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How to deal with the Layer2 and Layer3 network issues in the loop network ?

Gary.He
Occasional Contributor

How to deal with the Layer2 and Layer3 network issues in the loop network ?

Hi,there is a problem in a network I can not resolve it. This network topology is a loop,every device were link together,the topology as follow.But in this network the link between the 5406 and 6504 are use ospf protocol to connect,and then there exist two VLAN used to connect the acess swith to provide some specially application servers,this vlan need a layer2 connect to cisco6504, this lead may loop in the network,and must deploy STP to solve it ,as result the link may block,then the ospf can not use it. And before the network becomes stabal,the network experience a interval(STP convergence time add the ospf convergence time),but the network application do not allow this happen,and how can I resove this problem in this network topology,which use STP and OSPF on the backbone links?
2 REPLIES
Pieter 't Hart
Honored Contributor

Re: How to deal with the Layer2 and Layer3 network issues in the loop network ?

if you really want a loop-free network, you need to abandon L2-loops and spanning-tree.

- configure connected ports on your bacbone as "no switchport"
- give both an ip-address (mask 255.255.255.252)
- and let it route (L3) to the connected "no switchport"

you can still have dual connection to your 6500 and OSPF will select one of the available paths instead of STP blocking a port.

how about the "max 7 switches in ANY path" rule with your current setup ???
Gary.He
Occasional Contributor

Re: How to deal with the Layer2 and Layer3 network issues in the loop network ?

Thanks for your reply. and this network topology is designed by others,and i not very clear about it.
and I do not understang the rule you said the "max 7 switches in any path" ,this is a STP restritive or OSPF?
and there is a problem,when the STP reach a stable state,the link between the primary and secondary 5406zl may blocked,and how does the VRRP work?