Core switches between 2 data centers

[ssweehinlew]

Existing data center has 2 X Cisco 6500 series core switches, new data center has 2 X Cisco nexus core switches. For the connection between 2 data center, it will be using leased line. To establish the network connection for both side, should it use trunk port with layer 2 connection directly or layer 3 ip routing (configure the ip on switchport interface) ? What is the better approach for its design? Please share your idea.

[Joseph W. Doherty]

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Normally, when dealing with off-site traffic, L3 is better as it limits traffic to only what needs to go off-site.

However, as you're dealing with data centers, it's no longer uncommon that there's need to share L2 between them.  So, much depends on what your needs are.

[ssweehinlew]

When the trunk is built up (L2 connection is up), we would like to move the servers from existing Data Center to new Data Center. 

Should I migrate the routing configuration from Cisco 6500 series switches to Nexus switches and let it to forward the traffic between 2 sites? What would be your recommendation?

[Jon Marshall]

I would think it would be fairly obvious that you would route the server vlan on the local switches.

Why would you move the server vlan to the new DC but then route them in the old DC ?

Jon

[ssweehinlew]

The servers will be moved by phases. Both DC will have the servers to run at the same time.  

[Simon Hill]

If you're getting NEXUS 7K's then you can look at OTV to help mitigate the risk of spanning broadcast domains between data centres. Otherwise you need ASR 1K's for OTV.

Just the one NEXUS core switch for each data centre?

[ssweehinlew]

if only 1 Nexus 7k at new dc, can it form the OTV with Cisco 6500 core switch in existing DC?

[Simon Hill]

You will need an ASR 1K with AES or AIS feature set at the 6500 end. I think the ASR will need two LAN facing interfaces, one for routing and an OTV Internal Interface to carry the extended VLANs, but check with your Cisco partner. I recommend you get pre-sales engineering input to ensure the design is sound.

Ideally, you'd have dual links between your DCs and dual redundant hardware each end, but understandably this isn't always feasible.

The N7K will need M or F3 linecards, appropriate licencing and NX-OS version for OTV support:

http://www.cisco.com/c/en/us/td/docs/switches/datacenter/sw/nx-os/OTV/config_guide/b_Cisco_Nexus_7000_Series_NX-OS_OTV_Configuration_Guide/basic-otv.html#reference_9069D24E5E18471684D01FB2A60FC549

[Collin Clark]

IMO you should make it a L2 trunk. If you need L3 across it, you can always add a VLAN and put an IP on the SVI's.

[ssweehinlew]

what if the existing core switches only has 1 vlan? There are multiple subnet under single vlan?

[Collin Clark]

I would still do it that way.