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Versions: 00 01 02 03 RFC 2844

Internet Engineering Task Force                                  OSPF WG
Internet Draft                             T. Przygienda/P. Droz/R. Haas
draft-ietf-ospf-atm-03.txt                             Siara / IBM / IBM
August 24, 1999
Expires: February 24, 2000


                      OSPF over ATM and Proxy PAR

Status of this memo

This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.

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.

The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt

The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.


Abstract

This draft specifes for OSPF implementors and users mechanisms describ¡
ing how the protocol operates in ATM networks over PVC and SVC meshes
with the presence of Proxy PAR. These recommendations do not require any
protocol changes and allow for simpler, more efficient and cost-effec¡
tive network designs. It is recommended that OSPF implementations should
be able to support logical interfaces, each consisting of one or more
virtual circuits and used either as numbered logical point-to-point
links (one VC), logical NBMA networks (more than one VC) or point-to-
multipoint networks (more than one VC), where a solution simulating
broadcast interfaces is not appropriate. PAR can help to distribute
across the ATM cloud configuration set-up and changes of such interfaces
when OSPF capable routers are (re-)configured. Proxy-PAR can in turn be
used to exchange this information between the ATM cloud and the routers
connected to it.

1 Introduction

Proxy-PAR and PAR have been accepted as standards by the ATM Forum in
January 1999 [1]. A more complete overview of Proxy PAR than in the



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section below is given in [2].

1.1 Introduction to Proxy PAR

Proxy PAR [1] is an extension allowing for different ATM attached
devices (like routers) to interact with PAR capable switches and query
information about non-ATM services without executing PAR themselves. The
Proxy PAR client side in the ATM attached device is much simpler in
terms of implementation complexity and memory requirements than a com¡
plete PAR protocol stack (which includes the full PNNI [3] protocol
stack) and should allow easy implementation in e.g. existing IP routers.
Additionnaly, clients can use Proxy PAR to register different non-ATM
services and protocols they support. Proxy PAR has consciously not been
included as part of ILMI [4] 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 signaling, although
this normally will be the case.

The protocol in itself does not specify how the distributed service reg¡
istration and data delivered to the client is supposed to be driving
other protocols so e.g. OSPF routers finding themselves through Proxy
PAR could use this information in a Classical IP over ATM [5] fashion,
forming a full mesh of point-to-point connections to interact with each
other to simulate broadcast interfaces. For the same purpose LANE [6] or
MARS [7] could be used. As a by-product, Proxy PAR could provide the ATM
address resolution for IP attached devices but such resolution can be
achieved by other protocols under specification at the IETF as well,
e.g. [8]. And last but not least, it should be mentioned here that the
protocol coexists with and complements the ongoing work in IETF on
server detection via ILMI extensions [9,10,11].

1.1.1 Proxy PAR Scopes

Any Proxy PAR registration is carried only within a defined scope that
is set during registration and is equivalent to the PNNI routing level.
Since no assumptions except scope values can be made about the informa¡
tion 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), registration information cannot be summarized.  This makes a
careful handling of scopes necessary to preserve the scalability.  More
details on the usage of scope can be found in [2].

1.2 Introduction to OSPF

OSPF (Open Shortest Path First) is an Interior Gateway Protocol (IGP)
and described in [12] from which most of the following paragraphs has
been taken almost literally. OSPF distributes routing information



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between routers belonging to a single Autonomous System. The OSPF proto¡
col is based on link-state or SPF technology. It was developed by the
OSPF working group of the Internet Engineering Task Force. It has been
designed expressly for the TCP/IP internet environment, including
explicit support for IP subnetting, and the tagging of externally-
derived routing information. OSPF also utilizes IP multicast when send¡
ing/receiving the updates. In addition, much work has been done to pro¡
duce a protocol that responds quickly to topology changes, yet involves
small amounts of routing protocol traffic.

To cope with the needs of NBMA and demand circuits capable networks such
as Frame Relay or X.25, [13] has been made available that standardizes
extensions to the protocol allowing for efficient operation over on-
demand circuits.

