Question : How do I design network for failover to a secondary internet connection?

Hi!
I am trying to come up with an improved network design that would allow our network to stay up in case of loss of primary internet connection. I have attached the document that describes how our network is set up now.

We have TWO locations with Sonicwalls TZ170 on each end with site-to-site VPN. We also have VLS between the same two locations with CISCO RV42s that handle all internal traffic between 4.0 and 1.0 networks.
When either one of our services goes down, I have to manually change routes to make things work again.
I am trying to utilize the dual WAN advantage of CISCO routers, however, they are 'behind' our main Sonicwalls and I can't figure out a good way to reorganize things to create a more stable system with automatic failover.

Should I just get rid of Sonicwalls completely?

Would RV042 be a good replacement for TZ 170?

Thank you,

Attachments:

diagram.doc (20 KB) (File Type Details) 

network diagram

Answer : How do I design network for failover to a secondary internet connection?

I would suggest removing the TZ170's and just use the Cisco's. The throughput on the devices are similar, if a little better for the Cisco. So replacing the TZ170 with the RV042 should be fine.

You could get Enhanced OS for the TZ170 or upgrade to a TZ100 to get dual-WAN on the SonicWALL. But since the Cisco supports that already, I would switch over to using them completely.

Here are the datasheets to compare throughput for reference:
http://www.sonicwall.com/us/products/TZ_170_Series.html
http://www.cisco.com/en/US/prod/collateral/routers/ps9923/ps9925/data_sheet_c78-501225.html