Network Working Group D. Cheng
Internet-Draft Huawei Technologies
Intended status: Standards Track J. Korhonen
Expires: April 10, 2012 Nokia Siemens Networks
October 8, 2011
Radius Extensions for CGN Configurations
draft-cheng-behave-cgn-cfg-radius-ext-01
Abstract
This document defines new RADIUS attributes that can be used by a
Carried Grade NAT device to communicate with a RADIUS server using
RADIUS protocol to configure or report TCP/UDP ports and ICMP
identifiers mapping behavior for specific Internet subscribers.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 10, 2012.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
Cheng & Korhonen Expires April 10, 2012 [Page 1]
Internet-Draft Radius Extensions for CGN October 2011
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Managing CGN Port Behavior using RADIUS . . . . . . . . . . . 5
3.1. Configure CGN Session Limit . . . . . . . . . . . . . . . 6
3.2. Report CGN Session Allocation or De-allocation . . . . . . 8
3.3. Configure CGN Forwarding Port Mapping . . . . . . . . . . 10
3.4. An Example . . . . . . . . . . . . . . . . . . . . . . . . 12
4. RADIUS Attributes . . . . . . . . . . . . . . . . . . . . . . 13
4.1. CGN-Session-Limit Attribute . . . . . . . . . . . . . . . 13
4.2. CGN-Session-Range Attribute . . . . . . . . . . . . . . . 15
4.3. CGN-Forwarding-Port-Map Attribute . . . . . . . . . . . . 17
5. Table of Attributes . . . . . . . . . . . . . . . . . . . . . 19
6. Security Considerations . . . . . . . . . . . . . . . . . . . 19
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
7.1. RADIUS Attributes . . . . . . . . . . . . . . . . . . . . 19
7.2. Name Spaces . . . . . . . . . . . . . . . . . . . . . . . 20
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
9.1. Normative References . . . . . . . . . . . . . . . . . . . 20
9.2. Informative References . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21
Cheng & Korhonen Expires April 10, 2012 [Page 2]
Internet-Draft Radius Extensions for CGN October 2011
1. Introduction
In a broadband network, customer information is usually stored on a
RADIUS [RFC2865] server and at the time when a user initiates an
Internet 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. In many cases, the Carrier
Grade NAT (CGN) function is 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
[I-D.ietf-behave-lsn-requirements], NAT64 [RFC6146], or Dual-Stack
Lite [RFC6333] function.
When IP packets traverse a CGN device, 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 an IP connection or session. Since the
number space of TCP/UDP ports and ICMP identifiers in CGN's external
realm is shared by multiple users sharing the same IPv4 address, the
total number of a user's live IP sessions is usually limited.
In order to support the communication between a BNG-based CGN and
RADIUS server as described above, this document proposes three new
RADIUS attributes as RADIUS protocol's extensions, and they are used
for separate purposes as follows:
o A session limit is configured on a RADIUS server based on service
agreement with a specific user, and this parameter imposes the
limit of total number of TCP/UDP ports plus ICMP identifiers that
the user can use behind the CGN. 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 CGN-Session-Limit, which is included in a RADIUS
Access-Accept message sent by the RADIUS server to the BNG based
CGN. This new RADIUS attribute can also be included in a RADIUS
CoA message sent by the RADIUS server to the BNG based CGN in
order to change the session limit previously configured.
Cheng & Korhonen Expires April 10, 2012 [Page 3]
Internet-Draft Radius Extensions for CGN October 2011
o A CGN may allocate or de-allocate some consecutive 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
CGN-Session-Range, which is included in a RADIUS Accounting-
Request message sent by the BNG based CGN to the RADIUS server.
o A user may require the CGN device to perform port forwarding
function, i.e., a port mapping is pre-configured on the CGN so
that inbound IP packets sent by some applications from CGN
external realm can pass through the CGN and reach the user. The
port mapping information includes the CGN internal port, external
port, and may also include the associated internal IPv4 or IPv6
address, and is carried by a new RADIUS attribute CGN-Port-
Forwarding-Map, which is included in a RADIUS Access-Accept
message sent by the RADIUS server to the BNG based CGN. This new
RADIUS attribute can also be included in a RADIUS CoA message sent
by the RADIUS server to the BNG based CGN in order to change the
forwarding port mapping previously configured.