OSPF supports three types of networks today:


     ¸ Point-to-point networks: A network that joins a single pair of
       routers. Point- to-point networks can either be numbered or
       unnumbered in the latter case the interfaces do not have IP
       addresses nor masks. Even when numbered, both sides of the link
       do not have to agree on the IP subnet.


     ¸ Broadcast networks: Networks supporting many (more than two)
       attached routers, together with the capability to address a sin¡
       gle physical message to all of the attached routers (broadcast).
       Neighboring routers are discovered dynamically on these networks
       using the OSPF Hello Protocol. The Hello Protocol itself takes
       advantage of the broadcast capability. The protocol makes further
       use of multicast capabilities, if they exist. An Ethernet is an
       example of a broadcast network.


     ¸ Non-broadcast networks: Networks supporting many (more than two)
       attached routers, but having no broadcast capability. Neighboring
       routers are maintained on these nets using OSPF's Hello Protocol.
       However, due to the lack of broadcast capability, some configura¡
       tion information is necessary for the correct operation of the
       Hello Protocol. On these networks, OSPF protocol packets that are
       normally multicast need to be sent to each neighboring router, in
       turn. An X.25 Public Data Network (PDN) is an example of a non-
       broadcast network.

       OSPF runs in one of two modes over non-broadcast networks. The
       first mode, called non-broadcast multi-access (NBMA), simulates
       the operation of OSPF on a broadcast network. The second mode,



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       called Point-to-MultiPoint, treats the non-broadcast network as a
       collection of point-to-point links. Non-broadcast networks are
       referred to as NBMA networks or Point-to-MultiPoint networks,
       depending on OSPF's mode of operation over the network.


2 OSPF over ATM

2.1 Model

Contrary to broadcast-simulation based solutions such as LANE [6] or
Classical IP over ATM [5], this document elaborates on how to handle
virtual OSPF interfaces over ATM such as NBMA, point-to-multipoint or
point-to-point and allow for their auto-configuration in presence of
Proxy PAR. One advantage is the circumvention of server solutions that
often present single points of failure or hold large amounts of configu¡
ration information.

The other main benefit is the possibility to execute OSPF on top of NBMA
and point-to-multpoint ATM networks, and still benefit from the auto¡
matic discovery of OSPF neighbors. As opposed to broadcast networks,
broadcast-simulation based networks (like LANE or Classical IP over
ATM), and point-to-point networks, where an OSPF router dynamically dis¡
covers its neighbors by sending Hello packets to the AllSPFRouters mul¡
ticast address, this is not the case on NBMA and point-to-multipoint
networks. On NBMA networks, the list of all other attached routers to
the same NBMA network has to be manually configured or discovered by
some other means: Proxy PAR allows to automate this configuration. Also
on point-to-multipoint networks, the set of routers that are directly
reachable can be either manually configured or dynamically discovered by
Proxy PAR or through mechanisms like Inverse ATMARP. In an ATM network,
(see 8.2 in [5]) Inverse ATMARP can be used to discover the IP address
of the router at the remote end of a given PVC, whether or not its ATM
address is known. But Inverse ATMARP does not return for instance
whether the remote router is running OSPF, as opposed to Proxy PAR.

Parallel to [14] that describes the recommended operation of OSPF over
Frame Relay networks, a similar model is assumed where the underlying
ATM network can be used to model single VCs as point-to-point interfaces
or collections of VCs as non-broadcast interfaces, whether in NBMA or
point-to-multipoint mode. Such a VC or collection of VCs is called a
logical interface and specified through its type (either point-to-point,
NBMA or point-to-multipoint), VPN ID (the Virtual Private Network to
which interface belongs), address and mask. Layer 2 specific configura¡
tion such as address resolution method, class and quality of service of
used circuits and other must be also included. As logical consequence
thereof, a single, physical interface could encompass multiple IP sub¡
nets or even multiple VPNs. In contrary to layer 2 and IP addressing



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information, when running Proxy PAR, most of the OSPF information needed
to operate such a logical interface does not have to be configured into
routers statically but can be provided through Proxy PAR queries. This
allows for much more dynamic configuration of VC meshes in OSPF environ¡
ments than e.g. in Frame Relay solutions.

Proxy PAR queries can also be issued with a subnet address set to
0.0.0.0, instead of a specific subnet address. This type of query
returns information on all OSPF routers available in all subnets, within
the scope specified in the query. This can be used for instance when the
IP addressing information has not been configured.

