As per Relevance of the word contains, we have this rfc below:
Network Working Group D.
Request for Comments: 2643 T.
Category: Informational J.
Cabletron Systems
August 1999
Cabletron's SecureFast VLAN Operational
Version 1.8
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 (1999). All Rights Reserved
Cabletron's SecureFast VLAN (SFVLAN) product implements a
connection-oriented switching protocol that provides fast
of data packets at the MAC layer. The product uses the concept
virtual LANs (VLANs) to determine the validity of call
requests and to scope the broadcast of certain flooded messages
Table of
1. Introduction............................................. 3
1.1 Data Conventions..................................... 3
1.2 Definitions of Commonly Used Terms................... 4
2. SFVLAN Overview.......................................... 6
2.1 Features............................................. 7
2.2 VLAN Principles...................................... 8
2.2.1 Default, Base and Inherited VLANs.............. 8
2.2.2 VLAN Configuration Modes....................... 8
2.2.2.1 Endstations............................ 8
2.2.2.2 Ports.................................. 9
2.2.2.3 Order of Precedence.................... 9
2.2.3 Ports with Multiple VLAN Membership............ 10
2.3 Tag/Length/Value Method of Addressing................ 10
2.4 Architectural Overview............................... 11
3. Base Services............................................ 13
4. Call Processing.......................................... 14
4.1 Directory Service Center............................. 14
4.1.1 Local Add Server............................... 15
Ruffen, et al. Informational [Page 1]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
4.1.2 Inverse Resolve Server......................... 15
4.1.3 Local Delete Server............................ 18
4.2 Topology Service Center.............................. 18
4.2.1 Neighbor Discovery Server...................... 18
4.2.2 Spanning Tree Server........................... 18
4.2.2.1 Creating and
the Spanning Tree........... 19
4.2.2.2 Remote Blocking........................ 19
4.2.3 Link State Server.............................. 20
4.3 Resolve Service Center............................... 21
4.3.1 Table Server................................... 22
4.3.2 Local Server................................... 22
4.3.3 Subnet Server.................................. 22
4.3.4 Interswitch Resolve Server..................... 22
4.3.5 Unresolvable Server............................ 23
4.3.6 Block Server................................... 23
4.4 Policy Service Center................................ 24
4.4.1 Unicast Rules Server........................... 24
4.5 Connect Service Center............................... 25
4.5.1 Local Server................................... 25
4.5.2 Link State Server.............................. 25
4.5.3 Directory Server............................... 26
4.6 Filter Service Center................................ 26
4.7 Path Service Center.................................. 26
4.7.1 Link State Server.............................. 26
4.7.2 Spanning Tree Server........................... 27
4.8 Flood Service Center................................. 27
4.8.1 Tag-Based Flood Server......................... 27
5. Monitoring Call Connections.............................. 27
5.1 Definitions.......................................... 27
5.2 Tapping a Connection................................. 28
5.2.1 Types of Tap Connections....................... 28
5.2.2 Locating the Probe and
the Tap Connection.......... 29
5.2.3 Status Field................................... 30
5.3 Untapping a Connection............................... 31
6. Interswitch Message Protocol (ISMP)...................... 32
6.1 General Packet Structure............................. 32
6.1.1 Frame Header................................... 32
6.1.2 ISMP Packet Header............................. 33
6.1.2.1 Version 2.............................. 33
6.1.2.2 Version 3.............................. 34
6.1.3 ISMP Message Body.............................. 35
6.2 Interswitch BPDU Message............................. 35
6.3 Interswitch Remote Blocking Message.................. 36
6.4 Interswitch Resolve Message.......................... 37
6.4.1 Prior to Version 1.8........................... 37
6.4.2 Version 1.8.................................... 41
Ruffen, et al. Informational [Page 2]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
6.5 Interswitch New User Message......................... 46
6.6 Interswitch Tag-Based Flood Message.................. 49
6.6.1 Prior to Version 1.8........................... 49
6.6.2 Version 1.8.................................... 52
6.7 Interswitch Tap/Untap Message........................ 55
7. Security Considerations.................................. 58
8. References............................................... 58
9. Authors' Addresses....................................... 59
10. Full Copyright Statement................................ 60
1.
This memo is being distributed to members of the Internet
in order to solicit reactions to the proposals contained herein
While the specification discussed here may not be directly
to the research problems of the Internet, it may be of interest
researchers and implementers
1.1 Data
The methods used in this memo to describe and picture data adhere
the standards of Internet Protocol documentation [RFC1700].
particular
The convention in the documentation of Internet Protocols is
express numbers in decimal and to picture data in "big-endian
order. That is, fields are described left to right, with the
significant octet on the left and the least significant octet
the right
The order of transmission of the header and data described in
document is resolved to the octet level. Whenever a diagram
a group of octets, the order of transmission of those octets
the normal order in which they are read in English
Whenever an octet represents a numeric quantity the left most
in the diagram is the high order or most significant bit.
