Brad sent me an interesting DCI encryption question a while ago. Our discussion started with:
We have a pair of 10GbE links between our data centers. We talked to a hardware encryption vendor who told us our L3 EIGRP DCI could not be used and we would have to convert it to a pure Layer 2 link. This doesn't make sense to me as our hand-off into the carrier network is 10GbE; couldn't we just insert the Ethernet encryptor as a "transparent" device connected to our routed port ?
The whole thing obviously started as a layering confusion. Brad is routing traffic between his data centers (the long-distance vMotion demon hasn’t visited his server admins yet), so he’s talking about L3 DCI.
The encryptor vendor has a different perspective and sent him the following requirements:
- MAC address MUST be preserved.
- The network between encryptors cannot modify the Ethernet MAC addresses.
- Transmission order MUST be preserved:
- QOS MUST occur outside of encryptors, not between encryptors. QOS may reorder frames.
- L2 MPLS VPN - the MPLS control word MUST be enabled to guarantee transmission order.
- L2 payload SHALL NOT be looked into by network between encryptors.
Their hardware is clearly using a proprietary encryption technology that looks like bump-in-the-wire at layer-2, so they can only work over L2 VPN offered by a Service Provider (VPLS or pseudowire). Fortunately, Brad is actually buying a L2 VPN (over which he runs L3 with EIGRP), so everything worked out just fine.
- When you buy standalone encryption devices, check whether they support IPSec or not.
- If the encryption device does not support IPSec, it might work as a layer-3 device (router) or as a layer-2 device (bump-in-the-wire).
- In both cases, using MPLS/VPN services from the service provider could be questionable, as you need to run PE-CE routing protocol across the encryption device.
- It’s easiest to combine external encryptors with layer-2 VPN services (VPLS, pseudowire) or dark fiber, regardless of whether you run L2 or L3 transport across the link.
- Even when the encryption vendor claims its device is a bump-in-the-wire, check whether it supports point-to-point or any-to-any encrypted sessions. If it’s a point-to-point device, it’s best used over a pseudowire.
Choose the Optimal VPN Service webinar (register here) describes numerous VPN services, including (layer 3) MPLS/VPN, (layer 2) VLPS and pseudowires. It also explains how each services looks from the enterprise network perspective and how it’s best used.
Data Center 3.0 for Networking Engineers webinar (buy a recording or yearly subscription). covers (among tens of other topics) four DCI scenarios, including pseudowires, VPLS-based solutions, OTV and multiple user-side EoMPLS variants. The Data Center Interconnects webinar goes even deeper into the DCI topics and describes active-active data center designs.