draft-ietf-ospf-atm-01.txt   draft-ietf-ospf-atm-02.txt 
Internet Engineering Task Force T. Przygienda/P. Droz/R.
Internet Engineering Task Force T. Przygienda/P. Droz Haas
INTERNET DRAFT Bell Labs/IBM INTERNET DRAFT Bell
5 March 1998 Labs/IBM
15 June
1999
OSPF over ATM and Proxy PAR OSPF over ATM and Proxy PAR
<draft-ietf-ospf-atm-01.txt> <draft-ietf-ospf-atm-02.txt>
Status of This Memo Status of This Memo
This document is an Internet Draft, and can be found as
draft-ietf-ospf-atm-01.txt in any standard internet drafts This document is an Internet Draft and is in full conformance with
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Abstract Abstract
This draft specifes for OSPF implementors and users mechanisms This draft specifes for OSPF implementors and users mechanisms
describing how the protocol operates in ATM networks over PVC and SVC describing how the protocol operates in ATM networks over PVC and
meshes with the presence of Proxy PAR. These recommendations do not SVC meshes with the presence of Proxy PAR. These recommendations
require any protocol changes and allow for simpler, more efficient do not require any protocol changes and allow for simpler, more
and cost-effective network designs. It is recommended that OSPF efficient and cost-effective network designs. It is recommended that
implementations should be able to support logical interfaces, each OSPF implementations should be able to support logical interfaces,
consisting of one or more virtual circuits and used as numbered each consisting of one or more virtual circuits and used either
logical point-to-point links (one VC) or logical NBMA networks (more as numbered logical point-to-point links (one VC), logical NBMA
than one VC) where a solution simulating broadcast interfaces is not networks (more than one VC) or point-to-multipoint networks (more
appropriate. PAR can help to distribute configuration changes of than one VC), where a solution simulating broadcast interfaces is
such interfaces when OSPF capable routers are reconfigured on the ATM not appropriate. PAR can help to distribute across the ATM cloud
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.
Internet Draft OSPF over ATM and Proxy PAR 15 June
1999
1. Introduction 1. Introduction
1.1. Introduction to PAR Proxy-PAR and PAR have been accepted as standards by the ATM Forum in
January 1999 [Dro99 ]. A more complete overview of Proxy PAR than in
the section below is given in [PD99 ].
PNNI Augmented Routing (PAR) [For98] is an extension to PNNI [AF96b] 1.1. Introduction to Proxy PAR
routing to allow information about non-ATM services to be distributed
in an ATM network as part of the PNNI topology. The content and
format of the information is specified by PAR but is transparent to
PNNI routing. A PAR-capable device, one that implements PNNI and the
PAR extension, is able to create PAR PTSEs that describe the non-ATM
services located on or behind that device. Because this information
is flooded by PNNI routing, PAR-capable devices are also able to
examine the PAR PTSEs in the topology database that were originated
by other nodes to obtain information on desired services reachable
through the ATM network. An important example of how PAR can be used
is provided by overlay routing on ATM backbones. If the routers
are PAR-capable, they can create PTSEs to advertise the routing
protocol supported on the given interface (e.g., OSPF, RIP, or BGP),
along with their IP address and subnet, and other protocol-specific
details. The PAR-capable routers can also automatically learn about
"compatible" routers (e.g., supporting the same routing protocol,
in the same IP subnet) active in the same ATM network. In this
manner the overlay routing network can be established automatically
on an ATM backbone. The mechanism is dynamic, and does not require
configuration. One potential drawback of PAR is that a device must
implement PNNI in order to participate. Therefore an additional set
of optional protocols called Proxy PAR has been defined to allow a
client that is not PAR-capable to interact with a server that is
PAR-capable and thus obtain the PAR capabilities. The server acts as
a proxy for the client in the operation of PAR. The client is able to
register its own services, and query the server to obtain information
on compatible services available in the ATM network. A key feature
of PAR and Proxy PAR is the ability to provide VPN support in a
simple yet very effective manner. All PAR information is tagged
with a VPN ID and can therefore be filtered on that basis. This can
be used for example, in a service provider network. Each customer
can be provided with a unique VPN ID that is part of all Proxy PAR
registrations and queries. Usage of the correct VPN ID can easily
be enforced at the Proxy PAR server. In this way the services of a
given customer will be available only to clients in that customer's
network.
1.1.1. Overview of PNNI Augmented Routing (PAR) Proxy PAR [Dro99 ] 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 complete PAR protocol stack (which
includes the full PNNI [AF96b ] 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 [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
signaling, although this normally will be the case.
PNNI Augmented Routing (PAR) is an extension to PNNI to allow the The protocol in itself does not specify how the distributed service
flooding of information about non-ATM devices. PAR uses a new PTSE registration and data delivered to the client is supposed to be
type to carry this non-ATM-related information. The current version driving other protocols so e.g. OSPF routers finding themselves
of PAR specifies IGs for the flooding of IPv4-related protocol through Proxy PAR could use this information in a Classical IP over
information such as OSPF or BGP. In addition PAR also allows the use ATM [ML98 ] fashion, forming a full mesh of point-to-point connections
of the System Capabilities IG, which can be used to carry proprietary to interact with each other to simulate broadcast interfaces. For
or experimental information. the same purpose LANE [AF95 ] or MARS [Arm96 ] 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. [Col98 ].
