ITEC 3210: Backbone Networks

BNs are:

high speed networks that: Link an organization’s Access Layers (LANs) and Provide connections to other BNs, MANs, WANs and the Internet

In the structured design approach, BNs refer to

Distribution layer that connects access layers (or LANs) within a building (and the MAN/WAN/Internet if no core layer needed)

BNs Components: Layer-2 switches

are “transparent” devices that do not change messages, only read and forward them

BNs Components: VLAN switches

or layer-3 switches are a devices combine the features of Layer-2 switches and routers, primarily for virtual LANs

BNs Components: Routers

Network layer devices that connect different networks

TCP/IP gateways

Not “transparent” devices Messages are passed up to the network layer including stripping off data link layer frames Routers respond to ARP (and other messages)

Read IP addresses and determine best route Routing requires more processing than switching

Backbone Network Layers

Separate from the layers of the Internet or OSI models

Access layer - How users access network (LAN, WLAN)

Distribution layer - BN that connects access layer to core layer (within building) 

Core layer - Connects BNs between buildings and to WAN/Internet

Backbone Network Architectures

Three major types of BNs are based on the devices used

1. Switched backbones

2. Routed backbones

3. Virtual LANs

Routed (or hierarchical) BNs

Distribution layer switches are connected by

routers or Layer 3 switches

Within the LANs and distribution layers, traffic is

based on data link addresses (no role for routers!)

Between distribution layers, message are sent to

the core layer router, which forwards or routes

the message based on its network layer address

Benefits: Segmentation into broadcast domain +

security (packet filtering using ACL) + routing if

needed + some protocol conversions if needed

Limitations: hardware cost + management cost +

processing time

Virtual LANs (VLANs)

Normally, switches or routers segment networks based on physical location (i.e., the cables connected to it) 80/20 rule is used as a basis for a network segmentation
Each VLAN identified by VLAN ID which is mapped to traditional IP subnet

Each device assigned into a VLAN based on the physical port, device MAC address

VLANs are transparent

Virtual LANs Design: Single-switch VLAN

One VLAN switch physically connects all computers and assigns them to the different VLANs

Virtual LANs Design: Multi-switch VLAN

Each VLAN switch maintains a table that identifies membership with VLAN ID and IP addresses (Fig. 8-7) and interconnected VLAN switches exchange copies of those tables