RADIUS Extensions for Port Set Configuration and Reporting

In a broadband network, customer information is usually stored on a RADIUS server and at the time when a user initiates an IP connection request, the RADIUS server will populate the user's configuration information to the Network Access Server (NAS), which is usually co-located with the Border Network Gateway (BNG), after the connection request is granted. The Carrier Grade NAT (CGN) function may also implemented on the BNG, and therefore CGN TCP/UDP port (or ICMP identifier) mapping behavior can be configured on the RADIUS server as part of the user profile, and populated to the NAS in the same manner. In addition, during the operation, the CGN can also convey port/identifier mapping behavior specific to a user to the RADIUS server, as part of the normal RADIUS accounting process. The CGN device that communicates with a RADIUS server using RADIUS extensions defined in this document may perform NAT44 , NAT64 , or Dual-Stack Lite AFTR function. For the CGN example, when IP packets traverse a CGN, it would perform TCP/UDP source port mapping or ICMP identifier mapping as required. A TCP/ UDP source port or ICMP identifier, along with source IP address, destination IP address, destination port and protocol identifier if applicable, uniquely identify a session. Since the number space of TCP/UDP ports and ICMP identifiers in CGN's external realm is shared among multiple users assigned with the same IPv4 address, the total number of a user's simultaneous IP sessions is likely to subject to port quota. The attributes defined in this document may also be used to report the assigned port set in some deployment such as Provider Wi-Fi . For example, a visiting host can be managed by a CPE which will need to report the assigned port set to the service platform. This is required for identification purposes (see WT-146 for example). This document proposes three new RADIUS attributes as RADIUS protocol's extensions, and they are used for separate purposes as follows: A session limit is configured on a RADIUS server based on service agreement with a subscriber, and this parameter imposes the limit of total number of TCP/UDP ports and/or ICMP identifiers that the subscriber can use. Alternately, a separate session limit may be configured to limit the number of TCP ports, UDP ports, or the sum of the two, and ICMP identifiers, respectively, that the user can use. The session limit is carried by a new RADIUS attribute Port-Session-Limit, which is included in a RADIUS Access-Accept message sent by the RADIUS server to port-based device. This new RADIUS attribute can also be included in a RADIUS CoA message sent by the RADIUS server to the port-based device in order to change the session limit previously configured. A port-based device may allocate or de-allocate a set of TCP/UDP ports or ICMP identifiers for a specific subscriber. When it does so, the associated session range along with the shared IPv4 address can be conveyed to the RADIUS server as part of the accounting process. These parameters are carried by a new RADIUS attribute Port-Session-Range, which is included in a RADIUS Accounting- Request message sent by the port-based device to the RADIUS server. A user may require the port-based device to perform port forwarding function, i.e., a port mapping is pre-configured on the port-based so that inbound IP packets sent by some applications from the port-based external realm can pass through that device and reach the user. The port mapping information includes the port-based device internal port, external port, and may also include the associated internal IPv4 or IPv6 address, and is carried by a new RADIUS attribute Port- Forwarding-Map, which is included in a RADIUS Access-Accept message sent by the RADIUS server to the port-based device. This new RADIUS attribute can also be included in a RADIUS CoA message sent by the RADIUS server to the port-based device in order to change the forwarding port mapping previously configured.

