The DHCP and IPoE Subscriber Management feature supports the following functionalities:

DHCP Server

The cnBNG CP implementation supports the DHCPv4 server mode. The DHCP server FSM handles the DHCP packets from client, IP allocation, and IP lease management.

The FSM handles the following Rx control packets:

• Discover

• Request (DORA request and renew request)

• Decline

• Inform

• Release

The DHCP server FSM sends the following control packets to the client based on the FSM states and events:

• Offer

• Ack (DORA Ack, Renew Ack and Inform Ack)

• Noack

The DHCP server implementation associates a DHCP profile to a group of subscribers. This server implementation supports the following functionalities:

• IP address allocation for the client from the configured pool in the DHCP profile.

• IP address lease allocation based on DHCP profile configuration.

• Passing Host configurations to the client using the following configurable DHCP options in the DHCP profile:

  • IP subnet mask (Option 1)

  • Boot filename (Option 67)

  • Domain name (Option 15)

  • NetBIOS node type (Option 46)

  • NetBIOS name server (Option 44)

  • Domain name server (Option 6)

  • Default router (Option 3)

  • Time server (Option 4)

Processing Option 82

cnBNG supports Option 82, which is the relay agent information option to figure out the sub-options. The various sub-options that the DHCP processes are:

• Circuit ID (Sub option 1)

• Remote ID (Sub option 2)

The circuit ID and remote ID field is passed to the Session Manager during session start trigger and the same is used for north-bound interactions.

DHCPv4 RADIUS Proxy

The cnBNG CP supports DHCP IPv4 RADIUS proxy for RADIUS-based authorization of DHCP leases. This is a RADIUS-based address assignment mechanism in which a DHCP server authorizes remote clients and allocates IP addresses, based on replies from a RADIUS server.

These are the steps involved in the address assignment mechanism:

• The DHCP server sends the DHCP client information to the RADIUS server.

• The RADIUS server returns all required information, primarily IPV4 address, to the DHCP server in the form of RADIUS attributes. The subnet mask is derived from the CP based on the static pool configuration. The IPv4 address sent from the RADIUS must be part of the static pool associated to the UP.

• The DHCP server translates the RADIUS attributes into DHCP options and sends this information back in a DHCP Offer message to the DHCP client.

If the IETF attribute, such as Framed-IP-Address is received from the RADIUS server, and if it is present in the user profile, then this attribute is used instead of allocating the IP address from the configured pool. The basic attributes that can come from the RADIUS server that are relevant for DHCP server options are:

• Framed IPv4 Address

• IPv4 Subnet Mask (derived in the CP from the static pool configuration)

• IPv4 Default gateway (derived in the CP from the static pool configuration)

Apart from these attributes, the dhcp-class name and address pool name attribute also can come from RADIUS. If the RADIUS sets the address pool name, then it uses this for IP allocation instead of the pool that is specified as part of the DHCP profile.

If the RADIUS server sends the dhcp-class attribute to the DHCP server, then that attribute value is used to decide other configuration parameters in the reply that is to be sent to the DHCP client. For example, if the DHCPv4 server profile has both Class A and Class B in it, and if RADIUS server sends a reply to the DHCP server with the class name as 'B', then Class B is used to send the options back to the DHCP client. Classes can be defined under DHCP profile. The parameters and options that can be configured under DHCP profile can be configured under class also.

Additional RADIUS server attributes are allowed, but not mandatory. If a RADIUS server user profile contains a required attribute that is empty and is not available via configuration as well, the DHCP server does not generate the DHCP options.

DHCPv6 Local Server for IPv6 Subscribers

The DHCPv6 server assigns IPv6 address and prefix and other configuration attributes (such as domain name, the domain name server address and SIP servers and so on) to requesting clients. On receiving a valid request, the server assigns the client IPv6 address or prefix, a lease for the assigned IPv6 address or prefix and other requested configuration parameters. The DHCP server FSM is implemented to handle the address allocation and lease management. The FSM would handle the following control packets from the client:

• Solicit

• Request

• Renew

• Rebind

• Decline

• Information-Request

• Release

The DHCPv6 server FSM sends the following control packets to the client based on the FSM states and events:

• Advertisement

• Reply (SARR Reply, Release Reply, Renew Reply, Rebind Reply and Information request Reply)

• Relay-Reply

The DHCPv6 server implementation associates a DHCPv6 profile to a group of subscribers. The server implementation caters to the following functionalities:

• IANA address and IAPD address allocation for the client from configured pool in DHCPv6 profile.

• IANA and IAPD address lease allocation based on DHCPv6 profile configuration.

