vlans and gvrp curtis simonson bridge functions consortium interoperability lab july, 2000
TRANSCRIPT
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VLANs and GVRP
Curtis Simonson
Bridge Functions Consortium
InterOperability LabJuly, 2000
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Presentation Overview Standards Involved Bridging Background 802.1Q/1D:
– the problem
– the solution» GVRP
» Tagging Frames
Testing It
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The ISO OSI Model
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Standards Involved IEEE Standard The Bridge
Standards (802.1)
Most widely used with the 802.3 MAC (who doesn’t use Ethernet?)
Bridging is MAC independent
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Quick Review - Shared Medium All machines “share”
the network Only one machine can
talk at any one time Distance limitations Total throughput limit Collision likelihood
increased
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Shared Medium (Repeated Network)
All machines “share” the network
Only one machine can talk at any one time
Distance limitations– At most 205m.
Total throughput limit Collision likelihood
increased
Repeaters
End Stations
5m
100m
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Bridging Review Connects Separate
shared Networks Frame Translation/
Encapsulation (Token Ring to Ethernet)
Reduces Unicast Traffic
Switches: Allow for multiple conversations
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Bridging Background
Bridges work at layer 2 of the OSI Model
Their primary function is to relay frames
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Filtering Database Review
One database contains MAC addresses, which port they’re on, and if they’re active or disabled
Duplicate MAC addresses not allowed (the second one would replace the first)
Entry MAC Addr Port active1 0800900A2580 1 yes2 002034987AB1 1 yes3 00000C987C00 2 yes4 00503222A001 2 yes56789
101112
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802.1Q - Standard for VLANs
Defines a method of establishing VLANs
Establishes the Tagged Frame
Provides a way to maintain priority information across LANs
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Reasons For Standardizing VLANs
Old implementations could only be defined in one switch
To connect a VLAN to another network, each VLAN needed a router port
The only multi-switch VLANs were proprietary:– Cisco: ISL
– Bay: Lattisspan
– 3Com: VLT
– Cabletron: SecureFast
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Standards Based VLANs
Includes definition for a new GARP application called GVRP (GARP VLAN Registration Protocol)– Propagate VLAN registration across the net
Associate incoming frames with a VLAN ID De-associate outgoing frames if necessary Transmit associated frames between VLAN
802.1Q compliant switches
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What are VLANs - Virtual Local Area Networks? Divides switch into two or
more “virtual” switches with separate broadcast domains
Achieved by manual configuration through the switches’ management interface
Only that switch will be segmented
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Multiple VLANs in One Switch
Multiple VLANs can be defined on the same switch
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Why VLANs?
Lots of broadcast traffic wastes bandwidth– VLANs create separate broadcast domains
» Microsoft Networking
» Novell Networking
» NetBEUI
» IP RIP
» Multicast (sometimes acts like broadcast)
VLANs can span multiple switches and therefore create separate broadcast domains that span multiple switches
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More Reasons... Link Multiplexing
– slower speed technologies share the high-bandwidth uplink
– multiple IP subnets on one physical link with layer 3 switching (such as to connect Morse, Leavitt and Ocean if we were switched instead of routed)
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And One More Reason... Security
– Traffic is only seen by who it is intended for» example: Two separate VLANs, one for accounting
and one for sales. Sensitive accounting data transmitted over the network will only be seen by devices in the accounting VLAN.
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Basic VLAN Concepts Port-based VLANs
– Each port on a switch is in one and only one VLAN (except trunk links)
Tagged Frames
– VLAN ID and Priority info is inserted (4 bytes) Trunk Links
– Allow for multiple VLANs to cross one link Access Links
– The edge of the network, where legacy devices attach Hybrid Links
– Combo of Trunk and Access Links VID
– VLAN Indentifier
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Tagged Frames 4 Bytes inserted
after Destination and Source Address
Tagged Protocol Identifier (TPID) = 2 Bytes (x8100)– length/type field
Tagged Control Information (TCI) = 2 Bytes– contains VID
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Trunk Link
Attaches two VLAN switches - carries Tagged frames ONLY.
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Access Links
Access Links are Untagged for VLAN unaware devices - the VLAN switch adds Tags to received frames, and removes Tags when transmitting frames.
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Hybrid Links
Hybrid Links - ALL VLAN-unaware devices are in the same VLAN
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So Far So Good...
So one might ask: “how does the Filtering Database handle VLANs?”
Two answers:– multiple (distinct) tables: one for each VLAN– one table, with a VLAN column
They sound similar, but it turns out they are VERY different
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Entry MAC Addr Port active1 0800900A2580 1 yes2 002034987AB1 1 yes3 0500A1987C00 2 yes4 00503222A001 2 yes56789
101112
Multiple Tables Called MFD (multiple
Filtering Databases) or it might also be called Independent Learning
Each VLAN learns MAC addresses independently, so duplicate MAC addresses are OK as long as they are in different VLANs.
