As per Relevance of the word forwarding, we have this rfc below:
Network Working Group B.
Request for Comments: 2340 D.
Category: Informational D.
S.
Nortel (Northern Telecom) Ltd
May 1998
Nortel's Virtual Network Switching (VNS)
Status of this
This memo provides information for the Internet community. It
not specify an Internet standard of any kind. Distribution of
memo is unlimited
Copyright
Copyright (C) The Internet Society (1998). All Rights Reserved
This document provides an overview of Virtual Network
(VNS).
VNS is a multi-protocol switching architecture that provides COS
sensitive packet switching, reduces the complexity of
protocols like PPP and frame relay, provides logical networks
traffic segregation for Virtual Private Networks (VPNs), security
traffic engineering, enables efficient WAN broadcasting
multicasting, and reduces address space requirements. VNS reduces
number of routing hops over the WAN by switching packets based
labels
VNS has been proven in production networks for several years
Table of
1 Introduction ............................................ 2
2 What is VNS? ............................................ 3
3 VNS Header ............................................. 5
4 VNS Label Distribution .................................. 7
5 Logical Networks (LNs) .................................... 7
6 VNS Routing ............................................. 8
7 VNS Forwarding .......................................... 9
7.1 Unicast ................................................ 9
7.2 Multicast .............................................. 9
8 Traffic Engineering ..................................... 10
Jamoussi, et. al. Informational [Page 1]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
8.1 Equal Cost Multipaths .................................. 10
8.2 Trunk Load Spreading ................................... 10
9 Class of Service ........................................ 11
10 VNS Migration Strategies ................................ 11
11 Summary ................................................. 11
12 Security Considerations ................................. 12
13 Acknowledgments ......................................... 12
14 Authors' Addresses ...................................... 13
15 Full Copyright Statement ................................ 14
1.
There are several key problem areas with today's wide area
networks that carry LAN traffic: scalability,
differentiation, redundancy, administration, and traffic containment
First, scalability is becoming a major concern because of the
growth in bandwidth demand and geographical reach. As the size of
WAN network grows traditional point-to-point and NBMA topologies
network models lose their performance
Second, the need to provide several Classes of Service (CoS)
never been greater. The days of a single "best effort" service
over and service providers demand ways to differentiate the
of the service offered to their clients based on several policies
Third, the WAN is often carrying mission-critical traffic and loss
service is not acceptable. So far, path redundancy has been
inefficiently by requiring additional links or VCs
Fourth, network operators demand easy and simplified
administration. Large NBMA topologies require extensive
provisioning until SVC deployment becomes more ubiquitous.
Point-to-point models, IP address space may be used inefficiently
non-trivial network schemas are required to contain reserved
space
Finally, proper segregation of traffic is becoming a must.
requirement is being addressed today by adding leased lines or
used to separate traffic flows based on regions or interest
protocol
Nortel's Virtual Network Switching (VNS) is a technology
provides efficient solutions to these challenges
Jamoussi, et. al. Informational [Page 2]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
Section 2 provides an overview of VNS. The VNS header is specified
Section 3. Section 4 describes the VNS label distribution mechanism
Section 5 defines how a VNS network can be partitioned into
Networks (LN). Section 6 outlines VNS routing. Section 7 defines
unicast and multicast forwarding. Section 8 describes the
used to engineer the traffic. Section 9 defines the COS
switching of VNS. Section 10 provides network migration
using VNS. A summary of VNS is provided in Section 11.
2. What is VNS
Virtual Network Switching (VNS) is a CoS-sensitive multi-
label switching architecture that reduces or eliminates the number
layer 3 hops over the WAN by switching traffic based on labels
VNS makes a network of point to point links appear to be a
LAN (broadcast, multiple access) media. The network used by
particular instance of VNS is called a Logical Network (LN) which
described in more detail in Section 5.
