Network Working Group D. Hamilton
Request for Comments: 2641 D. Ruffen
Category: Informational Cabletron Systems Incorporated
August 1999

Cabletron's VlanHello Protocol Specification
Version 4

Status of this Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Copyright Notice

Copyright (C) The Internet Society (1999). All Rights Reserved.

Abstract

The VlanHello protocol is part of the InterSwitch Message Protocol
(ISMP) which provides interswitch communication between switches
running Cabletron's SecureFast VLAN (SFVLAN) prodUCt. Switches use
the VlanHello protocol to discover their neighboring switches and
establish the topology of the switch fabric.

Table of Contents

1. Introduction...................................... 2
1.1 Data Conventions.............................. 2
2. VlanHello Protocol Operational Overview........... 2
2.1 Neighbor Discovery............................ 2
2.2 Port States................................... 3
2.3 Topology Events............................... 5
2.4 Timers........................................ 9
3. InterSwitch Message Protocol...................... 9
3.1 Frame Header.................................. 10
3.2 ISMP Packet Header............................ 11
3.3 ISMP Message Body............................. 12
4. Interswitch Keepalive Message..................... 13
5. Security Considerations........................... 16
6. References........................................ 16
7. Authors' Addresses................................ 16
8. Full Copyright Statement.......................... 17

1. Introduction

This memo is being distributed to members of the Internet community
in order to solicit reactions to the proposals contained herein.
While the specification discussed here may not be directly relevant
to the research problems of the Internet, it may be of interest to
researchers and implementers.

1.1 Data Conventions

The methods used in this memo to describe and picture data adhere to
the standards of Internet Protocol documentation [RFC1700], in
particular:

The convention in the documentation of Internet Protocols is to
eXPress numbers in decimal and to picture data in "big-endian"
order. That is, fields are described left to right, with the most
significant octet on the left and the least significant octet on
the right.

The order of transmission of the header and data described in this
document is resolved to the octet level. Whenever a diagram shows
a group of octets, the order of transmission of those octets is
the normal order in which they are read in English.

Whenever an octet represents a numeric quantity the left most bit
in the diagram is the high order or most significant bit. That
is, the bit labeled 0 is the most significant bit.

Similarly, whenever a multi-octet field represents a numeric
quantity the left most bit of the whole field is the most
significant bit. When a multi-octet quantity is transmitted the
most significant octet is transmitted first.

2. VlanHello Protocol Operational Overview

Switches use the VlanHello protocol to detect their neighboring
switches and establish the topology of the switch fabric.

2.1 Neighbor Discovery

At initialization, each switch sends an Interswitch Keepalive message
out all local ports except those which have been preconfigured such
that they cannot be Network ports (see Section 2.2). Then, as each
switch discovers its neighboring switches via incoming Interswitch
Keepalive messages, it notifies its local topology services (see
Section 2.3), which then build the topology tables for the switching
fabric.

Each switch continues to send Interswitch Keepalive messages at
regular intervals (currently 5 seconds). If a switch has not heard
from one of its neighbors for some predetermined interval (see
Section 2.4), notification is sent to all interested services and the
neighboring switch is removed from the topology table.

Interswitch Keepalive messages are described in Section 4.

2.2 Port States

Each port on a switch can be in one of several different states.
These states are listed below. Figure 1 shows how the port state
changes within the VlanHello protocol.

o Unknown. This is the default state of all ports at
initialization.

o Network. A port is deemed a Network port when the switch has
received an Interswitch Keepalive message over the port from one
of its neighbor switches. A transition to this state triggers a
Neighbor Found event, notifying the local topology servers that
the interface is functioning and a 2-way conversation has been
established with the neighbor.

When the last switch is lost on a Network port, the state of the
switch reverts to either Network Only (see next state) or to
Unknown, and a Neighbor Lost event is triggered, notifying the
local topology servers that the interface is no longer
operational.

o Network Only. Certain types of port interfaces are incapable of
Accessing user endstations and can only be used to access other
switches. Such ports are deemed Network Only ports. If the last
switch is lost from a port that has already been deemed a Network
port, the VlanHello protocol checks the condition of the port
interface. If it is the type of interface that can only be used
to access other switches, the state of the port is set to Network
Only. Otherwise, it reverts to Unknown.

o Standby. A port is deemed a Standby port under the following
conditions:

o The neighbor switch on the port has a higher level of
functionality and it has determined that the local switch is
incompatible with that functionality. In this circumstance,
the MAC entry for the local switch in the Interswitch Keepalive
message received from the neighbor contains an assigned status
of Incompatible.

o The list of MAC entries in the Interswitch Keepalive message
received from the neighbor switch does not contain an entry for
the local switch. In this circumstance, the local switch
assumes that communication with its neighbor will be one-way
only.

