INTERNET DRAFT Jeffrey Lo
Expires July 1999 NEC USA
Michael Borella
David Grabelsky
3Com Corp
Realm Specific IP: A Framework
<draft-ietf-nat-rsip-framework-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
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Abstract
This document examines the general framework of Realm Specific IP
(RSIP). All RSIP solutions must solve the same set of problems, and
all RSIP-related proposals to date are similar in many ways. We
attempt to enumerate the similarities and differences of these
proposals, and expand the scope of RSIP to include several other
possible mechanisms. We do not advocate any one RSIP solution over
the other; instead, we present these solutions in the hope to clarify
RSIP issues and generate further discussion towards adoption of RSIP.
1. Introduction
While NAT has become a popular mechanism of sharing IP addresses
amongst a number of hosts, it suffers from a lack of flexibility. In
particular, a NAT router must examine and change the network and
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possibly the transport layer headers of each packet to or from the
NAT subnet(s) sharing its IP address(es). This causes NAT to break
the end-to-end nature of Internet connectivity, and disrupts network
layer]] security protocols, such as IPSec. Furthermore, any
application that transmits IP address or port content, such as FTP,
will require a proxy module within the NAT router. Given these
limitations, RSIP has emerged as an attempt to avoid the worst
complications of NAT.
RSIP is based on the concept of granting host from one realm (e.g.,
privately addressed realm) a presence in another realm (e.g.,
globally addressed realm) by granting it resources from the second
realm. While this document is limited to the discussion of IPv4
networks, RSIP is general and may be applied well beyond the
limitations of IPv4 networks, such as IPv4/IPv6 translators. In this
document we discuss the approaches of several possible RSIP systems
and address the issues that any RSIP solution must face. Since, at
this preliminary stage, we most likely have missed out certain issues
in the implementation of RSIP, we welcome thoughts and comments from
the experienced.
2. Terminology
Private Realm
A routing realm in which RSIP hosts assumes temporary presence in
another realm, the global realm. Examples of private realms are
privately addressed (10/8, 172.16/12, 192.168/16) IPv4 realms or
private IPv4 realms within IPv6 networks.
Global Realm
A routing realm with unique network addressed assigned by Internet
Assigned Number Authority (IANA) or an equivalent address
registry.
RSIP-server
An entity situated on the boundary between a private realm and a
global realm which is responsible for global parameter management
and assignment to RSIP-clients. In all cases, an RSIP-server may
act as a normal NAT box at the same time for hosts within the
private realm that are not RSIP enabled.
RSIP-client
An entity within the private realm that assumes globally unique
parameters from the RSIP server through the use of RSIP.
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All other terminology found in this document is consistent with that
of [1].
3. Specification of Requirements
The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
documents are to be interpreted as described in RFC 2119.
4. Architecture
In a typical scenario where RSIP is deployed, there is some number of
hosts in the private realm without globally-routable IP addresses
connected to the global realm by the RSIP server. The hosts are
likely to use private addresses from the range assigned by IANA
(10/8, 172.16/12 and 192.168/16), while the RSIP server is multi-
homed with one or more private addresses from this range and one or
more publicly-routable addresses.
The RSIP-server may act as a normal NAT device while at the same time
facilitating RSIP implementations by dynamically carrying out global
resource and/or parameter negotiation and assignments with RSIP-
clients. Using the global parameters assigned by the RSIP-server,
RSIP-clients route (usually tunnel) data packets to the RSIP-server
within the private realm. If tunneling is used, the RSIP-server acts
as the end point of such tunnels, stripping off the outer headers and
routing the inner packets onto the global realm. An RSIP-server
maintains a mapping of the demultiplexing tuples to RSIP-client
private addresses, such the mapping can be used to demultiplex data
traffic to RSIP-clients.
5. RSIP Fundamentals
We discuss the issues that all RSIP schemes must address in this
section. Note that these issues are not orthogonal; thus, by
addressing one, in some cases another issue is also addressed
sufficiently.
5.1. Negotiation and/or determination of Demultiplexing Fields
Assume that an RSIP-client within a private realm has transmitted
a request to a public server within a global realm, and the server
has sent a response packet that successfully arrived at the RSIP
server. Based on a pre-arranged mapping, the RSIP-server must be
able to determine the private IP address of the packet's
destination; i.e., the RSIP-client. The only information that the
RSIP-server may use is what is already contained within the
headers of the inbound data packet. We will refer to these header
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fields as the "demultiplexing fields" as they are used to spread
the incoming streams of packets to multiple destinations within
the private realm. Depending on the type of mapping used by the
RSIP server, demultiplexing parameters could either be global IPv4
addresses or port.
