Question | Answer |
What OSI layer does a switch operate on? | L2, unless its an intellegent switch that can operate on L# |
Name the functions of switches | -transfer data withinn the LAN using L2 protocols
-address learning
-can not break up broadcast domains
-breaks up collision domains
-loop avoidance |
what is address learning? | switches learnign address by reading the PDU frams source address |
What is L2 of the OSI model? | data-link layer |
What is loop avoidance? | a feature of switches using STP to avoid repeating paths to get to a destination |
What happens when network topology changes? | 1. Blocing, all traffic stops for 50 secs 2. listening, exchanging bridge protocol data units and checking for loops 3. learning all MAC addresses 4. forwarding |
forwarding delay | the process in the switch where it learns all MAC addresses before it can be forwarded |
What are the three modes for frame handling? | 1. cut-through, 2. fragment free, and 3. store-and-forward |
cut-through mode | frame handling mode that is the fastest, only the headeris checked (1st 13 bytes) |
Fragment Free mode | frame handling mode that reads the first 64 bytes checking for collision damage before forwarding...default mode for isr19XX series |
store and forward mode | entire frame check, reject if too short (<64) and reject if too long (>1518B) or if it has CRC failure, greatest latency |
What are the benifits to VLAs? | -improve security
-improve performance
-simplify computer movves, adds and changes
-cuts administraive costs |
Access link port | any ports connected to hosts. each access port is a member of a VLAN although host using the port is unaware of this b/cVLAN info is stripped from incoming frames |
Trunk link port | ports connect all or several VLANs from switches to routers, servers. or other switches. can have up to 1005 VLANs at one time. only one connection to the router |
tagging | is a LS means of identifying Eth frames by their VLAN membership... tagging assigns each frame a unique user-defined VLAN-ID or color. Fames are first tagged when thy go down a trucnked link, the switch then decides whether to send it on on another |
ISL | inter-Switch Link a Cisco proprietary method using only Fast- or Gigabit Eth . it is an external tagging method in which the original frame is not altered but further encapsulated in a new 26byte header and 4byte FCS tail |
DTP | Dynamic Trunking Protocol ...point to point protocol for 802.1 q used by newer cisco catalyst switches to control trunks in IS: or 802.1q |