Some terms that are used in this document are listed as follows: Session Limit - This is the maximum number of TCP ports, or UDP ports, or the total of the two, or ICMP identifiers, or the total of the three, that a device supporting port ranges can use when performing mapping on TCP/ UDP ports or ICMP identifiers for a specific user. Session Range - This specifies a set of TCP/UDP port numbers or ICMP identifiers, indicated by the port/identifier with the smallest numerical number and the port/identifier with the largest numerical number, inclusively. Internal IP Address - The IP address that is used as a source IP address in an outbound IP packet sent toward a device supporting port ranges in the internal realm. In IPv4 case, it is typically a private address . External IP Address - The IP address that is used as a source IP address in an outbound IP packet after traversing a device supporting port ranges in the external realm. In IPv4 case, it is typically a global and routable IP address. Internal Port - The internal port is a UDP or TCP port, or an ICMP identifier, which is allocated by a host or application behind a device supporting port ranges for an outbound IP packet in the internal realm. External Port - The external port is a UDP or TCP port, or an ICMP identifier, which is allocated by a device supporting port ranges upon receiving an outbound IP packet in the internal realm, and is used to replace the internal port that is allocated by a user or application. External realm - The networking segment where IPv4 public addresses are used in respective of the device supporting port ranges. Internal realm - The networking segment that is behind a device supporting port ranges and where IPv4 private addresses are used. Mapping - This term in this document associates with a device supporting port ranges for a relationship between an internal IP address, internal port and the protocol, and an external IP address, external port, and the protocol. Port-based device - A device that is capable of providing IP address and TCP/UDP port mapping services and in particular, with the granularity of one or more subsets within the 16-bit TCP/UDP port number range. A typical example of this device can be a CGN, CPE, Provider Wi-Fi Gateway, etc. Note the terms "internal IP address", "internal port", "internal realm", "external IP address", "external port", "external realm", and "mapping" and their semantics are the same as in , and .

[Discussion: should these attributes be allocated from the extended RADIUS attribute code space?] [Discussion: Should we define a dedicated attribute (port_set_policies) to configure the following policies: (1) enforce port randomization, (2) include/exclude the WKP in the port assignment, (3) preserve parity, (4) quota for explicit port mapping, (5) DSCP marking policy, (6) Port hold down timer, (7) port hold down pool, etc. Perhaps we don't need to cover all these parameters.]

This attribute is of type complex and specifies the limit of TCP ports, or UDP ports, or the sum of the two, or ICMP identifiers, or the sum of the three, which is configured on a device supporting port ranges corresponding to a specific subscriber. The Port-Session-Limit MAY appear in an Access-Accept packet, it MAY also appear in an Access-Request packet as a hint by the device supporting port ranges, which is co-allocated with the NAS, to the RADIUS server as a preference, although the server is not required to honor such a hint. The Port-Session-Limit MAY appear in an CoA-Request packet. The Port-Session-Limit MAY appear in an Accounting-Request packet. The Port-Session-Limit MUST NOT appear in any other RADIUS packets. The format of the Port-Session-Limit RADIUS attribute format is shown below. The fields are transmitted from left to right.

Type: TBA1 for Port-Session-Limit. Length: 5 octets. This field indicates the total length in octets of this attribute including the Type and the Length field. ST (Session Type): This one octet field contains an enumerated value that indicates the applicability of the Session Limit as follows: 0: The limit as specified is applied to each transport protocol (TCP/UDP) and ICMP Identifiers as a whole. 1: The limit as specified is applied to TCP and UDP ports. 2: The limit as specified is applied to TCP ports. 3: The limit as specified is applied to UDP ports. 4: The limit as specified is applied to ICMP Identifiers. 5-255: These values are undefined. Session Limit: This field contains the maximum number that is assigned to the transport sessions depending on the value in the Session Type (ST) field, that the specific user can use.

This attribute is of type complex and contains a range of numbers for TCP ports or UDP ports, or both, or for ICMP Identifiers, which has been allocated or de-allocated by a device supporting port ranges for a given subscriber, along with an external IPv4 address that is associated with any TCP/UDP port or ICMP identifier in the range. In some CGN deployment scenarios as described such as L2NAT , DS-Extra-Lite and Lightweight 4over6 , parameters at a customer premise such as MAC address, interface ID, VLAN ID, PPP session ID, IPv6 prefix, VRF ID, etc., may also be required to pass to the RADIUS server as part of the accounting record. The Port-Session-Range MAY appear in an Accounting-Request packet. The Port-Session-Range MUST NOT appear in any other RADIUS packets. The port range follows the encoding specified in ; as such both contiguous and non-contiguous port sets are supported. The format of the Port-Session-Range RADIUS attribute format is shown below. The fields are transmitted from left to right.