Demultiplexing of incoming streams of packet require pre-
assignment of the demultiplexing fields to RSIP clients. Hence
there exist a requirement for a negotiation process that enable
these parameters to be negotiated between RSIP server and RSIP
clients. Such a negotiation process can be based on the following
approaches.
As an extension of current host configuration or policy
protocols such as DHCP, COPS, RADIUS, DIAMETER, or SOCKS.
During tunnel establishment, for example as an extension to
L2TP parameter negotiation.
As a specialized RSIP-specific protocolm such as described in
[2].
5.2. Determination of other RSIP parameters
Apart from negotiation of demultiplexing parameters, other
information pertaining to the assignment of those demultiplexing
fields may also need to be negotiated. Examples of such parameters
are:
A binding identifier may be assigned for each global parameter
assignment. The binding identifier serves to uniquely identify
the resource that has been allocated by an RSIP server. It may
also be used during lookup to efficiently index existing
bindings. A time duration may be associated with each bind of
global parameters to a RSIP clients. If such time information
are used, it has to be negotiated.
RSIP-clients may require that the RSIP-server specify how it
allocates address and port resources. RSIP-servers may only
allocate a global IP address to each unique host, resulting in
a Basic-NAT-like operation. Or, RSIP-servers may distribute a
(potentially shared) global IP address and a unique port range
per that IP address to eachhost, resulting in a NAPT-like
operation.
The negotiation and assignment mechanism SHOULD facilitate
vendor specific parameters.
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5.3. Tunnel Use and Establishment
RSIP generally requires the use of tunnels within the private
realm, between the RSIP clients and the RSIP server. While it is
possibly to imagine an RSIP implementation that does not require
tunneling, it seems that tunneling is a flexible method for
solving a address ambiguity problems. The type of tunnel may be
IP-IP, GRE, an IPSEC mode, L2TP, or another form of tunnel.
Tunnels may be established statically or dynamically between RSIP
clients and servers. A static tunnel is established at host boot
and remains in service until the host is no longer using the
network. A dynamic tunnel is established at the beginning of a
session or flow and exists only for the lifetime of the session.
Both types of tunnels may allow for on-the-fly re-negotiation of
demultiplexing fields and re-assignment of parameters to RSIP
clients. If tunneling is used to route the globally addressed
packet within private realm, global parameter negotiation could be
associated with tunnel establishment mechanisms. Alternatively, a
negotiation protocol may enable the negotiation of tunnel type as
well.
5.4. Policy and Accounting
Having an RSIP MIB may be useful as a means of pre-configuring
RSIP-clients at set up and as a method for introducing RSIP
policy. It is particularly valuable in large-scale implementations
with thousands of RSIP-clients. In such cases, push technology
could be used to update RSIP-clients with the configuration and
policy information.
All RSIP-clients SHOULD have a mechansims of authenticating
themselves to RSIP-servers, in order to alleviate possible denial
of service attacks in which a malicious RSIP-client attempts
utilize the resources assigned to a different RSIP-client.
Any RSIP implementation SHOULD implement accounting of irregular
event seen by the RSIP-server. Events such as denial of service
attacks, illegal use of resources (traffic without bindings or
after binding expirations) and global resource depletion SHOULD be
logged.
6. Open Problems
The resolution of a number of RSIP issues are still open. Although
solutions may exist for these problems, they may have unattractive
side effects. In this section we discuss several such issues.
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6.1. Contacting Internal Servers
In order for an RSIP implementation to allow private hosts to run
servers that can be contacted from the public network, these
servers must be registered with the RSIP server. Registration of
servers with unique and/or well known listen ports may be limited
to one per private realm.
6.2. Determining Locality of Destinations
In general, an RSIP client must know, for a particular IP address,
whether it should transmit the packet normally for local delivery,
or tunnel the packet to the RSIP-server. Since more than one
subnet may be behind an RSIP-server, looking at a local subnet
mask will not work. We'd rather not have to propagate routing
tables to all RSIP-clients. A simple alternative, proposed in
[2], that will solve this problem is to require that the RSIP-
server knows all of the subnets that are on the private network
This information can be manually entered because it is not
expected to change often. Then, if an IP address in question is
not on a host's local subnet, the host can query the server with
the address. The RSIP server will return a simple "yes or "no"
answer - yes, this address is local, or no, it is not.
Alternatively, RSIP-clients could send all packets for
destinations without an explicit static route to the RSIP server.
