Internet Engineering Task Force P. Droz/T. Przygienda
INTERNET DRAFT IBM Corp./Bell Labs, Lucent
9 March 1998
Proxy PAR
<draft-ietf-ion-proxypar-arch-00.txt>
Status of This Memo
This document is an Internet Draft, and can be found as
draft-ietf-ion-proxypar-arch-00.txt in any standard internet drafts
repository. Internet Drafts are working documents of the Internet
Engineering Task Force (IETF), its Areas, and its Working Groups.
Note that other groups may also distribute working documents as
Internet Drafts.
Internet Drafts are draft documents valid for a maximum of six
months. Internet Drafts may be updated, replaced, or obsoleted by
other documents at any time. It is not appropriate to use Internet
Drafts as reference material, or to cite them other than as a
``working draft'' or ``work in progress.''
Please check the I-D abstract listing contained in each Internet
Draft directory to learn the current status of this or any other
Internet Draft.
Abstract
Proxy PAR is a minimal version of PAR (PNNI Augmented Routing) that
gives ATM attached devices the ability to interact with PNNI devices
without the necessity to fully support PAR. Proxy PAR is designed as
a client/server interaction where the client side is much simpler
than the server side to allow fast implementation and deployment.
The purpose of Proxy PAR is to allow non-ATM devices to use the
flooding mechanisms provided by PNNI for registration and automatic
discovery of services offered by ATM attached devices. The first
version of PAR addresses mainly protocols available in IPv4. But
it also disposes of a generic interface to access the flooding of
PAR. In addition, Proxy PAR capable servers provide filtering based
on VPN IDs, IP protocols and address prefixes. This enables for
instance routers in a certain VPN running OSPF to find OSPF neighbors
on the same subnet. The protocol is built using a registration/query
Droz, Przygienda Expires 8 September 1998 [Page 1]
Internet Draft Proxy PAR 9 March 1998
approach where devices can register their services and query for
services and protocols registered by other clients.
1. Introduction
In June 1996, the ATM Forum accepted the Proxy PAR contribution
[CPS96] as minimal subset of PAR [Ca96], a current work item of the
PNNI working group [AF96b]. The latest version of the specification
[For98] provides a detailed description of the protocol including
state machines and packet formats.
The intention of this I-D is to provide general information about
Proxy PAR. For the detailed protocol description we refer the reader
to [For98].
Proxy PAR is a protocol allowing for different ATM attached devices
(ATM and non-ATM devices) to interact with PAR capable switches
to exchange information about non-ATM services without executing
PAR themselves. The client side is much simpler in terms of
implementation complexity and memory requirements than a complete
PAR instance. This should allow an easy implementation on existing
IP device such as IP routers. Additionally, clients can use Proxy
PAR to register different non-ATM services and protocols they
support. The protocol has deliberately not been included as part of
ILMI [AF96a] due to the complexity of PAR information passed in the
protocol and the fact that it is intended for integration of non-ATM
protocols and services only. A device executing Proxy PAR does not
necessarily need to execute ILMI or UNI signalling although this
normally will be the case.
The protocol does not specify how a client should make use of the
obtained information to establish connectivity. For example, OSPF
routers finding themselves through Proxy PAR could establish a full
mesh of P2P VCs by means of RFC1577 [Lau94], or use RFC1793 [Moy95]
to interact with each other. For the same purpose LANE [AF95] or
MARS [Arm96] could be used. It is expected that the guidelines how
a certain protocol can make use of Proxy PAR should come out of the
appropriate working group or standardization body that is responsible
for the particular protocol. Currently, work in progress exists to
address the operation of OSPF in the context of ATM and Proxy PAR
[PD97]. Further work will address other protocols such as BGP-4.
The protocol has the ability to provide ATM address resolution for IP
attached devices, but such resolutions can also be achieved by other
protocols under specification in IETF, e.g. [CH97b, CH97a]. Again,
Droz, Przygienda Expires 8 September 1998 [Page 2]
Internet Draft Proxy PAR 9 March 1998
the main purpose of the protocol is to allow the automatic detection
of devices over an ATM cloud in a distributed fashion, omitting the
usual pitfalls of server based solutions. Last but not least, it
should be mentioned here as well that the protocol complements and
coexists with the ongoing work in the IETF on server detection via
ILMI extensions [Dav97a, Dav97b, Dav97c].
