Extreme Networks

Jay2009 · ‎11-26-2020

Currently going through a dev exercise. I will be using DvR in the DC. a Discussion came up as why not use it for campus access as well. I would not have any leaf nodes on the campus access, just 4 controllers. Looking for any advice on why I should or should not go that route.

Ludovico_Steven · ‎11-30-2020

Seems I have been summoned! Not sure I am the DVR guru, but will give a shot at it!

You can use DVR on any VSP, bar the XA1400; the VSP8600 also just got DVR controller support in 8.0

DVR was initially designed for Data Center operation but can also be used in the Campus and will become much more widely used in the Campus with the new unified edge platforms running in VOSS mode (5520, 5420).

The benefits of DVR are around 2 main areas:

Optimized shortest path for IP routed traffic entering the network on an access FC-enabled node (BEB). This would be a DVR-Leaf, which remains a L2 access switch from a config perspective but actually owns the DVR MAC and does L3 in the dataplane for any incomming traffic destined to a DVR Gateway interface. The DVR gateway is distributed to the DVR Leaf access, and so routing can happen on the 1st hop, so you always get the shortest path (no more need to go reach some VRRP IP inside the fabric and then get routed from there)
- In a campus design, if you have FA Proxy access switches and DVR Controller FA Servers, there is no difference between DVR and traditional VRRP with BackupMaster (or RSMLT-Edge); high bandwidth host-host East-West traffic is less common in the Campus, where most traffic will be North-South
- But if you are going for a VSP to the edge Campus design (with 5520/5420) then using traditional VRRP and L2 BEB access becomes sub-optimal (VRRP Backup-Master does not work on NNI interconnects) and here you will need DVR for optimal performance and shortest path.
Can solve traffic tromboning for traffic trying to reach the DVR IP subnets from far away. If you have DVR subnets which span geographically distant parts of the fabric (e.g. imagine 2 different Data Centers with the same server VLANs spanning both) then typically there will be a number (4 or more) VSP acting as L3 BEBs and advertizing the same IP subnet on the network. Under normal conditions distant traffic seeking to reach a host on that subnet will prefer to go to the nearest L3 BEB for that subnet, not the L3 BEB nearest to the destination host. Where that difference results in a sub-optimal forwarding path, DVR can help by allowing selected /32 host routes to get injected into the wider IP routing table. This mechanism works if DVR was deployed in different DVR Domains, so that a given host route will only be advertized by the DVR Controllers of the DVR Domain where that host actually resides. The need to leverage this capability will depend on the actual fabric topology and usually if WAN links are in use (not all networks have a need for it).

If you want to use DVR in the Campus as a replacement for VRRP (RSMLT), just keep in mind the DVR limitations.

DVR does host based routing. DVR Controllers and DVR Leaf nodes will hold host routes for every IP in a DVR VLANs (within the DVR domain if a Leaf / withing the whole network if DVR VLANs span the DVR Domains, if a DVR Controller); there is a limit to the size of that host route table (40000 on new VSP models, 32000 on older models; see Release Notes).
DVR VLANs must only contain IP hosts. You cannot connect an IP router or Firewall onto a DVR VLAN; things will not work properly if you do. Always Connect IP routers onto a VRRP VLAN (or an OSPF VLAN).
Currently DVR is IPv4 only; IPv6 and Microsoft NLB are not supported on it; in these cases simply use VRRP for these VLANs. You can still easily configure some VLANs to use VRRP (even if the VSP is a DVR Controller) and get these L2 extended to the access switch (even if this is a DVR Leaf).

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Jay2009 · ‎11-28-2020

I had some additional discussion. At this point I will be looking at moving forward with DvR. I only need 5520/5540 with VOSS if I am doing the routing at the user edge. In my case I am just doing L2 Fabric Attach back to my controllers. I have not seen any down sides to this. If I have 4 controllers in the building I get seamless roaming. 5520/5540 with some sort of stacking capability, policy and DvR would be awesome. Will be looking forward to seeing it when it’s available.

Miguel-Angel_RO · ‎11-28-2020

Hi Jay,

If I remember well you’ll have to use the new 5520/5540 to be able to use DVR at the edge.

For the others enhancements/limitations, maybe the DVR guru @Ludovico Stevens could give a view?

Regards

Mig

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