2.2 Configuration of OSPF interfaces with Proxy PAR

To achieve the goal of simplification of VC mesh reconfiguration, Proxy
PAR allows the router to learn automatically most of the configuration
that has to be provided to OSPF. Non-broadcast and point-to-point inter¡
face information can be learned across an ATM cloud as described in the
ongoing sections. It is up to the implementation to possibly allow for a
mixture of Proxy PAR autoconfiguration and manual configuration of
neighbor information.  Moreover, manual configuration could e.g. over¡
ride or complement information derived from a Proxy PAR client. Addi¡
tionally, OSPF extensions to handle on-demand circuits [13] can be used
to allow for graceful tearing down of VCs not carrying any OSPF traffic
over prolonged periods of time. The different interactions are described
in sections 2.2.1, 2.2.2 and 2.2.3.

Even after autoconfiguration of interfaces has been provided, the prob¡
lem of VC setups in an ATM network is unsolved since none of the nor¡
mally used mechanisms such as Classical IP [5] or LANE [6] are assumed
to be present. Section 2.5 describes the behavior of OSPF routers neces¡
sary to allow for router connectivity.

2.2.1 Autoconfiguration of Non-Broadcast Multiple-Access (NMBA) Inter¡
faces

Proxy PAR allows to autoconfigure the list of all routers residing on
the same IP network in the same VPN by simply querying the Proxy PAR
server. Each router can easily obtain the list of all OSPF routers on
the same subnet with their router priorities and corresponding ATM
addresses. This is the precondition for OSPF to work properly across
such logical NBMA interfaces. Note that this memberlist, when learned
through Proxy PAR queries, can dynamically change with PNNI (in)stabil¡
ity and general ATM network behavior. It maybe preferable for an imple¡
mentation to withdraw list membership (de-register itself as an OSPF
router) e.g. much slower than detect new members (done by querying).
Relying on OSPF mechanism to discover lack of reachability in the over¡
laying logical IP network could alleviate the risk of thrashing DR



T. Przygienda/P. Droz/R. Haas                                 [Page 5]


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elections and excessive information flooding. Once the DR registration
is completed and the router has not been elected DR or BDR, an implemen¡
tation of [13] can ignore the fact that all routers on the specific NBMA
subnet are available in its configuration since it only needs to main¡
tain VCs to the DR and BDR. Note that this information can serve other
purposes, like for the forwarding of data packets (see section 2.4).

Traditionally, router configuration for a NBMA network provides the list
of all neighboring routers to allow for proper protocol operation. For
stability purposes, the user may choose to provide a list of neighbors
through such static means but additionally enable the operation of Proxy
PAR protocol to complete the list. It is left to specific router imple¡
mentations whether the manual configuration is used in addition to the
information provided by Proxy PAR, used as filter of the dynamic infor¡
mation or whether a concurrent mode of operation is prohibited. In any
case it should be obvious that allowing for more flexibility may facili¡
tate operation but provides more possibilities for misconfiguration as
well.

2.2.2 Autoconfiguration of Point-to-Multipoint Interfaces

Point-to-Multipoint interfaces in ATM networks only make sense if no VCs
can be dynamically set up since an SVC-capable ATM network normally pre¡
sents a NBMA cloud to OSPF. This is e.g. the case if OSPF executes over
a network composed of a partial PVC or SPVC mesh or pre-determined SVC
meshes. Such a network could be modeled using the point-to-multipoint
OSPF interface and the neighbor detection could be provided by Proxy PAR
or other means. In the Proxy PAR case the router queries for all OSPF
routers on the same network in the same VPN but it installs in the
interface configuration only routers that are already reachable through
existing PVCs. The underlying assumption is that a router knows the
remote ATM address of a PVC and can compare it with appropriate Proxy
PAR registrations. If the remote ATM address of the PVC is unknown, it
can be discovered by mechanisms like Inverse ARP [15].

Proxy PAR provides a true OSPF neighbor detection mechanism, whereas a
mechanism like Inverse ARP only returns addresses of directly reachable
routers (which are not necessarily running OSPF), in the point-to-multi¡
point environment.