2. Proxy PAR Operation and Interaction with PNNI
The protocol is asymmetric and consists of a discovery and
query/registration part. The discovery is very similar to the
existing PNNI Hello protocol and is used to initiate and maintain
communication between adjacent clients and servers. The registration
and update part execute after a Proxy PAR adjacency has been
established. The client can register its own services by sending
registration messages to the server. The client obtains information
it is interested in by sending query messages to the server. When
the client needs to change it's set of registered protocols it has to
re-register with the server. The client can withdraw all registered
services by registering a null set of services. It is important
to note that the server side does not push new information to the
client, neither does the server keep any state describing which
information the client received. It is the responsibility of the
client to update and refresh its information and to discover new
clients or update its stored information about other clients by
issuing queries and registrations at appropriate time intervals.
This simplifies the protocol, but assumes that the client will not
store and request large amounts of data. The main responsibility of
the server is to flood the registered information through the PNNI
cloud such that potential clients can discover each other. The Proxy
PAR server side also provides filtering functions to support VPNs and
IP subnetting. It is assumed that services advertised by Proxy PAR
will be advertised by a relatively small number of clients and will
be fairly stable, so that polling and refreshing intervals can be
relatively long.
The Proxy PAR extensions rely on appropriate flooding of information
by the PNNI protocol. When the client side registers or re-registers
a new service through Proxy PAR, it associates an abstract membeship
scope with the service. The server side maps this membership scope
into a PNNI routing level that restricts the flooding. This allows
the changes of the PNNI routing level without reconfiguration of the
client. In addition, the server can setup the mapping table such
that a client can only flood information to a certain level. Nodes
Droz, Przygienda Expires 8 September 1998 [Page 3]
Internet Draft Proxy PAR 9 March 1998
+-+
| | PNNI peer group # PPAR capable @ PNNI capable * Router
+-+ switch switch
Level 40
+---------------------------+
| |
| |
| @ ---- @ ---- @ |
| | | |
+----- | ----------- | -----+
| |
Level 60 | |
+------------- | ---+ +-- | --------------+
| | | | | |
R1* ------#-P1------@ | | @---------P3-#------- * R3
| | | | | |
R2* ------#-P2------+ | | +---------P4-#------- * R4
| | | |
+-------------------+ +-------------------+
Figure 1: OSPF and BGP scalability with Proxy PAR autodetection (ATM
Topology)
within the PNNI network take into account the associated scope of the
information when it is flooded. It is thus possible to exploit the
PNNI routing hierarchy by announcing different protocols on different
levels of the hierarchy e.g. OSPF could be run inside certain
peer-groups whereas BGP could be run between the set of peer-groups
running OSPF. Such an alignment or mapping of non-ATM protocols to
the PNNI hierarchy can drastically increase the scalability and
flexibility of Proxy PAR service. Figure 1 helps to visualize such a
scenario. For this topology following registrations are issued:
1. R1 registers OSPF protocol as running on the IP interface 1.1.1.1
and subnet 1.1.1/24 with scope 60
2. R2 registers OSPF protocol as running on the IP interface 1.1.1.2
and subnet 1.1.1/24 with scope 60
Droz, Przygienda Expires 8 September 1998 [Page 4]
Internet Draft Proxy PAR 9 March 1998
3. R3 registers OSPF protocol as running on the IP interface 1.1.2.1
and subnet 1.1.2/24 with scope 60
4. R4 registers OSPF protocol as running on the IP interface 1.1.2.2
and subnet 1.1.2/24 with scope 60
and
5. R1 registers BGP4 protocol as running on the IP interface 1.1.3.1
and subnet 1.1/16 with scope 40 within AS101
6. R3 registers BGP4 protocol as running on the IP interface 1.1.3.2
and subnet 1.1/16 with scope 40 within AS100
For simplicity the real PNNI routing level have been specified which
are 60 and 40. Instead of these two values the clients would use as
abstract membership scope "local" and "local+1". In addition, all
registered information would be part of the same VPN ID.
Table 1 describes the resulting distribution and visibility of
registrations and whether the routers not only see but also utilize
the received information. After convergence of protocols and
building of necessary adjacencies and sessions the overlying IP
topology is visualized in Figure 2.
