • A C/S Msg with Elapsed Time/Client Identifier/IANA/FQDN/Vendor Class/Option Request returns (8,1,3,39,16,6).

  • A Relay Msg with Relay Message option only returns (9)

• alc.dhcpv6. get(op-code): Returns a tuple that includes all instances of the specified top level option as string The value of this string is the exact bytes of the option as it appears in packet (excludes option-code and option-len). If the specified option does not exist in the input packet, then it returns ().

  Examples:

  If there is a Status Code option in the packet, status-code 0 and status-msg:”Address Assigned”; then alc.dhcpv6.get(13) should return: (‛\x00\x00Address Assigned’,)

• alc.dhcpv6. set(op-code,valTuple): This function removes all the existing instances of the specified top level option and insert a list of new options. Each element in valTuple is a string, representing one instance of the new option to be inserted. For each new option, the option-code is specified in op-code, the option-len is the length of the element, reset of option is the element itself.

  To insert a Status Code options with status-code 0 and status-msg:”Address Assigned”; use alc.dhcpv6.set(13, (‛\x00\x00Address Assigned’,))

• alc.dhcpv6. clear(op-code): This function removes all the existing instances of specified top level option.

• Although alc.dhcpv6.get() and alc.dhcpv6.set() provide a generic way to manipulate DHCPv6 top level options, but some DHCPv6 options have more complex/hierarchical structure like IA_NA/IA_TA, and so on. To provide a friendly access to these kinds of options, the system provides the following options specific functions:

  • alc.dhcpv6.get_iana() / alc.dhcpv6.set_iana(OPDL)

  • alc.dhcpv6.get_iata() / alc.dhcpv6.set_iata(OPDL)

  • alc.dhcpv6.get_vendoropts() / alc.dhcpv6.set_vendoropts(OPDL)

  • alc.dhcpv6.get_iapd() / alc.dhcpv6.set_iapd(OPDL)

  All alc.dhcpv6.get_XXX() returns a data structure:‟OPDL” (Option Data structure List)

  • OPDL is a list. Each element in the list represents an instance of that option. For example, if there are 3 IANA in the packet, then get_iana() returns a list of 3 elements, each element represent one instance of IANA option in the packet.

  • Each element in OPDL is a list, referred to as ‟OPD” in this list.

    • Each element in OPD represent one field in the option(option-code and option-len are not included), the order of the element is as same as the fields appear in the option

    • For field that could be parsed into sub-option by RFC, then the element is a dict, the key of this dict is the sub-option type, if sub-option is one of following supported-sub-option, the value to the key is a sub-option_OPDL represent the list of that specific sub-option

    • IAADDR(5)

    • Status Code(13)

    • IAPREFIX(26)

    Else, if the sub-option is not one of the above, then the value to the key is a list of string of sub-option-data, each string represent one instance of the sub-option.

    • The structure of sub-option_OPDL of IAADDR is: [[v6_addr,prefer_lifetime, valid_lifetime,sub-option_OPDL], ]

    • The structure of sub-option_OPDL of Status Code is: [[status-code,status-msg], and so on]

    • The structure of sub-option_OPDL of IAPREFIX is: [[prefer_lifetime,valid_lifetime,prefix-len,v6prefix,sub-option_OPDL],..]

    • For the field (by RFC definition) could be parsed into sub-options, but it does not actually exist, then the dict is empty {}

    • For field that cannot be parsed into sub-option by RFC, the element is a string of exact bytes of that field

All alc.dhcpv6.set_XX(OPDL) accepts an OPDL as the parameter. Remove all existing instances of the corresponding options and then insert new options represented by the specified OPDL.

• alc.dhcpv6.get_iana()/alc.dhcpv6.get_iana(OPDL)

• The general OPDL structure for these two functions is: [[IAID_val,T1_val,T2_val, sub-option_dict]]

• The structure of sub-option_dict is:{sub-option-type:sub-option_val}

• If sub-option is supported-sub-option, then sub-option_val is a sub-option_OPDL

• For all other sub-options, the sub-option_val is a list of string of sub-option-data

Examples:

For a packet with an IANA option as in the following:

The option-data is (hex formatted)

‟0f:f0:de:f1:00:02:a3:00:00:04:38:00:00:05:00:18:20:01:05:58:60:45:00:47:45:cc:d9:f2:57:27:ea:e0:00:05:46:00:00:05:46:00”

