switch discussion 01

  a collision domain is defined by a network segment that has the potential for a  collision during a frame's transit... these segments are shared media, half duplex...
Carrier Sense Multiple Access/Collision Detection is the mechanism that allows for symbiosis among the collision domain's participants...

before transit, the media is listened to
if the media is determined clear, a frame is transmitted
if a collision is detected, all transmission stops
a backoff algrithm is performed to stop further transmission by the participants
after the completion of the backoff, transmission will recommence beginning with step1

this is known as a contention network

flooding, and the unknown unicast
  when a switch receives a frame, and it is broadcast or multicast, ship on all ports except that upon which it was received...
  if the destination is unicast and not in the mac-table, again, ship on all ports except that upon which it was received... in other words, flood the unkown unicast...
  if the destination is unicast, the address is in the table, and the associated interface is not that upon which it was received, ship to that interface
  if the above criteria are not met, drop the frame

multicast, broadcast and unknown unicast are always flooded

  multi-layer switching using specialized hardware is known as topology-based switching... layer 3 routing populates a database that delineates the network topology... this database is consulted so that packets can be forwarded at high speeds (wire speed)... this is also known as CEF... this table evolves dynamically

  mac table versus cam table
  these terms are interchangeable... a cam table lookup is a mac-address-table lookup... a cam (mac) table is a database of source and destination addresses associated by ingress and egress ports... this table changes dynamically and is constantly being consulted for proper layer 2 switching to occur...

  tcam (ternary content addressable memory) table is an extension of the mac (cam) table.  tcam allows for a third state for lookup, or don't care lookup, associated with layer 3 (ip addresses)


sw3550_01#sh tcam ?
  inacl   Show Ingress ACL TCAM
  outacl  Show Egress ACL TCAM
  pbr     Show PBR TCAM
  qos     Show Ingress QoS TCAM


  it is in these last three that we begin the journey to multi-layer switching...