AS101 DMZ AS100
######### ##########
# #
| # | # |
+-- R1 ---------+ # R4 --+
| # | # |
| # | BGP4 on # OSPF on |
| OSPF on # | subnet # subnet |
| subnet # | 1.1/16 # 1.1.2/24 |
| 1.1.1/24 # | # |
| # +------------------- R3 --+
+-- R2 # | # |
| # #
######### ##########
Figure 2: OSPF and BGP scalability with Proxy PAR autodetection (IP
Topology)
Droz, Przygienda Expires 8 September 1998 [Page 5]
Internet Draft Proxy PAR 9 March 1998
Reg# |1. |2. |3. |4. |5. |6.
___Router#_|___|___|___|___|___|____ R registered
R1 |R |U | | |R |U Q seen through query
R2 |U |R | | |Q |Q U used (implies Q)
R3 | | |R |U |R |U
R4 | | |U |R |Q |Q
Table 1: Flooding Scopes of Proxy PAR Registrations
Expressing the said above differently, one can say that if the scope
of the Proxy PAR information indicates that a distribution beyond
the boundaries of the peer group is necessary, the leader of a peer
group collects such information and propagates it into a higher
layer of the PNNI hierarchy. As no assumptions except scope values
can normally be made about the information distributed (e.g. IP
addresses bound to AESAs are not assumed to be aligned with them in
any respect), such information cannot be summarised. This makes a
careful handling of scopes necessary to preserve the scalability of
the approach as described above.
3. Proxy PAR Protocols
3.1. The Hello Protocol
The Proxy PAR Hello Protocol is closely related to the Hello protocol
specified in [AF96b]. It uses the same packet header and version
negotiation methods. For the sake of simplicity, states that are
irrelevant to Proxy PAR have been removed from the original PNNI
Hello protocol. The purpose of the Proxy PAR Hello protocol is to
bring up and maintain a Proxy PAR adjacency between the client and
server that supports the exchange of registration and query messages.
If the protocol is executed across multiple, parallel links between
the same server and client pair, individual registration and
query sessions are associated with a specific link. It is the
responsibility of the client and server to assign registration and
query sessions to the different communication instances. Proxy PAR
can be run in the same granularity as ILMI [AF96a] to support virtual
links and VP tunnels.
In addition, to the PNNI Hello, the Proxy PAR Hellos travelling from
the server to the client inform the client about the lifetime the
server assigns to registered information. The client has to retrieve
this interval from the Hello packet and set its refresh interval to
Droz, Przygienda Expires 8 September 1998 [Page 6]
Internet Draft Proxy PAR 9 March 1998
a value below the obtained time interval in order to avoid the aging
out of registered information by the server.
3.2. Registration/Query Protocol
The registration and query protocols enable the client to
announce and learn about protocols supported by the clients. All
query/register operations are initiated by the clients. The server
never tries to push information to the client. It is the client's
responsibility to register and refresh the set of protocols supported
and re-register them when changes occur. In the same sense, the
client must query the information from the server at appropriate
time intervals if it wishes to obtain the latest information. It is
important to note that neither client nor server is supposed to cache
any state information about the information stored by the other side.
Registered information is associated with an ATM address and
scope inside the PNNI hierarchy. From the IP point of view, all
information is associated with a VPN ID, IP address, subnet mask,
and IP protocol family. In this context, each VPN refers to a
completely separated IP address space. For example <A, 194.194.1.01,
255.255.255.0, OSPF> describes an OSPF interface in VPN A. In
addition to the IP scope further parameters can be registered that
contain more detailed information about the protocol itself. In the
above example this would be OSPF specific information such as the
area ID or router priority. However, Proxy PAR server only takes
the ATM and IP specific information into account when retrieving
information that was queried for. Protocol specific information is
never looked at by a Proxy PAR server.
3.2.1. Registration Protocol
The registration protocol enables a client to register the protocols
and services it supports. All protocols are associated with a
specific AESA and membership scope in the PNNI hierarchy. As the
default scope, implementations should choose the local scope of the
PNNI peer group. In this way, manual configuration can be avoided
unless information has to cross PNNI peergroup boundaries. PNNI is
responsible for the correct flooding either in the local peer group
or across the hierarchy.