[Editor's Note - This document is a merged version of
draft-cheng-behave-nat44-pre-allocated-ports-02.txt and
draft-cheng-behave-nat-fwd-port-radius-ext-00.txt with some updates.]
2. Terminology
Some terms that are used in this document are listed as follows:
o 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 CGN can use when performing mapping on TCP/
UDP ports or ICMP identifiers for a specific user.
o Session Range - This specifies a consecutive 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.
o Internal IP Address - The IP address that is used as a source IP
address in an outbound IP packet sent toward a CGN device in the
internal realm. In IPv4 case, it is typically a private address
[RFC1918].
o External IP Address - The IP address that is used as a source IP
address in an outbound IP packet after traversing a CGN device in
the external realm. In IPv4 case, it is typically a global and
Cheng & Korhonen Expires April 10, 2012 [Page 4]
Internet-Draft Radius Extensions for CGN October 2011
routable IP address.
o 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
CGN device for an outbound IP packet in the internal realm.
o External Port - The external port is a UDP or TCP port, or an ICMP
identifier, which is allocated by a CGN device 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.
o External realm - The networking segment where IPv4 public
addresses are used in respective of CGN.
o Internal realm - The networking segment that is behind a CGN and
where IPv4 private addresses are used.
o Mapping - This term in this document associates with CGN for a
relationship between an internal IP address, internal port and the
protocol, and an external IP address, external port, and the
protocol.
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 [I-D.ietf-pcp-base],
and [I-D.ietf-behave-lsn-requirements].
3. Managing CGN Port Behavior using RADIUS
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.
Cheng & Korhonen Expires April 10, 2012 [Page 5]
Internet-Draft Radius Extensions for CGN October 2011
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-based CGN, 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
Section 4.
3.1. Configure CGN Session Limit
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
[I-D.ietf-behave-lsn-requirements], Dual-Stack Lite [RFC6333], NAT64
[RFC6146], etc. As a result, a single IPv4 public address may be
shared by hundreds or even thousands of subscribers. As indicated in
[RFC6269], 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 [I-D.ietf-behave-lsn-requirements] 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 CGN-
Session-Limit (defined in Section 4.1), 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
Cheng & Korhonen Expires April 10, 2012 [Page 6]
Internet-Draft Radius Extensions for CGN October 2011
subscriber.
[Discussion: how the situation where CGN and RADIUS server
disagree on session limits e.g. due CGN malfunction or
configuration mistake in RADIUS server? Should the NAS include
its view of available ports in the request so that the RADIUS
server can do an intelligent check on provisioning side and
possible either adjust the session limit or just reject the
session request?]
Figure 1 illustrates how RADIUS protocol is used to configure the
maximum number of TCP/UDP ports for a given subscriber on a NAT44
device.
User NAT44/NAS AAA
| BNG Server
| | |
| | |
|----Service Request------>| |
| | |
| |-----Access-Request -------->|
| | |
| |<----Access-Accept-----------|
| | (CGN-Session-Limit) |
| | (for TCP/UDP ports) |
|<---Service Granted ------| |
| (other parameters) | |
| | |
| (NAT44 external port |
| allocation and |
| IPv4 address assignment) |
| | |
Figure 1: RADIUS Message Flow for Configuring NAT44 Port Limit
The session limit(s) created on a CGN device for a specific user
using RADIUS extension may be changed using RADIUS CoA message
[RFC5176] 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.
Figure 2 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.