is, the bit labeled 0 is the most significant bit
Ruffen, et al. Informational [Page 3]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
Similarly, whenever a multi-octet field represents a
quantity the left most bit of the whole field is the
significant bit. When a multi-octet quantity is transmitted
most significant octet is transmitted first
1.2 Definitions of Commonly Used
This section contains a collection of definitions for terms that
a specific meaning for the SFVLAN product and that are
throughout the text
Switch
A 10-octet value that uniquely identifies an SFVLAN switch
the switch fabric. The value consists of the 6-octet base
address of the switch, followed by 4 octets of zeroes
Network
The physical connection between two switches. A network link
associated with a network interface (or port) of a switch
Network
An interface on a switch that attaches to another switch
Access
An interface on a switch that attaches to a user endstation
Port
A 10-octet value that uniquely identifies an interface of
switch. The value consists of the 6-octet base MAC address of
switch, followed by the 4-octet local port number of
interface
Neighboring
Two switches attached to a common (network) link
Call
A mapping of user traffic through a switch that correlates
source and destination address pair specified within the packet
an inport and outport pair on the switch
Ruffen, et al. Informational [Page 4]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
Call connection
A set of 0 to 7 network links over which user traffic
between the source and destination endstations. Call
paths are selected from a list of alternate equal cost
calculated by the VLS protocol [IDvlsp], and are chosen to
balance traffic across the fabric
Ingress
The owner switch of the source endstation of a call connection
That is, the source endstation is attached to one of the
access ports of the switch
Egress
The owner switch of the destination endstation of a
connection. That is, the destination endstation is attached
one of the local access ports of the switch
Intermediate
Any switch along the call connection path on which user
enters and leaves over network links. Note that the
types of connections have no intermediate switches
- Call connections between source and destination
that are attached to the same switch -- that is, the
switch is the same as the egress switch. Note also that
path for this type of connection consists of 0 network links
- Call connections where the ingress and egress switches
physical neighbors connected by a single network link.
path for this type of connection consists of a single
link
InterSwitch Message protocol (ISMP
The protocol used for interswitch communication between
switches
Undirected
Messages that are (potentially) sent to all SFVLAN switches in
switch fabric -- that is, they are not directed to any
switch. ISMP messages with a message type of 5, 7 or 8
undirected messages
Ruffen, et al. Informational [Page 5]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
Switch flood
The path used to send undirected messages throughout the
fabric. The switch flood path is formed using a spanning
algorithm that provides a single path through the switch
that guarantees loop-free delivery to every other SFVLAN switch
the fabric
Upstream
That switch attached to the inport of the switch flood path --
that is, the switch from which undirected messages are received
Note that each switch receiving an undirected message has,
most, one upstream neighbor, and the originator of any
ISMP message has no upstream neighbors
Downstream
Those switches attached to all outports of the switch flood
except the port on which the undirected message was received
Note that for each undirected message some number of switches
no downstream neighbors
Virtual LAN (VLAN)
A VLAN is a logical grouping of ports and endstations such
all ports and endstations in the VLAN appear to be on the
physical (or extended) LAN segment even though they may
geographically separated
A VLAN identifier consists of a variable-length string of octets
The first octet in the string contains the number of octets in
remainder of the string -- the actual VLAN identifier value.
VLAN identifier can be from 1 to 16 octets long
VLAN
Each VLAN has an assigned policy value used to determine whether
particular call connection can be established. SFVLAN
two policy values: Open and Secure
2. SFVLAN
Cabletron's SecureFast VLAN (SFVLAN) product implements a
connection-oriented switching protocol that provides fast
of data packets at the MAC layer
Ruffen, et al. Informational [Page 6]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
2.1
Within a connection-oriented switching network, user traffic
routed through the switch fabric based on the source and
address (SA/DA) pair found in the arriving packet. For each SA/
pair encountered by a switch, a "connection" is programmed into
switch hardware. This connection maps the SA/DA pair and the port
which the packet was received to a specific outport over which
packet is to be forwarded. Thus, once a connection has
established, all packets with a particular SA/DA pair arriving on
particular inport are automatically forwarded by the switch
out the specified outport
A distributed switching environment requires that each switch
capable of processing all aspects of the call processing
switching functionality. Thus, each switch must synchronize
various databases with all other switches in the fabric or be
of querying other switches for information it does not have locally
SFVLAN accomplishes the above objectives by providing the
features
- A virtual directory of the entire switch fabric
- Call processing for IP, IPX and MAC protocols
- Automatic call connection, based on VLAN policy
- Automatic call rerouting around failed switches and links
In addition, SFVLAN optimizes traffic flow across the switch
by providing the following features
- Broadcast interception and address resolution at the ingress port
- Broadcast scoping, restricting the flooding of broadcast
to only those ports that belong to the same VLAN as the
source
- A single loop-free path (spanning tree) used for the flooding
undirected interswitch control messages. Only switches
the SFVLAN switching protocol are included in this spanning
calculation -- that is, traditional bridges or routers
for bridging are not included
- Interception of both service and route advertisements
readvertisement sourced from the MAC address of the
advertiser
Ruffen, et al. Informational [Page 7]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
2.2 VLAN
Each SFVLAN switch port, along with its attached endstations,
to one or more virtual LANs (VLANs). A VLAN is a logical grouping
ports and endstations such that all ports and endstations in the
appear to be on the same physical (or extended) LAN segment
though they may be geographically separated
VLAN assignments are used to determine the validity of
connection requests and to scope the broadcast of certain
messages
2.2.1 Default, Base and Inherited
Each port is explicitly assigned to a default VLAN. At start-up,
default VLAN to which all ports are assigned is the base VLAN --
permanent, non-deletable VLAN to which all ports belong at all times
The network administrator can change the default VLAN of a port
the base VLAN to any other unique VLAN by using a
application known here as the VLAN Manager. A port's default VLAN
persistent -- that is, it is preserved across a switch reset
When an endstation attaches to a port for the first time, it
the default VLAN of the port. Using the VLAN Manager, the
administrator can reassign an endstation to another VLAN
Note
When all ports and all endstations belong to the base VLAN,
switch fabric behaves like an 802.1D bridging system
2.2.2 VLAN Configuration
For both ports and endstations, there are a variety of
configuration types, or modes
2.2.2.1
For endstations, there are two VLAN configuration modes:
and static
-
An inherited endstation becomes a member of its port's
VLAN
Ruffen, et al. Informational [Page 8]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
-
A static port becomes a member of the VLAN to which it has
assigned by the VLAN Manager
The default configuration mode for an endstation is inherited
2.2.2.2
For ports, there are two VLAN configuration modes: normal
locked
-
All inherited endstations on a normal port become members of
port's default VLAN. All static endstations are members of
VLAN to which they were mapped by the VLAN Manager
If the VLAN Manager reassigns the default VLAN of a normal port
the VLAN(s) for the attached endstations may or may not change
depending on the VLAN configuration mode of each endstation.