The registration protocol is aligned with the standard initial
topology database exchange protocol used in link-state routing
protocols as far as possible. It uses a window size of one. A
Droz, Przygienda Expires 8 September 1998 [Page 7]
Internet Draft Proxy PAR 9 March 1998
single information element is registered at a time and must be
acknowledged before a new registration packet can be sent. The
protocol uses 'initialization' and 'more' bits in the same manner
PNNI and OSPF do. Any registration on a link unconditionally
overwrites all registration data previously received on the same
link. By means of a return code the server indicates to the client
whether the registration was successful or not.
Apart form the IP related information the protocol also offers a
generic interface to the PNNI flooding. By means of so called System
Capabilities Information Groups other information can be distributed
that can be used for proprietary or experimental implementations.
3.2.2. Query Protocol
The client uses the query protocol to obtain information about
services registered by other clients. The client requests services
registered within a specific membership scope, IP instance and
IP address prefix. It is always the client's task to request
information, the server never makes any attempt to push information
to the client. If the client needs to filter the returned data based
on service specific information, such as BGP AS, it must parse and
interpret the received information. The server never looks beyond
the IP scope.
The more generic interface to the flooding is supported similar to
the registration protocol.
4. Supported Protocols
Currently the protocols indicated in Table 2 have been included.
Furthermore, for protocols marked with a 'yes' additional information
has been specified that is beneficial for their operation. Many of
the protocol do not need additional information, it is sufficient to
know that they are supported and to know to which addresses they are
bound.
In order to include other information in an experimental manner the
generic information element can be used to carry such information.
5. Proxy PAR Detection
Since Proxy PAR is envisioned as being used by non-ATM devices
such as IP routers that implement UNI functionality to interact
with native ATM networks, an appropriate detection of Proxy PAR
Droz, Przygienda Expires 8 September 1998 [Page 8]
Internet Draft Proxy PAR 9 March 1998
Protocol | Additional Info
______________|__________________
OSPF | yes
RIP |
RIPv2 |
BGP3 |
BGP4 | yes
EGP |
IDPR |
MOSPF | yes
DVMRP |
CBT |
PIM-SM |
IGRP |
IS-IS |
ES-IS |
ICMP |
GGP |
BBN SPF IGP|
PIM-DM |
MARS |
NHRP |
ATMARP |
DHCP |
DNS | yes
Table 2: Additional Protocol Information Carried in PAR and PPAR
capabilities on the network as well as user side is crucial. The
necessary extensions to ILMI to perform this detection in an
automatic manner have been introduced in [Prz97].
6. VPN Support
In order to implement virtual private networks all information
distributed via PAR has a corresponding VPN ID. Based on this ID,
individual VPNs can be separated. Inside a certain VPN further
distinctions can be made according to IP address related information
and/or protocol type.
In most cases the best VPN support can be provided when Proxy PAR is
used between the client and server because in this way it is possible
Droz, Przygienda Expires 8 September 1998 [Page 9]
Internet Draft Proxy PAR 9 March 1998
to hide the real PNNI topology from the client. The PAR capable
server performs the translation from the abstract membership scope
into the real PNNI routing level. In this way the real PNNI topology
is hidden from the client and the server can apply restrictions in
the PNNI scope. The server can for instance have a mapping such
that the membership scope "global" is mapped to the highest level
peergroup to which a particular VPN has access. Thus the membership
scopes can be seen as hierarchical structuring inside a certain VPN.
With such mappings a network provider can also change the mapping
having to reconfigure the clients.
For more secure VPN implementations it will also be necessary to
implement VPN ID filters on the server side. In this way a client
can be restricted to a certain set (typically one) of VPN IDs. The
server will then allow queries and registrations only from the
clients that are in the allowed VPNs. In this way it is possible to
avoid an attached client from finding devices that are outside of
its own VPN. There is even room for further restriction in terms of
not allowing wildcard queries by a client. In terms of security,
some of the protocols have their own security methods, so PAR is only
used for the discovery of the counterparts. For instance OSPF has
authentication which can be used during the OSPF operation. So even
in the case where two wrong partners find each other, they will not
communicate because they will not be able to authenticate each other.
7. Interoperation with ILMI Server Discovery
PAR can be used to complement the server discovery via ILMI as
specified in [Dav97a, Dav97b, Dav97c]. It can be used to provide
the flooding of the information across the PNNI network. For this
purpose a server has to register with a PAR capable device. This
can be achieved via Proxy PAR or with a direct PAR interaction. For
instance the ATMARP server could register its service via Proxy PAR.