Type: TBA2 for Port-Session-Range. Length: 12 octets plus the length of optional field Local Session ID. This field indicates the total length in octets of this attribute including the Type and the Length field. ST (Session Type): This one octet field contains an enumerated value that indicates the semantics of the session range. The values follow the Session Type encoding defined in except that the following values are not valid in scope of this attribute: 0: The limit as specified is applied to the sum of TCP ports, UDP ports, and ICMP Identifiers as a whole. A-bit Flag: This field is set to 0 or 1, indicates that the session range has been allocated or de-allocated, respectively, by the device supporting port ranges. Reserved: This field MUST be set to zero by the sender and ignored by the receiver. Port Range Mask: The Port Range Mask indicates the position of the bits that are used to build the Port Range Value. By default, no PRM value is assigned. The 1 values in the Port Range Mask indicate by their position the significant bits of the Port Range Value. Refer to for more details. Port Range Value: The PRV indicates the value of the significant bits of the Port Mask. By default, no PRV is assigned. Refer to for more details. External IPv4 Address: This is an optional field. If present, this field contains the IPv4 address assigned to the associated subscriber to be used in the external realm. If set to 0/0, the allocation address policy is local to the device supporting port ranges. Local Session ID: This is an optional field and if presents, it contains a local session identifier at the customer premise, such as MAC address, interface ID, VLAN ID, PPP sessions ID, VRF ID, IPv6 address/prefix, etc. The length of this field equals to the total attribute length minus 12 octets. If this field is not present, the port range policies must be enforced to all subscribers using a local subscriber identifier.

This attribute is type of complex and contains a 16-bit Internal Port that identifies the source TCP/UDP port number of an IP packet sent by the user, or the destination port number of an IP packet destined to the user, and in both cases, the IP packet travels behind the NAT device. Also they contain a 16-bit Configured External Port that identifies the source TCP/UDP port number of an IP packet sent by the user, or the destination port number of an IP packet destined to the user, and in both cases, the IP packet travels outside of the NAT device. In addition, the attribute may contain a 32-bit IPv4 address or a 128-bit IPv6 address, respectively, as their respective NAT mappings internal IP address. Together, the port pair and IP address determine the port mapping rule for a specific IP flow that traverses a NAT device. The attribute MAY appear in an Access-Accept packet, and may also appear in an Accounting-Request packet. In either case, the attribute MUST NOT appear more than once in a single packet. The attribute MUST NOT appear in any other RADIUS packets. The format of the Port-Forwarding-Map RADIUS attribute format is shown below. The fields are transmitted from left to right.

Type: TBA3 for Port-Forwarding-Map. Length: This field indicates the total length in octets of this attribute including the Type and the Length field. Depending on the value of the AF field, the length could be 8, 12 or 24 octets. AF (Address Family): This one octet field contains a value that indicates address family of the internal IP address at the mapping as follows: 0: There is no internal address attached. 1: The internal address is an IPv4 address. 2: The internal address is an IPv6 address. 3-255: Unused. [Discussion: should we use IANA assigned protocol numbers here?] Reserved: This field is set to zero by the sender and ignored by the receiver. Internal Port: This field contains the internal port for the CGN mapping. Configured External Port: This field contains the external port for the CGN mapping. Internal IP Address: This field may or may not present, and when it does, contains the internal IPv4 or IPv6 address for the CGN mapping.

This section describes some applications and use cases to illustrate the use of the RADIUS port set attributes.