Cheng & Korhonen Expires April 10, 2012 [Page 7]
Internet-Draft Radius Extensions for CGN October 2011
User NAT/NAS AAA
| BNG Server
| | |
| TCP/UDP Port Limit (1024) |
| | |
| |<---------CoA Request----------|
| | (CGN-Session-Limit) |
| | (for TCP/UDP ports) |
| | |
| TCP/UDP Port Limit (2048) |
| | |
| |---------CoA Response--------->|
| | |
Figure 2: RADIUS Message Flow for changing a user's NAT44 port limit
3.2. Report CGN Session Allocation or De-allocation
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 in consecutive order, the information can be easily
conveyed to the RADIUS server by a new RADIUS attribute called the
CGN-Session-Range (defined in Section 4.2). 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 some
consecutive 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.
Cheng & Korhonen Expires April 10, 2012 [Page 8]
Internet-Draft Radius Extensions for CGN October 2011
At anytime, a CGN device may decide to "free" some consecutive 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.
Figure 3 illustrates how RADIUS protocol is used to report
consecutive ports allocated and de-allocated, respectively, by a
NAT44 device for a specific user to the RADIUS server.
User NAT44/NAS AAA
| BNG Server
| | |
| | |
|----Service Request------>| |
| | |
| |-----Access-Request -------->|
| | |
| |<----Access-Accept-----------|
|<---Service Granted ------| |
| (other parameters) | |
... ... ...
| | |
| | |
| (NAT44 decides to allocate |
| a TCP/UDP port range for the user) |
| | |
| |-----Accounting-Request----->|
| | (CGN-Session-Range |
| | for allocation) |
... ... ...
| | |
| (NAT44 decides to de-allocate |
| a TCP/UDP port range for the user) |
| | |
| |-----Accounting-Request----->|
| | (CGN-Session-Range |
| | for de-allocation) |
| | |
Figure 3: RADIUS Message Flow for reporting NAT44 allocation/
de-allocation of consecutive ports
Note using RADIUS extension as proposed in this document to report
back to the RADIUS server about allocation/de-allocation of TCP/UDP
ports and ICMP identifiers requires the ports/identifiers in the
Cheng & Korhonen Expires April 10, 2012 [Page 9]
Internet-Draft Radius Extensions for CGN October 2011
session range are consecutive. However, a CGN might choose bulk
session allocation but the ports/identifiers are not consecutive, or
the ports/identifiers are allocated on individual basis; efficient
mechanism to report session allocation/de-allocation to the RADIUS
server using these methods is under discussion and is currently
outside of the scope of this document. Also, the impacts on
utilization of TCP/UDP ports and ICMP identifiers, CGN logging,
security etc. with different allocation schemes are referred to
Section 5 of [I-D.ietf-behave-lsn-requirements].
3.3. Configure CGN Forwarding Port Mapping
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 or PCP [I-D.ietf-pcp-base], 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.
Figure 4 illustrates how RADIUS protocol is used to configure a
forwarding port mapping on a NAT44 device by using RADIUS protocol.
Cheng & Korhonen Expires April 10, 2012 [Page 10]
Internet-Draft Radius Extensions for CGN October 2011
User NAT/NAS AAA
| BNG Server
| | |
|----Service Request------>| |
| | |
| |---------Access-Request------->|
| | |
| |<--------Access-Accept---------|
| | (CGN-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------>|
| | (CGN-Port-Forwarding-Map) |
Figure 4: RADIUS Message Flow for configuring a forwarding port
mapping
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 [RFC5176] 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.
Figure 5 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
Cheng & Korhonen Expires April 10, 2012 [Page 11]
Internet-Draft Radius Extensions for CGN October 2011
User NAT/NAS AAA
| BNG Server
| | |
| Internal IP Address |
| Port Map (a:X) |
| | |
| |<---------CoA Request----------|
| | (CGN-Port-Forwarding-Map) |
| | |
| Internal IP Address |
| Port Map (a:Y) |
| | |
| |---------CoA Response--------->|
| | (CGN-Port-Forwarding-Map) |
Figure 5: RADIUS Message Flow for changing a user's forwarding port
mapping
3.4. An Example
An Internet Service Provider (ISP) assigns TCP/UDP 500 ports for the
subscriber Joe based on a service agreement. 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 CGN-Session-Limit attribute and CGN-Forwarding-Port-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 CGN-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
Cheng & Korhonen Expires April 10, 2012 [Page 12]
Internet-Draft Radius Extensions for CGN October 2011
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 CGN-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 CGN-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 CGN-
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.
