[cisco-voip] Redundancy Options for CME

Sun Jul 12 16:31:17 EDT 2009

In a perfect world, yes. However, depending on how your L2/L3 links are set up, it may be possible from some phones to register on each router. Definitely not ideal, and it should be avoided, however, it might be possible. With a dial peer on each router, you cover this scenario. 

HSRP is really only used to advertise to the phones where to register. Everything else is configured with the appropriate router address, most likely a loopback address. So, it's conceivable that the two routers can talk to each other via L3 via some advertised route, but not via L2 (over which HSRP is handshaked), in that case, each router will advertise it is the HSRP active router. 

That's just me and my "try to cover every scenario possible" attitude. It's helped me out in some cases, bitten me on the ascot tie others. ;) 

Then again, I don't try to be an L2/L3 expert and have been known to be laughed out of a network meeting trying to accomodate a scenario that costs 10K to provision and will happen once every election of a pope (that one sounds better in Italian). ;) 

--- 
Lelio Fulgenzi, B.A. 
Senior Analyst (CCS) * University of Guelph * Guelph, Ontario N1G 2W1 
(519) 824-4120 x56354 (519) 767-1060 FAX (JNHN) 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
"Bad grammar makes me [sic]" - Tshirt 

----- Original Message ----- 
From: "Bill Greenwood (US)" <bill.greenwood at us.didata.com> 
To: cisco-voip at puck.nether.net 
Sent: Sunday, July 12, 2009 4:20:02 PM GMT -05:00 US/Canada Eastern 
Subject: Re: [cisco-voip] Redundancy Options for CME 

Thinking more about this: 

If both routers run CME, on the standby router a general dial peer for the phones would point to the primary router. This dial peer would not be needed on the primary router as if it was up it would have the phone registered locally. This dial peer on the standby router would be in place all the time routing calls from the PSTN to the primary router under normal operation. In the case where the primary router has failed then the phones would register and create more specific dial peers which would route the call locally to the phones. Does that sound correct? 

Bill 

From: Lelio Fulgenzi [mailto:lelio at uoguelph.ca] 
Sent: Sunday, July 12, 2009 4:03 PM 
To: Bill Greenwood (US) 
Cc: cisco-voip at puck.nether.net 
Subject: Re: [cisco-voip] Redundancy Options for CME 

Each router would have dial-peers pointing to the other router for each set. There is a default setting (in SRST anyways) that prevents a routing loop via H323. 

I had a similar question, and it was discussed briefly on the list. One of the Cisco folk told me about the routing loop prevention. That's key. Because it's on by default, it helps. 

Here's a press release talking about it (in very general terms). 

http://www.cisco.com/en/US/prod/collateral/routers/ps5854/prod_case_study0900aecd80424090_ns431_Networking_Solutions_Case_Study.html 

--- 
Lelio Fulgenzi, B.A. 
Senior Analyst (CCS) * University of Guelph * Guelph, Ontario N1G 2W1 
(519) 824-4120 x56354 (519) 767-1060 FAX (JNHN) 
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ 
"Bad grammar makes me [sic]" - Tshirt 

----- Original Message ----- 
From: "Bill Greenwood (US)" <bill.greenwood at us.didata.com> 
To: cisco-voip at puck.nether.net 
Sent: Sunday, July 12, 2009 3:43:39 PM GMT -05:00 US/Canada Eastern 
Subject: Re: [cisco-voip] Redundancy Options for CME 

Even if the configurations are synchronized which would allow for the phones to register with either router, how would the calls from the PSTN be handled? If a call was received on the router that was not the primary it would see the phone as not being registered and forward to voice mail. There needs to be some method of having the routers communicate with each other similar to a publisher and subscriber. I have not been able to find anything to allow for this communication. Can the second router be configured with SRST? But that still leave the question on the PRIs, if both are connected to the primary router and it fails then you are left with no connection to the PSTN. 

From: mthompson729 at gmail.com [mailto:mthompson729 at gmail.com] 
Sent: Sunday, July 12, 2009 3:11 PM 
To: Bill Greenwood (US) 
Subject: Re: [cisco-voip] Redundancy Options for CME 

I've never tried to do this, but the only way I could think to do this is using HSRP on the FE interface. this is assuming that the HSRP address can be used as the source-address for the CME system. 

This would make proper documentation and config sync a critical process though. 

On Jul 12, 2009 3:03pm, "Bill Greenwood (US)" <bill.greenwood at us.didata.com> wrote: 

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> I am looking for information on how to provide redundancy for a CME based system. 
> The configuration is there are two identical routers at the 
> site, two PRI circuits to the PSTN and 60 or so phones. I am at a loss as 
> to how to recommend redundancy for this. Is it one router configured with 
> CME as normal, but how should the second router be configured? Is the 
> second router configured with CME or as an SRST router. How should the 
> second router appear to the primary CME router? How should the PRIs be 
> connected, if one is connected to each router I can set up the dial peer to 
> route the outbound calls, but how are the inbound (from the PSTN) routed? 
> If the PRIs are connected to only one router redundancy is lost. I have 
> be unable to locate any documentation that explains how to set this up. 

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