• Passing Host configurations to client using below configurable DHCP options in DHCP profile

  • AFTR support (Option 64)

  • Preference option (Option 7)

  • Domain list (Option 24)

  • DNS server IPv6 address (Option 23)

The DHCPv6 server sends the following options to the Policy plane:

• interface-id (DHCP Option 18)

• remote-id (DHCP Option 37)

• vendor-class (DHCP Option 16)

• user-class (DHCP Option 15)

• client-id(DHCP Options 1)

DHCPv6 Server - Prefix Delegation

The DHCPv6 Prefix Delegation feature enables the DHCPv6 server to hand out network address prefixes to the requesting clients. The clients use these network prefixes to assign /128 addresses to the hosts on their network. The RFC-3633 and RFC-3769 is supported for prefix delegation. The DHCPv6 Prefix Delegation feature is enabled by default for cnBNG DHCPv6 server. No other configuration is required to enable the prefix delegation. The DHCPv6 option OPTION_IA_PD (25) and OPTION_IAPREFIX (26) support to meet the prefix delegation requirement.

Note	Only one delegated prefix per subscriber and client is supported. Only one OPTION_IAPREFIX is supported under one OPTION_IA_PD (25).

The cnBNG allocates addresses from the prefix pool configured under the DHCP profile.

DHCPv6 Server - Address Assignment

The DHCPv6 Address Assignment feature enables the DHCPv6 server to hand out /128 addresses to the clients. The cnBNG DHCPv6 server implementation supports the DHCPv6 OPTION_IA_NA(3) and OPTION IAADDR(5) to enable address assignment to the client.

Note	Only one delegated prefix per subscriber and client is supported. Only one OPTION_IAPREFIX is supported under one OPTION_IA_PD (25).

The cnBNG allocates addresses from the prefix pool configured under the DHCP profile.

Prefix and Address Pool Support for IPv6

The cnBNG supports the configuring of the DHCPv6 address and prefix pool and associating it to the DHCPv4 and DHCPv6 server profiles. The address and prefix ranges is under the pool. cnBNG also supports downloading of the address and prefix pool name via the user profile on a per subscriber basis. The pool name downloaded via user profile is given priority over the pool name association via the DHCPv6 profile.

DHCPv6 Server with RADIUS-based Address Assignment

The cnBNG supports RADIUS-based address assignment, that is, the IANA address is downloaded as part of the user profile and is allocated to the client. Address from the user profile is given priority over the local configuration.

DHCPv6 Server with RADIUS-based Prefix Delegation

The cnBNG supports RADIUS-based prefix assignment, that is, the IAPD address is downloaded as part of the user profile and is allocated to the client. The delegated prefix from the user profile is given priority over the local configuration.

DHCPv6-provided IPv6 address of DNS server for IPv6 Subscribers

The cnBNG CP DHCPv6 server implementation supports the provision of DNS server information to clients via the DNS option (23). It supports a configuration of up to 8 DNS server ipv6 addressees via the DHCPv6 profile. The DHCPv6 server information is downloaded via the user profile on a per subscriber basis. The per subscriber DNS information in the user profile is given priority over the profile configuration.

DHCPv4 DHCPv6 Lease Timeout

The cnBNG CP provides the configuration to set the lease value under the DHCPv4 and DHCPv6 profile. This configuration determines the lease for the IP addresses allocated to the clients.

For DHCPv4 clients, the lease is set in the address time (T) option (option 51). By default, the renewal time is set as (½) * T [option 58] and rebinding time is set as (7/8) * T [option 59]. For DHCPv6 client, the lease is populated in the IA address and IA prefix option for the respective address types. By default, preferred time is set as 0.5 * T and valid time T2 is set as 0.8 * T. By default, renewal time (T1) is set as 0.5 * T and rebinding time T2 is set as 0.8 * T in OPTION_IA_PD.

The cnBNG CP tracks the lease time allocated to the clients. Ideally the client should renew (Renew request) the lease at T1 to extend the lease. If renew is failing, the client uses the rebind (broadcast request message for DHCPv4 and rebind message for DHCPv6). If the cnBNG CP does not receive the lease renewal request from the client, the lease times out after T and the corresponding address is released to the pool and removed from the client session. This can lead to an update or disconnect to the Session Manager based on the other address states. The lease timeout is applicable to both IPv4 and IPv6 addresses.

IPv6 IPoE Sessions

The IPv6 subscribers run the IPv6 from the CPE device to the BNG router and are created using the DHCPv6 protocol. The IPv6 subscribers natively run IPv6 on the CPE device and are connected to the router via a Layer-2 network or through Layer-2 aggregation.

The IPv6 subscribers are supported when they are directly connect to the cnBNG UP or via a Layer-2 aggregator. The cnBNG CP DHCPv6 server treats only DHCPv6 SOLICIT message from the subscriber / client as FSOL (First Sign Of Life) packet in case of IPoE and initiates the subscriber session creation.

Note	Routed subscribers are not supported.