The following is an example script:

import alc

iana_list=alc.dhcpv6.get_iana()
#iana_list will be [['\x0f\xf0\xde\xf1','\x00\x02\xa3\x00','\x00\x04\\x38\x00',{5:[['\x20\x01\x05\x58\x60\x45\x00\x47\x45\xcc\xd9\xf2\x57\x27\xea\xe0','\x00\x05\x46\x00','\x00\x05\x46\x00',{}]]}]]
iana_list[0][1]='\x00\x00\x04\xb0' #change T1 to 1200
alc.dhcpv6.set_iana(iana_list)#update the iana

• alc.dhcpv6.get_iata()/alc.dhcpv6.get_iata(OPDL)

  • The general OPDL structure for these two functions is: [[IAID_val, sub-option_dict]]

  • The structure of sub-option_dict is:{sub-option-type:sub-option_val}

  • If sub-option is supported-sub-option, then sub-option_val is a sub-option_OPDL

  • For all other sub-options, the sub-option_val is a list of string of sub-option-data

  Examples: These two function are very similar with IANA, so the examples are skipped here.

• alc.dhcpv6.get_iapd()/alc.dhcpv6.get_iapd(OPDL)

• The general OPDL structure for these two functions is: [[IAID_val,T1_va1,T2_val, sub-option_dict]]

• The structure of sub-option_dict is:{sub-option-type:sub-option_val}

• If sub-option is supported-sub-option, then sub-option_val is a sub-option_OPDL

• For all other sub-options, the sub-option_val is a list of string of sub-option-data

  Examples: For a packet with IA_PD as in the following:

  

  The option-data is (hex formatted)

  ‟00:00:00:01:00:00:07:08:00:00:0b:40:00:1a:00:19:00:00:0e:10:00:01:51:80:38:20:01:0d:b8:00:02:00:00:00:00:00:00:00:00:00:00”
  

• Following is an example script:

  
  import alc
  
  iapd_list=alc.dhcpv6.get_iapd()
  #iapd_list will be [['\x00\x00\x00\x01','\x00\x00\x07\x08','\x00\x00\x0b\x40',{26:[['\x00\x00\x0e\x10','\x00\x01\x51\x80','\x38', '\x20\x01\x0d\xb8\x00\x02\x00\x 00\x00\x00\x00\x00\x00\x00\x00\x00',{}]]}]]
  iapd_list[0][1]='\x00\x00\x04\xb0' #change T1 to 1200
  alc.dhcpv6.set_iapd(iapd_list)#update the iapd
  
  

• alc.dhcpv6.get_vendoropts()/alc.dhcpv6.get_vendoropts (OPDL)

  • The general OPDL structure for these two functions is: [[enterpriseid_val, sub-option_dict]]

  • The structure of sub-option_dict is:{sub-option-type:sub-option_val}

  • If sub-option is supported-sub-option, then sub-option_val is a sub-option_OPDL

  • For all other sub-options, the sub-option_val is a list of string of sub-option-data

Examples: For a packet with vendor options as in the following:

The option-data is (hex formatted)

‟00:00:19:7f:00:01:00:09:69:61:2d:6e:61:5f:30:30:31:00:02:00:09:69:61:2d:70:64:5f:30:30:31:00:03:00:01:38:00:04:00:01:40”

The following is an example script:

import alc

vendoropts_list=alc.dhcpv6.get_vendoropts()
# vendoropts_list will be [['\x00\x00\x19\x7f', {1:['\x69\x61\x2d\x6e\x61\x5f\x30\x30\x31'],2:[ '\x69\x61\x2d\x70\x64\x5f\x30\x30\x31'],3:['\x38'], 4:['\x40']}]]
iapd_list[0][1][4][0]='\x60' #change sub-option 4’s value to 0x60
alc.dhcpv6.set_vendoropts(vendoropts_list)#update the vendor options

• For DHCPv6 relay message, the ‟Relay Message” option embedded a full DHCPv6 packet and the embedded packet could itself have a ‟Replay Message” option which embedded another DHCPv6 packet.

  To provide direct access to embedded DHCPv6 packet, the system provides following functions:

  • alc.dhcpv6.get_relaymsg()

  • alc.dhcpv6.set_relaymsg(packet)

• alc.dhcpv6. get_relaymsg(): This function returns a populated alc.dhcpv6 object. which means the returned object was initialized with the DHCPv6 packet embedded in ‟Relay Message” option as the input.