A direct interaction with PAR will be required in order to provide an
appropriate flooding scope.
A PAR capable device that has the additional MIB variables in the
Service Registry MIB can set these variables when getting information
via PAR. All required information is either contained in PAR or
is static such as IP version. The only missing information in
the MIB is the VPN ID but this can be coded into the variable
atmfSrvcReqAddressIndex. The PAR device is then responsible to
synchronize its database entries with these MIB variables.
Droz, Przygienda Expires 8 September 1998 [Page 10]
Internet Draft Proxy PAR 9 March 1998
8. Security Consideration
The Proxy PAR protocol itself does not have its own security
concepts. As PAR is an extension to PNNI, it has all security
features that come with PNNI. In addition, the protocol is mainly
used for automatic discovery of peers for certain protocols. After
the discovery process the security concepts of the individual
protocol is used for the bring up. As explained in the section about
VPN support, the only security considerations are on the server side
where access filters for VPN IDs can be implemented and restrictive
membership scope mappings can be configured.
9. Conclusion
This I-D describes the basic functions of Proxy PAR being specified
within the ATM-Forum body. The main purpose of the protocol is to
provide automatic detection and configuration of non-ATM devices over
an ATM cloud.
In the future support for further protocols and address families may
be added to widen the scope of applicability of Proxy PAR.
References
[AF95] ATM-Forum. LAN Emulation over ATM 1.0. ATM Forum
af-lane-0021.000, January 1995.
[AF96a] ATM-Forum. Interim Local Management Interface (ILMI)
Specification 4.0. ATM Forum 95-0417R8, June 1996.
[AF96b] ATM-Forum. Private Network-Network Interface Specification
Version 1.0. ATM Forum af-pnni-0055.000, March 1996.
[Arm96] G. Armitage. Support for Multicast over UNI 3.0/3.1 based
ATM Networks, RFC 2022. Internet Engineering Task Force,
November 1996.
[Ca96] R. Callon and al. An Overview of PNNI Augmented Routing.
ATM Forum 96-0354, April 1996.
[CH97a] R. Coltun and J. Heinanen. Opaque LSA in OSPF. Internet
Draft, 1997.
Droz, Przygienda Expires 8 September 1998 [Page 11]
Internet Draft Proxy PAR 9 March 1998
[CH97b] R. Coltun and J. Heinanen. The OSPF Address Resolution
Advertisement Option. Internet Draft, 1997.
[CPS96] R. Coltun, T. Przygienda, and S. Shew. MIPAR: Minimal PNNI
Augmented Routing. ATM Forum 96-0838, June 1996.
[Dav97a] M. Davison. ILMI-Based Server Discovery for ATMARP.
Internet Draft, 1997.
[Dav97b] M. Davison. ILMI-Based Server Discovery for MARS. Internet
Draft, 1997.
[Dav97c] M. Davison. ILMI-Based Server Discovery for NHRP. Internet
Draft, 1997.
[For98] ATM Forum. PNNI Augmented Routing (PAR) Version 1.0. ATM
Forum PNNI-RA-PAR-01.04, 1998.
[Lau94] M. Laubach. Classical IP and ARP over ATM, RFC 1577.
Internet Engineering Task Force, January 1994.
[Moy95] J. Moy. Extending OSPF to Support Demand Circuits, RFC
1793. Internet Engineering Task Force, April 1995.
[PD97] T. Przygienda and P. Droz. OSPF over ATM and Proxy PAR.
Internet Draft, 1997.
[Prz97] T. Przygienda. User- and Network Side Proxy PAR Capable
Devices. Detection and Configuration. ATM Forum 97-0555,
July 1997.
Authors' Addresses
Tony Przygienda
Bell Labs, Lucent Technologies
101 Crawfords Corner Road
Holmdel, NJ 07733-3030
prz@dnrc.bell-labs.com
Patrick Droz
IBM Research Division
Zurich Research Laboratory
Droz, Przygienda Expires 8 September 1998 [Page 12]
Internet Draft Proxy PAR 9 March 1998
Saumerstrasse 4
8803 Ruschlikon
Switzerland
dro@zurich.ibm.com
Droz, Przygienda Expires 8 September 1998 [Page 13]