inherited endstations will become members of the new default VLAN
All others will retain membership in their previously
VLANs
-
All endstations attached to a locked port can be members only
the port's default VLAN
If the VLAN Manager reconfigures a normal port to be a
port, all endstations attached to the port become members of
port's default VLAN, regardless of any previous VLAN membership
The default configuration mode for ports is normal
2.2.2.3 Order of
On a normal port, static VLAN membership prevails over
membership
On a locked port, default VLAN membership prevails over any
VLAN membership
If a statically assigned endstation moves from a locked port back
a normal port, the endstation's static VLAN membership must
preserved
Ruffen, et al. Informational [Page 9]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
2.2.3 Ports with Multiple VLAN
A port can belong to multiple VLANs, based on the VLAN membership
its attached endstations
For example, consider a port with three endstations, a default
of "blue" and the following endstation VLAN assignments
- One of the endstations is statically assigned to VLAN "red."
- Another endstation is statically assigned to VLAN "green."
- The third endstation inherits the default VLAN of "blue."
In this instance, the port is explicitly a member of VLAN "blue."
note that it is also implicitly a member of VLAN "red" and
"green." Any tag-based flooding (Section 4.8) directed to any one
the three VLANs ("red," "green," or "blue") will be forwarded out
port
2.3 Tag/Length/Value Method of
Within most computer networks, the concept of "address" is
elusive because different protocols can (and do) use
addressing schemes and formats. For example, Ethernet (
layer) addresses are six octets long, while IP (network layer
addresses are only four octets long
To distinguish between the various protocol-specific forms
addressing, many software modules within the SFVLAN product
addresses in a format known as Tag/Length/Value (TLV). This
uses a variable-length construct as shown below
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value length | |
+-+-+-+-+-+-+-+-+ +
| Address value |
: :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
This 4-octet field specifies the type of address contained in
structure. The following address types are currently supported
Ruffen, et al. Informational [Page 10]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
Tag name Value Address
aoMacDx 1 DX ethernet dst/src/
aoIpxSap 2
aoIpxRIP 3
aoInstYP 4 YP (YP name and version
aoInstUDP 5 UDP (Port #)
aoIpxIpx 6
aoInetIP 7 IP (Net address
aoInetRPC 8 RPC (Program #)
aoInetRIP 9 INET
aoMacDXMcast 10 Multicast unknown
aoAtDDP 11 AppleTalk
aoEmpty 12 (no address type specified
aoVlan 13 VLAN
aoHostName 14 Host
aoNetBiosName 15 NetBIOS
aoNBT 16 NetBIOS on TCP
aoInetIPMask 17 IP Subnet
aoIpxSap8022 18 Sap 8022 type
aoIpxSapSnap 19 Sap Snap type
aoIpxSapEnet 20 Sap Enet type
aoDHCPXID 21 DHCP Transaction
aoIpMcastRx 22 IP class D
aoIpMcastTx 23 IP class D
aoIpxRip8022 24 Ipx Rip 8022 type
aoIpxRipSnap 25 Ipx Rip type
aoIpxRipEnet 26 Ipx Rip Enet
aoATM 27
aoATMELAN 28 ATM LAN Emulation
Value
This 1-octet field contains the length of the value of
address. The value here depends on the address type and
value
Address
This variable-length field contains the value of the address.
length of this field is stored in the Value length field
2.4 Architectural
The SFVLAN software executes in the switch CPU and consists of
following elements as shown in Figure 1:
Ruffen, et al. Informational [Page 11]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
- The SFVLAN base services that handles traffic intercepted by
switch hardware. The base services are described in Section 3.
+------------------------------------------------------+
| +-----+ |
| +------------+ | I | |
| | CALL TAP <--(8)--> N | |
| +------------+ | T | |
| | E | |
| +-----------+ +------------+ | R | |
| | PATH | | TOPOLOGY | | S | |
| | | | | | W | |
| | Lnk state <------> Lnk state <--(3)--> I | | Flood
| | | | | | T <----(5,7,8)-->
| | Span tree <------> Span tree <--(4)--> C | |
| +--^--------+ | | | H | |
| | | Discovery <--(2)--> | |
| | +------------+ | M | |
| | | E | |
| +------^--+ +--------+ | S | |
| | CONNECT >---------+--> FILTER | | S | |
| +--^------+ | +--------+ | A | |
| | | | G | | netwrk
| | +--------^-+ +-------+ | E <----(2,3,4)-->
| +-------< POLICY | | FLOOD >--(7)--> | |
| +------^---+ +-^-----+ | P | |
| | | | R | |
| +-----------+ +-^-----------V-+ | O | |
| | DIRECTORY <----> RESOLVE <------(5)--> T | |
| +-----^-----+ +---^-----------+ | O | |
| | | | C | |
| | +---------^-----------+ | O | |
| +----< Base Services | | L | |
| +-----^---------------+ +-----+ |
+------------------|-----------------------------------+
Switch CPU |
| Host control
+-----O----------------+
| ^ no cnx |
Layer 2 | | |
---------->O-----+--------------->O----------->
SA/DA pr | known cnx |
+----------------------+
Switch
Figure 1: SFVLAN Architectural
Ruffen, et al. Informational [Page 12]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
- Eight call processing service centers that provide the
services required to process call connections. The
processing service centers are described in Section 4.