Entry MAC Addr Port active1 0800900A2580 1 yes2 002034987AB1 1 yes3 0500A1987C00 2 yes4 00503222A001 2 yes56789
101112
Entry MAC Addr Port active1 0800900A2580 1 yes2 002034987AB1 1 yes3 0500A1987C00 2 yes4 00503222A001 2 yes56789
101112
Entry MAC Addr Port active1 0800900A2580 1 yes2 002034987AB1 1 yes3 0500A1987C00 2 yes4 00503222A001 2 yes56789
101112
Each Table is for One VLAN
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One (Big) Table
Called SFD (Single Filtering Database) or Shared Learning
No duplicate MAC addresses
Asymmetric VLAN possible
Entry MAC Addr Port active VLAN1 0800900A2580 1 yes 22 002034987AB1 1 yes 23 0500A1987C00 2 yes 24 00503222A001 2 yes 25 080034090478 3 yes 16 049874987AB1 5 yes 17 0555A1945600 5 yes 38 00503222A023 5 yes 29
101112
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Independent Learning I
Legacy router learns MAC addresses from both VLANs
Requires 2 physical links
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Independent Learning II
VLAN-aware router only needs one physical link
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Problems
Can’t combine SFD and MFD switches in one network
Some switches only do one or the other, and can’t be changed
Hybrids of SFD and MFD makes this tricky
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Future Additions
Layer 3 based VLANs– IP traffic on a different VLAN than IPX
Multiple Spanning Trees (one per VLAN)– allows for using the disabled links
ATM to IEEE VLAN mapping – Emulated LANs
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GARP (yeah, I know, “the world according to”… that’s a new one!)
Generic Attribute Registration Protocol Standard Defines:
– method to declare attributes to other GARP participants
– frame type to convey GARP messages: Protocol Data Unit (PDU)
– rules and timers for registering/de-registering attributes
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GARP - how?
A device wants to declare a certain attribute
It sends a declaration
The bridge receives it and propagates it throughout the network.
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GARP - two devices
A second device wants to declare a certain attribute
Now a “path” has been formed.
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GMRP
GARP Multicast Registration Protocol Defines a GARP Application (instance of
the generic framework) Allows devices to declare membership in a
multicast group
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GMRP - multiple devices
Devices declare membership in a multicast group
All multicast frames for that group propagate only to the proper devices.
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GMRP - Pros & Cons
Pros:– provides multicasting
that isn’t broadcasting
– works “through” legacy bridges
– allows asymmetric pruning
Cons:– end stations must
support 802.1p
– no interface between IGMP and GMRP (yet)
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GVRP - GARP VLAN Registration Protocol
Disadvantages to Static VLANs– Static VLANs are created via management– Must be maintained by a network admin– Static VLANs must be reconfigured for every
network topology change
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GVRP Simplifies All This!
GVRP creates dynamic VLANs– No manual configuration needed– GVRP is maintained by the devices themselves– Topology change? No problem, GVRP
recreates the dynamic VLAN automatically
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What can GVRP do for you?
Allows the creation of VLANs with a specific VID and a specific port, based on updates from GVRP-enabled devices.
Advertises manually configured VLANs to other GVRP-enabled device. As a result of this the GVRP-enable devices in the core of the network need no manual configuration in order to inter-operate.
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GVRP Info
GVRP is a GARP application that registers attributes for dynamic VLANs
GVRP deals only with the management of dynamic VLANs
Everything that you have learned about static VLAN packet format and transmission applies
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VLAN Data Frame Format Review
GVRP handles data in the same way as Static VLANs do.– Header, inserted after the destination and source
addresses, that contains Protocol Identifier and VID
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How GVRP does all this:
The method of advertisement used by GVRP-enabled devices consists of sending Protocol Data Units (PDUs), similar to Spanning Tree BPDUs, to a known multicast MAC address (01 80 C2 00 00 21) to which all GVRP-enabled devices listen to for updates. GVRP advertisement follows the definition of GARP.
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What do these PDUs contain?
A single PDU may contain several different messages telling the GVRP-enabled device to perform a specific action.– Join: register the port for the specified VLAN– Leave: de-register the port for the specified
VLAN» LeaveAll: de-register all VLAN registrations on
that port
– Empty: request to re-advertise dynamically and statically configured VLANs
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Industry Implementation Example– 3Com manufactures Network Interface Cards that take
advantage of GVRP
– Accessed via the Control Panel (DynamicAccess®
)
– Extremely easy to configure
Windows screenshot —>
Vendors (current): Cisco Systems, 3Com and Hewlett Packard
Several others are developing working implementations also.
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Example: GARP/GVRP
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