• alc.dhcpv6. set_relaymsg(packet): This function accepts an alc.dhcpv6 object as a parameter. This object replaces existing ‟Relay Message” option.

Example-1 script for single relay message:

import alc
#input packet is a relay-reply msg
embed_dhcpv6_packet=alc.dhcpv6.get_relaymsg()
iana_list=embed_dhcpv6_packet.get_iana()
iana_list[0][1]='\x00\x00\x04\xb0' #change T1 to 1200
embed_dhcpv6_packet.set_iana(iana_list)#update the iana of the embedded packet
alc.dhcpv6.set_relaymsg(embed_dhcpv6_packet)#update the Relay Message option

Example-2 script for double relay message (relay of relay):

import alc
#input packet is a relay-reply msg
embed_lv1_packet=alc.dhcpv6.get_relaymsg() #get the level=1 embedded packet
embed_lv2_packet= embed_lv1_packet.get_relaymsg()#get level-2 packet embedded in level-1 packet
iana_list=embed_dhcpv6_packet.get_iana()
iana_list[0][1]='\x00\x00\x04\xb0' #change T1 to 1200
embed_dhcpv6_packet.set_iana(iana_list)#update the iana
embed_lv1_packet.set_relaymsg(embed_lv2_packet)#update the Relay Message option of lv1 msg
alc.dhcpv6.set_relaymsg(embed_lv1_packet)#update the Relay Message option of the top level msg

The alc.diameter Python module provides an API for Diameter message manipulation.

Terminology used in the API description:

• top-level-AVP

  AVP appearing at the top level in a Diameter message, in other words, not embedded in the Data field of a grouped AVP

• embedded-AVP

  AVP embedded in the Data field of a grouped AVP. An embedded AVP can be a grouped AVP. This is called nesting.

• AVP-tuple

  Python tuple with following values:

  (AVP code, vendor ID, flags)

  • AVP code: integer, AVP header field

  • Vendor ID: integer, AVP header field

  • flags: string, AVP header field

• AVP-value-tuple

  Python tuple with following values:

  (flags, data)

  • flags: string, AVP header field

  • data: string, AVP data field

• AVP-key-tuple

  Python tuple with following values:

  (AVP code, Vendor ID)

  • AVP code: integer, AVP header field

  • Vendor ID : integer, AVP header field

• grouped-AVP-value-tuple

  Python tuple with following values:

  (flags, grouped-AVP-dictionary)

  flags: string, AVP header field

• grouped-AVP-dictionary

  Python dictionary with following key:value pairs:

  {AVP-key-tuple: [AVP-value-tuple or grouped-AVP-value-tuple, …], ... }

  • key = AVP-key-tuple

  • value = list of AVP-value-tuples or list of grouped-AVP-value-tuples

• grouped-AVP-decode-tuple

  Python tuple with the following values (AVP-key-tuple, …)

  tuple of AVP-key-tuples

• AVP-order-tuple

  Python tuple with the following values (AVP-key-tuple, …)

  tuple of AVP-key-tuples

Diameter message header alc.diameter attributes displays attributes available in alc.diameter module providing access to the Diameter message header:

Message and AVP manipulation functionality alc.diameter methods displays methods available in alc.diameter module providing message and AVP manipulation functionality:

To enable Diameter message manipulation using Python, a Python policy must be configured in the diameter-peer-policy. For example:

The Python policy specifies the Python script to use for each Diameter message type received or transmitted on a Diameter peer. In the ingress direction, the Python script is executed when the corresponding packet type is received on the Diameter peer but before further processing in the system. In the egress direction, the Python script is executed prior to sending the corresponding packet type on the Diameter peer. For example:

The Python script specifies the location of the script and optional protection mechanism. For example:

configure
    python
        python-script "diameter-1" create
            primary-url "ftp://usr:pwd@192.0.2.1/./py/diam-1.py"
            no shutdown
        exit
    exit

As an example, the diam-1.py script, clears the M-bit from the Event-Timestamp AVP (code 55):

    from alc import diameter
    avp55=diameter.get_avps(55,0)
    diameter.set_avps(55,0,[('\x00',avp55[0][1])])

A DHCP transaction cache (DTC) is a short-lived cache during DHCPv4/v6 transaction. The cache could be used to store user-chosen information or return ESM attributes via a Python script. The DTC’s lifetime is only during a single DHCP transaction (for example, only between discovery-offer, request-reply). This includes both alc.dtc.store() data and alc.dtc.setESM() data. DTC is also a transaction specific cache, which means the cached information could only be accessed by the Python script running in same DHCP transaction.