- A Call Tap module that supports the monitoring of
connections. The Call Tap module is described in Section 5.
- The InterSwitch Message Protocol (ISMP) that provides a
method of encapsulating and transmitting control
exchanged between SFVLAN switches. (Note that ISMP is not
discrete software module. Instead, its functionality
distributed among those service centers and software modules
need to communicate with other switches in the fabric.)
Interswitch Message Protocol and the formats of the
interswitch messages are described in Section 6.
3. Base
The SFVLAN base services act as the interface between the
hardware and the SFVLAN service centers running on the switch CPU
This relationship is shown in Figure 2. This figure is a
of the bottom portion of Figure 1.
| Directory Resolve |
| ^ ^ |
| | | |
| | +---------^-----------+ |
| +----< Base Services | |
| +-----^---------------+ |
+-------------------|--------------------------+
Switch CPU |
| Host control
+-----O----------------+
| ^ no cnx |
Layer 2 | | |
---------->O-----+--------------->O----------->
SA/DA pr | known cnx |
+----------------------+
Switch
Figure 2: Base
Ruffen, et al. Informational [Page 13]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
During normal operation of the switch, data packets arriving
any one of the local switch ports are examined in the
hardware. If the packet's source and destination address (SA/DA
pair match a known connection, the hardware simply forwards
packet out the outport specified by the connection
If the SA/DA pair do not match any known connection, the
diverts the packet to the host control port where it is picked
by the SFVLAN base services. The base services generate
structure known as a state box that tracks the progress of
call connection request as the request moves through the
processing service centers
After creating the call's state box, the base services check
determine if the call is a duplicate of a call already
processed. If not, a request is issued to the Directory
Center (Section 4.1) to add the call's source address to the
Node and Alias Tables. The base services then hand the call off
the Resolve Service Center (Section 4.3) for further processing
4. Call
Call connection processing is handled by a set of eight
centers, each with one or more servers. The servers within
service center are called in a particular sequence. Each
records the results of its processing in the call
request state box and passes the state box to the next server
the sequence
In the sections that follow, servers are listed in the order
which they are called
4.1 Directory Service
The Directory Service Center is responsible for cataloging the
addresses and alias information for both local and
endstations. The information is stored in two tables -- the
Table and the Alias Table
- The Node Table contains the MAC addresses of
attached to the local switch. It also contains a cache
remote endstations detected by the Resolve Service
(Section 4.3). Every entry in the Node Table has one or
corresponding entries in the Alias Table
Ruffen, et al. Informational [Page 14]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
- The Alias Table contains protocol alias information for
endstation. An endstation alias can be a network address (
as an IP or IPX address), a VLAN identifier, or any
protocol identifier. Since every endstation is a member of
least one VLAN (the default VLAN for the port), there is
at least one entry in the Alias Table for each entry in
Node Table
Note
The Node and Alias Tables must remain synchronized
That is, when an endstation's final alias is
from the Alias Table, the endstation entry is
from the Node Table
Note that the total collection of all Node Tables and Alias
across all switches is known as the "virtual" directory of
switch fabric. The virtual directory contains address mappings
all known endstations in the fabric
4.1.1 Local Add
The Directory Local Add server adds entries to the local Node
Alias Tables. It is called by the base services (Section 3)
add a local endstation and by the Interswitch Resolve (
4.3.4) server to add an endstation discovered on a remote switch
4.1.2 Inverse Resolve
The Directory Inverse Resolve server is invoked when a
endstation has been discovered on the local switch (that is,
the Local Add server was successful in adding the endstation).
