Spanning Tree Protocol and Path Cost

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  • Topic: Spanning tree protocol, Ethernet, Network switch
  • Pages : 24 (6462 words )
  • Download(s) : 23
  • Published : April 26, 2011
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PreLab
1. Describe the different between a LAN switch/bridge and a router. LAN switch/bridge operate at the data link layer(layer2) and works based on the MAC address, while a router operates at the IP layer (layer3) and works based on IP addresses.

2. What is the difference between an Ethernet switch and an Ethernet hub? Which is more suitable for a network with a high traffic load, a switch or a hub? Explain.

Ethernet switch is a store-and-forward device that operates at layer2. It forwards the packets to the destination based on the MAC address, thus no collision occurs. On the other hand, Ethernet hub operate at layer 1 of the OSI, it sends the packet to all connected ports(i.e. if flood the network) regardless of the destination thus producing collisions. A switch is more suitable for a network with a high traffic load because there are no collisions on the switch 3. What motivates the use of the term transparent in transparent bridges? Transparent bridges work without the knowledge of the hosts, they learn the network topology themselves, and thus no certain configuration of the hosts is required.

4. Which role does the spanning tree protocol play when interconnecting LAN switches/bridges? The spanning tree protocol prevents forwarding loops from occurring by organizing the bridges in a spanning tree topology, and by blocking certain bridge ports. 5. In the context of the IEEE 802.1d specification of the spanning tree protocol, define the following terms:

a.Root bridge
It is the bridge that is selected to be the root of the spanning tree; it is the bridge with the smallest Bridge ID (priority and MAC address), and that has the shortest path to other nodes in the networks

b.Root port
The bridge port that has the best path to the root bridge ( with minimum cost)

c.Designated bridge
The bridge on each LAN that provides the minimum path cost to the root bridge

d.Designated port
The port that is connected to the designated bridge of the LAN

e.Blocked port
It is the port that does not forward packets.

6. In a spanning tree protocol, how does a LAN switch/bridge decide which ports are in a blocking state? Each bridge decides which of its ports are parts of the spanning tree. Only the root port and the designated ports of a bridge are part of the spanning tree. All other ports are said to be in a blocking state.

EXERCISE 1(A)

PC #MAC Address of eth0MAC Address of eth1
100:04:23:60:06:4000:04:23:60:06:41
200:04:23:5F:98:7200:04:23:5F:98:73
300:04:23:5F:A7:8C00:04:23:5F:A7:8D
400:04:23:5F:99:D600:04:23:5F:99:D7

EXERCISE 1(C)

Ethereal on PC 1

Frame 1 (98 bytes on wire, 98 bytes captured)
.
.
.
Ethernet II, Src: 00:04:23:60:06:40, Dst: 00:04:23:5f:a7:8c
Destination: 00:04:23:5f:a7:8c (00:04:23:5f:a7:8c)
Source: 00:04:23:60:06:40 (00:04:23:60:06:40)
Type: IP (0x0800)
Internet Protocol, Src Addr: 10.0.1.11 (10.0.1.11), Dst Addr: 10.0.1.31 (10.0.1.31) Version: 4
Header length: 20 bytes
Differentiated Services Field: 0x00 (DSCP 0x00: Default; ECN: 0x00) 0000 00.. = Differentiated Services Codepoint: Default (0x00) .... ..0. = ECN-Capable Transport (ECT): 0
.... ...0 = ECN-CE: 0
Total Length: 84
Identification: 0x0000
Flags: 0x04
.1.. = Don't fragment: Set
..0. = More fragments: Not set
Fragment offset: 0
Time to live: 64
Protocol: ICMP (0x01)
Header checksum: 0x2480 (correct)
Source: 10.0.1.11 (10.0.1.11)
Destination: 10.0.1.31 (10.0.1.31)
Internet Control Message Protocol
Type: 8 (Echo (ping) request)
Code: 0
Checksum: 0xee48 (correct)
Identifier: 0x5508
Sequence number: 00:01
Data (56 bytes)

Ethereal on PC3
Frame 1 (98 bytes on wire, 98 bytes captured)
.
.
.
Ethernet II, Src: 00:04:23:60:06:40, Dst: 00:04:23:5f:a7:8c
Destination: 00:04:23:5f:a7:8c (00:04:23:5f:a7:8c)
Source:...
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