The VlanHello protocol continues to listen for Interswitch
Keepalive messages on a Standby port, but does not transmit any
Interswitch Keepalive messages over the port. If a message is
received that removes the condition under which the port state was
set to Standby, the state of the port is set to Network.

o Going to Access. When any packet other than an Interswitch
Keepalive message is received over an Unknown port, the state of
the port is changed to Going to Access and a timer is activated.
If the timer expires without an Interswitch Keepalive message
being received over the port, the port state changes to Access.

o Access. A port is deemed an Access port when any packet other
than an Interswitch Keepalive message has been received over the
port and the Going to Access timer has expired. A port can also
be administratively designated an Access "control" port, meaning
the port is to remain an Access port, regardless of the type of
messages that are received on it. Interswitch Keepalive messages
are not sent over Access control ports.

Three other types of ports are recognized: the host management port,
host data port, and host control port. These ports are designated at
initialization and are used to access the host CPU. Interswitch
Keepalive messages are not sent over these ports.

Packet in

V
+---------+
Packet in Unknown
+---------+
G-A V
Timer +----------+ no V
exp Going to <------[KA msg?] Packet in
<------ Access
+----------+ yes V
V V yes +---------+
+--------+ V [1-way?]------+--> Standby
Access [KA msg?] ^ +---------+
+--------+ no
V no V
yes [compatible?]----+ [KA msg?]

yes yes
V V
V +---------+ [1-way?]
+---------> Network <--+
+---------+ ^ no
yes V
lost last +<----[compatible?]
neighbor
V
[network]
[ only? ]

+--------------+ yes no +---------+
Network Only <-----------+-----------> Unknown
+--------------+ +---------+

Figure 1: Port State Machine

2.3 Topology Events

When the VlanHello protocol discovers new information about the
status of one of its network ports, it notifies its local topology
service center so that the service center can build or modify the
topology tables for the switch fabric. This notification takes the
form of a system event, described in a structure known as a topology
relay structure. These structures are linked in a first-in/first-out
(FIFO) queue and processed by the topology servers in the order in
which they were received.

A topology relay structure typically contains information from
Interswitch Keepalive messages received on the specified port, 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 Event
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
04 Delta options mask
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
08 Current options mask
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
12 Port number
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
16
+ Port neighbor switch identifier +

+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Port neighbor IP address ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
28 ... Port neighbor IP address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Neighbor chassis MAC addr +
32
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
36 Neighbor chassis IP address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
40 Neighbor functional level
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
44 Topology agent
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
48 Next event
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Event

This 4-octet field contains the number of the event.
Valid values are as follows:

1 A new neighbor switch was discovered on the
specified port.
2 The neighbor switch has gained the feature(s)
specified in the Delta options mask.
3 The neighbor switch has lost the feature(s)
specified in the Delta options mask.
4 The neighbor switch has timed out and is presumed
down.
5 The specified port is down.

6 The neighbor switch has been previously seen on a
different port. The specified port is the
previous port.
7 The specified port is being reassigned to another
topology agent. Event is generated by the current
(old) agent.
8 The port is looped -- that is, the Keepalive
message was generated by the receiving switch.
9 The port is crossed -- that is, a Keepalive message
was received on a port not owned by this topology
agent.
10 The neighbor switch's functional level has changed.
11 The neighbor switch is running an incompatible
version of the protocol.
12 Two-way communication with the neighbor switch has
been lost.
13 The neighbor switch's Keepalive message sequence
number has been reset, indicating the switch
itself has been reset.

Delta options mask

This 4-octet field contains a bit map specifying the feature(s)
gained or lost by the neighbor switch (events 2 and 3 only).
Valid values are as specified for the next field, Current options
mask.

Current options mask

This 4-octet field contains a bit map specifying the features of
the neighbor switch. Bit assignments are as follows:

1 (unused)
2 The switch is a VLAN switch.
4 The switch has link state capability.
8 The switch has loop-free flood path capability.
16 The switch has resolve capability.
32 (unused)
64 The switch has tag-based flood capability.
128 The switch has tap capability.
256 The switch has message connection capability.
512 The switch has redundant access capability.
1024 The switch is an isolated switch.
4096 The switch is an uplink. (SFVLAN V1.8 only)
8192 The switch is an uplink to core. (SFVLAN V1.8 only)
16384 The port is an uplink port. (SFVLAN V1.8 only)
32768 The port is an uplink flood port. (SFVLAN V1.8 only)

Port number

This 4-octet field contains the logical number of the local port
for which the event was generated.