The following are the DTC APIs:

• alc.dtc.derivedId: A string used as a LUDB lookup key

• alc.dtc.store(cache-key, cache-value): Store the value with the specified cache-key in DTC, both key and value are string.

• alc.dtc.retrieve(cache-key): Returns the cached value string according to the specified cache-key, raise exception if specified key does not exist.

• alc.dtc.setESM(ESM-key, value): Sets the specified ESM attribute, which could be used when system creating the ESM host.

  Note:

  Because of the short-lived nature of DTC, setESM should be used in final DHCP transaction before system create ESM host., such as DHCPv4 REQUEST-ACK.

• The following is a list of supported ESM-keys and corresponding Python type:

  • alc.dtc.accountingPolicy:str

  • alc.dtc.ancpString:str

  • alc.dtc.appProfileString:str

  • alc.dtc.catMapString:str

  • alc.dtc.defGw:str

  • alc.dtc.dhcpv4GIAddr:str

  • alc.dtc.dhcpv4Pool:str

  • alc.dtc.dhcpv4ServerAddr:str

  • alc.dtc.dhcpv6LinkAddr:str

  • alc.dtc.dhcpv6PreferredLifetime

  • alc.dtc.dhcpv6RebindTimer

  • alc.dtc.dhcpv6RenewTimer

  • alc.dtc.dhcpv6ServerAddr:str

  • alc.dtc.dhcpv6ValidLifetime

  • alc.dtc.intDestId:str

  • alc.dtc.ipAddress:str

  • alc.dtc.ipv4LeaseTime:int

  • alc.dtc.ipv4PrimDns:str

  • alc.dtc.ipv4SecDns:str

  • alc.dtc.ipv6Address:str

  • alc.dtc.ipv6DelegatedPrefix:str

  • alc.dtc.ipv6DelegatedPrefixLength:int

  • alc.dtc.ipv6PrefixPool:str

  • alc.dtc.ipv6PrimDns:str

  • alc.dtc.ipv6SecDns:str

  • alc.dtc.ipv6SlaacPrefix:str

  • alc.dtc.ipv6WanPool:str

  • alc.dtc.msapGroupInterface:str

  • alc.dtc.msapPolicy:str

  • alc.dtc.msapServiceId:str

  • alc.dtc.primNbns:str

  • alc.dtc.primNbns:str

  • alc.dtc.retailServiceId:str

  • alc.dtc.secNbns:str

  • alc.dtc.slaProfileString:str

  • alc.dtc.subIdent:str

  • alc.dtc.subnetMask:str

  • alc.dtc.subProfileString:str

The following are the system-provided Python API PPPoE packets:

• The system provides a Python object for input PPPoE packet: alc.pppoe.

• alc.pppoe class is always available even when Python script is trigger by other type of packet that encapsulated in PPPoE, such as LCP/IPCP/PAP/CHAP, and so on.

• alc.pppoe has the following attributes to represent the PPPoE header fields.

System provided Python API PPPoE packets displays information about system-provided Python API PPPoE packets.

The following is a list of functions of alic.pppoe:

• alc.pppoe.drop()

  The system drops the resulting packet.

• alc.pppoe.getTagList()

  The system returns a tuple that includes tag-type of existing PPPoE tags in the packet. The order of the element in the tuple is as same as the tags appear in the packet. If there are multiple instances of same option, then each instance is one element in the tuple.

• alc.pppoe.get(tag-type)

  The system returns a tuple of strings, each string represent one instance of the specified tags, the value of this string is exact bytes of the tag_value as it appears in packet (excludes tag_type and tag_len); if tag does not exist, return (); if a specific instance’s tag_length=0, return ‟” for this instance.

• alc.pppoe.set(tag-type,valTuple)

  This function removes all the existing instances of specified tags and insert a list of new tags. Each element in valTuple is a string, represent one instance of the new tag to be inserted. For each new option, the type is specified in tag-type, the option-len is the length of the element, reset of option is the element itself.