The server provides two functions
- It populates the Node and Alias Tables with local
during switch initialization
- It processes a new endstation discovered after the
topology has converged to a stable state
In both instances, the processing is identical
Ruffen, et al. Informational [Page 15]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
When a new endstation is detected on one of the switch's
ports, the Inverse Resolve server sends an Interswitch New
request message (Section 6.5) over the switch flood path to
other switches in the fabric. The purpose of the Interswitch
User request is two-fold
- It informs the other switches of the new endstation address
Any entries for that endstation in the local databases of
switches should be dealt with appropriately
- It requests information about any static VLAN(s) to which
endstation has been assigned
When a switch receives an Interswitch New User request
from one of its upstream neighbors, it first forwards the
to all its downstream neighbors. No actual processing or
resolution is attempted until the message reaches the end of
switch flood path and begins its trip back along the return path
This ensures that all switches in the fabric receive
of the new user and have synchronized their databases
If a switch receives an Interswitch New User request message
has no downstream neighbors, it does the following
- If the endstation was previously connected to one of
switch's local ports, the switch formulates an Interswitch
User Response message by loading the VLAN identifier(s) of
static VLAN(s) to which the endstation was assigned, along
its own MAC address. (VLAN identifiers are stored
Tag/Length/Value (TLV) format. See Section 2.3.) The
then sets the message status field to NewUserAck, and
the message to its upstream (requesting) neighbor
Otherwise, the switch sets the status field to
and returns the message to its upstream neighbor
- The switch then deletes the endstation from its local database
as well as any entries associated with the endstation in
connection table
When a switch forwards an Interswitch New User request message
its downstream neighbors, it keeps track of the number of
it has sent out and does not respond back to its upstream
until all requests have been responded to
Ruffen, et al. Informational [Page 16]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
- As each response is received, the switch checks the
field of the message. If the status is NewUserAck, the
retains the information in that response. When all
have been responded to, the switch returns the
response to its upstream neighbor
- If all the Interswitch New User Request messages have
responded to with a status of NewUserUnknown, the switch
to see if the endstation was previously connected to one of
local ports. If so, the switch formulates an Interswitch
User Response message by loading the VLAN identifier(s) of
static VLAN(s) to which the endstation was assigned, along
its own MAC address. The switch then sets the message
field to NewUserAck, and returns the message to its
(requesting) neighbor
Otherwise, the switch sets the status field to
and returns the message to its upstream neighbor
- The switch then deletes the endstation from its local database
as well as any entries associated with the endstation in
connection table
When the originating switch has received responses to all
Interswitch New User Request messages it has sent, it does
following
- If it has received a response message with a status
NewUserAck, it loads the new VLAN information into its
database
- If all responses have been received with a status
NewUserUnknown, the originating switch assumes that
endstation was not previously connected anywhere in the
and assigns it to a VLAN according to the VLAN membership
and order of precedence
If any Interswitch New User Request message has not been
to within a certain predetermined time (currently 5 seconds),
originating switch recalculates the switch flood path and
the Interswitch New User Request message
Ruffen, et al. Informational [Page 17]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
4.1.3 Local Delete
The Directory Local Delete server removes entries (both local
remote) from the local Node and Alias Tables. It is invoked
an endstation, previously known to be attached to one switch,
been moved and discovered on another switch
Note also that remote entries are cached and are purged from
tables on a first-in/first-out basis as space is needed in
cache
4.2 Topology Service
The Topology Service Center is responsible for maintaining
databases relating to the topology of the switch fabric
- The topology table of SFVLAN switches that are
neighbors to the local switch
- The spanning tree that defines the loop-free switch flood
used for transmitting undirected interswitch messages
- The directed graph that is used to calculate the best path(s
for call connections
4.2.1 Neighbor Discovery
The Topology Neighbor Discovery server uses Interswitch
messages to detect the switch's neighbors and establish
topology of the switching fabric. Interswitch Keepalive
are exchanged in accordance with Cabletron's VlanHello protocol
described in detail in [IDhello].
4.2.2 Spanning Tree
The Topology Spanning Tree server is invoked by the
Neighbor Discovery server when a neighboring SFVLAN switch
either discovered or lost -- that is, when the operational
of a network link changes
The Spanning Tree server exchanges interswitch messages
neighboring SFVLAN switches to calculate the switch flood
over which undirected interswitch messages are sent. There
two parts to this process
- Creating and maintaining the spanning
- Remote
Ruffen, et al. Informational [Page 18]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
4.2.2.1 Creating and Maintaining the Spanning
In a network with redundant network links, a packet traveling
switches can potentially be caught in an infinite loop --
intolerable situation in a networking environment. However, it
possible to reduce a network topology to a single
(known as a spanning tree) such that there is, at most, one
between any two switches
Within the SFVLAN product, the spanning tree is created
maintained using the Spanning Tree Algorithm defined by the
802.1d standard
Note
A detailed discussion of this algorithm is beyond the scope
this document. See [IEEE] for more information
To implement the Spanning Tree Algorithm, SFVLAN switches
Interswitch BPDU messages (Section 6.2) containing
IEEE-compliant 802.2 Bridge Protocol Data Units (BPDUs). There
two types of BPDUs
- Configuration (CFG) BPDUs are exchanged during the
discovery process, following the receipt of an
Keepalive message. They are used to create the initial
spanning tree
- Topology Change Notification (TCN) BPDUs are exchanged
changes in the network topology are detected. They are used
redefine the spanning tree to reflect the current topology
See [IEEE] for detailed descriptions of these BPDUs
4.2.2.2 Remote
After the spanning tree has been computed, each network port on
SFVLAN switch will be in one of two states
- Forwarding. A port in the Forwarding state will be used
transmit all ISMP messages
Ruffen, et al. Informational [Page 19]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
- Blocking. A port in the Blocking state will not be used
forward undirected ISMP messages. Blocking the rebroadcast
these messages on selected ports prevents message
arising from multiple paths that exist in the network topology
Note that all other types of ISMP message will be transmitted
Note
The IEEE 802.1d standard specifies other port states
during the initial creation of the spanning tree. These
are not relevant to the discussion here
Note that although a port in the Blocking state will not
undirected ISMP messages, it may still receive them. Any
message received will ultimately be discarded, but at the cost of
time necessary to process the packet
To prevent the transmission of undirected messages to a port,
port's owner switch can set remote blocking on the link by sending
Interswitch Remote Blocking message (Section 6.3) out over the port
This notifies the switch on the other end of the link that
messages should not be sent over the link, regardless of the state
the sending port
Each SFVLAN switch sends an Interswitch Remote Blocking message
over all its blocked network ports every 5 seconds. A flag
the message indicates whether remote blocking should be turned on
off over the link
4.2.3 Link State
The Topology Link State server is invoked by any process that
a change in the state of the network links of the local switch
These changes include (but are not limited to) changes in
or administrative status of the link, path "cost" or bandwidth
The Link State server runs Cabletron's Virtual LAN Link State (VLS
protocol which exchanges interswitch messages with neighboring
switches to calculate the set of best paths between the local
and all other switches in the fabric. (The VLS protocol is
in detail in [IDvlsp].)