Port neighbor switch identifier

This 10-octet field contains the internal identifier of the
neighbor switch discovered on the port. The identifier consists
of the 6-octet physical (MAC) address of the neighbor switch,
followed by the 4-octet logical port number (local to the neighbor
switch) on which the neighbor was discovered.

Port neighbor IP address

This 4-octet field contains the Internet Protocol (IP) address of
the neighbor switch.

Neighbor chassis MAC address

This 6-octet field contains the physical (MAC) address of the
chassis of the neighbor switch.

Neighbor chassis IP address

This 4-octet field contains the Internet Protocol (IP) address of
the chassis of the neighbor switch.

Neighbor functional level

This 4-octet field contains the functional level of the neighbor
switch, as determined by the version level of the SecureFast VLAN
software under which this switch is operating. Valid values are
as follows:

1 The switch is running a version of SFVLAN prior to Version 1.8.
2 The switch is running SFVLAN Version 1.8 or greater.

Topology agent

This 4-octet field contains a pointer to the topology agent that
generated the event. The pointer here can reference any of the
topology agents that send Interswitch Keepalive messages -- that
is, any agent running the VlanHello protocol.

Next event

This 4-octet field contains a pointer to the next event relay
structure in the list.

2.4 Timers

The VlanHello protocol uses three timers.

o Send Hello timer. The Send Hello timer is used to control the
interval at which Interswitch Keepalive messages are sent.

o Aging timer. The Aging Timer is used to detect when communication
with a neighboring switch has been lost.

o Going to Access timer. The Going to Access timer is used to
synchronize the transition of a port state to Access and prevent a
port from being prematurely designation as an Access port during
network initialization. If an Unknown port receives any packet
other than an Interswitch Keepalive message, the port state is set
to Going To Access. If the switch receives an Interswitch
Keepalive message over that port before the timer expires, the
port state is changed to Network. Otherwise, when the timer
expires, the port state is changed to Access.

3. InterSwitch Message Protocol

The VlanHello protocol operates as part of the InterSwitch Message
Protocol (ISMP) -- part of Cabletron's SecureFast VLAN (SFVLAN)
product, as described in [IDsfvlan]. ISMP provides a consistent
method of encapsulating and transmitting network control messages
exchanged between SFVLAN switches.

ISMP message packets are of variable length and have the following
general structure:

o Frame header
o ISMP packet header
o ISMP message body

3.1 Frame Header

ISMP packets are encapsulated within an IEEE 802-compliant frame
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 address

This 6-octet field contains the Media Access Control (MAC) address
of the multicast channel over which all switches in the fabric
receive ISMP packets. The destination address fields of all ISMP
packets contain a value of 01-00-1D-00-00-00.

Source address

This 6-octet field contains the physical (MAC) address of the
switch originating the ISMP packet.

Type

This 2-octet field identifies the type of data carried within the
frame. The type field of ISMP packets contains the value 0x81FD.

3.2 ISMP Packet Header

The ISMP packet header consists of a variable number of octets, 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 ///////////////////////////////////////////////////////////////
://////// Frame header /////////////////////////////////////////:
+//////// (14 octets) /////////+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
12 /////////////////////////////// ISMP Version
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
16 ISMP message type Sequence number
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
20 Code length
+-+-+-+-+-+-+-+-+ +
Authentication code
: :

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

: :

Frame header

This 14-octet field contains the frame header.

ISMP Version

This 2-octet field contains the version number of the InterSwitch
Message Protocol to which this ISMP packet adheres. The VlanHello
protocol uses ISMP Version 3.0.

ISMP message type

This 2-octet field contains a value indicating which type of ISMP
message is contained within the message body. VlanHello
Interswitch Keepalive messages have a message type of 2.

Sequence number

This 2-octet field contains an internally generated sequence
number used by the various protocol handlers for internal
synchronization of messages.

Code length

This 1-octet field contains the number of octets in the
Authentication code field of the message.

Authentication code

This variable-length field contains an encoded value used for
authentication of the ISMP message.

