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Understanding Spanning Tree Protocol: Preventing Loops in LAN Networks, Slides of Network security

An in-depth explanation of the spanning tree protocol (stp) used in bridges and switches to prevent loops in lan networks. Learn about the features, benefits, and limitations of bridges, the differences between bridges and routers, and the importance of using stp to create a loop-free network topology. Discover the process of electing root bridges and designated bridges, as well as the role of configuration messages and port states in maintaining a stable network.

Typology: Slides

2012/2013

Uploaded on 04/22/2013

sathaye
sathaye 🇮🇳

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Spanning Tree Protocol for
Bridges/Switches
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Spanning Tree Protocol for

Bridges/Switches

8-

Bridge = Switch

  • Bridge/switches are layer-2 switching device (look at the Ethernet destination address to decide how to forward a frame)
  • Used to separate collision domains (segment)
    • Reduce collision probability
    • Increase aggregate bandwidth
    • Extend LAN’s length
  • Can form a large and complicated network topology.

Docsity.com^ 8- 2

A Topology Example

Bridge/switch

Router

Same subnet

8- 4

Bridge’s Features

  • Listen promiscuously
  • Store and forward packets (not cut-through)
  • Learn where a packet should be forwarded to
  • Use spanning tree algorithm to avoid loops

8- 5

Desired Improvements

  • If the source and destination hosts are on

the same segment (port), the bridge need

not forward a received packet to all of other

segments (ports).

  • If the source and destination hosts are on

different segments (ports) and the

destination host is on port i, the received

packet should be forwarded to port i only,

rather than all of other ports.

8- 7

Simple Method 1

  • Humane type in addresses for each port and this database is keep at the bridge. (^) 8- 8

Simple Method 3

  • Let layer 2 addresses embed layer-

addresses (LAN).

8- 10

Management headache

  • All these simple methods cause management headache. - In method 1 and 2, the manager needs to key in many layer-2 address or range. - In method 2, the hosts need to be placed in a particular way. - In method 3, the hosts need to be able to configure its own layer-2 address. This may generate the same layer- 2 addresses by error.
  • The best method is that a bridge can learn which host is on which port itself.

8- 11

Example 1

The bridge concludes that Q and A are on the same segment, therefore the Q to A packet can be discarded. 8- 16

Example 2

Bridge B1 cannot distinguish between hosts that are on LAN 2 and LAN 3 because B2 connect LAN 2 and LAN 3 transparently.

8- 17

Example 2

From B1’s point of view, the network topology looks like this. 8- 19

Example 2

From B2’s point of view, the network topology looks like this.

The learning bridge concept works for any tree topology! 8- 20