Homework#4 Due June 15, 2006
1. Try to do web search and find out 3 VLAN products from different vendors. You
have to describe the detailed protocols of these products.
A. IEEE 802.1Q
The IEEE 802.1Q specification establishes a standard method for tagging
Ethernet frames with VLAN membership information. The IEEE 802.1Q
standard defines the operation of VLAN Bridges that permit the definition,
operation and administration of Virtual LAN topologies within a Bridged LAN
infrastructure. The 802.1Q standard is intended to address the problem of how to
break large networks into smaller parts so broadcast and multicast traffic would
not grab more bandwidth than necessary. The standard also helps provide a
higher level of security between segments of internal networks.
The key for the IEEE 802.1Q to perform the above functions is in its tags.
802.1Q-compliant switch ports can be configured to transmit tagged or untagged
frames. A tag field containing VLAN (and/or 802.1p priority) information can be
inserted into an Ethernet frame. If a port has an 802.1Q-compliant device
attached (such as another switch), these tagged frames can carry VLAN
membership information between switches, thus letting a VLAN span multiple
switches. However, it is important to ensure ports with non-802.1Q-compliant
devices attached are configured to transmit untagged frames. Many NICs for PCs
and printers are not 802.1Q-compliant. If they receive a tagged frame, they will
not understand the VLAN tag and will drop the frame. Also, the maximum legal
Ethernet frame size for tagged frames was increased in 802.1Q (and its
companion, 802.3ac) from 1,518 to 1,522 bytes. This could cause network
interface cards and older switches to drop tagged frames as "oversized."
Protocol Structure - VLAN: Virtual Local Area Network and the IEEE
802.1QIEEE 802.1Q Tagged Frame for Ethernet:
7 1 6 6 2 2 2 42-1496 4
Preamble SFD DA SA TPID TCI Type Length Data CRC
• Preamble (PRE)- 7 bytes. The PRE is an alternating pattern of ones and
zeros that tells receiving stations that a frame is coming, and that
provides a means to synchronize the frame-reception portions of
receiving physical layers with the incoming bit stream.
• Start-of-frame delimiter (SFD)- 1 byte. The SOF is an alternating
pattern of ones and zeros, ending with two consecutive 1-bits indicating
that the next bit is the left-most bit in the left-most byte of the destination
• Destination address (DA)- 6 bytes. The DA field identifies which
station(s) should receive the frame.
• Source addresses (SA)- 6 bytes. The SA field identifies the sending
• TPID- defined value of 8100 in hex. When a frame has the EtherType
equal to 8100, this frame carries the tag IEEE 802.1Q / 802.1P.
• TCI - Tag Control Information field including user priority, Canonical
format indicator and VLAN ID.
3bits 1bit 12bits
User Priority CFI Bits of VLAN ID (VIDI) to identify possible VLANs
• User Priority- Defines user priority, giving eight (2^3) priority levels.
IEEE 802.1P defines the operation for these 3 user priority bits.
• CFI- Canonical Format Indicator is always set to zero for Ethernet
switches. CFI is used for compatibility reason between Ethernet type
network and Token Ring type network. If a frame received at an Ethernet
port has a CFI set to 1, then that frame should not be forwarded as it is to
an untagged port.
• VID- VLAN ID is the identification of the VLAN, which is basically
used by the standard 802.1Q. It has 12 bits and allow the identification of
4096 (2^12) VLANs. Of the 4096 possible VIDs, a VID of 0 is used to
identify priority frames and value 4095 (FFF) is reserved, so the
maximum possible VLAN configurations are 4,094.
• Length/Type- 2 bytes. This field indicates either the number of MAC-
client data bytes that are contained in the data field of the frame, or the
frame type ID if the frame is assembled using an optional format.
• Data- Is a sequence of nbytes (42=< n =<1496) of any value. The total
frame minimum is 64bytes.
• Frame check sequence (FCS)- 4 bytes. This sequence contains a 32-bit
cyclic redundancy check (CRC) value, which is created by the sending
MAC and is recalculated by the receiving MAC to check for damaged
B. Cisco ISL (Inter-Switch Link) & DISL (Dynamic Inter-Switch Link)
Inter-Switch Link. Protocol (ISL), a Cisco-proprietary protocol, maintains
VLAN information as traffic flows between switches and routers.
Inter-Switch Link (ISL) tagging accomplishes the same task as 802.1Q
trunking but uses a different frame format. ISL trunks are Cisco proprietary
and define only a point-to-point connection between two devices, typically
switches. The name Inter-Switch Link hints at this design. ISL frame tagging
uses a low-latency mechanism for multiplexing traffic from multiple VLANs
on a single physical path. ISL has been implemented for connections among
switches, routers, and network interface cards (NICs) used on nodes such as
servers. To support the ISL feature, each connecting device must be ISL-
configured. A router that is ISL-configured can allow inter-VLAN
communications. A non-ISL device that receives ISL-encapsulated Ethernet
frames will most likely consider them protocol errors because of the format
and size of the frames.