In reference to the ISO Network Layering Model, the Data Link
is expanded to include VNS network layer. To the ISO Network Layer
(e.g., IP), VNS is treated as a Data Link Layer
------------------------
| Application |
------------------------
| Presentation |
------------------------
| Session |
------------------------
| Transport |
------------------------ -------------------------
| Network (e.g., IP) | / Network VNS |
----------------------------- |
| Data Link |--------------------------
----------------------------- |
| Physical | \ data link (e.g., ATM) |
------------------------ -------------------------
Figure 1. ISO Network Layering Model for
In a VNS Network, three separate nodal functions are defined.
ingress node, an egress node, and a tandem node. The ingress
egress nodes define the boundary between an IP network and the
network. Therefore, these nodes run both IP routing and VNS routing
However, tandem nodes need only run VNS routing
Jamoussi, et. al. Informational [Page 3]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
A LAN packet is encapsulated in a VNS header as it enters the LN.
label in the header is used to switch the packet across the LN.
encapsulation header contains the identifier of the last node (
egress node) that processes the packet as it traverses the LN. It
the first node (or ingress node) that decides to which egress
the packet is sent. All nodes between the ingress and egress
(known as tandem nodes) decide independently the best
forwarding route to the egress node identified in the packet
The network layer protocols view VNS as a shared broadcast media
where the speed to reach any node on the media is the same for
nodes. VNS ensures that traffic destined to other nodes is
optimally. This transparent view of the VNS means that all
details of the network (for example, topology and link states) can
hidden from the Upper Layer Protocols (e.g. Layer 3
protocols) and their applications. VNS also ensures that changes
topology and link state are hidden
The network layer protocol on the ingress node views the
layer protocol on the egress node as its logical and
connected neighbor. This is significant because the network
protocols always decide which directly connected neighbor
receive a forwarded packet. The details of the actual
supporting the connectionless network are managed entirely by
Virtual Network Switching and are hidden from the network
protocols. To the network layer, VNS simply appears to be
Data Link Layer (or media), even though VNS is a network layer
running on top of the actual Data Link Layer (for example,
trunks).
For the ingress node to choose the egress node that provides the
path to the packet's final destination, it must have knowledge of
following
- the nodes that can be reached in the
- the topology of the network that is using the VNS services
transport across the network (but not necessarily the
of the full network
This knowledge is obtained through the network layer
mechanisms such as, IP's Open Shortest Path First (OSPF) and
Resolution Protocol (ARP).
Once the network layer protocol on the ingress node has decided
neighbor to transmit the packet to, it is the responsibility of
forwarding, a part of VNS, to deliver the packet to that node.
the packet arrives at the egress node, the packet is delivered to
network layer protocol, which then forwards it to its
Jamoussi, et. al. Informational [Page 4]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
destination
Tandem nodes have no interaction with the network layer protocols
They only require knowledge of the VNS network topology. They
their packet forwarding decision on the egress node identifier
LN identifier carried in the VNS header of the packet
3. VNS
VNS defines a unicast header shown in Figure 2 and a multicast
shown in Figure 3.
3 2 1 0
1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL | LNN |x|LS-Key |x|DP | CmnHdr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Type | Destination Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| COS |x x x x| Source Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Layer Header (e.g. IP) |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2. Unicast VNS
The unicast header includes the following fields
- Common Header (CmnHdr): The common header identifies the packet
be a VNS encapsulated packet
- Discard Priority: Indicates the level of congestion at which
packet should be discarded. The value of this field is assigned
the originating node based on policy information (see Section 9).
- Load Spreading Key: indicates the stream to which the
belongs for the purposes of equal cost multipath and trunk
spreading (see Section 8).
- LNN: The Logical Network Number defines the logical network
packet belongs to. This field in is used in conjunction with
destination node identifier as the VNS switching label (see
5).
Jamoussi, et. al. Informational [Page 5]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
- TTL: The Time To Live field is used to detect and discard
caught in temporary routing loops
- Destination Node Identifier: This field contains an ID
uniquely identifies the destination node. This ID is unique to
physical network not just the LN. In conjunction with the LNN,
forms a global VNS switching label
- Protocol Type: indicates the type of Network layer protocol
carried in the packet. Examples include IP, IPX, and Bridging. If
packet is a multicast packet then this is indicated in this field
- Source Node Identifier: This field contains an ID which
identifies the source node (ingress node).