2.2.3 Autoconfiguration of Numbered Point-to-Point Interfaces

OSPF point-to-point links do not necessarily have an IP address assigned
and even when having one, the mask is undefined. As a precondition to
successfully register a service with Proxy PAR, IP address and mask is
required. Therefore, if a router desires to use Proxy PAR to advertise
the local end of a point-to-point link to the router it intends to form
an adjacency with, an IP address has to be provided and a netmask set or



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a default of 255.255.255.252 (this gives as the default case a subnet
with 2 routers on it) assumed. To allow the discovery of the remote end
of the interface, IP address of the remote side has to be provided and a
netmask set or a default of 255.255.255.252 assumed. Obviously the dis¡
covery can only be successfull when both sides of the interface are con¡
figured with the same network mask and are within the same IP network.
The situation where more than two possible neighbors are discovered
through queries and the interface type is set to point-to-point presents
a configuration error.

Sending multicast Hello packets on the point-to-point links allows to
automatically discover OSPF neighbors. On the other hand, using Proxy
PAR instead avoids sending Hello messages to routers which are not nec¡
essarily running OSPF.

2.2.4 Autoconfiguration of Unnumbered Point-to-Point Interfaces

For reasons given already in [14] using unnumbered point-to-point inter¡
faces with Proxy PAR is not a very attractive alternative since the lack
of an IP address prevents efficient registration and retrieval of con¡
figuration information. Relying on the numbering method based on MIB
entries generates conflicts with the dynamic nature of creation of such
entries and is beyond the scope of this work.

2.3 Registration of OSPF interfaces with Proxy PAR

To allow other routers to discover an OSPF interface automatically, the
IP address, mask, Area ID, interface type and router priority informa¡
tion given must be registered with the Proxy PAR server at an appropri¡
ate scope. A change in any of these parameters has to force a reregis¡
tration with Proxy PAR.

It should be emphasized here that since the registration information can
be used by other routers to resolve IP addresses against NSAPs as
explained in section 2.4, whole IP address of the router must be regis¡
tered. It is not enough to just indicate the subnet up to the mask
length but all address bits must be provided.

2.3.1 Registration of Non-Broadcast Multiple-Access Interfaces

For an NBMA interface the appropriate parameters are available and can
be registered through Proxy PAR without further complications.

2.3.2 Registration of Point-to-Multipoint Interfaces

In case of a point-to-multipoint interface the router registers its
information in the same fashion as in the NBMA case except that the
interface type is modified accordingly.



T. Przygienda/P. Droz/R. Haas                                 [Page 7]


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2.3.3 Registration of Numbered Point-to-Point Interfaces

In case of point-to-point numbered interfaces the address mask is not
specified in the OSPF configuration. If the router has to use Proxy PAR
to advertise its capability, a mask must be defined or a default value
of 255.255.255.252 used.

2.3.4 Registration of Unnumbered Point-to-Point Interfaces

Due to the lack of a configured IP address and difficulties generated by
this fact as described earlier, registration of unnumbered point-to-
point interfaces is not covered in this document.

2.4 IP address to NSAP Resolution Using Proxy PAR

As a byproduct of Proxy PAR presence, an OSPF implementation could use
the information in registrations for the resolution of IP addresses to
ATM NSAPs on a subnet without having to use static data or mechanisms
such as ATMARP [5]. This again should allow for drastic simplification
of number of mechanisms involved in operation of OSPF over ATM to pro¡
vide an IP overlay.

In a system perspective, the OSPF component, the Proxy PAR client, the
IP to NSAP address resolution table, and the ATM circuit manager can be
depicted as in Figure 1. Figure 1 shows an example of components inter¡
actions triggered by the result of a Proxy PAR query from the Proxy PAR
client.


2.5 Connection Setup Mechanisms

This sections describes OSPF behavior in an ATM network under different
assumptions in terms of signaling capabilities and preset connectivity.

2.5.1 OSPF in PVC Environments

In environments where only partial PVCs (or SPVCs) meshes are available
and modeled as point-to-multipoint interfaces, the routers see reachable
routers through autodiscovery provided by Proxy PAR. This leads to
expected OSPF behavior. In cases where a full mesh of PVCs is present,
such a network should preferably be modeled as NBMA. Note that in such a
case, PVCs failures will translate into not so obvious routing failures.