In a broadband network, customer information is usually stored on a RADIUS server, and the BNG hosts the NAS. The communication between the NAS and the RADIUS server is triggered by a subscriber when the user signs in to the Internet service, where either PPP or DHCP/DHCPv6 is used. When a user signs in, the NAS sends a RADIUS Access-Request message to the RADIUS server. The RADIUS server validates the request, and if the validation succeeds, it in turn sends back a RADIUS Access-Accept message. The Access-Accept message carries configuration information specific to that user, back to the NAS, where some of the information would pass on to the requesting user via PPP or DHCP/DHCPv6. A CGN function in a broadband network would most likely reside on a BNG. In that case, parameters for CGN port/identifier mapping behavior for users can be configured on the RADIUS server. When a user signs in to the Internet service, the associated parameters can be conveyed to the NAS, and proper configuration is accomplished on the CGN device for that user. Also, CGN operation status such as CGN port/identifier allocation and de-allocation for a specific user on the BNG can also be transmitted back to the RADIUS server for accounting purpose using the RADIUS protocol. RADIUS protocol has already been widely deployed in broadband networks to manage BNG, thus the functionality described in this specification introduces little overhead to the existing network operation. In the following sub-sections, we describe how to manage CGN behavior using RADIUS protocol, with required RADIUS extensions proposed in .

In the face of IPv4 address shortage, there are currently proposals to multiplex multiple subscribers' connections over a smaller number of shared IPv4 addresses, such as Carrier Grade NAT , Dual-Stack Lite , NAT64 , etc. As a result, a single IPv4 public address may be shared by hundreds or even thousands of subscribers. As indicated in , it is therefore necessary to impose limits on the total number of ports available to an individual subscriber to ensure that the shared resource, i.e., the IPv4 address remains available in some capacity to all the subscribers using it, and port limiting is also documented in as a requirement. There are two practical granularities to impose such a limit. One is to define a session limit that is imposed to the total number of TCP and UDP ports, plus the number of ICMP identifiers, for a specific subscriber. Alternatively, a session limit can be specified for the sum of TCP ports and UDP ports, or a separate session limit for TCP ports and UDP ports, respectively, and another session limit for ICMP identifiers. The per-subscriber based session limit(s) is configured on a RADIUS server, along with other user information such as credentials. The value of these session limit(s) is based on service agreement and its specification is out of the scope of this document. When a subscriber signs in to the Internet service successfully, the session limit(s) for the subscriber is passed to the BNG based NAS, where CGN also locates, using a new RADIUS attribute called Port-Session-Limit (defined in ), along with other configuration parameters. While some parameters are passed to the subscriber, the session limit(s) is recorded on the CGN device for imposing the usage of TCP/UDP ports and ICMP identifiers for that subscriber. illustrates how RADIUS protocol is used to configure the maximum number of TCP/UDP ports for a given subscriber on a NAT44 device.

| | | | | | |-----Access-Request -------->| | | | | |<----Access-Accept-----------| | | (Port-Session-Limit) | | | (for TCP/UDP ports) | |<---Service Granted ------| | | (other parameters) | | | | | | (NAT44 external port | | allocation and | | IPv4 address assignment) | | | | ]]> The session limit(s) created on a CGN device for a specific user using RADIUS extension may be changed using RADIUS CoA message that carries the same RADIUS attribute. The CoA message may be sent from the RADIUS server directly to the NAS, which once accepts and sends back a RADIUS CoA ACK message, the new session limit replaces the previous one. illustrates how RADIUS protocol is used to increase the TCP/UDP port limit from 1024 to 2048 on a NAT44 device for a specific user.