4. RADIUS Attributes
[Discussion: should these attributes be allocated from the
extended RADIUS attribute code space?]
4.1. CGN-Session-Limit Attribute
This attribute is of type complex [RFC6158] 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 CGN
device corresponding to a specific subscriber for CGN operation.
The CGN-Session-Limit MAY appear in an Access-Accept packet, it MAY
also appear in an Access-Request packet as a hint by the CGN device,
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 CGN-Session-Limit MAY appear in an CoA-Request packet.
Cheng & Korhonen Expires April 10, 2012 [Page 13]
Internet-Draft Radius Extensions for CGN October 2011
The CGN-Session-Limit MAY appear in an Accounting-Request packet.
The CGN-Session-Limit MUST NOT appear in any other RADIUS packets.
The format of the CGN-Session-Limit RADIUS attribute format is shown
below. The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | ST | Session
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Limit |
+-+-+-+-+-+-+-+-+
Type:
TBA1 for CGN-Port-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 the sum of TCP ports,
UDP ports, and ICMP Identifiers as a whole.
1:
The limit as specified is applied to the sum of TCP ports
and UDP ports.
2:
The limit as specified is applied to TCP ports.
3:
The limit as specified is applied to UDP ports.
Cheng & Korhonen Expires April 10, 2012 [Page 14]
Internet-Draft Radius Extensions for CGN October 2011
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 imposed to the
total number of TCP ports, or UDP ports, or the sum of the two,
or ICMP Identifiers, or the sum of the three, depending on the
value in the Session Type field, that the specific user can use
during CGN operation.
4.2. CGN-Session-Range Attribute
This attribute is type of complex [RFC6158] and contains a range of
consecutive numbers for TCP ports or UDP ports, or both, or for ICMP
Identifiers, which has been allocated or de-allocated by a CGN device
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
[I-D.miles-behave-l2nat] and DS-Extra-Lite
[I-D.arkko-dual-stack-extra-lite], parameters at a customer premise
such as MAC address, interface ID, VLAN ID, PPP session ID, VRF ID,
etc., may also be required to pass to the RADIUS server as part of
the accounting record.
The CGN-Session-Range MAY appear in an Accounting-Request packet.
The CGN-Session-Range MUST NOT appear in any other RADIUS packets.
The format of the CGN-Session-Range RADIUS attribute format is shown
below. The fields are transmitted from left to right.
Cheng & Korhonen Expires April 10, 2012 [Page 15]
Internet-Draft Radius Extensions for CGN October 2011
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | ST |A| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Session Range Start | Session Range End |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Local Session ID ....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+--
Type:
TBA2 for CGN-Alloc-Port-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 Section 4.1 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 CGN for
a specific user.
Reserved:
This field MUST be set to zero by the sender and ignored by the
receiver.
External Session Range Start:
Cheng & Korhonen Expires April 10, 2012 [Page 16]
Internet-Draft Radius Extensions for CGN October 2011
This field contains the smallest TCP/UDP Port number or the
smallest ICMP identifier number in the session range, which
contains consecutive TCP/UDP ports or ICMP identifiers,
depending on the value of Session Type.
External Session Range End:
This field contains the largest TCP/UDP port number or the
largest ICMP identifier number in the session range, which
contains consecutive TCP/UDP ports or ICMP identifiers,
depending on the value of Session Type.
External IPv4 Address:
This field contains the IPv4 address assigned to the associated
subscriber to be used in the external realm.