• alc.pppoe.clear(tag-type)

  This function removes all the existing instances of specified tags. In fact this function is a shortcut version of alc.pppoe.set(tag-type,()).

• alc.pppoe.getPPP()

  This function returns an alc.ppp object which represent the LCP/IPCP/IP6CP packet encapsulated inside the PPPoE packet. It returns none if there is no such packet.

• alc.pppoe.getPAP()

  This function returns an alc.pap object which represents the PAP packet encapsulated inside the PPPoE packet. It returns none if there is no PAP packet.

• alc.pppoe.setPAP(pap_obj)

  This function accepts an alc.pap object as the parameter and replace the existing PAP packet that encapsulated in the PPPoE packet. An exception is raised when there is no existing PAP packet.

• alc.pppoe.getCHAP()

  This function returns an alc.chap object, which represent the CHAP packet encapsulated inside the PPPoE packet. It returns none if there is no CHAP packet.

• alc.pppoe.setCHAP(chap_obj)

  This function accepts an alc.chap object as the parameter and replace the existing CHAP packet that encapsulated in the PPPoE packet. An exception is raised when there is no existing CHAP packet.

The system provides a Python object for PPP packet encapsulated in PPPoE packets: alc.ppp.

PPP header field attributes displays information about PPP header field attributes.

The following is a list of functions of alc.ppp:

• alc.ppp.getOptionList()

  Returns a tuple that includes type of existing PPP options in the packet. The order of the element in the tuple is as same as the options appear in the packet. If there are multiple instances of same option, then each instance is one element in the tuple.

• alc.ppp.get(op-type)

  Returns a tuple of strings, each string represent one instance of the specified option, the value of this string is exact bytes of the option_data as it appears in packet (excludes option_type and option_len); if the option does not exist, return (); if a specific instance’s option_length=0, return ‟” for this instance.

The system provides a python object for PAP packet encapsulated in the input PPPoE packets: alc.pap.

Use alc.pppoe.getPAP() to get the alc.pap object in the input PPPoE packet.

To apply changes to PAP packet, alc.pppoe.setPAP(new_alc.pap_obj) must be called.

PAP header fields provides PAP header field information. alc.pap has following attributes to represent the PAP header fields:

The following is a list of functions in the class:

• alc.pap.getCred()

  Only apply to Authentication-Request packet. Returns a tuple: (peer-id, password), both are str. If either of them has 0 length, it is ‟”; if the system failed to parse the packet, such as the length < 6 bytes or the packet is not an authentication-request, then the system raises an exception. If the packet has a wrong type it returns None (that is, no exception is raised).

• alc.pap.setCred(cred_tuple)

  Only apply to Authentication-Request packet. Set the peer-id and password to cred_tuple; cred_tuple is a tuple:(peer-id, password) both are str. ‟” is allowed as the value for either of them. If the packet is not authentication-request, then system raises an exception.

• alc.pap.getMsg()

  Only apply to Authentication-Ack/Nak packet. Return the message in the packet as a str; return ‟” if len of message is 0; raise an exception for wrong type of packet (such as an auth-request). If the packet has a wrong type it returns None (that is, no exception is raised).

• alc.pap.setMsg(msg)

  Only apply to Authentication-Ack/Nak packet. set the message in the packet to parameter msg; msg is a str; ‟” is allowed; raise an exception for wrong type of packet (such as an auth-request).

The system provides a python object for CHAP packet encapsulated in the input PPPoE packets: alc.chap.

Use alc.pppoe.getCHAP() to get the alc.chap object in the input PPPoE packet.

To apply changes to PAP packet, alc.pppoe.setCHAP(new_alc.pap_obj) need to be called.

CHAP header fields provides CHAP header field information. alc.chap has following attributes to represent the CHAP header fields:

The following is a list of functions in the class:

• alc.chap.getCred()

  Only apply to challenge/response packet. Returns a tuple: (name, challenge, response), both are str. If either of them has 0 length, it is be ‟”; if system failed to parse the packet, such as the length < minimal_length or the packet is not challenge/response, then system raise an exception. If the packet has a wrong type it returns None (that is, no exception is raised). The second value in the returned tuple either contains the challenge (in a challenge packet) or the response (in a response packet) value.

