MPLS conversion to Layer 2 advice

[theloftycloud]

Looking for some guidance and advice...So planning a MPLS migration to an ATT Layer 2 ASE(switched ethernet network).Infrastructure is pretty standard as in 20 sites that are connected thru MPLS i.e. BGP. We use EIGRP internally throughout the netwrok. We have 2 data centers that are primary exit points for the sites. The data centers also have SIP trucks associated with them as well as 1 of the sites.

Anyone have any experience with such a conversion? We are thinking of eliminating all the branch routers and upgrading the current switches to newer C9300/9400 and just using the Layer 3 function to route traffic using our EIGRP as BGP will going away.

My main concern is the elimination of the routers which we are being told we don't need. BGP will essentially go away and we use our EIGRP across the VPLS. However I'm unclear as to how QoS would work on the 9300/9400 which we have set on our current routers. Are there are downsides to not using the router I guess or are we handicapping ourselves for future designs like SD WAN?

[Joseph W. Doherty]

"However I'm unclear as to how QoS would work on the 9300/9400 which we have set on our current routers. Are there are downsides to not using the router I guess or are we handicapping ourselves for future designs like SD WAN?

Much depends on what your current QoS policies look like on the routers. The 9300/9400 support QoS, but as typical with Cisco switches, it doesn't provide as many QoS features as found on a Cisco router.

One "gotcha" when moving to a L2 environment, it's often more of a "shared" multi-point topology than some L3 environments, although MPLS environments are often setup as multi-point too. For either, from a QoS perspective, you often can have the issue of congestion leaving the service provider's "cloud" to a busy site. Generally, MPLS providers will offer some QoS features that can be used against this congestion but L2 providers may offer little to no QoS support for "cloud" egress.

I cannot comment on switch vs. router SD WAN support. The 9300/9400, though, have more design growth ability but likely will not be a capable, feature wise, as a router driven/controlled more by software.

[theloftycloud]

Thanks for the quick response.Our current ISP(ATT) does preform some QoS on their routers but I don't know off hand. I know we have our own QoS policy applied at 40% for all VOIP traffic.  Currently most sites range from 10-20mbps with larger ones at 100mbps. With that being said some sites have "voice issues" like jitter and static. We use 3 SIP trucks provided the same ISP. With the amount of bandwidth that we are upgrading to we are being advised that VOIP issues will go away so no need to worry. I take that with a grain of salt...needless to say you do bring up some valid points...the QoS functions on a router will differ, how much I'm not too sure and does the ISP offer any L2 QoS for "cloud" egress traffic. I will follow up with them regarding the last point. 

I would hate to remove all branch routers, upgrade to new switches and then come a day wheres there some congestion or VOIP quality...someone in the background... "I told you so"

[Joseph W. Doherty]

The only way you can truly guarantee having sufficient bandwidth will always avoid the need for network QoS is where there's no over-subscription of bandwidth anywhere in the network, which generally isn't possible, even in theory. (Consider more than one host communicating with one host; how do you avoid over-subscription in at least one direction? Further, the host's network connection is a bottleneck too.)

Yea, do take the idea more bandwidth will solve any and all VoIP issues with a vary large dose of salt! ;)