Risanuri Hidayat. 13/03/2012 Jurusan Teknik Elektro dan Tekn Informasi UGM

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Dwight O’Brien’
6 years ago
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1 Risanuri Hidayat 1

2 Ilustrasi 2

3 VLAN JTETI UGM 3

4 Virtual LAN A virtual LAN (VLAN) is a group of PCs, servers, and other network resources that behave as if they were connected to a single network segment even though they may not be. Personnel who are physically separated from each other are virtually connected on a VLAN. A VLAN is often easier to design, administer, and manage than a physical LAN. VLAN provides better quality control and security because the network can be segmented more effectively. 4

5 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. 5

6 IEEE 802.1Q The key for the IEEE 802.1Q to perform the above functions is in its tags Q-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." 6

7 Tagging A VLAN tag is 4-bytes long and is inserted in the Ethernet frame after the source address The first two bytes or 16 bits of the VLAN tag identify the tag as an 802.1q protocol tag. This tag is always set at 0x8100 and serves as an indication that the length/type field has moved four bytes further down the frame. 7

8 Tagging 8

9 Tagging 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. 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. 9

10 References: es/ethernet-prerequisite.pdf VLAN: Virtual Local Area Network and IEEE 802.1Q, 10

Table of Contents 1 VLAN Configuration 1-1

Table of Contents 1 VLAN Configuration 1-1 Overview 1-1 Introduction to VLAN 1-1 VLAN Fundamentals 1-2 Types of VLAN 1-3 Introduction to Port-Based VLAN 1-3 Configuring a VLAN 1-4 Configuration Task List