tcam info...

here:

http://etherealmind.com/tcam-detail-review/

and this:

http://www.enterprisenetworkingplanet.com/netsysm/article.php/3527301/On-Your-Network-What-the-Heck-is-a-TCAM.htm

note there is no allocation for pbr...

dlsw1#sh sdm prefer                                                               
 The current template is "desktop IPv4 and IPv6 default" template.                
 The selected template optimizes the resources in                                 
 the switch to support this level of features for                                 
 8 routed interfaces and 1024 VLANs.                                              
                                                                                  
  number of unicast mac addresses:                  2K                            
  number of IPv4 IGMP groups + multicast routes:    1K                            
  number of IPv4 unicast routes:                    3K                            
  number of directly-connected IPv4 hosts:        2K                            
  number of indirect IPv4 routes:                 1K                            
  number of IPv6 multicast groups:                  1.125k                        
  number of directly-connected IPv6 addresses:      2K                            
  number of indirect IPv6 unicast routes:           1K                            
  number of IPv4 policy based routing aces:         0                             
  number of IPv4/MAC qos aces:                      0.5K                          
  number of IPv4/MAC security aces:                 1K                            
  number of IPv6 policy based routing aces:         0                             
  number of IPv6 qos aces:                          0.625k                        
  number of IPv6 security aces:                     0.5K

 

from:

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750x_3560x/software/release/12.2_55_se/configuration/guide/swsdm.html

looks like ipv4-and-ipv6 routing may be the best choice... at least a little is spared for pbr...

and from wiki: http://en.wikipedia.org/wiki/Content-addressable_memory#Ternary_CAMs

Content-addressable memory is often used in computer networking devices. For example, when a network switch receives a data frame from one of its ports, it updates an internal table with the frame's source MAC address and the port it was received on. It then looks up the destination MAC address in the table to determine what port the frame needs to be forwarded to, and sends it out on that port. The MAC address table is usually implemented with a binary CAM so the destination port can be found very quickly, reducing the switch's latency.


Ternary CAMs are often used in network routers, where each address has two parts: the network address, which can vary in size depending on the subnet configuration, and the host address, which occupies the remaining bits. Each subnet has a network mask that specifies which bits of the address are the network address and which bits are the host address. Routing is done by consulting a routing table maintained by the router which contains each known destination network address, the associated network mask, and the information needed to route packets to that destination. Without CAM, the router compares the destination address of the packet to be routed with each entry in the routing table, performing a logical AND with the network mask and comparing it with the network address. If they are equal, the corresponding routing information is used to forward the packet. Using a ternary CAM for the routing table makes the lookup process very efficient. The addresses are stored using "don't care" for the host part of the address, so looking up the destination address in the CAM immediately retrieves the correct routing entry; both the masking and comparison are done by the CAM hardware.

sdm and ipv6...

very good article here:

http://nurdland.blogspot.com/2010/09/trouble-with-tcam.html

one of the first things i did with my new gear was to light up ipv6... i thought nothing of it and used this command:

dlsw1(config)#sdm prefer dual                                                  
dlsw1(config)#sdm prefer dual-ipv4-and-ipv6 ?                                  
  default  Default bias                                                        
  routing  Unicast bias                                                        
  vlan     VLAN bias          

quite honestly, i chose default mostly because it sounded good... or maybe i was just a good dummy that day...

dlsw1#sh sdm prefer                                                               
 The current template is "desktop IPv4 and IPv6 default" template.                
 The selected template optimizes the resources in                                 
 the switch to support this level of features for                                 
 8 routed interfaces and 1024 VLANs.                                              
                                                                                  
  number of unicast mac addresses:                  2K                            
  number of IPv4 IGMP groups + multicast routes:    1K                            
  number of IPv4 unicast routes:                    3K                            
  number of directly-connected IPv4 hosts:        2K                            
  number of indirect IPv4 routes:                 1K                            
  number of IPv6 multicast groups:                  1.125k                        
  number of directly-connected IPv6 addresses:      2K                            
  number of indirect IPv6 unicast routes:           1K                            
  number of IPv4 policy based routing aces:         0                             
  number of IPv4/MAC qos aces:                      0.5K                          
  number of IPv4/MAC security aces:                 1K                            
  number of IPv6 policy based routing aces:         0                             
  number of IPv6 qos aces:                          0.625k                        
  number of IPv6 security aces:                     0.5K 

it requires a reboot to take effect...  the guy in the link chose vlan and that gave him no room for v4 unicast routing according to the article...

whoops...

cam again...

the cam table is the mac table spelled backwards... actually the cam (content addressable memory) and mac address table are the same... i spent quite some time trying to find if there was indeed some subtle difference between the two; and i have found there is no difference... the tcam table is the ternary content addressable memory table... for this i will paste from wikipedia;

Binary CAM is the simplest type of CAM which uses data search words consisting entirely of 1s and 0s. Ternary CAM (TCAM) allows a third matching state of "X" or "Don't Care" for one or more bits in the stored dataword, thus adding flexibility to the search. For example, a ternary CAM might have a stored word of "10XX0" which will match any of the four search words "10000", "10010", "10100", or "10110". The added search flexibility comes at an additional cost over binary CAM as the internal memory cell must now encode three possible states instead of the two of binary CAM. This additional state is typically implemented by adding a mask bit ("care" or "don't care" bit) to every memory cell.

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...