- CoS: The Class of Service field is used to provide routing class
service. The COS field also affects the Emission Priority of
packet in the scheduler (see Section 9).
- Reserved Fields: All the fields marked with "x" are Reserved
3 2 1 0
1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL | LNN |x|LS-Key |x|DP | CmnHdr |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PT = Multicast| Destination Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| COS |x x x x| Source Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Protocol Type |x x x x x x x x| Multicast Group |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Layer Header (e.g. IP) |
/ /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
/ Data /
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3. Multicast VNS
The multicast header shown in Figure 3, includes all the fields
the unicast header. In addition, the multicast header includes
following fields
- Multicast Group: this field is used to identify a sub-group
the logical network that receives the multicast packets
Jamoussi, et. al. Informational [Page 6]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
- Protocol Type: indicates the type of Network layer protocol
carried in the packet. Examples include IP, IPX, and Bridging
4. VNS Label
Label distribution in VNS is based on a distributed
topology driven approach. Standard ARP or address gleaning is used
distribute and map network layer addresses to VNS addresses
A VNS Label is an 6 byte encoding of the LNN and the node ID.
Labels are treated as MAC addresses by the network layer. This
that labels are distributed by the same means network layers use
distribute MAC addresses. Thus, VNS leverages existing L2/L3
techniques and doesn't require a separate Label
Protocol
5. Logical Networks (LNs
A logical network consists of a subset of the nodes in a
together with a subset of the trunking facilities that link
nodes. Logical networks partition the network into subnetworks
serve a subset of the overall topology
Each of the logical networks supported on any given node has
separate routing and forwarding table (built by VNS). Therefore
routing decisions are based on the resources available to the
network, not the entire network
Each instance of VNS will discover all the trunks which are
to neighbors which support a matching LNN. This provides a
administrative saving, since VNS provisioning is on a per-node basis
not on a per-link basis. VNS provisioning requires only a
node ID and an LNN. Discovery of which trunks support which LNNs
done at run time, relieving administrative effort, and allowing
LN to dynamically adapt to topology changes
Multiple Logical Networks provide the following benefits to
network system
- Logical networks allow service providers to service
private networks or (Virtual Private Internets) easily over
network
- Logical networks can be used to limit the impact of one
layer protocol on the others. This is particularly true
protocols that broadcast or multicast a large percentage of
their control or data packets. This increases the
bandwidth of the trunks and allows the overall network to
Jamoussi, et. al. Informational [Page 7]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
better
- Logical networks allow for the configuration of the network
meet individual community of interest and
subnetworking needs
- Routing control traffic has significance only in the
subnetwork that is isolated to that subnetwork
- Logical networks allow different instances of the same
to share trunk facilities
6. VNS
VNS routing is a link state routing system which uses many
similar to OSPF and PNNI. One of the most significant departures
the others is its ability to calculate shortest path trees
routing unicast traffic and spanning trees for routing
traffic within a Logical Network
There is only one type of interface that VNS routing supports
this is known as a VNS link. A link is a set of trunks that join
VNS neighbor nodes. Each node in a VNS network maintains
about the state of locally attached links. This information
flooded throughout the network whenever there is a significant
to the link's state or attributes (i.e. up/down, speed change
available bandwidth change).