Dual Stack IPv6/IPv4 over IPoE

The cnBNG CP supports dual-stack IPoE subscribers, that is, both IPv4 and IPv6 address allocation for the same subscriber. In this release, cnBNG supports up to one IPv4 address, one IANA address, and one IAPD address.

Subscriber Termination over Non-default VRF

The cnBNG CP DHCPv4 and DHCPv6 servers are VRF aware. The DHCPv4 and DHCPv6 servers support the access interface in either default VRF or non-default VRF. The following table shows the VRF combination supported by DHCPv6 server.

DHCPv4 Raw Option Support

The cnBNG DHCP Profile configuration enables the operator to configure specific DHCPv4 options, under the DHCPv4 profile. The option value can range from 1 to 255. The option value can be either an ascii string or a hexadecimal string.

DHCPv4 and DHCPv6 Class Support

The cnBNG DHCP Profile configuration enables the operator to configure classes of DHCP options and to selectively associate them during the session setup. The DHCP Options class are selected based on certain matching DHCP options received from access network against the configured class key parameters. The DHCP Options class can also be selected based on the class name received from Policy plane. The priority is always given to the DHCP class name that the Policy plane provides. However, if the Policy plane does not provide a class name, then class selection depends on the operator-configured key parameters. The operator can configure multiple DHCP option classes for DHCPv4 and DHCPv6 separately.

The DHCP Profile consist of profile elements. Each of the DHCPv4 and DHCPv6 profiles contain the ‘default’ DHCP options list and zero or more classes of DHCP options of corresponding DHCP version.

The DHCPv4 and DHCPv6 Options Class contains a list of DHCP options and the “Match-Info” holds the information about the keys to be matched to select that class. The operator can also specify under Match-Info” the class selection that should match ‘any’ or ‘all’ the key parameters of that class.

If the DHCP Option class does not match an ongoing session or any requested DHCP Options is not found in the selected class, then the requested option is selected from the ‘default’ DHCP Options of that profile.

This section provides a brief of how the DHCP and IPoE Subscriber Management feature works.

Use the following commands to configure the IPv4 DHCP server profile.

configure
   profile dhcp  dhcp_profile_name        
   ipv4         
   server { boot-filename boot_filename } | { dns-servers dns_server } | { domain-name  domain_name} |
   { netbios-name-server netbios_name_server } | { netbios-node-type { broadcast-node | hexadecimal | hybrid-node | mixed-node | peer-to-peer-node } |
   { next-server ipv4_address } | { ntp-servers ipv4_address } | { pool-name ipam_pool_name} |
   { option-codes option_codes_range { ascii-string  value | force insert { true | false } | hex-string value|
   { ip-address ip_address  } | { lease { days  value| hoursvalue| minutesvalue}
   exit
exit 

NOTES:

• profile dhcp dhcp_profile_name : Specifies the DHCP profile name.

• ipv4 : Enters IPv4 configuration mode.

• server { boot-filename boot_filename } | { dns-servers dns_server } | { domain-name domain_name} |{ netbios-name-server netbios_name_server } | { netbios-node-type { broadcast-node | hexadecimal | hybrid-node | mixed-node | peer-to-peer-node } |{ next-server ipv4_address } | { ntp-servers ipv4_address } | { pool-nameipam_pool_name} |{ option-codes option_codes_range { ascii-string value | force insert { true | false } | hex-stringvalue|{ ip-addressip_address } | { lease { days value| hoursvalue| minutesvalue} : Specifies the IPv4 server details.

  • boot-filenameboot_filename : Configures the boot file.

  • dns-serversdns_server : Specifies the Domain Name System (DNS) IPv4 servers available to a DHCP for an IPv4 client.

  • domain-namedomain_name : Specifies the domain name for the IPv4 client.

  • netbios-name-servernetbios_name_server : Configures the NetBIOS name servers.

  • netbios-node-type { broadcast-node | hexadecimal | hybrid-node | mixed-node | peer-to-peer-node } : Configures the NetBIOS node as a broadcast, hexadecimal, hybrid, mixed, or peer-to-peer node. The valid values for each of these nodes are:

    • broadcast-node: 0x1 B-node

    • hexadecimal: Operator provided custom 1 byte hex value

    • hybrid-node: 0x8 H-node

    • mixed-node: 0x4 M-node

    • peer-to-peer-node: 0x2 P-node

  • next-serveripv4_address : Specifies the TFTP-server IP address for the client to use.

  • pool-nameipam_pool_name : Specifies the IP Address Management (IPAM) assigned pool name.

  • option-codes option_codes_range { ascii-string value | force insert { true | false } | hex-string value | ip-address ip_address } : Specifies the values for the ASCII string of length 128, force insert, hex string of length 128, or IP address (IPv4 IP address).