| | | | ]]>

Upon obtaining the session limit(s) for a subscriber, the CGN device needs to allocate a TCP/UDP port or an ICMP identifiers for the subscriber when receiving a new IP flow sent from that subscriber. As one practice, a CGN may allocate a bulk of TCP/UDP ports or ICMP identifiers once at a time for a specific user, instead of one port/identifier at a time, and within each session bulk, the ports/identifiers may be randomly distributed or in consecutive fashion. When a CGN device allocates bulk of TCP/UDP ports and ICMP identifiers, the information can be easily conveyed to the RADIUS server by a new RADIUS attribute called the CGN-Session-Range (defined in ). The CGN device may allocate one or more TCP/UDP port ranges or ICMP identifier ranges, or generally called session ranges, where each range contains a set of numbers representing TCP/UDP ports or ICMP identifiers, and the total number of sessions must be less or equal to the associated session limit defined for that subscriber. A CGN device may choose to allocate a small session range, and allocate more at a later time as needed; such practice is good because its randomization in nature. At the same time, the CGN device also needs to decide the shared IPv4 address for that subscriber. The shared IPv4 address and the pre-allocated session range are both passed to the RADIUS server. When a subscriber initiates an IP flow, the CGN device randomly selects a TCP/UDP port or ICMP identifier from the associated and pre-allocated session range for that subscriber to replace the original source TCP/UDP port or ICMP identifier, along with the replacement of the source IP address by the shared IPv4 address. A CGN device may decide to "free" a previously assigned set of TCP/UDP ports or ICMP identifiers that have been allocated for a specific subscriber but not currently in use, and with that, the CGN device must send the information of the de-allocated session range along with the shared IPv4 address to the RADIUS server. illustrates how RADIUS protocol is used to report a set of ports allocated and de-allocated, respectively, by a NAT44 device for a specific user to the RADIUS server.

| | | | | | |-----Access-Request -------->| | | | | |<----Access-Accept-----------| |<---Service Granted ------| | | (other parameters) | | ... ... ... | | | | | | | (NAT44 decides to allocate | | a TCP/UDP port range for the user) | | | | | |-----Accounting-Request----->| | | (Port-Session-Range | | | for allocation) | ... ... ... | | | | (NAT44 decides to de-allocate | | a TCP/UDP port range for the user) | | | | | |-----Accounting-Request----->| | | (Port-Session-Range | | | for de-allocation) | | | | ]]>

In most scenarios, the port mapping on a NAT device is dynamically created when the IP packets of an IP connection initiated by a user arrives. For some applications, the port mapping needs to be pre-defined allowing IP packets of applications from outside a CGN device to pass through and "port forwarded" to the correct user located behind the CGN device. Port Control Protocol , provides a mechanism to create a mapping from an external IP address and port to an internal IP address and port on a CGN device just to achieve the "port forwarding" purpose. PCP is a server-client protocol capable of creating or deleting a mapping along with a rich set of features on a CGN device in dynamic fashion. In some deployment, all users need is a few, typically just one pre-configured port mapping for applications such as web cam at home, and the lifetime of such a port mapping remains valid throughout the duration of the customer's Internet service connection time. In such an environment, it is possible to statically configure a port mapping on the RADIUS server for a user and let the RADIUS protocol to propagate the information to the associated CGN device. illustrates how RADIUS protocol is used to configure a forwarding port mapping on a NAT44 device by using RADIUS protocol.

| | | | | | |---------Access-Request------->| | | | | |<--------Access-Accept---------| | | (Port-Forwarding-Map) | |<---Service Granted ------| | | (other parameters) | | | | | | (Create a port mapping | | for the user, and | | associate it with the | | internal IP address | | and external IP address) | | | | | | | | |------Accounting-Request------>| | | (Port-Forwarding-Map) | ]]> A port forwarding mapping that is created on a CGN device using RADIUS extension as described above may also be changed using RADIUS CoA message that carries the same RADIUS associate. The CoA message may be sent from the RADIUS server directly to the NAS, which once accepts and sends back a RADIUS CoA ACK message, the new port forwarding mapping then replaces the previous one. illustrates how RADIUS protocol is used to change an existing port mapping from (a:X) to (a:Y), where "a" is an internal port, and "X" and "Y" are external ports, respectively, for a specific user with a specific IP address

