Does VXLAN must have multicast connectivity between nodes?

[Alex Kitaichik]

Hello,

This's the first time I'm implementing VXLAN in my network. Basically, we're talking about pair of witches, pointing each to the other. I'll have 2 such pairs. From what I've saw from Ciscos' documentation of VXLAN, setting multicast connectivity between VTEPs is a REQUIREMENT.
The question is – is with my simple scenario, switches pointing to each other, am I still must setup multicast between VTEPs in order VXLAN to work?

Any answer will be appreciated.

Thank you.

Alex.

[Peter Paluch]

Hi Alex,

I haven't worked with VXLAN personally. However, as far as I understand the concept, in your situation, you do not need to set up any specific multicast support. Your VTEPs are on the same switched network and within the same broadcast domain - that is what you have implied. Propagation of multicasts over a single broadcast domain does not require any specific configuration.

Specific multicast configuration would be required if the VTEPs resided on different VLANs, or in general, on different broadcast domains. In such case, multicast routing would be required to allow these VTEPs to deliver their own broadcast/multicast traffic to each other. In addition, IGMP Snooping could be used to optimize the flooding of the multicast. However, these are optimalization measures and do not add to the basic multicast connectivity.

My two cents...

Best regards,
Peter

[Alex Kitaichik]

Hello Peter,

thank you for answering.

I think you're referencing to multicast forwarding thru L2 domain, which you're right - should be forwarded across L2 domain without additional configuration. What I was asking about is the following - http://www.cisco.com/c/en/us/products/collateral/switches/nexus-9000-series-switches/white-paper-c11-729383.html (look at the 'Remote VTEP Discovery and Tenant Address Learning' section). This says VTEPs are communicating between themselves using multicast (for VXLAN operational purposes).

This means that the underlying IP network, used by VXLAN, must support multicast routing. Am I wrong? May I use VXLAN across network supporting unicast only?

P.S. at least, regarding my intended scenario - 2 switches communication one with the other, only.

[Peter Paluch]

Hi Alex,

This means that the underlying IP network, used by VXLAN, must support multicast routing. Am I wrong? May I use VXLAN across network supporting unicast only?

The support for IP Multicast routing in your IP network is only required if the VTEPs are located in different IP networks - in other words, if there is at least one router on the path between any two VTEPs. If all VTEPs are in the same IP network then you do not need to worry about running IP Multicast routing.

So until the VTEPs are in the same IP network with no router between them, you do not need to be worried with IP Multicast routing.

Best regards,
Peter

[Alex Kitaichik]

I see, thank you.

Indeed, the VTEPs located several hops away.

[Peter Paluch]

Alex,

In that case, I am afraid, you will need to run IP multicast routing between the subnets in which the VTEPs are located. Will it be possible for you to run the multicast routing?

Best regards,
Peter

[nwekechampion]

Hi @Peter Paluch ,

Just clarifying on this thread.. if you are using VXLAN - which means to extend your layer 2 (end hosts) VLAN over Layer 3 (Multiple ROuters or Hops), u will definitely need either an IR(not scalable) or Multicast Routing across both VTEPS.. Would this be accurate?

[aftabsiddiqui]

Its an old thread now but Just replying in case someone end up here. Multicast and Unicast discovery totally depends upon the platform. CSR1000v (IOS-XE) and Nexus both supports unicast discovery so you don't need Multicast routing but if you are using ASR (IOS-XR) then somehow Cisco doesn't want you to use unicast discovery. 

I've successfully used VXLAN with CSR1000v (unicast) with Arista, CumulusLinux and Pica8.