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Hosted IP Centrex and LAN redundancy question


Please see attached sketch showing existing IP Centrex solution.


I am trying to provide LAN (switch) redundancy in case of failure of 3750 Distribution switch.

My recommendation:

I would bring an additional fiber run from Building A and Building B.

I would add another 3750(L2) Distribution switch. I would connect the 3750-Distribution-Switch2 to Router 2811 secondary fastethernet interface.


Someone mentioned that since the DHCP and call control is coming from Service Provider (HIPC), I can't just plug and use the Secondary interface on the 2811.

Such concern does not make sense to me.

Please let me know if in a typical HIPC scenario I can or cannot improve the Distribution Layer redundancy by adding another switch as I stated above.



Cisco Employee

Re: Hosted IP Centrex and LAN redundancy question

The issue isn't really that DHCP is hosted by the Centrex.  The issue is that if connectivity between the IP phone and Centrex is lost, where would the IP phone register?  But if you can get L3 connectivity to continue to Centrex when the L2  switch goes down by providing alternate paths, the phones should  probably be okay.  You can probably ask in the switching forum if you want more details on L2 redundancy best practices and that sort.  From a voice perspective, you just need to be concerned about maintaining L3 connectivity through to your provider during a failing state.  Treat it as you would any other device.

Because these aren't Cisco IP phones, I don't know how they do call preservation/survivability during an outage from the call agent/registrar.

In the Cisco world, if Cisco phones lost connectivity to the head end, they'd use SRST and register to a local device running SRST.  If your phones are running SIP and can take an alternate IP for registration, you can maybe look into SIP SRST at the local site for this.