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 [Dav99a , Dav99b , Dav99c ].
PAR supports extensive filtering possibilities, which allow the 1.1.1. Proxy PAR Scopes
implementation of virtual private networks (VPN). As PAR is a
PNNI extension, it can reuse existing PNNI routing level scopes.
In addition, PAR provides filtering in terms of a VPN ID, IP
address, including a subnet mask, as well as protocol flags. The
correct filtering according to these parameters is part of a PAR
implementation.
1.1.2. Overview of Proxy PAR 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 information distributed (e.g. IP addresses bound to NSAPs
Proxy PAR is a protocol that allows for different ATM attached Przygienda, Droz, Haas Expires 15 December 1999 [Page
devices to interact with PAR-capable switches and obtain information 2]
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 easy
implementation in, for example, existing IP routers. Clients can use
Proxy PAR to register different non-ATM services and protocols they
support. This protocol has deliberately not been included as part of
ILMI [AF96a] owing 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 will
normally be the case.
The protocol does not specify how the distributed service
registration and data delivered to the client are supposed to drive
other protocols. For example, OSPF routers finding themselves
through Proxy PAR could use this information to form a full mesh of
P2P VCs and communicate using RFC1483 [Hei93] encapsulation. In
terms of the discovery of other devices such as IP routers, Proxy PAR
is an alternative to LANE [AF95] or MARS [Arm96]. It is expected
that the guidelines defining how a certain protocol can make use of
Proxy PAR and PAR should come from the group or standardization body
that is responsible for the particular protocol.
PAR and Proxy PAR have the ability to provide ATM address resolution Internet Draft OSPF over ATM and Proxy PAR 15 June
for IP attached devices, but such resolution can also be achieved by 1999
other protocols under specification in IETF e.g. [CH97a, CH97b].
However, the main purpose of the protocol is to allow the automatic are not assumed to be aligned with them in any respect such as
detection of devices over an ATM cloud in a distributed fashion, not encapsulation or functional mapping), registration information cannot
relying on a broadcast facility. Finally, it should be mentioned be summarized. This makes a careful handling of scopes necessary to
that the protocol complements and coexists with server detection via preserve the scalability. More details on the usage of scope can be
ILMI extensions. found in [PD99 ].
1.2. Introduction to OSPF 1.2. Introduction to OSPF
OSPF (Open Shortest Path First) is an Interior Gateway Protocol (IGP)
and described in [Moy94, Moy97] from which most of the following OSPF (Open Shortest Path First) is an Interior Gateway Protocol
(IGP) and described in [Moy98 ] from which most of the following
paragraphs has been taken almost literally. OSPF distributes routing paragraphs has been taken almost literally. OSPF distributes routing
information between routers belonging to a single Autonomous System. information between routers belonging to a single Autonomous System.
The OSPF protocol is based on link-state or SPF technology. It was The OSPF protocol is based on link-state or SPF technology. It was
developed by the OSPF working group of the Internet Engineering developed by the OSPF working group of the Internet Engineering
Task Force. It has been designed expressly for the TCP/IP internet Task Force. It has been designed expressly for the TCP/IP internet
environment, including explicit support for IP subnetting, and environment, including explicit support for IP subnetting, and
the tagging of externally-derived routing information. OSPF also the tagging of externally-derived routing information. OSPF also
utilizes IP multicast when sending/receiving the updates. In utilizes IP multicast when sending/receiving the updates. In
addition, much work has been done to produce a protocol that responds addition, much work has been done to produce a protocol that responds
quickly to topology changes, yet involves small amounts of routing quickly to topology changes, yet involves small amounts of routing
skipping to change at page 4, line 39 skipping to change at line 140
- Point-to-point networks: A network that joins a single pair - Point-to-point networks: A network that joins a single pair
of routers. Point- to-point networks can either be numbered of routers. Point- to-point networks can either be numbered
or unnumbered in the latter case the interfaces do not have IP or unnumbered in the latter case the interfaces do not have IP
addresses nor masks. Even when numbered, both sides of the link addresses nor masks. Even when numbered, both sides of the link
do not have to agree on the IP subnet. do not have to agree on the IP subnet.
- Broadcast networks: Networks supporting many (more than two) - Broadcast networks: Networks supporting many (more than two)
attached routers, together with the capability to address attached routers, together with the capability to address
a single physical message to all of the attached routers a single physical message to all of the attached routers
(broadcast). Neighboring routers are discovered dynamically (broadcast). Neighboring routers are discovered dynamically on
on these nets using OSPF's Hello Protocol. The Hello Protocol these networks using the OSPF Hello Protocol. The Hello Protocol
itself takes advantage of the broadcast capability. The protocol itself takes advantage of the broadcast capability. The protocol
makes further use of multicast capabilities, if they exist. An makes further use of multicast capabilities, if they exist. An
Ethernet is an example of a broadcast network. Ethernet is an example of a broadcast network.
