Frequent Questions      

Communication Between VLANs 

 

 

Communicating within VLANs:  There are different protocols available for communicating between VLANs. These encapsulation schemes are also known as VLAN trunking protocols. These protocols are based on Layer 2 of the OSI model.

These are:

  1. Inter-Switch Link Protocol (ISL)

  2. IEEE 802.10 Protocol

  3. IEEE 802.1Q Protocol

  4. ATM LANE Protocol

  5. ATM LANE Fast Simple Server Replication Protocol (FSSRP)

Inter-Switch Link Protocol (ISL): The ISL protocol is used to interconnect two VLAN-capable Ethernet, Fast Ethernet, or Gigabit Ethernet devices. Here, VLAN information is tagged to the standard Ethernet frame. The packets on the ISL link contain a standard Ethernet, FDDI, or Token Ring frame and the VLAN information associated with that frame. ISL is a Cisco proprietary protocol.

IEEE 802.10 Protocol: This protocol provides connectivity between VLANs. The protocol incorporates authentication and encryption techniques to ensure data confidentiality and integrity. The protocol operates at layer 2 of OSI model, and hence ensures greater efficiency.

IEEE 802.1Q Protocol: This protocol is used to interconnect multiple switches and routers, and for defining VLAN topologies. IEEE 802.1Q is the industry standard for communicating within VLANs.

ATM LANE Emulation Protocol (LANE): Using LANE, you can benefit from the legacy LAN hardware. The LANE protocol operates over traditional LAN, emulating a broadcast environment like IEEE802.3. LANE makes. LANE allows standard LAN drivers like NDIS and ODI to be used. Applications can use normal LAN functions without the underlying complexities of the ATM implementation. Client work stations need LAN Emulation Client for running LANE protocol. The switches or routers also need to support appropriate LANE functionalities.

ATM LANE Fast Simple Server Replication Protocol (FSSRP): Cisco introduced the ATM LANE Fast Simple Server Replication Protocol (FSSRP). FSSRP provides better network redundancy. If a single LANE server is unavailable due to any technical reasons, the LANE client transparently switches over to the next LANE server and BUS.

Example:

Question: 

Match the trunking protocols with respective media:

1. Inter Switch Link         A. FDDI
2. LANE                         B. Fast Ethernet
3. 802.10                         C. ATM

Choose the correct choice.

A. 1-> C, 2->B, 3->A

B. 1->B, 2->C, 3->A

C. 1->B, 2->A, 3->C

D. 1->A, 2->B, 3->C

Ans: B

Explanation: ISL, 802.1Q are the VLAN trunking protocols associated with Fast Ethernet. The VLAN trunking protocol defined by 802.10 is associated with FDDI. LANE (LAN Emulation) is associated with ATM.

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