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What forwarding decision does a switch (bridge) make on receiving a broadcast or multicast frame?

Flood on all ports except the one it was received on.

If the destination is in the switch CAM table, then forward only to the associated port.

If destination is not known, broadcast (flood) on all ports except the originating one.

Hubs will flood all traffic on all ports in one large collision domain.

Bridges/switches separate collision domains and will forward frames more intelligently/efficiently. Bridges/switches can also segment LANs using VLAN.

Switches switch in hardware; bridges in software

Generally:

Switches have more ports/higher port density

Bridges are generally slower

Store and Forward

Cut Through

Fragment Free

Only mode that bridges can also use.

The entire frame is buffered and CRC/FCS is run to ensure validity.

When all devices connecting to a switch is in full duplex mode, it creates a zero-collision environment, because every device has been segmented into its own collision domain.

Switch with lowest Bridge ID is Root

Bridge ID = [ Admin Priority | MAC ]

What are the packets STP uses called?

What does it stand for?

What IEEE spec describes it?

BPDU

Bridge Protocol Data Unit

802.1d

Root port is the port on the switch with the lowest cost path to the root switch.

If tiebreak - go with lowest MAC

Lower cost = Higher link speed

Port that forwards least cost path to switches on same segment.

If tiebreak - go with lowest MAC

Blocked ports are ports that were not selected to be root ports or designated ports.

Blocked ports do not sent any data, but does listen for BPDU's.

All ports are either blocked or forwarding.

All ports are determined to be root, desginated, or blocked ports.

What are the four port states in STP?

What are their characteristics?

Listening + Learning states

15 + 15 = 30 seconds by default

This is the interval between blocked and forwarding

1. When the port is not a root or desginated port after STP convergence

2. When a switch first boots up, all ports start in blocking state

3. When a Topology Change Notification (TCN) is received, all ports of a switch go into blocking state

What determines the time interval between an link failure and the start of STP re-convergence?

How long is it by default?

After receiving TCN, the time between Forward Delay and STP reconvergence is determined by the Max Age Timer

By default it is 20 seconds

(which is also 10 missed BPDUs)

RSTP port states   (...STP port states)
 

Discarding (= Blocking/Listening)

Learning == Learning

Forwarding == Forwarding

What are the different port types under RSTP?

What are the characterstics of the ports that differ from STP?

Root

Desginated

Alternate - will become root port if the primary root port fails

Backup - will become the desginated port if the desginated port fails

Rapid Spanning Tree Protocol

- converges faster than STP due to less port states

- faster reconvergence due to lower timer delays

- less need for reconvergence due to more port types for backing up forwarding ports

VLANs logically divide

- a switch into multiple independent switches at L2

- broadcast domains (each should be a domain)

- subnets (each VLAN should be a subnet)

switch(config)#vlan n

switch(config-if)#switchport access vlan n

Dynamic VLAN Membership automatically assigns switchports to a VLAN based on the MAC of the connected host

Requires VMPS (VLAN Membership Policy Server) to run on the switch

Trunk ports connect multiple VLANs with a single link between switches

(by default, all VLANs are allowed over a trunk)

What are the two supported VLAN frame tagging trunk encapsulations?

What are their main characteristics and which is more common?

What are the characteristics of the five switchport modes?

1. off

2. on

3. NoNegotiate

4. (Dynamic) Desirable

5. (Dynamic) Auto

What switch port mode on the neighboring port is required to trunk for the following port modes:

1. On

2. NoNegotiate

3. Desirable

4. Auto

1. On - On, Auto, Desirable, NoNegotiate

2. NoNegotiate - On, NoNegotiate

3. Desireable - On, Auto, Desirable

4. Auto - On, Desirable

What are the commands to configure the following port modes:

1. off

2. on

3. NoNegotiate

4. (Dynamic) Desirable

5. (Dynamic) Auto

switchport trunk encapsulation isl

switchport trunk encapsulation dot1q

VLAN Trunking Protocol

takes care of creating and naming VLANs on all switches in the system

What are the three VTP switch modes?

What do they do?

What is the purpose of inter-VLAN routing?

What devices are required?

How does it work?

Route traffic from one VLAN to another

Requires a L3 device to route (router)

Trunk link connecting router to the switch. Then subinterfaces are configured on the router interface for each VLAN.

100 Mbps Ethernet (FastEthernet)

1 Gigabit Ethernet

10 Gigabit Ethernet

Immediately brings up access or trunk link from blocked to forwarding state.

Normally used on ports connecting to an end host, or to trunks.

Router(config-sub-if)#encapsulation dot1q 1 native

or

Router(config-sub-if)#encapsulation dot1q [vlan#]

VLAN divides a switch at L2 to separate broadcast domains, and have switchports assigned.

VAN interface is a virtual interface that is the only place on a L2 switch that will accept an IP address/mask. VLAN 1 interface is default and used for managing switch remotely.