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- Non-broadcast networks: Networks supporting many (more than - Non-broadcast networks: Networks supporting many (more than
two) attached routers, but having no broadcast capability. two) attached routers, but having no broadcast capability.
Neighboring routers are maintained on these nets using Neighboring routers are maintained on these nets using
OSPF's Hello Protocol. However, due to the lack of broadcast OSPF's Hello Protocol. However, due to the lack of broadcast
capability, some configuration information is necessary for the capability, some configuration information is necessary for the
correct operation of the Hello Protocol. On these networks, OSPF correct operation of the Hello Protocol. On these networks, OSPF
protocol packets that are normally multicast need to be sent to protocol packets that are normally multicast need to be sent to
each neighboring router, in turn. An X.25 Public Data Network each neighboring router, in turn. An X.25 Public Data Network
(PDN) is an example of a non-broadcast network. (PDN) is an example of a non-broadcast network.
OSPF runs in one of two modes over non-broadcast networks. The OSPF runs in one of two modes over non-broadcast networks. The
first mode, called non-broadcast multi-access (NBMA), simulates first mode, called non-broadcast multi-access (NBMA), simulates
skipping to change at page 5, line 22 skipping to change at line 170
OSPF runs in one of two modes over non-broadcast networks. The OSPF runs in one of two modes over non-broadcast networks. The
first mode, called non-broadcast multi-access (NBMA), simulates first mode, called non-broadcast multi-access (NBMA), simulates
the operation of OSPF on a broadcast network. The second mode, the operation of OSPF on a broadcast network. The second mode,
called Point-to-MultiPoint, treats the non-broadcast network as a called Point-to-MultiPoint, treats the non-broadcast network as a
collection of point-to-point links. Non-broadcast networks are collection of point-to-point links. Non-broadcast networks are
referred to as NBMA networks or Point-to-MultiPoint networks, referred to as NBMA networks or Point-to-MultiPoint networks,
depending on OSPF's mode of operation over the network. depending on OSPF's mode of operation over the network.
2. OSPF over ATM 2. OSPF over ATM
2.1. Model 2.1. Model
Contrary to broadcast-simulation based solutions such as LANE [AF95] Contrary to broadcast-simulation based solutions such as LANE
or RFC1577 [Lau94], this RFC elaborates on how to handle virtual OSPF [AF95 ] or Classical IP over ATM [ML98 ], this document elaborates
interfaces over ATM such as NBMA, point-to-multipoint or point-to-point on how to handle virtual OSPF interfaces over ATM such as
and allow for their auto-configuration in presence of Proxy PAR. NBMA, point-to-multipoint or point-to-point and allow for their
One advantage is the circumvention of server solutions that often auto-configuration in presence of Proxy PAR. One advantage is the
present single points of failure or hold large amounts of configuration circumvention of server solutions that often present single points of
information. The other main benefit is the possibility to execute OSPF failure or hold large amounts of configuration information.
on top of partially meshed VC topologies.
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 automatic 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
discovers its neighbors by sending Hello packets to the AllSPFRouters
multicast 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 must be configured: it can be dynamically discovered
by Proxy PAR or through mechanisms like Inverse ATMARP. In an ATM
network, (see 8.2 in [ML98 ]) Inverse ATMARP can be used to discover the
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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 [dR94] that describes the recommended operation of Parallel to [dR94] that describes the recommended operation of
OSPF over Frame Relay networks, a similar model is assumed where OSPF over Frame Relay networks, a similar model is assumed where
the underlying ATM network can be used to model single VCs as the underlying ATM network can be used to model single VCs as
point-to-point interfaces or collections of VCs can be accessed as an point-to-point interfaces or collections of VCs as non-broadcast
non-broadcast interface in NBMA or point-to-multipoint mode. Such a interfaces, whether in NBMA or point-to-multipoint mode. Such
VC or collection of VCs is called a logical interface and specified a VC or collection of VCs is called a logical interface and
through its type (either point-to-point, NBMA or point-to-point), specified through its type (either point-to-point, NBMA or
IP instance (presenting an incarnation of IP with its own address point-to-multipoint), VPN ID (the Virtual Private Network to which
spaces), address and mask. Layer 2 specific configuration such as interface belongs), address and mask. Layer 2 specific configuration
address resolution method, class and quality of service of used such as address resolution method, class and quality of service
circuits and other must be also included. As logical consequence of used circuits and other must be also included. As logical
thereof, a single, physical interface could encompass multiple IP consequence thereof, a single, physical interface could encompass
subnets or even multiple, independent IP instances. In contrary to multiple IP subnets or even multiple VPNs. In contrary to layer 2
layer 2 and IP addressing information, when running Proxy PAR, most and IP addressing information, when running Proxy PAR, most of the
of the OPSF information needed to operate such a logical interface OSPF information needed to operate such a logical interface does not
does not have to be configured into routers statically but can be have to be configured into routers statically but can be provided
provided through Proxy PAR queries. This allows for much more through Proxy PAR queries. This allows for much more dynamic
dynamic configuration of VC meshes in OSPF environments than e.g. in configuration of VC meshes in OSPF environments than e.g. in Frame
Frame Relay solutions. 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
2.2. OSPF Configuration Interaction with Proxy PAR
To achieve the goal of simplification of VC mesh reconfiguration, To achieve the goal of simplification of VC mesh reconfiguration,
Proxy PAR allows the router to learn automatically most of the Proxy PAR allows the router to learn automatically most of the
configuration that has to be provided to OSPF. Non-broadcast configuration that has to be provided to OSPF. Non-broadcast
and point-to-point interface information can be learned across and point-to-point interface information can be learned across
an ATM cloud as described in the ongoing sections. It is up to an ATM cloud as described in the ongoing sections. It is up to
the implementation to possibly allow for a mixture of Proxy PAR the implementation to possibly allow for a mixture of Proxy PAR
autoconfiguration and manual configuration of neighbor information. autoconfiguration and manual configuration of neighbor information.
