Knowledge Checks

Different types of addressing (a).

We've now learned about both IPv4 addresses and MAC addresses. Consider the address properties below, and use the pulldown menu to indicate which of these properties is only a property of MAC addresses (and therefore is not a property of IPv4 addresses - careful!).

This is a network-layer address.

This address is allocated by DHCP.

This is a 32-bit address.

This is a link-layer address.

This address must be unique among all hosts in a subnet.

This is a 128-bit address.

This is a 48-bit address.

This address remains the same as a host moves from one network to another.

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1/9

Different types of addressing (b).

We've now learned about both IPv4 addresses and MAC addresses. Consider the address properties below, and use the pulldown menu to indicate which of these properties is only a property of IPv4 addresses (and therefore is not a property of MAC addresses - careful!).

This is a 48-bit address.

This address must be unique among all hosts in a subnet.

This is a link-layer address.

This address is allocated by DHCP.

This is a 32-bit address.

This is a 128-bit address.

This address remains the same as a host moves from one network to another.

This is a network-layer address.

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2/9

Different types of addressing (c).

We've now learned about both IPv4 addresses and MAC addresses. Consider the address properties below, and use the pulldown menu to indicate which of these properties is a property of both IPv4 addresses and MAC addresses.

This is a 48-bit address.

This is a network-layer address.

This is a 128-bit address.

This is a link-layer address.

This address is allocated by DHCP.

This address must be unique among all hosts in a subnet.

This is a 32-bit address.

This address remains the same as a host moves from one network to another.

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3/9

Fields in an Ethernet frame.

Use the pulldown menus below to match the name of the field with the function/purpose of a field within an Ethernet frame.

Question List:

Cyclic redundancy check (CRC) field

Source address field

Data (payload) field

Type field.

Sequence number field

Answer List:

Used to demultiplex the payload up to a higher level protocol at the receiver.
This field does not exist in the Ethernet frame
Used only to detect, but never correct, bit-level errors in the frame.
48-bit MAC address of the sending node.
The contents of this field is typically (bit not always) a network-layer IP datagram.
Used for flow control.
Used to detect and possibly correct bit-level errors in the frame.

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4/9

Switch forwarding and filtering.

Suppose an Ethernet frame arrives to an Ethernet switch, and the Ethernet switch does not know which of its switch ports leads to the node with the given destination MAC address? In this case, what does the switch do?

Flood the frame on all ports except the port on which the frame arrived.

Choose a port randomly and forward the frame there.

Drop the frame without forwarding it.

Use the address resolution protocol (ARP) to determine the appropriate outgoing port.

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5/9

Self-learning switches.

Which of the following statements are true about a self learning switch?

A self-learning switch will age-out (forget) a self-learned association of a MAC address x and switch port y if it doesn’t see a frame with MAC address x incoming on switch port y after some amount of time.

A self-learning switch never forgets a self-learned association of a MAC address x and switch port y.

A self learning switch associates the source MAC address on an incoming frame with the port on which it arrived, and stores this matching in a table. The switch has now learned the port that leads to that MAC address.

A self-learning switch frees a network manager from a least one configuration task that might be associated with managing a switch

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6/9

Learning switch scenario.

Consider the simple star-connected Ethernet LAN shown below, and suppose the Ethernet switch is a learning switch, and that the switch table is initially empty. Suppose C sends an Ethernet frame address to C' and C ' replies back to C. How many of these two frames are also received at B's interface?

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7/9

Learning switch state removal.

Consider the simple star-connected Ethernet LAN shown below, and suppose the switch table contains entries for each of the 6 hosts. How will those entries be removed from the switch table?

An entry for a hostwill be removed if that host doesn't transmit any frames for a certain amount of time (that is, table entries will timeout).

A table entry for a host will be removed by the STPP (Switch Table Purge Protocol) which will be used by a host to signal the switch when it (the host) is shutting down or otherwise leaving the network.

They'll remain in the switch forever (or until it is re-booted).

The table entry can only be removed by the network manager, who would use the SNMP protocol to remove the entry.

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8/9

MAC addresses (versus other types of addresses and identifiers).

Which of the following statements are true about MAC (link-layer) addresses? Select one or more statements below.

Generally does not change, and is associated with a device when it is manufactured/created.

Is contained in a SIM card and used when a device identifies itself and connects to an LTE network.

Has 32 bits.

Generally stays unchanged as a device moves from one network to another.

A portion of the address bits are associated with the network to which the device is attached, and so changes as the device moves from one network to another.

Has 48 bits.

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9/9

Knowledge checks

Different types of addressing (a).

Different types of addressing (b).

Different types of addressing (c).

Fields in an Ethernet frame.

Question List:

Answer List:

Switch forwarding and filtering.

Self-learning switches.

Learning switch scenario.

Learning switch state removal.

MAC addresses (versus other types of addresses and identifiers).