Dark Fiber design question

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I appreciate your input, I have 4 sites that are going to be connecting with dark fiber -see attached diagram- all 6500's with 10GB xenpaks, my question is: should all interfaces on the 6500'S be on the same network or should I have /30 networks between each site to site connection. Also, if you note from the diagram, should I place a patch cable to bridge sites A and C together bypassing site B? if I do that then I won't be able to use the /30 and would need a larger subnet or put them all interfaces on the same network...I hope this makes sense, I'm also assuming Layer 3 between sites is the way to go instead of Layer 2, what is the best approach from a IP design perspective? Thanks again.

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Correct Answer by Jon Marshall about 8 years 8 months ago

Okay, didn't realise you had run out if 10Gb interfaces.

Only thing i can suggest is if you have a 1Gbps interface on both switches you could interconnect A & C that way and the routing protocol would only use this as a backup if the other links failed. But as i say you do have redundant paths anyway.

Jon

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Jon Marshall Wed, 04/02/2008 - 23:36

Borman

The best approach is the one that meets your requirements :-).

Seriously it depends on your applications and whether or not you need to extend vlans between data centres. Some technologies such as clustering often require L2 adjacency so if you wanted to cluster 2 servers, one server begin in data centre A and another in B then you would need a L2 link between the 2 data centres, or run a L3 link and have to use something like L2TPv3 to extend the vlan.

If you have no specific requirements to have the same vlans in different DC's then i would look to go with L3 links as this eliminates STP from the interconnect links ie. a broadcast storm in one DC would not propogate to the other DCs.

Do you need to connect A directly to C, well A has 2 paths to get to C ie.

A -> B -> C

A -> D -> C

so you could rely on that for resilience although you would want theh fibres to terminate in different racks on different equipment. Again a lot depends on your traffic patterns.

If there is a lot of traffic going between A & C then B & D become transit sites and the links will have traffic that does not need to go across them. Bear in mind you could connect A -> C with a /30 L3 link as well.

These are a few things to think about. You need to have a good understanding of traffic patterns between your DC's and also what type of services eg firewalling, load-balancing, IDS you want to deploy. So although i say i would use L3 links to interconnect that may not be the right solution for you. It is a very generic answer.

Jon

Jon,

Thank you very much for your response, since I don't really have a good reason for using L2 I would configure them as L3, one other question: You mentioned I could connect A-->C directly with a /30 as well, this means I would need to connect to another interface on the 6500, correct? I only have one 10GB interface left on the 6500 that will be used for the A-->B connection, any suggestions? Thanks again.

Correct Answer
Jon Marshall Thu, 04/03/2008 - 06:34

Okay, didn't realise you had run out if 10Gb interfaces.

Only thing i can suggest is if you have a 1Gbps interface on both switches you could interconnect A & C that way and the routing protocol would only use this as a backup if the other links failed. But as i say you do have redundant paths anyway.

Jon

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