ISL functions at Layer 2 of the OSI model like 802.1Q, but it differs by
encapsulating the entire Layer 2 Ethernet frame inside an ISL header and
trailer. Because ISL encapsulates the entire frame, it is protocol-independent
and can carry any type of Layer 2 frame or upper-layer protocol between the
switches. The encapsulated frames may be token-ring or Fast Ethernet, and
are carried unchanged from transmitter to receiver.
ISL has the following characteristics:
• Performed with application-specific integrated circuits (ASIC)
• Not intrusive to client stations; client does not see the ISL header
• Effective between switches, routers and switches, and switches and
servers with ISL NICs
Dynamic Inter-Switch Link Protocol (DISL), also a Cisco protocol, simplifies
the creation of an ISL trunk from two interconnected Fast Ethernet devices.
Fast EtherChannel technology enables aggregation of two full-duplex Fast
Ethernet links for high-capacity backbone connections. DISL minimizes VLAN
trunk configuration procedures because only one end of a link needs to be
configured as a trunk.
Protocol Structure - ISL & DISL: Inter-Switch Link and Dynamic ISL
ISL header structure:
40 4 4 48 16 8 24 15 1 16 16bit
DA Type User SA Len AAA03 HSA VLAN BP DU Index Resv
• DA - 40-bit multicast destination address.
• Type - 4-bit descriptor of the encapsulated frame types - Ethernet
(0000), Token Ring (0001), FDDI (0010), and ATM (0011).
• User - 4-bit descriptor used as the type field extension or to define
Ethernet priorities. This is a binary value from 0, the lowest priority,
to 3, the highest priority.
• SA - 48-bit source MAC address of the transmitting Catalyst switch.
• LEN - 16-bit frame-length descriptor minus DA type, user, SA, LEN,
• AAAA03 - Standard SNAP 802.2 LLC header.
• HSA - First 3 bytes of SA (manufacturer's ID or organizational unique
• VLAN - 15-bit VLAN ID. Only the lower 10 bits are used for 1024
• BPDU - 1-bit descriptor identifying whether the frame is a Spanning
Tree bridge protocol data unit (BPDU). Also set if the encapsulated
frame is a Cisco Discovery Protocol (CDP) frame.
• INDEX - 16-bit descriptor that identifies the transmitting port ID.
Used for diagnostics.
• RES - 16-bit reserved field used for additional information, such as
Token Ring and Fiber Distributed Data Interface (FDDI) frame Frame
Check (FC) field.
C. 3Com VLT (Virtual LAN Trunk)
3Com VLT 是由 3Com 提出的 VLAN protocol，只有在 3Com 的產品上
被支援，自從 IEEE 802.1Q 出來後，已經有越來越多人放棄使用
2. Try to do web search to find 3 different WLAN security protocols which has been
deployed in the commercial products. You should address 3 different products
from different vendors for your description.
i. WEP (Wired Equivalent Privacy)
ii. WPA (WiFi Protected Access)
• 240 MIMO: Advanced MIMO technology, double speed than 108 MIMO, Data Rate:
240Mbps, Actual throughput: 100Mbps
• Faster than wire Ethernet: Boost wireless transfer speed up to 100Mbps
• Boost coverage area of 802.11g standard by 8X
• WMM (Wi-Fi Multimedia) - Enhance wireless transfers of audio/video content
• Data Security - WPA2, WPA-PSK, TKIP, WEP
• Support 802.11e
Model # Buffalo Notebook Card
Wireless LAN (802.11g, 802.11b)
Standards Compliance 802.11g (Wireless LAN standard)
802.11b (Wireless LAN Standard)
Frequency Range 2,412 - 2,462GHz
Transmission Mode 802.11g: 6, 9, 12, 18, 24, 36, 48, 54Mbps
802.11b: 1, 2, 5.5, 11Mbps
Security WPA, AES, 802.1x and up to 128-bit WEP
Access Mode Infrastructure Mode / AdHoc Mode
Antenna Diversity Antenna (Internal)
External Antenna Connector MC
Output Power 15dBm (32mW)
Interface 32-bit CardBus
Communication Protocol Direct Sequence Spread Spectrum (DSSS), Half-Duplex,
Dimensions W2.1 x H4.3 x D.25in (W54 x H110 x D6mm)
Weight 1.6 oz (45g)
Operating Environment 0-55° C, 20-80% humidity (non-condensing)
Power Consumption TX peak: 550mA@3.3VDC
RX peak: 350mA@3.3VDC
DWL-G650 > High Speed 2.4GHz (802.11g) Wireless 108Mbps1 Cardbus Adapter
• Up to 108Mbps*
• Works with 802.11b Devices
• Great for Video Streaming
• 802.11g, 802.11b Compatible
• Increased Security with 802.1X and