2.5.2 OSPF in SVC Environments


In SVC-capable environments the routers can initiate VCs after having
discovered the appropriate neighbors, preferably driven by the need to



T. Przygienda/P. Droz/R. Haas                                 [Page 8]


Internet Draft         OSPF over ATM and Proxy PAR       August 24, 1999




        __________                      _________
       |          |                    |         |
       |   OSPF   |<-------------------|Proxy PAR|<---(Proxy PAR query)
       |__________|  notify            | client  |
            ^        neighbor changes  |_________|
            |                               |
   send and |                               | maintain Proxy PAR
   receive  |                               | entries in table
   OSPF msg |                               |
            |                               |
            |                               |
        ____V____                       ____V_____
       |   ATM   |                     |          |
       | circuit |-------------------->|IP to NSAP|
       | manager | check               |  table   |
       |_________| IP to NSAP bindings |__________|




    Figure 1: System perspective of typical components interactions





          +           +                             +
          |   +---+   |                             |
   +--+   |---|RTA|---|          +-------+          |   +--+
   |H1|---|   +---+   |          | ATM   |          |---|H2|
   +--+   |           |   +---+  | Cloud |  +---+   |   +--+
          |LAN Y      |---|RTB|-------------|RTC|---|
          +           |   +---+  | PPAR  |  +---+   |
                      +          +-------+          +



     Figure 2: Simple Topology with Router B and Router C operating
               across NBMA ATM interfaces with Proxy PAR


send data such as Hello-packets. This can lead to race conditions where
both sides can open a VC simultaneously. It is generally desirable to
avoid wasting this valuable resource: if the router with lower Router ID
detects that the VC initiated by the other side is bidirectional, it is
free to close its own VC and use the detected one. Note that this either



T. Przygienda/P. Droz/R. Haas                                 [Page 9]


Internet Draft         OSPF over ATM and Proxy PAR       August 24, 1999


requires the OSPF implementation to be aware of the VCs used to send and
receive Hello messages, or the component responsible of managing VCs to
be aware of the usage of particular VCs.

Observe that this behavior operates correctly in case OSPF over Demand
Circuits extensions are used [13] over SVC capable interfaces.

It is possible to avoid most of the time the set-up of redundant VCs by
delaying the sending of the first OSPF Hello from the router with the
lower Router ID, by an amount of time larger than the interval between
the queries from the Proxy PAR client to the server. Chances are that
the router with the higher Router ID opens the VC (or use an already
existing VC) and sends the OSPF Hello first, if its interval between
queries is smaller than the Hello delay of the router with the lower
Router ID. Since this interval can vary depending on particular needs
and implementations, the race conditions described above can still be
expected to happen, albeit presumably less often.

The existence of VCs used for OSPF exchanges is orthogonal to the number
and type of VCs the router chooses to use within the logical interface
to forward data to other routers. OSPF implementations are free to use
any of these VCs (in case they are aware of their existence) to send
packets if their endpoints are adequate and must accept hello packets
arriving on any of the VCs belonging to the logical interface even if
OSPF operating on such an interface is not aware of their existence. An
OSPF implementation may ignore connections being initiated by another
router that has not been discovered by Proxy PAR. The OSPF implementa¡
tion will anyway ignore a neighbor whose Proxy PAR registration indi¡
cates that it is not adjacent.

As an example consider the topology in Figure 2 where router RTB and RTC
are connected to a common ATM cloud offering Proxy PAR services. Assum¡
ing that RTB's OSPF implementation is aware of SVCs initiated on the
interface and RTC only makes minimal use of Proxy PAR information the
following sequence could develop illustrating some of the cases
described above:

     1.   RTC and RTB register with ATM cloud as Proxy PAR capable and
          discover each other as adjacent OSPF routers.

     2.   RTB sends a hello which forces it to establish a SVC connec¡
          tion to RTC.

     3.   RTC sends a hello to RTB but disregards the already existing
          VC and establishes a new VC to RTB to deliver the packet.

     4.   RTB sees a new bi-directional VC and assuming here that RTC's
          OSPF Id is higher, closes the VC originated in step 2.