Moreover, manual configuration could e.g. override or complement Moreover, manual configuration could e.g. override or complement
information derived from a proxy PAR client. Additionally, OSPF information derived from a Proxy PAR client. Additionally, OSPF
extensions to handle on-demand circuits [Moy95] can be used to allow extensions to handle on-demand circuits [Moy95] can be used to allow
for graceful tearing down of VCs not carrying any OSPF traffic over for graceful tearing down of VCs not carrying any OSPF traffic over
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prolonged periods of time. The different interactions are described prolonged periods of time. The different interactions are described
in sections 2.2.1, 2.2.2 and 2.2.3. in sections 2.2.1, 2.2.2 and 2.2.3.
Even after autoconfiguration of interfaces has been provided, the Even after autoconfiguration of interfaces has been provided, the
problem of VC setups in an ATM network is unsolved since none of the problem of VC setups in an ATM network is unsolved since none of the
normally used mechanisms such as RFC1577 [Lau94] or LANE [AF95] are normally used mechanisms such as Classical IP [ML98 ] or LANE [AF95 ]
assumed to be present. Section 2.5 describes the behavior of OSPF are assumed to be present. Section 2.5 describes the behavior of
routers to allow for router connectivity necessary. OSPF routers necessary to allow for router connectivity.
2.2.1. Autoconfiguration of Non-Broadcast Interfaces 2.2.1. Autoconfiguration of Non-Broadcast Multiple-Access (NMBA)
Interfaces
Proxy PAR allows to autoconfigure the list of all routers residing Proxy PAR allows to autoconfigure the list of all routers residing on
on the same IP network in the same IP instance by simply querying the same IP network in the same VPN by simply querying the Proxy PAR
the Proxy PAR server. Each router can easily obtain the list of server. Each router can easily obtain the list of all OSPF routers
all OSPF routers on the same subnet with their router priorities on the same subnet with their router priorities and corresponding
and ATM address bindings. This is the precondition for OSPF to ATM addresses. This is the precondition for OSPF to work properly
work properly across such logical NBMA interfaces. Note that the across such logical NBMA interfaces. Note that this memberlist, when
memberlist, when learned through Proxy PAR queries, can dynamically learned through Proxy PAR queries, can dynamically change with PNNI
change with PNNI (in)stability and general ATM network behavior. It (in)stability and general ATM network behavior. It maybe preferable
maybe preferable for an implementation to withdraw list membership for an implementation to withdraw list membership (de-register
e.g. much slower than detect new members. Relying on OSPF mechanism itself as an OSPF router) e.g. much slower than detect new members
to discover lack of reachability in the overlaying logical IP network (done by querying). Relying on OSPF mechanism to discover lack of
could alleviate the risk of thrashing DR elections and excessive reachability in the overlaying logical IP network could alleviate the
information flooding. Once the DR registration is completed and the risk of thrashing DR elections and excessive information flooding.
router has not been elected DR or BDR, an implementation of [Moy95] Once the DR registration is completed and the router has not been
can ignore the fact that all routers on the specific NBMA subnet are elected DR or BDR, an implementation of [Moy95 ] can ignore the fact
available in its configuration since it only needs to maintain VCs to that all routers on the specific NBMA subnet are available in its
the DR and BDR. configuration since it only needs to maintain VCs to the DR and BDR.
