Ring Topology - Private dark fiber

[Ashfaq Habeeb]

Hi guys,

I have a question and need your wise recommendation regarding the scenario. 

Requirement: One of our customers has decided to have their own private dark fiber connection - ring topology. We as partners have to recommend and design their network for this topology. They are also looking to replace their Core Switches and terminate this fiber on the same.

Tricky part: In the ring topology the connection is 1-> 2 -> 3 -> 4. Now the tricky thing is, 1 is their MAIN site, and 3 is their DR Site. Since MAIN and DR are supposed to be directly connected, this won't be a case in this. This is how they are connecting the dark fiber - say cost constraint and distance. 

Suggestions: 

1. Use of DWDM technology for fiber termination.
2. Configure L2 switches and use VLANs for traffic forwarding. 

I am not sure if there is any Technology where I can have 1->3 direct connection to avoid latency. Please suggest if there is any technology which can be used in this case. Appreciate your support! Thanks!

Warm Regards,

[chrihussey · Accepted solution]

Hello,

With DWDM you can dedicate wavelength(s) that pass through the intermediate site to allow for a direct connection between the main and DR site and even have redundancy going both ways around the ring. So physically it would be a ring, but logically you could define the desired topology. This would also eliminate having to route traffic through the intermediate site which is probably best.

Hope this helps.

[Joseph W. Doherty]

You could, as Chris suggested, build an optical network to carry a DWDM lambda between your main site and DR site, but that will add to your expense.

If your 1, 2, 3 and 4 site devices are all L3 switches, you could just pass a VLAN through a transit switch, making the main<>DR connection look like a p2p. I.e. you shouldn't need another L2 switch. Also, using VLANs, you could use DWDM (or CWDM) or "regular" optics.

If your 1, 2, 3 and 4 site devices support MPLS, you could do the same with a MPLS tunnel between main<>DR. Again, your choice of DWDM (or CWDM) or "regular" optics.

[Ashfaq Habeeb]

Thank you, both Chris and Joseph for your valuable input and suggestion regarding this! 

Suggestion:
3. Resilient Ethernet Protocol - REP for the Ring topology, can this be used? The consultant working with customer suggested this technology.
I never came across this before.

[chrihussey]

Never heard of REP before, but after reading about it I wouldn't entirely be sure it would be a good fit in your scenario. It seems it would be more applicable to a LAN environment. I also don't think you'd want your ring to be a big layer 2 domain. Just my personal thoughts. Some may have other ideas.

Regards

[Joseph W. Doherty · Accepted solution]

Not all Cisco equipment supports REP. For "smaller" Cisco devices, they often need to be MetroE devices.

REP, like STP, can be used to break a L2 loop, but if you will be routing, you can create a pair of logical p2p links between main and DR, so no need to use REP.