T. Przygienda/P. Droz/R. Haas                                [Page 10]


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     5.   Host H1 sends data to H2 and RTB establishes a new data SVC
          between itself and RTC.

     6.   RTB sends a Hello to RTC and decides to do it using the newly
          establish data SVC. RTC must accept the hello despite the min¡
          imal implementation.

3 Acknowledgments

Comments and contributions from several sources, especially Rob Coltun,
Doug Dykeman, John Moy and Alex Zinin are included in this work.

4 Security Consideration

Several aspects are to be considered when talking about security of
operating OSPF over ATM and/or Proxy PAR.  The security of registered
information handed to the ATM cloud must be guaranteed by the underlying
PNNI protocol.  Extensions to PNNI are available and given their imple¡
mentation spoofing of registrations and/or denial-of-service issues can
be addressed [16]. The registration itself through proxy PAR is not
secured and appropriate mechanisms are for further study. However, even
if the security at the ATM layer is not guaranteed, OSPF security mecha¡
nisms can be used to verify that detected neighbors are authorized to
interact with the entity discovering them.

5 Bibliography

[1] P. Droz, "PNNI Augmented Routing (PAR) Version 1.0." ATM Forum af-
ra-0104.000, January 1999.

[2] T. P. P. Droz, "Proxy PAR." Internet Draft draft-ietf-ion-proxypar-
arch-01, February 1999.

[3] ATM-Forum, "Private Network-Network Interface Specification Version
1.0." ATM Forum af-pnni-0055.000, March 1996.

[4] ATM-Forum, "Interim Local Management Interface (ILMI) Specification
4.0." ATM Forum 95-0417R8, June 1996.

[5] J. H. M. Laubach, "Classical IP and ARP over ATM, RFC 2225." Inter¡
net Engineering Task Force, April 1998.

[6] ATM-Forum, "LAN Emulation over ATM 1.0." ATM Forum af-lane-0021.000,
January 1995.

[7] G. Armitage, "Support for Multicast over UNI 3.0/3.1 based ATM net¡
works, RFC 2022." Internet Engineering Task Force, November 1996.




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Internet Draft         OSPF over ATM and Proxy PAR       August 24, 1999


[8] R. Coltun, "The OSPF Opaque LSA Option, RFC 2370." Internet Engi¡
neering Task Force, July 1998.

[9] M. Davison, "ILMI-Based Server Discovery for ATMARP, RFC 2601."
Internet Engineering Task Force, June 1999.

[10] M. Davison, "ILMI-Based Server Discovery for MARS, RFC 2602."
Internet Engineering Task Force, June 1999.

[11] M. Davison, "ILMI-Based Server Discovery for NHRP, RFC 2603."
Internet Engineering Task Force, June 1999.

[12] J. Moy, "OSPF Version 2 - RFC 2328." Internet Engineering Task
Force, April 1998.

[13] J. Moy, "Extending OSPF to Support Demand Circuits, RFC 1793."
Internet Engineering Task Force, April 1995.

[14] O. deSouza and M. Rodrigues, "Guidelines for Running OSPF Over
Frame Relay Networks, RFC 1586." Internet Engineering Task Force, March
1994.

[15] A. M. T. Bradley, C. Brown, "Inverse Address Resolution Protocol,
RFC 2390." Internet Engineering Task Force, September 1999.

[16] T. Przygienda and C. Bullard, "Baseline Text for PNNI Peer Authen¡
tication and Cryptographic Data Integrity." ATM Forum 97-0472, July
1997.


Authors' Addresses



Tony Przygienda
Siara Systems
300 Ferguson Drive
Mountain View
California 94043
prz@siara.com

Patrick Droz
IBM Research Division
Saumerstrasse 4
8803 Ruschlikon
Switzerland
dro@zurich.ibm.com




T. Przygienda/P. Droz/R. Haas                                [Page 12]


Internet Draft         OSPF over ATM and Proxy PAR       August 24, 1999


Robert Haas
IBM Research Division
Saumerstrasse 4
8803 Ruschlikon
Switzerland
rha@zurich.ibm.com













































T. Przygienda/P. Droz/R. Haas                                [Page 13]


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