Traditionally, router configuration for a NBMA network provides Traditionally, router configuration for a NBMA network provides
the list of all neighboring routers to allow for proper protocol the list of all neighboring routers to allow for proper protocol
operation. For stability purposes, the user may choose to provide a operation. For stability purposes, the user may choose to provide a
list of neighbors through such static means but additionally enable the list of neighbors through such static means but additionally enable
operation of Proxy PAR protocol to complete the list. It is left to the operation of Proxy PAR protocol to complete the list. It is left
specific router implementations whether the manual configuration is used to specific router implementations whether the manual configuration
in addition to the information provided by Proxy PAR, used as filter of is used in addition to the information provided by Proxy PAR, used
the dynamic information or whether a concurrent mode of operation is as filter of the dynamic information or whether a concurrent mode
prohibited. In any case it should be obvious that allowing for more of operation is prohibited. In any case it should be obvious that
flexibility may facilitate operation but provides more possibilities for allowing for more flexibility may facilitate operation but provides
misconfiguration as well. more possibilities for misconfiguration as well.
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2.2.2. Autoconfiguration of Point-to-Multipoint Interfaces 2.2.2. Autoconfiguration of Point-to-Multipoint Interfaces
Point-to-Multipoint interfaces in ATM networks only make sense if Point-to-Multipoint interfaces in ATM networks only make sense if
no VCs can be dynamically set up since an SVC-capable ATM network no VCs can be dynamically set up since an SVC-capable ATM network
normally presents a NBMA cloud to OSPF. This is e.g. the case if normally presents a NBMA cloud to OSPF. This is e.g. the case if
the intended use of the network is only to execute OSPF in presence OSPF executes over a network composed of a partial PVC or SPVC mesh
of a partial PVC or SPVC mesh or pre-determined SVC meshes. Such or pre-determined SVC meshes. Such a network could be modeled using
a collection could be modeled using the point-to-multipoint OSPF the point-to-multipoint OSPF interface and the neighbor detection
interface and the neighbor detection could be provided by Proxy could be provided by Proxy PAR or other means. In the Proxy PAR case
PAR or other means. In Proxy PAR case the router queries for all the router queries for all OSPF routers on the same network in the
OSPF routers on the same network in the same IP instance but it same VPN but it installs in the interface configuration only routers
installs in the interface configuration only routers that are already that are already reachable through existing PVCs. The underlying
reachable through preset PVCs. The underlying assumption is that a assumption is that a router knows the remote ATM address of a PVC
router understands the remote NSAP of a PVC and can compare it with and can compare it with appropriate Proxy PAR registrations. If the
appropriate Proxy PAR registrations. If the remote NSAP of the PVC remote ATM address of the PVC is unknown, it can be discovered by
is unknown, alternative autodiscovery mechanisms have to be used e.g. mechanisms like Inverse ARP [TB99 ].
inverse ARP [BB92, LH96].
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-multipoint environment.
2.2.3. Autoconfiguration of Numbered Point-to-Point Interfaces 2.2.3. Autoconfiguration of Numbered Point-to-Point Interfaces
OSPF point-to-point links do not necessarily have an IP address OSPF point-to-point links do not necessarily have an IP address
assigned and even when having one, the mask is undefined. As a assigned and even when having one, the mask is undefined. As a
precondition to successfully register a service with Proxy PAR, IP precondition to successfully register a service with Proxy PAR, IP
address and mask is required. Therefore, if a router desires to use 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 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 router it intends to form an adjacency with, an IP address has to
be provided and a netmask set or a default of 255.255.255.254 (this be provided and a netmask set or a default of 255.255.255.254 (this
gives as the default case a subnet with 2 routers on it) assumed. To 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 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 the remote side has to be provided and a netmask set or a default
of 255.255.255.254 assumed. Obviously the discovery can only be of 255.255.255.254 assumed. Obviously the discovery can only be
successfull when both sides of the interface are configured with the successfull when both sides of the interface are configured with the
same network mask and are within the same IP network. The situation same network mask and are within the same IP network. The situation
where more than two possible neighbors are discovered through where more than two possible neighbors are discovered through
queries and the interface type is set to point-to-point presents a queries and the interface type is set to point-to-point presents a
configuration error. 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
necessarily running OSPF.
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2.2.4. Autoconfiguration of Unnumbered Point-to-Point Interfaces 2.2.4. Autoconfiguration of Unnumbered Point-to-Point Interfaces
For reasons given already in [dR94] using unnumbered point-to-point For reasons given already in [dR94] using unnumbered point-to-point
interfaces with Proxy PAR is not a very attractive alternative interfaces with Proxy PAR is not a very attractive alternative
since the lack of an IP address prevents efficient registration and since the lack of an IP address prevents efficient registration and
retrieval of configuration information. Relying on the numbering retrieval of configuration information. Relying on the numbering
method based on MIB entries generates conflicts with the dynamic method based on MIB entries generates conflicts with the dynamic
nature of creation of such entries and is beyond the scope of this nature of creation of such entries and is beyond the scope of this
work. work.
