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SRP521 + IP Passthrough

Unanswered Question
Mar 6th, 2012
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Anyone have any experience getting the SRP521 to pass the WAN IP information through to a downstream router?  The goal would be to take advangate of the 3G backup without using the routing functionality of the device.

Also, does the SRP521 support IPv6?

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bclarkuncc531 Tue, 03/06/2012 - 17:07
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Ive got the 521 model...not the 526.  What about if we use dhcp or a static ip instead of ppp?

Andrew Hickman Wed, 03/07/2012 - 03:07
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Hi Bryan,

It is not possible to have the SRP pass through an assigned WAN IP to a local client.  The closest thing would be use the hosted software DMZ feature - but this would still require the local client to have a private IP address.... which I realise is not the same as what you are asking for.

Also correct that there is no IPv6 support for the SRP series.



andrewbruner Wed, 03/07/2012 - 05:53
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Andrew, I work with Bryan Clark also. 

Could you possibly provide some instructions on how to configure this? 

Some background on our requirements might help: We're an ISP getting ready to deploy a "business continuity" product with a 3G failover device to our business class customers.  As our customers generally have their own equipment beyond the cable modem, we are attempting to integreate a device (Cisco SRP521) in line where we don't have to re-work anything. 

We’ve been testing a number of products including the Cisco 521 SRP router.   The 3G failover process seems to work great on the device and appropriately turns off when the WAN connection is restored.  One of the requirements from our Plant department is having this function in bridge mode (sometimes referred to as “ip passthrough”).  Essentially we want the WAN IP address that is presented to the cable modem to pass through the 521 device and present itself to any of the customers equipment beyond that.  The customer may already have equipment in place which they manage and serve DHCP so we don’t want to get into scenarios of the 521 device providing a 192.168.15.x address or where we have to rework a customers network. 

We're open to any solution/configuration to make this happen.  If we can get this working, it will probably mean we purchase a few thousand of these Cisco devices so there is definitely a benefit if we can find a solution to this challenge/requirement.

Any assistance is much appreciated.

Andrew Bruner

jasbryan Wed, 03/07/2012 - 07:06
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yeah got my models confused on the earlier post, you can only bridge the SRP that acts as the modems ISP(ADSL models). Also for as i know the 3G card is acting as the modem from your Wireless provider, and i don't think we can pass the public information to the device that is behind the SRP router. Maybe Andrew can shed some light on 3G capabilities but I'm thinking it's won't be able too do as you need.


Andrew Hickman Wed, 03/07/2012 - 08:29
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That's correct - we don't have that passthrough feature at all on the SRP500 series.

I just rechecked and its also not possible host a DMZ client on the 3G interface - not sure why as you can port forward from it, I'll check.

If you have the SRP in line with the customer product, wouldn't it be better to use the SRP NAT functionality to hide the changing WAN addresses?