Each node stores and forwards the link state information
from all other nodes. This allows each node to have the same view
all of the nodes in the network together with all of their link
information. This data is used to compute both the shortest path
reach each node in the Logical Network and a spanning tree for
Logical Network
Logical networks are not bound to a particular trunk or link.
are configured on a node. By default, a link will support a
logical network if the two nodes which it connects both
configured to support the logical network number. This provides
significant savings in operations over having to configure
networks on links or trunks
When a link first comes into service, a protocol is run which
the two neighboring nodes to exchange information about the
networks they support. This allows the two nodes to determine if
links are to be considered as a locally attached link for a
network
Jamoussi, et. al. Informational [Page 8]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
7. VNS
VNS supports two types of forwarding: unicasting and multicasting.
the first type, the data packet arrives on the ingress node
unicasting forwards the data packet to a single destination (
node). In the second type, the data packet arrives on the
node and multicasting forwards the data packet to all other nodes
the logical network
7.1
When a packet first enters the LAN internetwork, the network
routing protocol determines the next hop of the best route for
packet to reach its final destination. If the best route is through
VNS Logical Network, the network layer routing protocol relies on
forwarding to get the packet to the egress node. A VNS packet
containing the node ID (the unique ID assigned to each node) of
egress node is added to the front of the packet and VNS forwarding
invoked to deliver the packet. The network layer routing
learns the egress node ID through an Address Resolution
(ARP) for IP and Source Address learning for bridging
As the packet traverses the LN, routing decisions are made
determine the next hop in the route to reach the destination node
specified in the VNS header. A forwarding table is built on each
that assists in making the routing decision
Each VNS instance on each node builds and maintains a
table for its LN. Each forwarding table has an entry for every
that is a member of the logical network
7.2
In addition to the unicast forwarding function, VNS also supports
multicast forwarding service for traffic within an LN at the
layer. Multicast packets are delivered to all nodes supporting
logical network to which the multicast packet belongs. The
are sent along the branches of a spanning tree that is built by
node supporting the logical network and is based on a common
node (so that each node's view of the tree is the same as
nodes). In other words, multicast packets are sent intelligently
consuming a minimum of network bandwidth. If the network topology
stable, each node receives each multicast packet only once
Multicast packets received at any node are not acknowledged. They
simply forwarded to the specified network layer interface and sent
any other neighbor nodes on the spanning tree
Jamoussi, et. al. Informational [Page 9]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
8. Traffic
VNS forwarding supports two types of traffic engineering mechanisms
equal cost multipaths and trunk load spreading
Equal cost multipaths allows different streams (unique network
source and destination address pairings) to be load spread
multiple relatively equal cost paths, through the Logical Network
the egress node
Trunk load spreading between two neighbors can take place
multiple VNS trunks are defined between neighbors. Again, the
spreading is based on network layer streams
8.1 Equal Cost
From any point in a logical network, there may be multiple paths
reach a specific egress node. If VNS routing determines that
than one of these paths are of equal cost, VNS packets will be
spread between two of them
Equal cost multipath forwarding is supported not only on
nodes but on tandem nodes as well. Each packet on an ingress node
tagged with an equal cost multipath key. This key is acted upon
the ingress node and stored in the VNS header to be used on
nodes
The equal cost multipath key is calculated by running an
over the source and destination network layer addresses. This
that, in a stable network, any given stream will always take the
path through a Logical Network avoiding the problems that
would otherwise cause
8.2 Trunk Load Spreading Between
VNS allows multiple trunks to be configured between neighboring
nodes. VNS routing considers the aggregate bandwidth of those
to determine the metric between the nodes. Also, VNS load spreads
traffic amongst those trunks
As is the case with equal cost multipaths, the trunk load
key is calculated on the ingress node from an algorithm run over
source and destination network layer addresses. The key is
stored in the VNS header to be used on all tandem nodes through
Logical Network
Jamoussi, et. al. Informational [Page 10]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
9. Class of
At the ingress to a VNS Network, packets are classified according
the Class of Service (Cos) policy settings. The CoS
is achieved through different Emission and Discard priorities.
semantics of the classification is carried in the VNS label (DP
COS Fields described in Section 3) to be used at the ingress node
well as all tandem points in the VNS network to affect queuing
scheduling decisions
10. VNS Migration
VNS supports several upper layer protocols such as IP, IPX,
Bridging. Therefore, it is a multiprotocol label
architecture. In addition, VNS is not tied to a particular L
technology. It runs on cell (e.g., ATM) trunks, frame trunks, or
mixture of both
VNS can be gradually introduced in a network. It can be
between switching elements interconnected by point to point links
Each of the switching nodes can run layer 3 routing
with packet switching. VNS also allows for the interconnection of
clouds through an ATM VC
Since VNS can run on a mixture of Frame and Cell trunks, it
for the graceful migration of the frame links to ATM
requiring a complete immediate overhaul
11.