2.3. Proxy PAR Interaction with OSPF Configuration 2.3. Registration of OSPF interfaces with Proxy PAR
To allow other routers to discover an OSPF interface automatically, To allow other routers to discover an OSPF interface automatically,
the IP address, mask, Area ID, interface type and router priority the IP address, mask, Area ID, interface type and router priority
information given must be registered with the Proxy PAR server at an information given must be registered with the Proxy PAR server at an
appropriate scope. A change in any of these parameters has to force appropriate scope. A change in any of these parameters has to force
a reregistration with Proxy PAR. a reregistration with Proxy PAR.
It should be emphasized here that since the registration information It should be emphasized here that since the registration information
can be used by other routers to resolve IP addresses against NSAPs as can be used by other routers to resolve IP addresses against NSAPs as
explained in section 2.4 already, whole IP address of the router must explained in section 2.4 already, whole IP address of the router must
be registered. It is not enough to just indicate the subnet up to be registered. It is not enough to just indicate the subnet up to
the mask length but all address bits must be provided. the mask length but all address bits must be provided.
2.3.1. Registration of Non-Broadcast Interfaces 2.3.1. Registration of Non-Broadcast Multiple-Access Interfaces
For an NBMA interface the appropriate parameters are available and For an NBMA interface the appropriate parameters are available and
can be registered through Proxy PAR without further complications. can be registered through Proxy PAR without further complications.
2.3.2. Registration of Point-to-Multipoint Interfaces 2.3.2. Registration of Point-to-Multipoint Interfaces
In case of a point-to-multipoint interface the router registers its 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 information in the same fashion as in the NBMA case except that the
interface type is modified accordingly. interface type is modified accordingly.
2.3.3. Registration of Point-to-Point Interfaces 2.3.3. Registration of Numbered Point-to-Point Interfaces
In case of point-to-point numbered interfaces the address mask is not 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 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 PAR to advertise its capability, a mask must be defined or a default
value of 255.255.255.254 used. value of 255.255.255.254 used.
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2.3.4. Registration of Unnumbered Point-to-Point Interfaces 2.3.4. Registration of Unnumbered Point-to-Point Interfaces
Due to the lack of a configured IP address and difficulties generated Due to the lack of a configured IP address and difficulties generated
by this fact as described earlier, registration of unnumbered by this fact as described earlier, registration of unnumbered
point-to-point interfaces is not covered in this document. point-to-point interfaces is not covered in this document.
2.4. IP address to NSAP Resolution Using Proxy PAR 2.4. IP address to NSAP Resolution Using Proxy PAR
As a byproduct of Proxy PAR presence, an OSPF implementation As a byproduct of Proxy PAR presence, an OSPF implementation could
could use the information in registrations for the resolution of IP use the information in registrations for the resolution of IP
addresses to ATM NSAPs on a subnet without having to use static data or addresses to ATM NSAPs on a subnet without having to use static data
mechanisms such as ATMARP [LH96]. This again should allow for drastic or mechanisms such as ATMARP [ML98 ]. This again should allow for
simplification of number of mechanisms involved in operation of OSPF drastic simplification of number of mechanisms involved in operation
over ATM to provide an IP overlay. of OSPF over ATM to provide an IP overlay.
2.5. Connection Setup Mechanisms 2.5. Connection Setup Mechanisms
This sections describes OSPF behavior in an ATM network under This sections describes OSPF behavior in an ATM network under
different assumptions in terms of signaling capabilities and preset different assumptions in terms of signaling capabilities and preset
connectivity. connectivity.
2.5.1. OSPF in PVC Environments 2.5.1. OSPF in PVC Environments
In environments where only partial PVCs (or SPVCs) meshes are In environments where only partial PVCs (or SPVCs) meshes are
available and modeled as point-to-multipoint interfaces, the routers available and modeled as point-to-multipoint interfaces, the routers
see reachable routers through autodiscovery provided by Proxy PAR. see reachable routers through autodiscovery provided by Proxy PAR.
This leads to expected OSPF behavior. In cases where a full mesh of This leads to expected OSPF behavior. In cases where a full mesh of
PVCs is present, such an interface should preferably be modeled as PVCs is present, such a network should preferably be modeled as NBMA.
broadcast and Proxy PAR discovery should be superfluous.
2.5.2. OSPF in SVC Environments 2.5.2. OSPF in SVC Environments
In SVC-capable environments the routers can initiate VCs after having In SVC-capable environments the routers can initiate VCs after having
discovered the appropriate neighbors, preferably driven by the need discovered the appropriate neighbors, preferably driven by the need
to send data such as Hello-packets. Since this can lead to race to send data such as Hello-packets. Since this can lead to race
conditions where both sides can open a VC and it is desirable to conditions where both sides can open a VC and it is desirable to
minimize this valuable resource, if the router with lower Router ID minimize 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.
Observe that this behavior operates correctly in case OSPF over
Demand Circuits extensions are used [Moy95 ] over SVC capable
interfaces.