If they arrive at the RSIP server, it informs the host that it
should instead tunnel the packet. The host then acquires the
necessary global parameters and tunnels the packet, to the RSIP
server. This approach may require further changes to the TCP/IP
stack at the host, since, in the case of TCP traffic, a half-open
TCP socket must be discarded. Likewise, the RSIP client could at
first tunnel the packets to the RSIP server. If the server
determines that the destination is local, it would inform the host
of this fact and the host could then transmit the packet in the
standard fashion. Regardless of the solution chosen, RSIP clients
caching the "locality" of recently-contacted IP addresses may be
beneficial.
7. Cascaded RSIP
It is possible for RSIP to allow for cascading of RSIP-servers. For
example, consider an ISP that uses RSIP for address sharing amongst
its customers. It might assign resources (e.g., IP addresses and
ports) to a particular customer. This customer may further subdivide
the port ranges and address(es) amongst individual end hosts. A
reference architecture is depicted below.
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+-----------+
| |
| RSIP |
| server +---- 10.0.0.0/8
| B |
| |
+-----+-----+
|
| 10.0.1.0/24
+-----------+ | (149.112.240.0/25)
| | |
149.112.240.0/24| RSIP +--+
----------------+ server |
| A +--+
| | |
+-----------+ | 10.0.2.0/24
| (149.112.240.128/25)
|
+-----+-----+
| |
| RSIP |
| server +---- 10.0.0.0/8
| C |
| |
+-----------+
RSIP-server A is in charge of the IP addresses of subnet
149.112.240.0/24. It distributes these addresses to RSIP-clients and
RSIP-servers. In the given configuration, it distributes addresses
149.112.240.0 - 149.112.240.127 to RSIP-server B, and addresses
149.112.240.128 - 149.112.240.254 to RSIP-server C. Note that the
subnet broadcast address, 149.112.240.255, must remain unclaimed, so
that broadcast packets can be distributed to arbitrary hosts behind
RSIP-server A. Also, the subnets between RSIP-server A and RSIP-
servers B and C will use private addresses.
Due to the tree-like fashion in which addresses will be cascaded, we
will refer to RSIP-servers A as the 'parent' of RSIP-servers B and C,
and RSIP-servers B and C as 'children' of RSIP-servers A. An
arbitrary number of levels of children may exist under a parent RSIP-
server.
A parent RSIP-server will not necessarily be aware that the
address(es) and port blocks that it distributes to a child RSIP-
server will be further distributed. Thus, the RSIP-clients MUST
tunnel their outgoing packets to the nearest RSIP-server. This
server will then verify that the sending host has used the proper
address and port block, and then tunnel the packet on to its parent
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RSIP-server.
For example, in the context of the diagram above, host 10.0.0.1,
behind RSIP-server C will use its assigned external IP address (say,
149.112.240.130) and tunnel its packets over the 10.0.0.0/8 subnet to
RSIP-server C. RSIP-server C strips off the outer IP header. After
verifying that the source public IP address and source port number is
valid, RSIP-server C will tunnel the packets over the 10.0.2.0/8
subnet to RSIP-server A. RSIP-server A strips off the outer IP
header. After verifying that the source public IP address and source
port number is valid, RSIP-server A transmits the packet on the
public network.
While it may be more efficient in terms of computation to have a
RSIP-client tunnel directly to the overall parent of an RSIP-server
tree, this would introduce significant state and administrative
difficulties.
A RSIP-server that is a child MUST take into consideration the
parameter assignment constraints that it inherits from its parent
when it assigns parameters to its children. For example, if a child
RSIP-server is given a lease time of 3600 seconds on an IP address,
it MUST compare the current time to the lease time and the time that
the lease was assigned to compute the maximum allowable lease time on
the address if it is to assign the address to a RSIP-client or child
RSIP-server.
8. References
[1] P. Srisuresh and Matt Holdrege, "IP Network Address Translator
(NAT) Terminology and Considerations," <draft-ietf-nat-
terminology-01.txt>, Work in progress
[2] Michael Borella, David Grabelsky, Jeffrey Lo and Kuni Taniguchi,
"Realm Specific IP: Protocol Specification," <draft-ietf-nat-rsip-
protocol-00.txt>, Work in progress.
9. Authors' Addresses
Jeffrey Lo
NEC USA
C&C Research Labs.
110 Rio Robles
San Jose, CA 95134
(408) 943 3033
jlo@ccrl.sj.nec.com
Michael Borella
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3Com Corp.
Advanced Technologies Research Center
1800 W. Central Rd.
Mount Prospect IL 60056
(847) 842 6093
mike_borella@3com.com
David Grabelsky
3Com Corp.
Advanced Technologies Research Center
1800 W. Central Rd.
Mount Prospect IL 60056
(847) 222 2483
david_grabelsky@3com.com
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