The following are the Python variables and APIs related to DTC:
Subscriber Host Identification
alc.dtc.derivedId
A read or write (from the Python perspective) string to store the LUDB lookup key for subscriber host identification. This key is derived from the contents of the packet. This string is used as a match criteria in LUDB. The derived-id can only be used when the lookup is performed in ESM. If the LUDB is attached to the local DHCP server, then the lookup based on the derived-id cannot be performed as the DHCP server has no means to derive such an ID from the DHCP message.
Caching Any Data During the Lifetime of a Transaction
alc.dtc.store(key,value)
The operator can store any data needed in one or more entries. The key can be any arbitrary string (printable ASCII characters), up to 32 bytes. The value part is ‛unlimited’ (memory permitting) in size.
alc.dtc.retrieve(key)
Retrieve data from the DTC. The key must be an existing key, which is a string consisting of printable ASCII characters, up to 32 bytes.
For example, this can be used to cache the DHCP options that the client inserts but the server does not echo back. Those options can still be retrieved in 7750 SR and 7450 ESS by cache in case that their presence is needed for any reason.
The lifespan of the cached data is tied to a DHCP transaction (a pair or corresponding DHCP messages flowing in opposite direction).
ESM Related Parameters (ESM strings, routing context)
DTC provides an API to supply a subset of configuration parameters that can otherwise come from RADIUS and LUDB and are used by the ESM code to setup the subscriber host.
DTC parameters as defined below should not be considered as DHCP options that can be blindly returned to the DHCP client, but instead they should be considered as real configuration settings. For example, the lease-time option is used in LUDB to enforce the lease time for the client. As such, the ESM keeps state of the lease-time. The following parameters can be used to setup a subscriber host:
alc.dtc.setESM (key-from-below, value)
Store data that is used by ESM. This data is write-only.
The keys are predefined (only these can be used) and are described in Table: ESM-related Python variables . These keys are read-only static variables.
The LUDB column indicates the configuration option under the config>subscr-mgmt>loc-user-db>ipoe>host context in LUDB.
| DTC variable | Type | LUDB | RADIUS attribute | Comment |
|---|---|---|---|---|
alc.dtc.subIdent |
string |
identification-strings >subscriber-id |
Alc-Subsc-ID-Str |
— |
alc.dtc.subProfileString |
string |
identification-strings >sub-profile-string |
Alc-Subsc-Prof-Str |
— |
alc.dtc.slaProfileString |
string |
identification-strings >sla-profile-string |
Alc-SLA-Prof-Str |
— |
alc.dtc.spiSharingGroupId |
integer |
identification-strings >spi-sharing-group-id |
Alc-SPI-Sharing-Id |
— |
alc.dtc.ancpString |
string |
identification-strings >ancp-string |
Alc-ANCP-Str |
— |
alc.dtc.appProfileString |
string |
identification-strings >app-profile-string |
Alc-App-Prof-Str |
— |
alc.dtc.intDestId |
string |
identification-strings >inter-dest-id |
Alc-Int-Dest-Id-Str |
— |
alc.dtc.catMapString |
string |
identification-strings >category-map-name |
Alc-Credit-Control-CategoryMap |
— |
alc.dtc.ipAddress |
string |
address |
Framed-IPAddress |
— |
alc.dtc.dhcp4DefaultGateway |
string |
options>default-router |
Alc-Default-Router |
— |
alc.dtc.subnetMask |
string |
address |
Framed-IPNetmask |
— |
alc.dtc.ipv4LeaseTime |
integer |
options>lease-time |
Alc-Lease-Time |
— |
alc.dtc.ipv4PrimDns |
string |
options>dns-server |
Alc-Primary-Dns Client-DNS-Pri |
— |
alc.dtc.ipv4SecDns |
string |
— |
Alc-Secondary-Dns Client-DNS-Sec |
— |
alc.dtc.primNbns |
string |
options>netbios-name-server |
Alc-Primary-Nbns RB-Client-NBNSPri |
|
alc.dtc.secNbns |
string |
— |
Alc-Secondary-Nbns RB-Client-NBNSSec |
— |
alc.dtc.msapGroupInterface |
string |
msap-defaults>group-interface |
Alc-MSAP-Interface |
— |
alc.dtc.msapPolicy |
string, integer |
msap-defaults>policy |
