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Spanning tree issues

James Simpson
Beginner
Beginner

Hi All

My monitoring tool has reported some dropped pings

I have Etherchannels set up between two 4506 switches, but spanning tree seems to treat these as 4 x single 1GB. The problem is that this can result in data between routed htrough an edge switch, rather than directly between teh two core switches, and if the edge switch goes down for any reason, there is a minor disruption to the network.

Is there some way to tell spanning tree to "prefer" the direct etherchannel path between two core switches, rather than sending traffic via an edge switch ?

I have some concerns on whetehr the default path costs will work properly when I move to 10 GE, Will spanning tree effect this in any way ?

Many thanks

9 REPLIES 9

mahmoodmkl
Rising star
Rising star

Hi,

Can you please paste the config of these ports and in addition verify which of ur switch is the root for u r vlans.

Generally your core switches will be acting as the root bridges for u r vlans.

Thanks

Thanks

Jon Marshall
VIP Community Legend VIP Community Legend
VIP Community Legend

jamessimo wrote:

Hi All

My monitoring tool has reported some dropped pings

I have Etherchannels set up between two 4506 switches, but spanning tree seems to treat these as 4 x single 1GB. The problem is that this can result in data between routed htrough an edge switch, rather than directly between teh two core switches, and if the edge switch goes down for any reason, there is a minor disruption to the network.

Is there some way to tell spanning tree to "prefer" the direct etherchannel path between two core switches, rather than sending traffic via an edge switch ?

I have some concerns on whetehr the default path costs will work properly when I move to 10 GE, Will spanning tree effect this in any way ?

Many thanks

James

What is the connection between the 4500 and the edge switch ? is it etherchannel and how many links.

Can you post  "sh etherchannel summary" from 4500 switch and indicate which is the etherchannel to the other 4500 and which is the connection to the edge switch ?

Are the edge switches L2 connected to the 4500 switches ?

Finally, have you set the 4500 switches to be STP root and secondary for all vlans ?

Jon

Hi Jon

I have attached the config to the post

James

I can't see it.

I also noticed from your posted config that different vlans have different STP priorities set.

Can you run "sh spanning-tree vlan " for the vlan(s) that are taking the wrong path and see which ports are blocked and which aren't.

I'm just trying to ascertain whether the switch is indeed seeing the etherchannel as 4 separate links or whether it is simply the STP priorities which are at fault.

Jon

Here is etherchannel out put

James

I'm trying to help you , but i do need some help with information.

Firstly, there is no etherchannel in your output with 4 ports in it. So is that because it hasn't formed an etherchannel or is the etherchannel between the 4500 switches actually there but not with 4 ports ?

Basically, if traffic is going via an edge switch, and the edge to 4500 is L2 (which you still haven't confirmed) then you should be looking at -

1) STP output per vlan. For a vlan that goes the wrong way check the output and see which ports are blocking. If the 4500 interconnect is blocking you then need to check -

2) the size of the uplink (in terms of links etc.) vs the size of the interconnect.

3) the STP priorities for that vlan on the edge switch and the 4500 switches. Make sure the 4500 switches have lower STP costs than the edge switch for those vlan(s) that are taking the wrong path

4) check all config to make sure STP specific port priorities have not been configured that influence the path taken.

Jon

I have atatched config I dont know why u cant see it

James

I can see etherchannel config attached but it's niot enough info to solve the problem.

Perhaps if you tried looking at what i suggested in last post.

Jon

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