STP help

fadhil

I have tried to think so much but I don get the answer of getting the cost of STP eg when bandwidth of 100Mbps is used the cost is 19.
any to help me please.

georgemc

I'm not exactly sure what your question is...but prior to the introduction of gigabit + links the cost was calculated by dividing 1000 by the bandwidth in Mbps. This left you with an integer cost value of 1 for a 1 Gbps link or 10 for a 100Mbps link. Because this calculation cannot account for links greater than 1 Gbps it is no long used. IEEE carefully selected new values (you should have a table in the book you're using) to accommodate the common bandwidths in use today and account for future growth. So, it's pretty much arbitrary now and you pretty much need to memorize the STP bandwidth cost table.

fadhil

It is hard to memorize all the table,that's I look for a simplest way

r_durant

I'm not sure if there is a "simple way"! I think you just have to memorize them. I don't know of any shortcut that will help you. Subject to correction, they normally reference the standard bandwidths, and would probably not vary beyond these, for example:

Bandwidth

---

STP Cost Value
10 Mbps

---

100
100 Mbps

---

19
1 Gbps

---

4
10 Gbps

---

2

If I understand what you're asking, is it how does Cisco come up with these cost values?

kurosaki00

do cisco really ask you Whats the value of a 10gb line?
I doubt so...
Just learn a bit about the exacts value but focus more on the higher the rate the lower the cost.
And how STP uses the values to determine the ports (root/forward/block etc)