Internet DRAFT - draft-droz-proxypar-arch
draft-droz-proxypar-arch
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Internet Engineering Task Force P. Droz/T. Przygienda
INTERNET DRAFT IBM/Bell Labs, Lucent
19 November 1997
Proxy PAR
<draft-droz-proxypar-arch-00.txt>
Status of This Memo
This document is an Internet Draft, and can be found as
draft-droz-proxypar-arch-00.txt in any standard internet drafts
repository. Internet Drafts are working documents of the Internet
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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 for 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 registered in the network. The mechanisms
are protocol independent but in first version support for IPv4
services mainly has been specified. In addition, Proxy PAR server
capable nodes provide filtering based on IP protocols and address
prefixes. This makes, e.g. possible for router running OSPF to find
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OSPF neighbors on the same subnet. The protocol is built using a
registration/query 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
[PD97b] 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 [PD97b].
Proxy PAR is a protocol allowing for different ATM attached devices
(ATM and non-ATM devices) to interact with PAR capable switches
and obtain 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 and should allow for easy implementation in, for example,
existing 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 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 context or reference model is therefore aligned with the
one included in [AF96a].
The protocol does not specify how a client should make use of the
obtained information, e.g. OSPF routers finding themselves through
Proxy PAR could use this information in RFC1577 [Lau94] fashion,
forming a full mesh of P2P VCs 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 [PD97a].
Further work will address other protocols such as BGP-4.
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The protocol has the ability to provide ATM address resolution for IP
attached devices as well, but such resolution can also be achieved by
other protocols under specification in IETF, e.g. [CH97b, CH97a].
Again, the main purpose of the protocol is to allow the automatic
detection of devices over an ATM cloud in a distributed fashion,
ommitting 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
communications between adjacent clients and servers. The registra-
tion 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. 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 a PNNI routing level
(scope) with the service that restricts the flooding of the service
definition within the PNNI network. Nodes within the PNNI network
take into account the associated scope of the information when
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+-+
| | 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)
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. In
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
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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
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.
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
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)
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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
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 NSAPs are not assumed to be aligned with them
in any respect such as encapsulation or functional mapping), 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 relation 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 and set its refresh interval to a value
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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 an IP instance, IP address, subnet
mask, and IP protocol family. In this context, each IP instance
refers to a completely separate IP address space. For example <A,
194.191.1.01, 255.255.255.0, OSPF> describes an OSPF interface in the
IP instance A. In addition to the IP scope further information can be
registered that includes 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 in query
descriptions. 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 NSAP and 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.
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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
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.
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 PNNI routing level, 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.
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 a
generic information element exists that 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
capabilities on the network as well as user side is crucial. The
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Protocol | Additional Info
______________|__________________
OSPF | yes
RIP |
RIPv2 |
BGP3 |
BGP4 | yes
EGP |
IDPR |
MOSPF | yes
DVMRP |
CBT |
PIMS |
IGRP |
IS-IS |
ES-IS |
ICMP |
GGP |
BBN SPF IGP|
MARS |
NHRP |
ATMARP |
DHCP |
DNS | yes
Table 2: Additional Protocol Information Carried in Proxy PAR
necessary extensions to ILMI to perform this detection in an
automatic manner have been introduced in [Prz97].
6. Security Consideration
Security aspects are not addressed in this memo.
7. 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
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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.
[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.
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[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.
[PD97a] T. Przygienda and P. Droz. OSPF over ATM and Proxy PAR.
Internet Draft, 1997.
[PD97b] T. Przygienda and P. Droz. Proxy PAR. ATM Forum 97-0495,
97-0705, 97-0882, July 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
Saumerstrasse 4
8803 Ruschlikon
Switzerland
dro@zurich.ibm.com
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