I'm having a hard time finding information about whether implementing ipv6 or using a stretched vlan is a better option for geographically dispersed sites is better. Does anyone know:
- Problems with stretched vlans (mac address broadcasting etc)
- costs for devices to solve those problems
- pros for using IPv6 instead
EDIT. What I am looking for is pros and cons against implementing the equipment required to implement stretched IPv4 vlans vs simply using IPv6 to solve the same problems. Eg admins stretch vlans instead of route because protocol X can't be routed, but IPv6 can encapsulate protocol X so there is no need to worry about that problem.
Edit 2: Lets say that one of the problems to be solved is migrating VMs across physical datacenters, Will IPv6 solve the problem of needing to stretch the vlan?
I am looking for a detailed explanation of which project will provide the most bang for the buck as well as reduce network complexity. So far the answers have centered around them as if they are not related (which I see as them being related as IPv6 removes vlan requirements entirely- making it extremely difficult to implement any vlan stretching infrastructure) - but have the same requirements of supporting multiple datacenters in a dispersed environment. All of my providers support IPv6 and we'll probably get a provider independent /48 (if we go that route)
You are asking about things that are orthogonal to each other (independent of each other) as if you need to make a choice to implement one or the other. Why?
If you have an IPv4 network between two locations then for simple tasks like copying data between the two locations, there's nothing that IPv6 will do for you that IPv4 can't already do.
As a separate question, you might want to extend vlans to the other location, perhaps because you want to avoid the overhead of a router. This motivation for using stretched vlans would be equally valid for IPv4 or IPv6.
One thing has nothing to do with the other.
You mentioned protocols that can't be routed. Non-IP protocols? In that case you should use stretched vlans. Switching to IPv4 to IPv6 won't suddenly make these protocols routable. You also mentioned tunelling these unroutable protocols in IP (and this tunnel carrier could be either v4 or v6, either one is good). I would not recommend tunelling unless necessary because it will add much more overhead than stretched vlans and complicate the network topology a lot. You should resort to this kind of tunelling if the stretched vlans solution is unscalable or unavailable. Reasons why stretched vlans might be unscalable could porentially include limits of spanning tree protocol capabilities, or MAC address leaning difficulties due to unidirectional layer 2 network flows or too many hosts on a single vlan. Reasons why stretched vlans might be unavailable could include a third party router in the link which is outside of your control and cannot be replaced with a bridge.
When looking at the problems related to migrating VMs between physical data centres IPv6 will not make a difference. IPv6 is routed in the same way as IPv4, so you would need stretched VLANs in both cases.
As mentioned previously stretched VLANs are not such a great idea. You might want to consider LISP for this. Cisco has some very good support for that these days, and VM mobility is something they specifically target on the Nexus 7000 (see Nexus 7000 NX-OS Innovations) in their LISP implementation (see Cisco Locator/ID Separation Protocol for Virtual Machine Mobility). And best of all: it supports both IPv4 and IPv6 :-)
Layer 2 data center interconnects are basically a horrible idea. See http://blog.ioshints.info/2011/11/busting-layer-2-data-center.html for a great explanation.
You want to route between your sites, which means different subnets and an L3 switch or router (even if that router is just a server configured with static routing).