DTC: DHCP Transaction Cache
The system provides a Python object alc.dtc that allows data to be cached temporarily between DHCP packets.
A DHCP transaction cache (DTC) is a short-lived cache during a DHCPv4/v6 transaction. The cache can be used to store user-chosen information or return ESM attributes. The DTC’s lifetime is only during a single DHCP transaction (for example, only between discovery and offer, or request and 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 can only be accessed by the Python script running in the same DHCP transaction.
The alc.dtc object
Attributes
- alc.dtc.derivedId
The derivedId attribute is an attribute which can be set by a Python script and be used as a LUDB match criterion. The current value can be read from this attribute. A new value for the derivedId can be set by assigning a new value to this attribute.
The type of this attribute is str.
If the derivedId is not supported, a RuntimeException is raised when retrieving or setting this attribute.
If no derivedId has been set, None is returned. This behavior has changed with respect to the Python 2 implementation.
Methods
- alc.dtc.store(key, value, /)
Stores a value associated with a key.
- Parameters
str (key) – key to associate the value with
bytes (value) – value to cache
- Raises
RuntimeError – if the value cannot be stored.
- alc.dtc.retrieve(key, /)
Retrieves a previously stored value.
- Parameters
str (key) – key the value was associated with
- Raises
KeyError – if no value is associated with the specified key
- alc.dtc.setESM(key, value, /)
Sets an attribute on the current subscriber to the specified value.
- Parameters
int (key) – Integer representing which attribute to set. See Constants for an enumeration of all supported attributes.
value – value to set the attribute to
- Raises
KeyError if the key is not valid
- Raises
ValueError if the type of the value or the actual value is not valid for the specified key.
- alc.dtc.setDhcpv6LinkAddr(value, /)
Sets the DHCPv6 link-address.
- Parameters
bytes (value) – the bytes-representation of an IPv6-address to set as link-address
- alc.dtc.setDhcpv6ServerAddr(value, /)
Sets the DHCPv6 server-address.
- Parameters
bytes (value) – the bytes-representation of an IPv6-address to set as server-address
Constants
The alc.dtc object provides a list of constants which can be used as a key parameter to choose which attribute to set.
The following table lists all attributes and the supported object-types for the corresponding value.
Attribute |
Types |
|---|---|
subIdent |
str |
subProfileString |
str |
slaProfileString |
str |
ancpString |
str |
appProfileString |
str |
intDestId |
str |
catMapString |
str |
msapGroupInterface |
str |
msapPolicy |
str |
msapServiceId |
str | int |
retailServiceId |
str | int |
ipAddress |
str |
ipv6Address |
str |
ipv6DelegatedPrefix |
str |
ipv6DelegatedPrefixLength |
int |
ipv6SlaacPrefix |
str |
ipv6WanPool |
str |
ipv6PrefixPool |
str |
accountingPolicy |
str |
dhcpv4ServerAddr |
str |
dhcpv4GIAddr |
str |
dhcpv4SrcAddr |
str |
dhcpv4Pool |
str |
dhcpv6LinkAddr |
str |
dhcpv6ServerAddr |
str |
dhcpv6SrcAddr |
str |
defGw |
str |
subnetMask |
str |
ipv4LeaseTime |
int |
ipv4PrimDns |
str |
ipv4SecDns |
str |
primNbns |
str |
secNbns |
str |
ipv6PrimDns |
str |
ipv6SecDns |
str |
dhcpv6PreferredLifetime |
int |
dhcpv6RebindTimer |
int |
dhcpv6RenewTimer |
int |
dhcpv6ValidLifetime |
int |
spiSharingGroupId |
int |
Breaking changes
Derived Id
Warning
With Python 2 API, reading a derived-id which is not yet set raises a RuntimeError. With Python 3, the value None is returned.