Alc-MSAP-Policy |
— |
alc.dtc.msapServiceId |
string, integer |
msap-defaults>service |
Alc-MSAP-Serv-Id |
— |
alc.dtc.retailServiceId |
string |
Retail-service-id |
Alc-Retail-Serv-Id |
— |
alc.dtc.ipv6Address |
string |
ipv6-address |
Alc-Ipv6-Address |
— |
alc.dtc.ipv6DelegatedPrefix |
string |
ipv6-delegated-prefix |
Delegated-IPv6-Prefix |
— |
alc.dtc.ipv6SlaacPrefix |
string |
ipv6-slaac-prefix |
Framed-IPv6-Prefix |
— |
alc.dtc.ipv6WanPool |
string |
ipv6-wan-address-pool |
Framed-IPv6-Pool |
— |
alc.dtc.ipv6PrefixPool |
string |
ipv6-delegated-prefix-pool |
Alc-Delegated- IPv6-Pool |
— |
alc.dtc.ipv6DelegatedPrefixLength |
integer |
ipv6-delegated-prefix-len |
Alc-Delegated-IPv6-Prefix-Length |
— |
alc.dtc.accountingPolicy |
string |
acct-policy |
— |
— |
alc.dtc.dhcpv4GIAddr |
string |
gi-address |
— |
— |
alc.dtc.dhcv4ServerAddress |
string |
server |
— |
— |
alc.dtc.dhcp4SrcAddr |
string |
— |
— |
— |
alc.dtc.dhcp4Pool |
string |
address>pool |
Framed-Pool Ip-Address-Pool-Name |
prim | sec (‟|” – delimiter) |
alc.dtc.linkAddress |
string |
link-address |
— |
— |
alc.dtc.dhcp6SrcAddr |
string |
— |
— |
— |
alc.dtc.dhcv6ServerAddr |
string |
server6 |
— |
— |
alc.dtc.setDhcpv6LinkAddr |
string |
link-address |
— |
This API applies only to regular numbered or unnumbered IPv6 interfaces (no ESM) |
alc.dtc.setDhcpv6ServerAddr |
string |
server6 |
— |
This API applies only to regular numbered or unnumbered IPv6 interfaces (no ESM) |
alc.dtc.ipv6PrimDns |
string |
options6>dns-server |
Alc-Ipv6-Primary-Dns |
— |
alc.dtc.ipv6SecDns |
string |
— |
Alc-Ipv6-Secondary-Dns |
— |
alc.dtc.dhcpv6PreferredLifetime |
integer |
ipv6-lease-times>preferred-lifetime |
Alc-v6-Preferred-Lifetime |
— |
alc.dtc.dhcpv6RebindTimer |
integer |
ipv6-lease-times>rebind-timer |
Alc-Dhcp6-Rebind-Time |
— |
alc.dtc.dhcpv6RenewTimer |
integer |
ipv6-lease-times>renew-timer |
Alc-Dhcp6-Renew-Time |
— |
alc.dtc.dhcpv6ValidLifetime |
integer |
ipv6-lease-times>valid-lifetime |
Alc-v6-Valid-Lifetime |
— |
For example, an IP address is assigned to a DTC variable as a string:
alc.dtc.ipAddress = 192.168.0.10
This is performed through the following ALU API: alc.dtc.setESM(alc.dtc.ipAddress, 192.168.0.10). The DTC logic then parses this variable and converts it into appropriate format for consumption by ESM code.
The values defined above are the ones that are mostly defined in the LUDB. Main use, however, is assigning ESM strings for the subscriber host instantiation phase during the processing of DHCP ACK/Reply messages. Consequently, the Python script needs to be run only on DHCP Request messages (no need to run it on Discoveries for ESM string assignment, unless the LUDB derived ID is also needed).
DHCP options that are blindly returned to the DHCP client without the ESM code being aware of them cannot be configured with DTC. These options should be configured with RADIUS (Alc-ToCLient-Dhcp-Options IPv4 only) or they can be inserted directly into DHCP messages with Python (bypassing DTC).
Other possible uses for DTC variables are:
Assigning routing context information with Python (service-id, msap, msap-policy, retail service-id, and so on). For example, AN can insert specific hints in various DHCP options that would suggest (by Python) the service context to place the subscriber host.
IP address assignment by Python (DTC). This would address the DTC-to-DHCP-Proxy case where Python script is invoked on DHCP Discovery/Solicit. For example:
Discover arrives.
Python generates an IP address, for example based on some DHCP options.
The script stores the IP address by using alc.dtc.setEsm(alc.dtc.ipAddress, 10.0.1.2).
After the script is finished, ESM starts processing the packet (no LUDB/RADIUS authentication configured).
ESM finds the IP address already in DTC and decides to handle all DHCP and execute proxy function instead of relay.
ESM sends an offer with the address that Python generated.
DHCP options should be provided as well in this case (lease-times, and so on).
The same applies to the DHCP Request.