vty stands for Virtual Teletype. What is Teletype?
The teletype, or teleprinter, is a device used for communicating text over telegraph lines, public switched telephone network, Telex, radio, or satellite links.
This means vty is essentially like a virtual computer screen plugged into the router that we can remotely access.
Both SSH and Telnet use this virtual monitor to let you see the router/switch.
The command
line vty 0 4
Configures 5 of these virtual teletypes (vty’s) for us to use. Can think of it having 5 monitors connected to the router. When you SSH to it, you are claiming one of these monitors. Cisco devices support up to a maximum of 16. 0-15
The following is some basic info on STP and RSTP. This list is not comprehensive. Refer to the link at the bottom of the page for more in depth details.
RSTP Priority
Default Priority is 32768 + VLAN ID
For example, if we are using vlan 10, then our default priority is 32768 + 10 = 32778
RSTP Priority can be set from 0 – 61440 in increments of 4096.
RSTP Port Roles
Ports can fill 1 of 4 roles.
Port Role
Description
Root Port
Port closest to the Root Bridge (Switches going to the Root switch)
Designated Port
Ports going away from the Root Bridge (To clients)
Alternate Port
A “backup” port for the Root port. If the Root Port fails, this port takes over
Backup Port
Essentially a backup port for the designated port
RSTP Port Roles
RSTP Port States
A port can be in one of 3 states. Well technically 4 states if you include down/unplugged.
Port State
Description
Discarding
Port discards packets (Alternate and Backup Ports)
Learning
Port learns MACs and doesn’t forward data
Forwarding
Port forwards data and learns MACs
RSTP Port States
RSTP Port Types
There are 3 port Types. Not to be confused with port States or Roles.
Port Type
Description
Point to Point
Switch to Switch
Point to Point Edge
Edge of Network. Connected to a PC, Printer etc.
Shared
Half Duplex, Port connected to a Hub
STP/RSTP Port Types
RSTP Timers
There are three RSTP timers. STP has the same timers, but the MaxAge is 10 seconds, and the Forward Delay is used for both Learning and Listening states which takes a total of 30 seconds to complete.
Timer Name
Default Value
Description
Hello Timer
2 Seconds
Time between Hellos created by Root
MaxAge
6 Seconds (Hello Timer * 3)
How long a Switch should wait before trying to readjust the network
Forward Delay
15 Seconds
Delay used for Learning/Listening in STP. Shouldn’t be necessary if legacy bridges are not used.
RSTP/STP Timers
Port Cost
There are technically two types of cost. The newer cost values were introduced so we could use faster ethernet speeds.
By default Cisco switches use the old cost values, but they can be changed to use the new ones.
spanning-tree pathcost method long
Ethernet Speed
Old Cost
New Cost
10 Mbps
100
2,000,000
100 Mbps
19
200,000
1 Gbps
4
20,000
10 Gbps
2
2000
100 Gbps
N/A
200
1 Tbps
N/A
20
STP/RSTP Path Cost
More information can be found at the following link.