VNS addresses scalability problems in several ways
1. By a generally distributed design which doesn'
require a Label Distribution Protocol, or servers of any kind
2. By providing an efficient, distributed multicast mechanism
3. By allowing administrators to control the size of
Logical Network, limiting traffic to a subset of the
topology
4. By reducing layer 3 address space/subnet requirements in
WAN which reduces the routing table size
VNS provides redundancy transparent to the network layer protocol
managing the network of trunks independently of the network layer
VNS will automatically discover any topology changes and re-
traffic accordingly
Jamoussi, et. al. Informational [Page 11]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
VNS eases network administration by dynamically keeping track
which trunks are available for each LNN. Network
don't have to configure VNS or network layer addresses on a per
basis. Network layer addresses only have to be assigned on a
Logical Network basis. For nodes which will only be tandem
nodes, network layer addresses aren't required at all
Since VNS traffic is constrained within an LNN, administrators
control of where VNS traffic is allowed to flow
Finally, VNS supports switching of several Upper Layer Protocols
supports several media (cell and Frame) or a mixture thereof
Switching in the core of the WAN removes the need for routers
improves the performance due to a reduction in the number of
that need to processed
12. Security
Logical networks provide a means of restricting traffic flow
security purposes. VNS also relies on the inherent security of the L
media such as an ATM Virtual Circuit
13.
The authors would like to acknowledge the valuable comments of
Boland, Pierre Cousineau, Robert Eros, Robert Tomkins, and
Whatman
Jamoussi, et. al. Informational [Page 12]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
14. Authors'
Bilel
Nortel (Northern Telecom), Ltd
PO Box 3511 Station
Ottawa ON K1Y 4H
EMail: jamoussi@Nortel.
Dwight
Nortel (Northern Telecom), Ltd
PO Box 3511 Station
Ottawa ON K1Y 4H
EMail: djamies@Nortel.
Dan
Nortel (Northern Telecom), Ltd
PO Box 3511 Station
Ottawa ON K1Y 4H
EMail: danwil@Nortel.
Stephen
Nortel (Northern Telecom), Ltd
PO Box 3511 Station
Ottawa ON K1Y 4H
EMail: spgabe@Nortel.
Jamoussi, et. al. Informational [Page 13]
RFC 2340 Nortel's Virtual Network Switching (VNS) May 1998
15. Full Copyright
Copyright (C) The Internet Society (1998). All Rights Reserved
This document and translations of it may be copied and furnished
others, and derivative works that comment on or otherwise explain
or assist in its implementation may be prepared, copied,
and distributed, in whole or in part, without restriction of
kind, provided that the above copyright notice and this paragraph
included on all such copies and derivative works. However,
document itself may not be modified in any way, such as by
the copyright notice or references to the Internet Society or
Internet organizations, except as needed for the purpose
developing Internet standards in which case the procedures
copyrights defined in the Internet Standards process must
followed, or as required to translate it into languages other
English
The limited permissions granted above are perpetual and will not
revoked by the Internet Society or its successors or assigns
This document and the information contained herein is provided on
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED,
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE
Jamoussi, et. al. Informational [Page 14]
if you see any problems within the linking, don't worry be happy,
this is version 0.1 of the Relevance System and you gotta expect some crappy subroutines sometimes,
just be content we did not write this in Java, which would have made this "bigger and better" HAHAHHA.
RFC documents can be found at I.E.T.F.
Relevance System Copyright © 2002 Spectrum WorldResearch
other technical nosh by ServerMasters Corporation
collaboration of BobX
