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Metro Design Query


I have a scenario where I need to provide redundant PEs for Layer 3 services. Currently we have a single PE connected to a switch (dot1q) where customers aggregate. And appropriate VRFs are configured on these PEs.

Now we are thinking of connecting an access ring (3 switches) of 3560s to redundant PEs that are 7600s.

The questions which come in my mind are:-

1) How do I protect the access ring (RSTP/MSTP??)

2) Is HSRP (on 7600) the only option for providing redundant PE connectivity.

3) If my Access devices are dual homed to my PEs, how do I configure STP and FRR Protection on PE.

I am sorry if I am sounding a little confusing... you can guess the reasons :-)

Looking forward for further discussions...



Re: Metro Design Query

HI Kumar, [Pls RATE if HELPS]

All you will have to do is, configure STP in your Metro Network this will normally avoid to loop in the Network. Configure VTP for the same, where one which act as VTP Server and rest all are VTP Client.

For the Customers running VRF, the Primary & Secondary PE's are managed depends upon the Routing Protocol you run in the LAST MILE. In case of BGP in last mile, either Local Pref or Weight attribute can be used to vary the Pri / Secondary.

Whereas in the L2 Path (Metro Switches), allow the VLAN in the Cross-Connect Points and make sure the PE MAC Address is learnt in the Switches & the Customer CE MAC is also learnt to confirm the communication.

Hope I am Informative.


Best Regards,

Guru Prasad R


Re: Metro Design Query

1. Since ring has only two possible ways (clockwise/counterclockwise) MST would be most wise. It will allow your services to grow without additional processing load.

2. Because you want to provide L3 redundancy, you need to use L3 redundancy protocol. Those are HSRP, VRRP and GLBP.

In SP environment VRRP would be wise. It is the open version of HSRP.

3. See #1. You need to synchronize STP and Gateway redundancy protocol so there is as little PE-PE traffic as possible.

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