The Link State server also notifies the Connect Service
(Section 4.5) of any remote links that have failed,
necessitating potential tear-down of current connections
Ruffen, et al. Informational [Page 20]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
4.3 Resolve Service
The Resolve Service Center is responsible for resolving
destination address of broadcast data packets (such as an IP
packet) to a unicast MAC address to be used in mapping the
connection. To do this, the Resolve Service Center attempts
resolve such broadcast packets directly at the access port of
ingress switch
Address resolution is accomplished as follows
1) First, an attempt is made to resolve the address from the switch'
local databases by calling the following servers
- The Table server attempts to resolve the address from
Resolve Table (Section 4.3.1).
- Next, the Local server attempts to resolve the address from
Node and Alias Tables (Section 4.3.2).
- If the address is not found in these tables but is an
address, the Resolve Subnet server (Section 4.3.3) is
called
2) If the address cannot be resolved locally, the Interswitch
server (Section 4.3.4) is called to access the "virtual directory
by sending an Interswitch Resolve request message out over
switch flood path
3) If the address cannot be resolved either locally or via
Interswitch Resolve message -- that is, the destination
is unknown to any switch, perhaps because it has never
a packet to its switch -- the following steps are taken
- The Unresolvable server (Section 4.3.5) is called to record
unresolved packet
- The Block server (Section 4.3.6) is called to determine
the address should be added to the Block Table
- The Flood Service Center (Section 4.8) is called to
the packet to other SFVLAN switches using a tag-based
mechanism
Ruffen, et al. Informational [Page 21]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
4.3.1 Table
The Resolve Table server maintains the Resolve Table which contains
collection of addresses that might not be resolvable in the
fashion. This table typically contains such things as the
of "quiet" devices that do not send data packets or special
of IP addresses behind a router. Entries can be added to or
from the Resolve Table via an external management application
4.3.2 Local
The Resolve Local server checks the Node and Alias Tables
by the Directory Service Center (Section 4.1) to determine if it
resolve the address
4.3.3 Subnet
If the address to be resolved is an IP address but cannot be
via the standard processing described above, the Resolve
server applies the subnet mask to the IP address and then does
lookup in the Resolve Table
4.3.4 Interswitch Resolve
If the address cannot be resolved locally, the Interswitch
server accesses the "virtual directory" by sending an
Resolve request message (Section 6.4) out over the switch flood path
The Interswitch Resolve request message contains the
address as it was received within the packet, along with a list
requested addressing information
When a switch receives an Interswitch Resolve request message
one of its upstream neighbors, it checks to see if the
endstation is connected to one of its local access ports. If so,
formulates an Interswitch Resolve response message by filling in
requested address information, along with its own MAC address.
then sets the message status field to ResolveAck, and returns
message to its upstream (requesting) neighbor
If the receiving switch cannot resolve the address, it forwards
Interswitch Resolve request message to its downstream neighbors.
the switch has no downstream neighbors, it sets the message
field to Unknown, and returns the message to its
(requesting) neighbor
Ruffen, et al. Informational [Page 22]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
When a switch forwards an Interswitch Resolve request message to
downstream neighbors, it keeps track of the number of requests it
sent out and received back. It will only respond back to
upstream (requesting) neighbor when one of the following
occurs
- It receives any response with a status of
- All downstream neighbors have responded with a status of
Any Interswitch Resolve request message that is not responded
within a certain predetermined time (currently 5 seconds) is
to have a response status of Unknown
When the Interswitch Resolve server receives a successful
Resolve response message, it records the resolved address
in the remote cache of its local directory for use in resolving
packets for the same endstation. Note that this process results
each switch building its own unique copy of the virtual
containing only the endstation addresses in which it is interested
4.3.5 Unresolvable
The Unresolvable server is called when a packet destination
cannot be resolved. The server records the packet in a table
can then be examined to determine which endstations are
unresolvable traffic
Also, if a particular destination is repeatedly seen to
unresolvable, the server calls the Block server (Section 4.3.6)
determine whether the address should be blocked
4.3.6 Block
The Resolve Block server is called when a particular destination
been repeatedly seen to be unresolvable. This typically
when, unknown to the packet source, the destination endstation
either not currently available or no longer exists
If the Block server determines that the unresolved address
exceeded a configurable request threshold, the address is added
the server's Block Table. Interswitch Resolve request messages
addresses listed in the Block Table are sent less frequently,
reducing the amount of Interswitch Resolve traffic throughout
fabric
Ruffen, et al. Informational [Page 23]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
If an address listed in the Block Table is later
resolved by and Interswitch Resolve request message, the address
removed from the table
4.4 Policy Service
Once the destination address of the call packet has been resolved
the Policy Service Center is called to determine the validity of
requested call connection based on the VLAN policy of the source
destination VLANs
4.4.1 Unicast Rules
The Policy Unicast Rules server recognizes two VLAN policy values
Open or Secure. The default policy for all VLANs is Open
The policy value is used as follows when determining the validity
a requested call connection
- If the VLAN policy of either the source or destination cannot
determined, the Filter Service Center is called to establish
filter (i.e., blocked) for the SA/DA pair
- If the source and destination endstations belong to the same VLAN
then the connection is permitted regardless of the VLAN policy
- If the source and destination endstations belong to
VLANs, but both VLANs are running with an Open policy, then
connection is permitted, providing cut-through switching
different VLAN(s).