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,etc. The length
of this field equals to the total attribute length minus 12
octets.
4.3. CGN-Forwarding-Port-Map Attribute
This attribute is type of complex [RFC6158] 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 CGN-Forwarding-Port-Map RADIUS attribute format is
Cheng & Korhonen Expires April 10, 2012 [Page 17]
Internet-Draft Radius Extensions for CGN October 2011
shown below. The fields are transmitted from left to right.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | AF | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Internal Port | Configured External Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Internal IP Address .....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type:
TBA3 for CGN-Forwarding-Port-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:
Cheng & Korhonen Expires April 10, 2012 [Page 18]
Internet-Draft Radius Extensions for CGN October 2011
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.
5. Table of Attributes
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. # Attribute
Request
0-1 0-1 0 0 0-1 TBA1 CGN-Session-Limit
0-1 0-1 0 0 0-1 TBA2 CGN-Session-Range
0-1 0-1 0 0 0-1 TBA3 CGN-Forwarding-Port-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.
6. Security Considerations
This document does not introduce any security issue than what has
been identified in [RFC2865].
7. IANA Considerations
7.1. RADIUS Attributes
This document requires new code point assignment for the three new
RADIUS attributes as follows:
Cheng & Korhonen Expires April 10, 2012 [Page 19]
Internet-Draft Radius Extensions for CGN October 2011
o CGN-Session-Limit
o CGN-Session-Range
o CGN-Forwarding-Port-Map
7.2. Name Spaces
This document establishes a new name space for Session Type (see
Section 4.1 for the initial reservation of values. The allocation of
future values is according to RFC Required policy [RFC5226].
8. Acknowledgements
Many thanks to Dan Wing, Roberta Maglione, Daniel Derksen, and David
Thaler for their useful comments and suggestions.
9. References
9.1. Normative References
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2865] Rigney, C., Willens, S., Rubens, A., and W. Simpson,
"Remote Authentication Dial In User Service (RADIUS)",
RFC 2865, June 2000.
9.2. Informative References
[]
Arkko, J., Eggert, L., and M. Townsley, "Scalable
Operation of Address Translators with Per-Interface
Bindings", draft-arkko-dual-stack-extra-lite-05 (work in
progress), February 2011.
[I-D.ietf-behave-lsn-requirements]
Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
and H. Ashida, "Common requirements for Carrier Grade NAT
(CGN)", draft-ietf-behave-lsn-requirements-03 (work in
progress), August 2011.
Cheng & Korhonen Expires April 10, 2012 [Page 20]
Internet-Draft Radius Extensions for CGN October 2011
[I-D.ietf-pcp-base]
Wing, D., Cheshire, S., Boucadair, M., Penno, R., and P.
Selkirk, "Port Control Protocol (PCP)",
draft-ietf-pcp-base-13 (work in progress), July 2011.
[I-D.miles-behave-l2nat]
Miles, D. and M. Townsley, "Layer2-Aware NAT",
draft-miles-behave-l2nat-00 (work in progress),
March 2009.
[RFC5176] Chiba, M., Dommety, G., Eklund, M., Mitton, D., and B.
Aboba, "Dynamic Authorization Extensions to Remote
Authentication Dial In User Service (RADIUS)", RFC 5176,
January 2008.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6158] DeKok, A. and G. Weber, "RADIUS Design Guidelines",
BCP 158, RFC 6158, March 2011.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269,
June 2011.
[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, August 2011.
Authors' Addresses
Dean Cheng
Huawei Technologies
2330 Central Expressway
95050
USA
Email: dean.cheng@huawei.com
Cheng & Korhonen Expires April 10, 2012 [Page 21]
Internet-Draft Radius Extensions for CGN October 2011
Jouni Korhonen
Nokia Siemens Networks
Linnoitustie 6
Espoo FIN-02600
Finland
Email: jouni.nospam@gmail.com
Cheng & Korhonen Expires April 10, 2012 [Page 22]