spanning tree (temporarily disables loops in the network)
bridged lan, page 188, fig3.13

assign unique ID for different ports, bridge ID, port ID

spanning tree al gore rhythm
	select root bridge
		with lowest bridge ID
	determine root (R) port for each bridge
		port with lowest cost path to root bridge
			not necessarily the closest, but usually
		tie broken using port ID
	determine designated (D) bridge for each lan
		offers lowest cost path to root
		tie broken using bridge ID
	all root parts and all designamted ports are placed into a forwarding state, others in a blocking state

routers used to interconnect arbitrary topologies
MTU
	ethernet	1500
	token ring
		4mbps	4464
		16mbps	17914

ip datagram: version, header length, tos(8bits), total length(16 bit), id(16bits), f, fragmentation off.(13bits), ttl, protocol, header check(16 bits), source IP(32bits), dest IP(32bits), options(max 40 bytes), payload (variable length)

header check uses internet checksum algorithm

netvanta basic operation
2 kinds of lab, router based and in class
netvanta 3200
	physical layout
	boot process
	connect to router
	describe security modes
	config modes
	blah blah blah

basic layout
	each workstation on its own router, all routers connected to netvanta 4308, to switch, to 2 servers
	10.10.x.2 workstation ip
	10.10.x.1 3200 ip
	192.168.x.1 outside 3200 ip

2 kinds of memory, flash and ram
boot code, compressed app code, non-volatile config data (startup-config), nvram aka flash
running app code, running config, cleared on powerdown, ram
bootstrap mode if app code DNE
factory defaults if startup-config DNE
connect with rs232, 9600 8n1 no flow control, minicom!
security mode:
	basic aka initial "router>"
	enable (root) "router#"

? for help
t? for commands starting with t
show ? for commands usable after show
tab completion aka "autofinish" <- lulz
from enable mode, configure terminal, can then set enable passwd, config system global IP params, enter any other config modes, makes GLOBAL changes
line config mode, configure console and telnet access into unit
interface configuration mode, assign interface specific options

interface ? lists configurable interfaces
int e 0/1 to enter interface 0/1 configuration mode
ctrl+z goes back to enable mode
exit goes back to previous level
show startup-config to show current startup config
show running-config ....
copy running-config startup-config "cop run start", "write memory" also works
	
back to class
classfull ip addressing
	netid	hostid
A 0	7bit	24bit
B 10	14	16
C 110	21	8
D 1110		24 (multicast)
E 1111		24 (reserved for future use)