• alc.chap.setCred(chap_cred_tuple)

  Only apply to challenge/response packets. Set the name and challenge to chap_cred_tuple; chap_cred_tuple is a tuple: (name, challenge, response) both are str. ‟” is allowed as the value for either of them. If packet is not challenge/response, then system raises an exception. The second value in the supplied tuple either contains the challenge (in a challenge packet) or the response (in a response packet) value.

• alc.chap.getMsg()

  Only apply to Success/Failure packet. Return the message in the packet as a str; return ‟” if len of message is 0; raise an exception for wrong type of packet (such as challenge). If the packet has a wrong type it returns None (that is, no exception is raised).

• alc.chap.setMsg(msg)

  Only apply to Success/Failure packet. set the message in the packet to parameter msg; msg is a str; ‟” is allowed; raise an exception for wrong type of packet (such as challenge).

The system provides a python object: alc.esm, to provide flexible LUDB lookup and return ESM attributes directly from script.

alc.esm support both DHCPv4/v6 and PPPoE hosts.

alc.esm has following attribute and function:

• alc.esm.derivedId: A string used as LUDB lookup key

• alc.esm.set(ESM-key, value): Set the value of specified ESM attribute, it is used for ESM host creation.

alc.esm.derivedId should be set for all types of ingress packets that system used to access LUDB; for example PPPoE PADI and PADR, DHCP discovery and request.

The following is a list of supported ESM-key and its corresponding Python type:

• alc.esm.accountingPolicy:str

• alc.esm.ancpString:str

• alc.esm.appProfileString:str

• alc.esm.catMapString:str

• alc.esm.defGw:str

• alc.esm.dhcpv4GIAddr:str

• alc.esm.dhcpv4Pool:str

• alc.esm.dhcpv4ServerAddr:str

• alc.esm.dhcpv6LinkAddr:str

• alc.esm.dhcpv6ServerAddr:str

• alc.esm.intDestId:str

• alc.esm.ipAddress:str

• alc.esm.ipv4LeaseTime:int

• alc.esm.ipv4PrimDns:str

• alc.esm.ipv4SecDns:str

• alc.esm.ipv6Address:str

• alc.esm.dhcpv6PreferredLifetime

• alc.esm. dhcpv6RebindTimer

• alc.esm. dhcpv6RenewTimer

• alc.esm. dhcpv6ValidLifetime

• alc.esm.ipv6DelegatedPrefix:str

• alc.esm.ipv6DelegatedPrefixLength:int

• alc.esm.ipv6PrefixPool:str

• alc.esm.ipv6PrimDns:str

• alc.esm.ipv6SecDns:str

• alc.esm.ipv6SlaacPrefix:str

• alc.esm.ipv6WanPool:str

• alc.esm.msapGroupInterface:str

• alc.esm.msapPolicy:str

• alc.esm.msapServiceId:str

• alc.esm.primNbns:str

• alc.esm.retailServiceId:str

• alc.esm.secNbns:str

• alc.esm.slaProfileString:str

• alc.esm.spiSharingGroupId:int

• alc.esm.subIdent:str

• alc.esm.subProfileString:str

• alc.esm.subnetMask:str

• alc.dtc.dhcpv6PreferredLifetime

• alc.dtc.dhcpv6RebindTimer

• alc.dtc.dhcpv6RenewTimer

• alc.dtc.dhcpv6ValidLifetime

The following are PPPoE-specific keys:

• alc.esm.padoDelay: int

• alc.esm.pppAuthProtocol: str, {‛pap’|’chap’|’pref-chap’|’pref-pap’}

• alc.esm.pppMTU: int

With PPPoE, alc.esm.set() could only be called ingress discovery (PADI, PADR) and authentication (PAP Authenticate, CHAP Response) packets. If it is called multiple times, the first one wins except the derived-id, while the alc.esm.padoDelay only applies when the system receives PADI. alc.esm.pppAuthProtocol and alc.esm.pppMTU can only be set when a PADR is received.

alc.esm.set() is blocked during LCP/IPCP/IP6CP phase.

The system raises an exception if alc.esm.set() is called at wrong time. Setting the ESM keys that do not apply to the host type are ignored; for example, setting PPP(oE) keys for DHCP hosts is ignored.

The value returned by alc.esm.set() take highest precedence than other sources like CLI/LUDB.

For alc.esm.set(ESM-key, value)

• PPPoE can only be called for ingress discovery (PADI, PADR) and authentication (PAP Authenticate, CHAP Response) packets. An exception is raised otherwise (for example, wrong time, including egress discovery PADO and PADS, and authentication PAP Ack/Nak and CHAP Success/Failure).

