Ethernet Switching Flashcards
What is the size of ethernet frames?
Minimum 64 bytes, maximum 1518 bytes
What is an ethernet frame smaller than 64 bytes called?
Collision fragment or runt frame
What is a frame more than 1500 bytes called?
Jumbo or baby giant frame
What happens to ethernet frames that are too small or too big?
They are discarded
Properties of a MAC address?
6 bytes in length
Must be unique
FF-FF-FF-FF-FF-FF
What is the unique 6 hexadecimal code (3 bytes) at the start of a MAC address called?
Organisationally Unique Identifier (OUI)
What is the last 3 bytes of a MAC address called?
Vendor code
What happens if the MAC address destination doesn’t match the physical MAC address of the device?
The device discards the frame
IPv4 and IPv6 name of protocol used to resolve IP addresses to MAC addresses?
Address Resolution Protocol (ARP) - IPv4 Neighbour Discovery (ND) - IPv6
What are the 3 ways of sending a message?
Unicast - MAC address matches destination IP address
Broadcast - FF-FF-FF-FF-FF-FF - all hosts in local network receive packet
Multicast - 01-00-5E (IPv4) or 33-33 (IPv6) - hosts in the same multicast group will receive the packet
How is a MAC address table built
By examining the source MAC addresses and port number of the frames received.
How long is a MAC address table entry kept?
5 mins.
Can multiple MAC addresses be associated with a single port?
Yes
When will the MAC address be the default gateway
When the destination IP address is on a remote network
What are the two different methods of switch forwarding?
Store-and-forward switching
Cut-through switching
What is the name of the error detection algorithm used in store-and-forward switching?
CRC - cyclic redundancy check
Describe store-and-forward switching
Receives entire frame and checks for errors before forwarding the frame. Discards frame if there is an error. Required for QoS analysis.
Describe cut-through switching
Forwards frame before it is fully received, at least once destination address is read. No error checking performed.
What are the two types of cut-through switching?
Fast-forward switching
Fragment-free switching
Describe fast-forward switching
Lowest level of latency
Typical cut-through switching method
Packets may be relayed with errors, NIC will discard if so.
Describe fragment-free switching
Stores first 64 bytes before forwarding. Most network errors and collisions occur during the first 64 bytes. Performs small error check on first 64 bytes before forwarding frame.
Compromise between store-and-forward switching and fast-forward switching
What are the two types of memory buffering
Port-based memory - frames stored in queues at ports, possible for single frame to delay transmission of all frames due to busy destination port
Shared memory - deposits all frames into a common memory buffer shared by all switch ports. amount of buffer memory is dynamically allocated.
What is autonegotiation?
Optional function which allows best speed and duplex options to be selected based on capabilities of the device.