  • lease { days value | hours value | minutes value } : Specifies the lease time duration in the number of days, hours, and minutes. The number of lease days supported is from 0 to 365. The number of leave hours supported ranges from 0 to 23 and minutes from 0 to 59.

Use the following commands to configure the IPv4 DHCP class.

configure
   profile dhcp dhcp_profile_name        
   ipv4         
   classdhcp_class_name
   matches { match { dhcpv4-circuit-id { ascii  value | hex value } | dhcpv4-remote-id { ascii  value | 
    hex value  } | dhcpv4-vendor-class { ascii  value | hex  value } | dhcpv4-user-class { ascii  value | 
    hex value } } | match-type { all match_key_value| any match_key_value} }  
   end 

NOTES:

• profile dhcp dhcp_profile_name : Specifies the DHCP profile name.

• ipv4 : Enters IPv4 configuration mode.

• class dhcp_class_name : Creates a proxy profile class (DHCP), which can be used to enter the proxy profile class sub-configuration mode.

• matches { match { dhcpv4-circuit-id { ascii value | hex value } | dhcpv4-remote-id { ascii value | hex value } | dhcpv4-vendor-class { ascii value | hex value } | dhcpv4-user-class { ascii value | hex value } } | match-type { all match_key_value| any match_key_value} } : Specifies the list of match keys and values. The match values supported are DHCPv4 circuit ID, DHCPv4 remote ID, DHCPv4 vendor class, and DHCPv4 user class. Each of the values must specify either an ASCII or hexadecimal value.

  match-type { all | any } : Specifies if the match value should apply to any of the specified keys or to all the keys.

Use the following commands to configure the IPv6 DHCP server profile.

configure
   profile dhcp  dhcp_profile_name        
      ipv6
         server { aftr-name value | dns-servers dns_server
         | domain-name domain_name| iana-pool-name ipam_pool_name
         | iapd-pool-name  ipam_pool_name| lease { days  value | hours  value | minutes  value } 
         | preference value } 

NOTES:

• profile dhcp dhcp_profile_name : Specifies the DHCP profile name.

• ipv6 : Enters IPv6 configuration mode.

• server { aftr-name value | dns-servers dns_server| domain-name domain_name| iana-pool-name ipam_pool_name| iapd-pool-name ipam_pool_name| lease { days value | hours value | minutes value } | preference value } : Specifies the IPv6 server details.

  • aftr-name value : Specifies the FQDN string.

  • dns-servers dns_server : Specifies the Domain Name System (DNS) IPv4 servers available to a DHCP for an IPv4 client.

  • domain-name domain_name : Specifies the domain name for the IPv4 client.

  • iana-pool-name ipam_pool_name : Specifies the Internet Assigned Numbers Authority (IANA) pool name.

  • iapd-pool-name ipam_pool_name : Specifies the Identity Association for Prefix Delegation (IAPD) pool name.

  • lease { days value | hours value | minutes value } : Specifies the lease time duration in the number of days, hours, and minutes. The number of lease days supported is from 0 to 365. The number of leave hours supported ranges from 0 to 23 and minutes from 0 to 59.

  • preference value : Specifies the DHCP server preference. The preference value ranges from 1 to 255.

Use the following commands to configure the IPv6 DHCP class.

configure
   profile dhcp  dhcp_profile_name       
      ipv6
        class  dhcp_class_name
         server { aftr-name value| dns-servers dns_server| domain-name domain_name|
         iana-pool-name ipam_pool_name| iapd-pool-name ipam_pool_name|lease { days  value|
         hours  value | minutes  value } preference  value   
         end 

NOTES:

• profile dhcp dhcp_profile_name : Specifies the DHCP profile name.

• ipv6 : Enters IPv6 configuration mode.

• class dhcp_class_name : Creates a proxy profile class (DHCP), which can be used to enter the proxy profile class sub-configuration mode.

• server { aftr-name value | dns-servers dns_server| domain-name domain_name| iana-pool-name ipam_pool_name| iapd-pool-name ipam_pool_name| lease { days value | hours value | minutes value } | preference value } : Specifies the IPv6 class server details.

  • aftr-name value : Specifies the FQDN string.

  • dns-servers dns_server : Specifies the Domain Name System (DNS) IPv6 servers available to a DHCP for an IPv6client.

  • domain-name domain_name : Specifies the domain name for the IPv6 client.

  • iana-pool-name ipam_pool_name : Specifies the Internet Assigned Numbers Authority (IANA) pool name.

  • iapd-pool-name ipam_pool_name : Specifies the Identity Association for Prefix Delegation (IAPD) pool name.

  • lease { days value | hours value | minutes value } : Specifies the lease time duration in the number of days, hours, and minutes. The number of lease days supported is from 0 to 365. The number of leave hours supported ranges from 0 to 23 and minutes from 0 to 59.

  • preference value : Specifies the DHCP server preference. The preference value ranges from 1 to 255.