Cisco SD-WAN Multicast Join Propagation Protocol

300-415 By islever Editorial Last updated

Describe multicast support in Cisco SD-WAN Configure OMP

Short answer

C OMP propagates multicast join requests over the fabric.

Question

Which protocol is used to propagate multicast join requests over the Cisco SD-WAN fabric?
  1. Auto-RP
  2. ARP
  3. OMP Correct Answer
  4. IGMP

Key Takeaways

The main trap is confusing local access protocols like IGMP with overlay control protocols. IGMP handles local joins, but OMP carries that state across the SD-WAN fabric.

Learn which protocol propagates multicast join requests over the Cisco SD-WAN fabric. The correct answer is OMP, as it handles control plane state distribution across the overlay.

Common mistake: Many candidates choose IGMP because it is the standard protocol for multicast joins. However, IGMP does not traverse the SD-WAN overlay; only OMP does.

Expert Analysis

The question asks specifically about the protocol used to propagate multicast join requests over the Cisco SD-WAN fabric. This distinction is critical because it separates local access-layer behavior from overlay transport behavior.

Local vs. Overlay Behavior:

  • IGMP (Internet Group Management Protocol) operates at Layer 2/3 within a local subnet or VLAN. It allows hosts to request membership in multicast groups. However, IGMP packets do not traverse the SD-WAN overlay tunnel itself; they terminate at the WAN Edge router's ingress interface. Therefore, option D is incorrect for propagation over the fabric.
  • OMP (Overlay Management Protocol) is the control plane protocol for Cisco SD-WAN. It distributes routing information, including multicast routes and join states, between WAN Edge routers and vSmart controllers. When an edge router receives an IGMP join locally, it translates this intent into OMP messages to propagate the multicast state across the fabric to other edges or sources. Thus, OMP is the mechanism that carries this information over the overlay.

Why other options fail:

  • Auto-RP (Option A) is a legacy Cisco protocol for PIM-SM group-to-rp mapping, irrelevant to the SD-WAN overlay control plane.
  • ARP (Option B) resolves IP to MAC addresses on local segments and has no role in overlay routing.

Community Context: Comments highlight a common confusion between local protocols (IGMP) and overlay protocols (OMP). While one comment cites documentation mentioning PIM/IGMP support, this refers to the protocols supported by the edge devices for local processing, not the protocol carrying state over the fabric. The consensus among knowledgeable contributors correctly identifies OMP as the overlay carrier for these joins.

Correct answer: C — OMP propagates multicast join requests over the fabric.

Official Reference

https://www.cisco.com/c/en/us/td/docs/routers/sdwan/configuration/bridging-routing-segmentation-qos/vedge/bridging-routing-segmentation-qos-book/multicast-overlay-routing.html

This link opens the official vendor documentation in a new tab.

Exam Strategy

When analyzing SD-WAN questions, always distinguish between 'local' actions (what happens at the edge interface) and 'overlay' actions (what happens across the fabric). If a question asks about traffic or state moving 'over the fabric' or 'between edges,' think OMP. If it asks about host-to-router communication, think IGMP/PIM.

Frequently Asked Questions

Does IGMP work over the SD-WAN overlay?

No. IGMP terminates at the WAN Edge router. The router then uses OMP to advertise the multicast state across the fabric.

What is the role of OMP in multicast?

OMP distributes multicast routing information and join states between WAN Edge routers and vSmart controllers to ensure consistent multicast delivery.

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Community Votes

C
60%
D
40%

60% of anonymous learners picked answer C. Votes are pick records left by other test-takers — they are not the verified answer.

Discussion 6 contributions

Compiled from public community threads and reader submissions, lightly edited for clarity. Handles and vote tallies are shown as recorded, and comments reflect the views of individual contributors.

From public community threads 6

  1. MANDY13 👍 3 Answered D
    https://www.cisco.com/c/en/us/td/docs/routers/sdwan/configuration/bridging-routing-segmentation-qos/vedge/bridging-routing-segmentation-qos-book/multicast-overlay-routing.html#:~:text=The%20Cisco%20SD%2DWAN%20multicast%20overlay%20software%20uses%20Protocol%20Independent,traffic%20on%20the%20overlay%20network.
  2. 2e6bc5f 👍 3 Answered C
    It’s OMP, on page 62 of Cisco Catalyst SD-WAN: Design, Deploy and Secure you WAN (2nd edition) it states “On the transport side, OMP is responsible for exchanging multicast routing info”
  3. RMascarell 👍 2 Answered C
    IGMP is limited to the VLAN, it doesn't propagate nothing over the fabric. OMP sends this information to the vSmart, and so, over the fabric.
  4. rensoo 👍 2 Answered D
    Cisco SD-WAN overlay multicast network supports the Protocol Independent Multicast (PIM) and Internet Group Management Protocol (IGMP)
  5. westh4m1234 👍 1 Answered C
    Over the Cisco Catalyst SD-WAN fabric, OMP (Overlay Management Protocol) is used to propagate multicast join requests and control-plane state across the overlay
Show 1 more comment
  1. Stanleymahamadi 👍 1
    Correct D

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