Need to know the behaviour

[ravi310859]

Hi Team,

I need some information about the behaviour of topology on which we are going to upgrade . 

Current Scenario ( Fig-1)

We are on the legacy network and using Nexus as an Edge device. Our WAN links are terminated on the nexus. All the traffic from remote sites are passing through nexus. We are going to upgrade on SD-WAN.

Post Migration Scenario ( Fig-2)

We have extended our topology and added the C-Edges and extended the WAN links which will be connected via VPN0.

For Remote site prefixes we have extended another physical connectivity to inject the remote site prefixes towards C-Edges via service side VPN.

Query

Do we require two different interfaces one for Transport VPN and another for Service side VPN ?

or We can use only one interface  for both Service side VPN and Transport Side VPN traffic.

Doubt

If we use two interfaces between Nexus and C-Edge Would it work or any STP related issue comes .

I am attaching here topology for Existing(Fig-1) and Post Migration (Fig-2)>
Kindly share your points.

[Kanan Huseynli]

Hi,

technically you can use one physical interface with different subinterfaces which belong to different VRF (i.e VPN in SD-WAN).

Recommended, to use separate physical interfaces. For service-side it is even better to have dual links (etherchannel which is supported now via CLI-template).

There will not be issue with STP, this is because L3 termination happens on router side. Router does not pass STP messages from one interface to another nor it participate in STP process (note: some models may have LAN switching module if you purchased, don't use those interfaces. Normal interface are pure L3 - without any STP process, use them).

[ravi310859]

Hi , 

Can you share any relevant document or any use case ?

[Kanan Huseynli]

Actually, these are fundamental topics, thus are not mentioned explicitly in anywhere.

You can, generally, refer to Cisco Validated Design guide (if needed)

https://www.cisco.com/c/en/us/td/docs/solutions/CVD/SDWAN/cisco-sdwan-design-guide.html