Internetworking hardware: Bridging

Question 1

What are local bridges?

Answer 1

Provide direct connection between multiple LAN segments in same area

Question 2

What are remote bridges?

Answer 2

• connect multiple LANs in different areas, often over telecom lines

Question 3

What are some challenges and solutions for remote bridges?

Answer 3

• LAN speeds generally > WAN speeds

- buffering can compensate for discrepancies

Question 4

What are collision domains?

Answer 4

• way that bridges segment traffic on a network
• small cluster of stations on a network that share bandwidth
• make LANs more manageable and reduce congestion
• traffic does not cross domains unless addressed to go there

Question 5

Are bridges used today?

Answer 5

Only on legacy networks.
Today: routers using tunnelling technology with Layer 3 devices
Networks with hubs may use Layer 3 switches instead.

Question 6

Name 4 types of internet working devices.

Answer 6

Switches, routers, bridges, gateways

Question 7

Describe switches and applicable OSI layer.

Answer 7

Most elementary type of device to connect 2 networks. Opens/closes switches. Layers 1 and 2.

Question 8

Describe routers and name applicable OSI layers.

Answer 8

Interface between 2 networks; recognize protocols and node addressed; more expensive and intelligent than switches, but also slower.

Layers 1, 2, 3

Question 9

Describe bridges and name associated OSI layers.

Answer 9

• Connect 2+ network segments and forward info between them

- operate at layer 1; can also connect disparate LANs at layers 1 and 2

Question 10

What were old vs new bridges?

Answer 10

Old: 2 NICs in one PC running special software

New: different protocols bridges together through bridges; data forward between networks

Question 11

Describe what gateways do and name associated OSI layers.

Answer 11

• connect unlike networks (different architectures and environments) and can repackage info
• provide mapping at all 7 layers
• different gateways are dedicated to each type of transfer due to forwarding complexity

Question 12

What does a bridge do when it recognizes or does not recognize the MAC address in a packet?

Answer 12

Knows: forwards

Doesn’t know: broadcasts to all ports but the one it received the packet from

Question 13

Name three link layer control functions that bridges perform.

Answer 13

• flow control
• error handling
• physical addressing

Question 14

What is the difference between transparent bridging and source-rate bridging?

Answer 14

Transparent: frames are forwarded one at a time

Source-rate: entire path is contained in each frame

Question 15

What is spanning tree protocol?

Answer 15

A protocol that enables Ethernet networks to achieve some redundancy in the network, but to limit loops between bridges, which can result in a data storm.

Bridges transmit PDUs to find other bridges in the network and build a tree, from which they can enable or disable links.

Question 16

What type of bridge links two dissimilar networks?

Answer 16

Translating bridge.

Question 17

What are the two most important functions that bridges perform?

Answer 17

Filtering and flooding

Question 18

What is filtering?

Answer 18

A bridge looks at data link layer fields and blocks any that should not be forwarded, thereby reducing congestion.

Question 19

What is flooding?

Answer 19

Broadcasting information out of all ports on the bridge or to all ports on an associated switch.