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+ + + + + +
| +---+ | | | +---+ | |
+--+ |---|RTA|---| +-------+ | +--+ +--+ |---|RTA|---| +-------+ | +--+
|H1|---| +---+ | | ATM | |---|H2| |H1|---| +---+ | | ATM | |---|H2|
+--+ | | +---+ | Cloud | +---+ | +--+ +--+ | | +---+ | Cloud | +---+ | +--+
|LAN Y |---|RTB|-------------|RTC|---| |LAN Y |---|RTB|-------------|RTC|---|
+ | +---+ | PPAR | +---+ | + | +---+ | PPAR | +---+ |
+ +-------+ + + +-------+ +
Figure 1: Simple Topology with Router B and Router C operating across Figure 1: Simple Topology with Router B and Router C operating across
NBMA ATM interfaces with Proxy PAR NBMA ATM interfaces with Proxy PAR
detects that the VC initiated by the other side is bidirectional, it
is free to close its own VC and use the detected one. Observe that
this behavior operates correctly in case OSPF over Demand Circuits
extensions are used [Moy95] over SVC capable interfaces.
The existence of VCs used for OSPF exchanges is orthogonal to the 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 number and type of VCs the router chooses to use within the logical
interface to forward data to other routers. OSPF implementations are interface to forward data to other routers. OSPF implementations are
free to use any of these VCs (1) to send packets if their endpoints free to use any of these VCs (1) to send packets if their endpoints
are adequate and must accept hello packets arriving on any of the VCs 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 belonging to the logical interface even if OSPF operating on such an
interface is not aware of their existence. An OSPF implementation interface is not aware of their existence. An OSPF implementation
may not accept or close connections being initiated by another router may not accept or close connections being initiated by another router
that has either not been discovered by Proxy PAR or whose Proxy PAR that has either not been discovered by Proxy PAR or whose Proxy PAR
registration is indicating that it is not adjacent. registration is indicating that it is not adjacent.
skipping to change at page 10, line 41 skipping to change at line 480
As an example consider the topology in figure 2.5.2 where router As an example consider the topology in figure 2.5.2 where router
RTB and RTC are connected to a common ATM cloud offering Proxy PAR RTB and RTC are connected to a common ATM cloud offering Proxy PAR
services. Assuming that RTB's OSPF implementation is aware of SVCs services. Assuming that RTB's OSPF implementation is aware of SVCs
initiated on the interface and RTC only makes minimal use of Proxy initiated on the interface and RTC only makes minimal use of Proxy
PAR information the following sequence could develop illustrating PAR information the following sequence could develop illustrating
some of the cases described above: some of the cases described above:
1. RTC and RTB register with ATM cloud as Proxy PAR capable and 1. RTC and RTB register with ATM cloud as Proxy PAR capable and
discover each other as adjacent OSPF routers. discover each other as adjacent OSPF routers.
___________________________________________
1. in case they are aware of their existence
2. RTB sends a hello which forces it to establish a SVC connection 2. RTB sends a hello which forces it to establish a SVC connection
to RTC. to RTC.
___________________________________________
1. in case they are aware of their existence
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3. RTC sends a hello to RTB but disregards the already existing VC 3. RTC sends a hello to RTB but disregards the already existing VC
and establishes a new VC to RTB to deliver the packet. 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 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. OSPF Id is higher, closes the VC originated in step 2.
5. Host H1 sends data to H2 and RTB establishes a new data SVC 5. Host H1 sends data to H2 and RTB establishes a new data SVC
between itself and RTC. between itself and RTC.
6. RTB sends a Hello to RTC and decides to do it using the newly 6. RTB sends a Hello to RTC and decides to do it using the newly
skipping to change at page 11, line 35 skipping to change at line 522
Several aspects are to be considered when talking about security of Several aspects are to be considered when talking about security of
operating OSPF over ATM and/or Proxy PAR. The security of registered operating OSPF over ATM and/or Proxy PAR. The security of registered
information handed to the ATM cloud must be guaranteed by the underlying information handed to the ATM cloud must be guaranteed by the underlying
PNNI protocol. Extensions to PNNI are available and given their PNNI protocol. Extensions to PNNI are available and given their
implementation spoofing of registrations and/or denial-of-service issues implementation spoofing of registrations and/or denial-of-service issues
can be addressed [PB97]. The registration itself through proxy PAR is can be addressed [PB97]. The registration itself through proxy PAR is
not secured and appropriate mechanisms are for further study. However, not secured and appropriate mechanisms are for further study. However,
even if the security at the ATM layer is not guaranteed, OSPF security even if the security at the ATM layer is not guaranteed, OSPF security
mechanisms can be used to verify that detected neighbors are authorized mechanisms can be used to verify that detected neighbors are authorized
to interact with the entity discovering them. to interact with the entity discovering them.
References References
[AF95] ATM-Forum. LAN Emulation over ATM 1.0. ATM Forum [AF95] ATM-Forum. LAN Emulation over ATM 1.0. ATM Forum
af-lane-0021.000, January 1995. af-lane-0021.000, January 1995.
[AF96a] ATM-Forum. Interim Local Management Interface (ILMI) [AF96a] ATM-Forum. Interim Local Management Interface (ILMI)
Specification 4.0. ATM Forum 95-0417R8, June 1996. Specification 4.0. ATM Forum 95-0417R8, June 1996.
