ā04-23-2010 10:30 AM - edited ā03-06-2019 10:46 AM
Hi all,
we have switch which has gigabit ports and 4 ports are bundled and all 4 are up in port channel
i know cost of 2gigbit is 3
but here we have 4 ports and cost of stp is 3?
can some one explain why this so
thanks
mahesh
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ā04-23-2010 02:17 PM
mahesh18 wrote:
Hi Jon
so it means any speed between 2Gbps to 9 gbps will have cost of 3 right?
mahesh
Mahesh
Good question. I suspect so although without a switch to test it may be that an 8Gbps etherchannel for example goes to 2 but i suspect not. Unfortunately don't have switches to test with.
But what we can say is that between 2Gbps and 9Gbps the cost shouldn't be anything other than 3 or 2.
Jon
ā04-23-2010 01:36 PM
mahesh18 wrote:
Hi all,
we have switch which has gigabit ports and 4 ports are bundled and all 4 are up in port channel
i know cost of 2gigbit is 3
but here we have 4 ports and cost of stp is 3?
can some one explain why this so
thanks
mahesh
Mahesh
Because there are only so many values to use ie. 10Gbps = 2, 20Gbps = 1. So you are kind of limted with what values you can use, hence the reason 4Gbps and 2Gbps are both 3. Don't forget you can alter the cost if you want to influence which path traffic takes within your network.
Jon
ā04-23-2010 01:50 PM
Hi jon
thanks for reply
if you can explanin me in more detail please
Port-channel: Po1
------------
Age of the Port-channel = 705d:19h:39m:50s
Logical slot/port = 14/10 Number of ports = 4
GC = 0x00000000 HotStandBy port = null
Port state = Port-channel Ag-Inuse
Protocol = -
Ports in the Port-channel:
Index Load Port EC state No of bits
------+------+------+------------------+-----------
0 11 Gi1/19 On 2
1 22 Gi1/20 On 2
2 44 Gi2/19 On 2
3 88 Gi2/20 On 2
sh spanning-tree int Po1
Vlan Role Sts Cost Prio.Nbr Type
---------------- ---- --- --------- -------- --------------------------------
VLAN0076 Desg FWD 3 128.1674 P2p
we know 1gb cost is 4 and here we have 4 interfaces with each bandwidth of 1GB and if we add them all it comes
to 16GB i did not got how cost comes out to 3?
thanks
mahesh
ā04-23-2010 02:00 PM
mahesh18 wrote:
we know 1gb cost is 4 and here we have 4 interfaces with each bandwidth of 1GB and if we add them all it comes
to 16GB i did not got how cost comes out to 3?
thanks
mahesh
Mahesh
With STP costs -
1Gbps = 4
2Gbps = 3
10Gbps = 2
20Gbps = 1
So the faster the link the lower the cost. So 1Gbps = 4 but 10Gbps does not mean 10 x 4 = 40 because 40 would be slower than 1Gbps.
Jon
ā04-23-2010 02:14 PM
Hi Jon
so it means any speed between 2Gbps to 9 gbps will have cost of 3 right?
mahesh
ā04-23-2010 02:17 PM
mahesh18 wrote:
Hi Jon
so it means any speed between 2Gbps to 9 gbps will have cost of 3 right?
mahesh
Mahesh
Good question. I suspect so although without a switch to test it may be that an 8Gbps etherchannel for example goes to 2 but i suspect not. Unfortunately don't have switches to test with.
But what we can say is that between 2Gbps and 9Gbps the cost shouldn't be anything other than 3 or 2.
Jon
ā04-23-2010 02:26 PM
Hi jon
i just checked on switch its cost is 3 with 8 port gig channel
so u were right.
regards
mahesh
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