3.3 ISMP Message Body

The ISMP message body is a variable-length field containing the
actual data of the ISMP message. The length and content of this
field are determined by the value found in the message type field.

The format of the VlanHello Interswitch Keepalive message is
described in the next section.

4. Interswitch Keepalive Message

The VlanHello Interswitch Keepalive message consists of a variable
number of octets, 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
+ Frame header / +
: ISMP packet header :

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
n Version Switch IP address ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
n+4 ... Switch IP address
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
n+8
+ Switch ID +

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
n+16
+ Chassis MAC address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Chassis IP address ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
n+24 ... Chassis IP address Switch type
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
n+28 Functional level
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
n+32 Options
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
n+36 Base MAC count
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
n+40
: Base MAC entries :

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

n = 21 + length of the authentication code of the packet

Frame header/ISMP packet header

This variable-length field contains the frame header and the ISMP
packet header.

Version

This 2-octet field contains the version number of the VlanHello
protocol to which this message adheres. This document describes
VlanHello Version 4.

Switch IP address

This 4-octet field contains the Internet Protocol (IP) address of
the sending switch.

Switch ID

This 10-octet field contains the internal ISMP identifier of the
sending switch. The identifier is generated by the sending switch
and consists of the 6-octet physical (MAC) address of the switch,
followed by a 4-octet value containing the logical port number
over which the switch sent the packet.

Chassis MAC

This 6-octet field contains the physical (MAC) address of the
chassis of the sending switch.

Chassis IP address

This 4-octet field contains the Internet Protocol (IP) address of
the switch chassis.

Switch type

This 2-octet field contains the type of the switch. Currently, the
only value recognized here is as follows:

2 The switch is an SFVLAN switch.

Functional level

This 4-octet field contains the functional level of the sending
switch, as determined by the version level of the SecureFast VLAN
software under which this switch is operating. Valid values are
as follows:

1 The switch is running a version of SFVLAN prior to Version
1.8.
2 The switch is running SFVLAN Version 1.8 or greater.

Options

This 4-octet field contains a bit map specifying the features of
the switch. Bit assignments are as follows:

1 (unused)
2 The switch is a VLAN switch.
4 The switch has link state capability.
8 The switch has loop-free flood path capability.
16 The switch has resolve capability.
32 (unused)
64 The switch has tag-based flood capability.
128 The switch has tap capability.
256 The switch has message connection capability.
512 The switch has redundant access capability.
1024 The switch is an isolated switch.
4096 The switch is an uplink. (SFVLAN V1.8 only)
8192 The switch is an uplink to core. (SFVLAN V1.8 only)
16384 The port is an uplink port. (SFVLAN V1.8 only)
32768 The port is an uplink flood port. (SFVLAN V1.8 only)

Base MAC count

This 2-octet field contains the number of entries in the list of
Base MAC entries.

Base MAC entries

This variable-length field contains a list of entries for all
neighboring switches that the sending switch has previously
discovered on the port over which the message was sent. The number
of entries is found in the Base MAC count field.

Each MAC entry is 10 octets long, structured as follows:

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

+ Switch MAC address +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Assigned neighbor state ...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
... Assigned neighbor state
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Switch MAC address

This 6-octet field contains the base MAC address of the
neighboring switch.

Assigned neighbor state

This 4-octet field contains the assigned state of the neighboring
switch as perceived by the sending switch. Currently, the only
value valid here is 3, indicating a state of Network

5. Security Considerations

Security concerns are not addressed in this document.

6. References

[RFC1700] Reynolds, J. and J. Postel, "Assigned Numbers", STD 2,
RFC1700, October 1994.

[IDsfvlan] Ruffen, D., Len, T. and J. Yanacek, "Cabletron's
SecureFast VLAN Operational Model", RFC2643, August
1999.

[IDvlsp] Kane, L., "Cabletron's VLS Protocol Specification", RFC
2642, August 1999.

7. Authors' Addresses

Dave Hamilton
Cabletron Systems, Inc.
Post Office Box 5005
Rochester, NH 03866-5005

Phone:(603) 332-9400
EMail: daveh@ctron.com

Dave Ruffen
Cabletron Systems, Inc.
Post Office Box 5005
Rochester, NH 03866-5005

Phone:(603) 332-9400
EMail: ruffen@ctron.com

17. Full Copyright Statement

Copyright (C) The Internet Society (1999). All Rights Reserved.

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included on all such copies and derivative works. However, this
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The limited permissions granted above are perpetual and will not be
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TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
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Acknowledgement

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