• The PPPoE key alc.esm.padoDelay can only be set when PADI is received (otherwise, it is too late).

• Setting ESM keys for a PPPoE host which do not apply is ignored (that is, no exception is raised).

• PPP keys alc.esm.pppAuthProtocol and alc.esm.pppMTU can only be set when PADR is received. It has no effect when PADI is received.

• Setting PPP(oE) keys for a DHCP host is ignored.

Python cache support allows information to be shared across different run times of the same python script or even different python scripts in a programmatic way. It essentially provides a central memory cache and a set of APIs which allows the user store and retrieve strings. For example, a DHCP python-script could store a DHCP option into cache and later a RADIUS python-script could retrieve stored string and add it into access-request.

Each cached entry in the cache is a tuple of (key, val). key is used as entry ID. val is the string to be cached. Both key and val are strings. The max length of the key is 512 bytes. Future more, the combine length of key+val is limited by the configured value of entry-size size command in the python-policy.

The Python cache can be enabled per python-policy. Each python policy has its own cache memory which script in other python-policy cannot access. This also implies that the key of a cached entry in different a python policy could overlap.

The user can also specify the max number cache entry per python policy the command max-entries command. System has a global limit for python cache memory of 256MB.

The cached entries could be made persistent by saving it to CF card. This can be enabled with the persistence command in the Python policy.

The system also supports syncing the python cache across chassis with MCS. This can be configured per python policy with the mcs-peer command in the python policy.

Each cached entry has a remaining lifetime. If it decreases over time, the system removes the cached entry if its remaining lifetime is 0. The remaining lifetime can be changed using a system- provided API. The initial lifetime of a newly created cache entry is 600 seconds. Python cache is supported only with CPM-based Python policies.

The following are the Python cache APIs in a module alc.cache:

• alc.cache.save(val, key)

  Saves the val identified by the key into the cache. If there is an existing cache entry with same key, then it is overwritten with the new val. An exception is raised if the save failed (for example, because the maximum number of entries is exceeded).

• alc.cache.retrieve(key)

  Returns the stored entry’s val identified by the key. A KeyError exception is raised if the specified entry does not exist.

• alc.cache.clear(key)

  Removes the cached entry identified by the key. Raise KeyError exception if the specified entry does not exist.

• cache.get_lifetime(key)

  The system returns a integer as seconds of remaining lifetime of the specified entry. It returns none if the specified entry does not exist. An exception is raised for any other error.

• cache.set_lifetime(key,new_lifetime)

  The new_lifetime value is an integer. The system sets the remaining lifetime of the specified entry to the number of seconds of the new_lifetime. An exception is raised for any error including specified entry does not exist. If the new_lifetime>=max_lifetime(configurable using the max-entry-life command in the python policy), then the system sets the actual lifetime to the max_lifetime.

The following is a list of places that a Python policy could be applied:

• Under capture SAP

  Apply to the DHCPv4/v6 packets sent/received on the capture SAP

• Under group-interface

  Apply to DHCPv4/v6 packets sent/received on the group-interface

• Under subscriber-interface

  Apply to DHCPv4 packets on the retail subscriber interface

• In the radius-server-policy

  Apply to the RADIUS packets sent, received to, or from the RADIUS servers configured in the radius-server-policy

• In the radius-proxy-server

  Apply to the RADIUS packets on the client side of proxy

• In the diameter-peer-policy

  Apply to the Diameter packets sent or received on the Diameter peers configured in the policy

To protect the Python script from unintended changes, the SR OS supports a new Python script file format:SRPY. SRPY includes a key based hash (HMAC) of the original script content. When the system loads a script with SRPY format, a hash is computed by using a configured key and script content. The result hash is compared to the embedded hash. If it is the same, then this script is considered valid. Otherwise, the system aborts with a warning message.

Users can configure protection hmac-sha256 key key within a Python script. To mandate, all configured scripts must be in SRPY format.

The system provides a tools command (tools perform python-script protect) to convert a Python script into SRPY format.

There are also running time limitations for Python scripts to prevent DoS attacks:

• Centralized:

  • Initial run: 100 ms

  • Subsequent run: 10ms

• Distributed:

  • Initial run: 10 ms

  • Subsequent run: 1ms