- If the source and destination endstations belong to
VLANs and one or both of the VLANs are running with a
policy, then the Flood Service Center (Section 4.8) is called
broadcast the packet to other SFVLAN switches having ports
endstations that belong to the same VLAN as the packet source
Note that if any of the VLANs to which the source or
belong has a Secure policy, then the policy used in the
algorithm is Secure
Ruffen, et al. Informational [Page 24]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
4.5 Connect Service
Once the Policy Service Center (Section 4.4) has determined that
requested call connection is valid, the Connect Service Center
called to set up the connection. Note that connectivity between
endstations within the fabric is established on a switch-by-
basis as the call progresses through the fabric toward
destination. No synchronization is needed between switches
establish an end-to-end connection
The Connect Service Center maintains a Connection Table
information for all connections currently active on the switch'
local ports
Connections are removed from the Connection Table when one of
endstations is moved to a new switch (Section 4.1.2) or when
Topology Link State server (Section 4.2.3) notifies the
Service Center that a network link has failed. Otherwise
connections are not automatically aged out or removed from
Connection Table until a certain percentage threshold (HiMark)
table capacity is reached and resources are needed. At that point
some number of connections (typically 100) are aged out and
at one time
4.5.1 Local
If the destination endstation resides on the local switch,
Connect Local server establishes a connection between the source
destination ports. Note that if the source and destination
reside on the same physical port, a filter connection is
by calling the Filter Service Center (Section 4.6).
4.5.2 Link State
The Connect Link State server is called if the destination
of the proposed connection does not reside on the local switch
The server executes a call to the Path Link State server (
4.7.1) which returns up to three "best" paths of equal cost from
local switch to the destination switch. If more than one path
returned, the server chooses a path that provides the best
balancing of user traffic across the fabric
Ruffen, et al. Informational [Page 25]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
4.5.3 Directory
The Connect Directory server is called if the Connect Link
server is unable to provide a path for some reason
The server examines the local directory to determine on which
the destination endstation resides. If the port of access to
destination switch is known, then a connection is established
that port as the outport of the connection
4.6 Filter Service
The Filter Service Center is responsible for establishing
connections. This service center is called by the Connect
server (Section 4.5.1) if the source and destination
reside on the same physical port, and by the Policy Service
(Section 4.4) if the VLAN of either the source or destination
indeterminate
A filter connection is programmed in the switch hardware with
specified outport. That is, the connection is programmed to
any traffic for that SA/DA pair
4.7 Path Service
The Path Service Center is responsible for determining the path
a source to a destination
4.7.1 Link State
The Path Link State server is called by the Connect Link State
(Section 4.5.2) to return up to three best paths of equal
between a source and destination pair of endstations. These
paths are calculated by the Topology Link State server (
4.2.3).
The Path Link State server is also called by the Connect
Center to return a complete source-to-destination path consisting
a list of individual switch port names. A switch port name
of the switch base MAC address and a port instance relative to
switch
Ruffen, et al. Informational [Page 26]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
4.7.2 Spanning Tree
The Path Spanning Tree server is called by any server needing
forward an undirected message out over the switch flood path.
server returns a port mask indicating which local ports are
enabled as outports of the switch flood path. The switch flood
is calculated by the Topology Spanning Tree server (Section 4.2.2).
4.8 Flood Service
If the Resolve Service Center (Section 4.3) is unable to resolve
destination address of a packet, it invokes the Flood Service
to broadcast the unresolved packet
4.8.1 Tag-Based Flood
The Tag-Based Flood server encapsulates the unresolved packet into
Interswitch Tag-Based Flood message (Section 6.6), along with a
of Virtual LAN identifiers specifying those VLANs to which the
endstation belongs. The message is then sent out over the
flood path to all other switches in the fabric
When a switch receives an Interswitch Tag-Based Flood message,
examines the encapsulated header to determine the VLAN(s) to
the packet should be sent. If any of the switch's local access
belong to one or more of the specified VLANs, the switch strips
the tag-based header and forwards the original packet out
appropriate access port(s).
The switch also forwards the entire encapsulated packet along
switch flood path to its downstream neighboring switches, if any
5. Monitoring Call
The SecureFast VLAN product permits monitoring of user traffic
between two endstations by establishing a call tap on the
between the two stations. Traffic can be monitored in one or
directions along the connection path
5.1
In addition to the terms defined in Section 1.2, the following
are used in this description of the call tap process
Ruffen, et al. Informational [Page 27]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
Originating
The originating switch is the switch that requests the call tap
Any switch along a call connection path may request a tap on
call connection
The tap probe is the device to receive a copy of the
connection data. The probe is attached to a port on the
switch
Probe
The probe switch (also known as the terminating switch) is
switch to which the probe is attached. The probe switch can
anywhere in the topology
5.2 Tapping a
A request to tap a call connection between two endstations
originate on any switch along the call connection path -- the
switch, the egress switch, or any of the intermediate switches.
