Metro link and Spanning tree problem

[kamlesh.sharma]

HI all,

We have 4 switches connected like the diagram given below.

What happens when link between mux to mux goes down mean any fiber cut in SP network our ethernet interface from switch 1 doesn't go down and for vlan 2 all data goes black holed.

bcos switch 1 interface connected to mux is getting keepalive from tejas mux and it remains up even if fiber goes down between both the mux's.

and if link doesn't go down than all the data from vlan 2 goes black holed

please help ASAP

[balajitvk]

Hi Kamlesh,

I don't see any error on this, and it is the nature of layer2 device and if you wants to find break in network connectivity behind directly connected divice (in your case mux), better use a layer 3 device on both ends and try to run a dynamic protocol between them.

Rgs,

[kamlesh.sharma]

Hi Bala,

Thanks for your reply but in our network we would be using only L2 device as we are extending L2 network and all vlan's from one office to other office. what we are trying to achive here is to have loadd balancing here for vlan's so that one link which is of 10 Mbps and other which is 20 Mbps should be utilized properly.

if you know something to do with L2 device to detect link failiur between mux to mux please advice.

Thanks

kamlesh

[balajitvk]

Hi Kamlesh,

Could u tell us what muxes ur using???

Becz there are muxes where the link integrity feature is available.... by which u can let the mux to shutdown itzz ethernet port when there is a break on the wan part or on the remote side lan part (ie) anywhere on the end to end circuit....

So better chk with ur mux vendor or with service provider.....

Rate if it does,

Rgs,

[Francois Tallet]

Hi Kamlesh,

Could you give additional explanation on your setup? I don't understand exactly what the combination of the two muxes + this center device is looking like at layer 2. Right now, is STP blocking one port? I guess so because you talked about black holing. Is it simply that the switch 2 for instance is blocking its port to the mux as a resul of receiving BPDUs from switch 1 on vlan 2 from switch 1 directly and from switch 1 through the mux?

Could you detail what kind of redundancy you are expecting when the link between the muxes is going down? (i.e. what path do you expect the traffic to go through).

Regards,

Francois

[ananddiwakar]

If I understand this correctly, the central device is actually the ISP cloud.

You have switched two vlans over two links. One link is active for VLAN 2 and other is backup and vice versa for VLAN 3. Logically this setup is perfect. The issue is what you are using are metro ethernet links. So if there is a fiber cut in ISP cloud, your switch does not understand it beause its link with MUX is up. So traffic never shifts to backup link.

Now, this is the problem with ME links. since this is ethernet and your connection with mux is always going to remain up, device will never understand a failure in SP cloud. You will need to use L3 devices and a dynamic protocol. Static routing will also fail because of same reason.

[kamlesh.sharma]

Hi Francois & Anand,

Francois has got all the explanation that you wanted. but using L3 devices in out network is not possible as we are extending our L2 networks means vlan. it will be great to have a work around at L2 level.

please advice

Thanks

[Francois Tallet]

Sorry, still not clear to me.

If STP does not unblock a port as a result of a failure between the mux and the provider network, it means that it keeps receiving BPDUs through the mux. That means that the mux is switching traffic for the corresponding vlan between the two switches, and that means that no way STP can unblock without creating a loop (which is not the desired effect I guess).

Now, when this link between the mux and the provider network fails, why do you lose connectivity? You have two links between the mux and the provider network and the vlan exists in the two mux. Does it mean that the link between the mux and the provider network only carry one vlan? If this is the case, can't you prevent the mux from switching traffic between the two switches for the given vlan.

You see that there are way too many "ifs" in what I've just written. We need to understand what the "muxes" are.

Regards,

Francois

[kamlesh.sharma]

Hi,

Mux are just connecting device here they are no in STP topology.

When any fiber cut is there in the provider network switch 1 don't detect that and still be root for vlan 2 and does not forward the traffic. because all the traffic from switch 2 for vlan 2 is coming to this switch and it get's stuk in switch 1.

Please advice

Thanks

[balajitvk]

Hi Kamlesh,

Could u tell us what muxes ur using???

Becz there are muxes where the link integrity feature is available.... by which u can let the mux to shutdown itzz ethernet port when there is a break on the wan part or on the remote side lan part (ie) anywhere on the end to end circuit....

So better chk with ur mux vendor or with service provider.....

Rate if it does,

Rgs,