[AF96b] ATM-Forum. Private Network-Network Interface Specification [AF96b] ATM-Forum. Private Network-Network Interface Specification
Version 1.0. ATM Forum af-pnni-0055.000, March 1996. Version 1.0. ATM Forum af-pnni-0055.000, March 1996.
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[Arm96] G. Armitage. Support for Multicast over UNI 3.0/3.1 based [Arm96] G. Armitage. Support for Multicast over UNI 3.0/3.1 based
ATM Networks, RFC 2022. Internet Engineering Task Force, ATM networks, RFC 2022. Internet Engineering Task Force,
November 1996. November 1996.
[BB92] T. Bradley and C. Brown. Inverse Address Resolution [Col98] R. Coltun. The OSPF Opaque LSA Option, RFC 2370. Internet
Protocol, RFC 1293. Internet Engineering Task Force, January Engineering Task Force, July 1998.
1992.
[CH97a] R. Coltun and J. Heinanen. Opaque LSA in OSPF. Internet [Dav99a] M. Davison. ILMI-Based Server Discovery for ATMARP, RFC
Draft, 1997. 2601. Internet Engineering Task Force, June 1999.
[CH97b] R. Coltun and J. Heinanen. The OSPF Address Resolution [Dav99b] M. Davison. ILMI-Based Server Discovery for MARS, RFC 2602.
Advertisement Option. Internet Draft, 1997. Internet Engineering Task Force, June 1999.
[Dav99c] M. Davison. ILMI-Based Server Discovery for NHRP, RFC 2603.
Internet Engineering Task Force, June 1999.
[dR94] O. deSouza and M. Rodrigues. Guidelines for Running OSPF [dR94] O. deSouza and M. Rodrigues. Guidelines for Running OSPF
Over Frame Relay Networks, RFC 1586. Internet Engineering Over Frame Relay Networks, RFC 1586. Internet Engineering
Task Force, March 1994. Task Force, March 1994.
[For98] ATM Forum. PNNI Augmented Routing (PAR) Version 1.0. ATM [Dro99] P. Droz. PNNI Augmented Routing (PAR) Version 1.0. ATM
Forum PNNI-RA-PAR-01.04, 1998. Forum af-ra-0104.000, January 1999.
[Hei93] J. Heinanen. Multiprotocol Encapsulation over ATM Adaptation
Layer 5, RFC 1483. Internet Engineering Task Force, July
1993.
[Lau94] M. Laubach. Classical IP and ARP over ATM, RFC 1577.
Internet Engineering Task Force, January 1994.
[LH96] M. Laubach and J. Halpern. Classical IP and ARP over ATM.
Internet Draft, 1996.
[Moy94] J. Moy. OSPFv2, RFC 1583. Internet Engineering Task Force, [ML98] J. Halpern M. Laubach. Classical IP and ARP over ATM, RFC
March 1994. 2225. Internet Engineering Task Force, April 1998.
[Moy95] J. Moy. Extending OSPF to Support Demand Circuits, RFC 1793. [Moy95] J. Moy. Extending OSPF to Support Demand Circuits, RFC
Internet Engineering Task Force, April 1995. 1793. Internet Engineering Task Force, April 1995.
[Moy97] J. Moy. OSPFv2, RFC 2178. Internet Engineering Task Force, [Moy98] J. Moy. OSPF Version 2 - RFC 2328. Internet Engineering
July 1997. Task Force, April 1998.
[PB97] T. Przygienda and C. Bullard. Baseline Text for PNNI Peer [PB97] T. Przygienda and C. Bullard. Baseline Text for PNNI Peer
Authentication and Cryptographic Data Integrity. ATM Forum Authentication and Cryptographic Data Integrity. ATM Forum
97-0472, July 1997. 97-0472, July 1997.
[PD99] T. Przygienda P. Droz. Proxy PAR. Internet Draft
draft-ietf-ion-proxypar-arch-01, February 1999.
[TB99] A. Malis T. Bradley, C. Brown. Inverse Address Resolution
Protocol, RFC 2390. Internet Engineering Task Force,
September 1999.
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Authors' Addresses Authors' Addresses
Tony Przygienda Tony Przygienda
Bell Labs, Lucent Technologies Bell Labs, Lucent Technologies
101 Crawfords Corner Road 101 Crawfords Corner Road
Holmdel, NJ 07733-3030 Holmdel, NJ 07733-3030
prz@dnrc.bell-labs.com prz@dnrc.bell-labs.com
Patrick Droz Patrick Droz
IBM Research Division IBM Research Division
Saumerstrasse 4 Saumerstrasse 4
8803 Ruschlikon 8803 Ruschlikon
Switzerland Switzerland
dro@zurich.ibm.com dro@zurich.ibm.com
Robert Haas
IBM Research Division
Saumerstrasse 4
8803 Ruschlikon
Switzerland
rha@zurich.ibm.com
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