| | | (Port-Forwarding-Map) | ]]>

An Internet Service Provider (ISP) assigns TCP/UDP 500 ports for the subscriber Joe. This number is the limit that can be used for TCP/UDP ports on a NAT44 device for Joe, and is configured on a RADIUS server. Also, Joe asks for a pre-defined port forwarding mapping on the NAT44 device for his web cam applications (external port 5000 maps to internal port 80). When Joe successfully connects to the Internet service, the RADIUS server conveys the TCP/UDP port limit (1000) and the forwarding port mapping (external port 5000 to internal port 80) to the NAT44 device, using Port-Session-Limit attribute and Port-Forwarding-Map attribute, respectively, carried by an Access-Accept message to the BNG where NAS and CGN co-located. Upon receiving the first outbound IP packet sent from Joe's laptop, the NAT44 device decides to allocate a small port pool that contains 40 consecutive ports, from 3500 to 3540, inclusively, and also assign a shared IPv4 address 192.0.2.15, for Joe. The NAT44 device also randomly selects one port from the allocated range (say 3519) and use that port to replace the original source port in outbound IP packets. For accounting purpose, the NAT44 device passes this port range (3500-3540) and the shared IPv4 address 192.0.2.15 together to the RADIUS server using Port-Session-Range attribute carried by an Accounting-Request message. When Joe works on more applications with more outbound IP sessions and the port pool (3500-3540) is close to exhaust, the NAT44 device allocates a second port pool (8500-8800) in a similar fashion, and also passes the new port range (8500-8800) and IPv4 address 192.0.2.15 together to the RADIUS server using Port-Session-Range attribute carried by an Accounting-Request message. Note when the CGN allocates more ports, it needs to assure that the total number of ports allocated for Joe is within the limit. Joe decides to upgrade his service agreement with more TCP/UDP ports allowed (up to 1000 ports). The ISP updates the information in Joe's profile on the RADIUS server, which then sends a CoA-Request message that carries the Port-Session-Limit attribute with 1000 ports to the NAT44 device; the NAT44 device in turn sends back a CoA-ACK message. With that, Joe enjoys more available TCP/UDP ports for his applications. When Joe travels, most of the IP sessions are closed with their associated TCP/UDP ports released on the NAT44 device, which then sends the relevant information back to the RADIUS server using Port-Session-Range attribute carried by Accounting-Request message. Throughout Joe's connection with his ISP Internet service, applications can communicate with his web cam at home from external realm directly traversing the pre-configured mapping on the CGN device. When Joe disconnects from his Internet service, the CGN device will de-allocate all TCP/UDP ports as well as the port-forwarding mapping, and send the relevant information to the RADIUS server.

illustrates an example of the flow exchange which occurs when a visiting UE connects to a CPE offering Wi-Fi service. For identification purposes (see ), once the CPE assigns a port set, it issues a RADIUS message to report the assigned port set.

| | | | | | |-----Access-Request -------->| | | | | |<----Access-Accept-----------| |<---Service Granted ------| | | (other parameters) | | ... | ... ... |<---IP@----| | | | | | | | (CPE assigns a TCP/UDP port | | range for this visiting UE) | | | | | |--Accounting-Request-...------------------->| | | (Port-Session-Range | | | for allocation) | ... | ... ... | | | | | | | | | (CPE withdraws a TCP/UDP port | | range for a visiting UE) | | | | | |--Accounting-Request-...------------------->| | | (Port-Session-Range | | | for de-allocation) | | | | ]]>

The following table provides a guide as the attributes may be found in which kinds of RADIUS packets, and in what quantity. Request Accept Reject Challenge Acct. Request # Attribute 0-1 0-1 0 0 0-1 TBA1 Port-Session-Limit 0 0 0 0 0-1 TBA2 Port-Session-Range 0-1 0-1 0 0 0-1 TBA3 Port-Forwarding-Map The following table defines the meaning of the above table entries. 0 This attribute MUST NOT be present in packet. 0+ Zero or more instances of this attribute MAY be present in packet. 0-1 Zero or one instance of this attribute MAY be present in packet.

This document does not introduce any security issue than what has been identified in .

This document requires new code point assignment for the three new RADIUS attributes as follows: Port-Session-Limit Port-Session-Range Port-Forwarding-Map

This document establishes a new name space for Session Type (see for the initial reservation of values. The allocation of future values is according to RFC Required policy .

Many thanks to Dan Wing, Roberta Maglione, Daniel Derksen, and David Thaler for their useful comments and suggestions.