call connection must have already been established before a call
request can be issued. The probe device can be attached to
switch in the topology
5.2.1 Types of Tap
A call tap is enabled by setting up an auxiliary tap
associated with the call being monitored. Since the tap
originate on a switch somewhere along the call connection path,
tap connection path will pass through one or more of the
along the call path. However, since the probe switch can be
in the switch fabric, the tap path and the call path may diverge
some point
Therefore, on each switch along the tap path, the tap connection
established in one of three ways
- The existing call connection is used with no modification
When both the call path and tap path pass through the switch
and the inport and outports of both connections are identical
the switch uses the existing call connection to route the tap
- The existing call connection is modified
Ruffen, et al. Informational [Page 28]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
When both the call path and tap path pass through the switch
but the call path outport is different from the tap
outport, the switch enables an extra outport in either one
both directions of the call connection, depending on
direction of the tap. This happens under two conditions
- If the switch is also the probe switch, an extra outport
enabled to the probe
- If the switch is the point at which the call path and the tap
diverge, an extra outport is enabled to the downstream
on that leg of the switch flood path on which the probe
is located
- A new connection is established
If the call path does not pass through the switch (because
tap path has diverged from the call path), a completely
connection is established for the tap
5.2.2 Locating the Probe and Establishing the Tap
To establish a call tap, the originating switch formats
Interswitch Tap request message (Section 6.7) and sends it out
the switch flood path to all other switches in the topology
Note
If the originating switch is also the probe switch,
Interswitch Tap request message is necessary
As the Interswitch Tap request message travels out along the
flood path, each switch receiving the message checks to see if it
the probe switch and does the following
- If the switch is the probe switch, it establishes the
connection by either setting up a new connection or modifying
call connection, as appropriate (see Section 5.2.1). It
reformats the Tap request message to be a Tap response
with a status indicating that the probe has been found, and
the message back to its upstream neighbor
- If the switch is not the probe switch, it forwards the Tap
message to all its downstream neighbors (if any).
- If the switch is not the probe switch and has no
neighbors, it reformats the Tap request message to be a
response message with a status indicating that the probe is
Ruffen, et al. Informational [Page 29]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
located on that leg of the switch flood path. It then sends
response message back to its upstream neighbor
When a switch forwards an Interswitch Tap request message to
downstream neighbors, it keeps track of the number of requests
has sent out
- If a response is received with a status indicating that the
switch is located somewhere downstream, the switch establishes
appropriate type of tap connection (see Section 5.2.1). It
formats a Tap response message with a status indicating that
probe has been found and passes the message to its
neighbor
- If no responses are received with a status indicating that
probe switch is located downstream, the switch formats a
response message with a status indicating that the probe has
been found and passes the message to its upstream neighbor
5.2.3 Status
The status field of the Interswitch Tap request/response
contains information about the state of the tap. Some of
status values are transient and are merely used to track the
of the tap request. Other status values are stored in the tap
of each switch along the tap path for use when the tap is torn down
The possible status values are as follows
- StatusUnassigned. This is the initial status of the
Tap request message
- OutportDecisionUnknown. The tap request is still
downstream along the switch flood path. The probe switch had
yet been found
- ProbeNotFound. The probe switch is not located on this leg of
switch flood path
- DisableOutport. The probe switch is located on this leg of
switch flood path, and the switch has had to either modify
call connection or establish a new connection to implement the
(see Section 5.2.1). When the tap is torn down, the switch
have to disable any additional outports that have been enabled
the tap
- KeepOutport. The probe switch is located on this leg of
switch flood path, and the switch was able to route the tap
the existing call path (see Section 5.2.1). Any ports used
Ruffen, et al. Informational [Page 30]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
the tap will remain enabled when the tap is torn down
5.3 Untapping a
A request to untap a call connection must be issued on the
originating switch -- that is, the same switch that issued the
request
To untap a call connection, the originating switch sends
Interswitch Untap request message (Section 6.7) out over the
flood path to all other switches in the topology. The message
sent over the switch flood path, rather than the tap connection path
to ensure that all switches that know of the tap are
notified, even if the switch topology has changed since the tap
established
When a switch receives an Interswitch Untap request message,
checks to see if it is handling a tap for the specified
connection. If so, the switch disables the tap connection,
follows
- If a new connection was added for the tap, the connection
deleted from the connection table
- If additional outports were enabled on the call connection,
are disabled
The switch then forwards the Interswitch Untap request message to
downstream neighbor (if any). If the switch has no
neighbors, it formats an untap response and sends the message back
its upstream neighbor
When a switch forwards an Interswitch Untap request message to
downstream neighbors, it keeps track of the number of requests it
sent out and does not respond back to its upstream neighbor until
untap requests have been responded to. Once all responses have
received, the switch handles any final cleanup for the tap and
sends a single Interswitch Untap response message to its
neighbor
Ruffen, et al. Informational [Page 31]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
6. Interswitch Message Protocol (ISMP
The InterSwitch Message protocol (ISMP) provides a consistent
of encapsulating and transmitting messages exchanged between
to create and maintain the databases and provide other
services and functionality required by the SFVLAN product
6.1 General Packet
ISMP packets are of variable length and have the following
structure
- Frame
- ISMP packet
- ISMP message
Each of these packet segments is discussed separately in
following subsections
6.1.1 Frame
ISMP packets are encapsulated within an IEEE 802-compliant
using a standard header as shown below
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
00 | |
+ Destination address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
04 | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Source address +
08 | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
12 | Type | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
16 | |
+ +
: :
Destination
This 6-octet field contains the Media Access Control (MAC)
of the multicast channel over which all switches in the
receive ISMP packets. Except where otherwise noted, this
Ruffen, et al. Informational [Page 32]
RFC 2643 Cabletron's SecureFast VLAN Operational Model August 1999
contains the multicast address of the control channel over
all switches in the fabric receive ISMP packets -- a value of 01-
00-1D-00-00-00.
Source
Except where otherwise noted, this 6-octet field contains
physical (MAC) address of the switch originating the ISMP packet
This 2-octet field identifies the type of data carried within 