Multicast Forwarding in EVPN Multi-Homed Networks
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Solution Overview
Problem
In Ethernet Virtual Private Network (EVPN) multi-homed networks, non-Designated Forwarder (DF) PE devices cannot forward multicast traffic to hosts despite attracting it, leading to blackholing issues when an IGMP Join message is sent to a PE device that is not the DF.
Innovation Solution
Implementing a method where non-DF PE devices send EVPN type-6 route advertisements with ES-Import Route Targets (RTs) when receiving an IGMP join message, allowing designated forwarders to re-originate these messages with EVPN Instance RTs, ensuring multicast traffic reaches the host through designated forwarders.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If non-DF PE devices attract multicast traffic, then multicast traffic can be received at multiple PE devices, but the traffic cannot be forwarded to hosts causing blackholing
Solution Approach 1:
The patent segments the multicast forwarding function by introducing a designated forwarder (DF) election mechanism among PE devices. Only the elected DF device forwards multicast traffic to hosts, while other PE devices (non-DF) attract traffic but do not forward it. This segmentation resolves the contradiction by allowing multiple devices to participate in traffic attraction while ensuring reliable forwarding through a single designated device.
Solution Approach 2:
The patent introduces an intermediary mechanism through EVPN type-6 route advertisements with ES-Import Route Targets. These advertisements act as intermediaries that carry multicast group information from non-DF PE devices to the DF PE device, enabling the DF to attract and forward traffic appropriately without losing the benefits of multi-device traffic attraction.
2Ease of operation
If IGMP join messages are sent to any PE device, then hosts can join multicast groups flexibly, but traffic blackholing occurs when sent to non-DF devices
Solution Approach 1:
The patent uses EVPN type-6 route advertisements as intermediaries to bridge the gap between flexible IGMP join message sending and reliable multicast traffic delivery. When a host sends an IGMP join to any PE device, that device propagates the multicast group information through type-6 advertisements to the DF device, which then ensures reliable traffic delivery. This intermediary mechanism preserves both flexibility and reliability.
Solution Approach 2:
The patent implements a feedback mechanism where PE devices monitor IGMP join messages and respond by sending appropriate EVPN type-6 route advertisements. This feedback loop ensures that multicast traffic is properly routed to the DF device based on actual host joining behavior, maintaining both operational flexibility and delivery reliability.
3Reliability
If multiple PE devices handle multicast traffic, then network redundancy is improved, but traffic forwarding complexity increases
Solution Approach 1:
The patent segments the complex multicast forwarding task into distinct roles: DF devices handle traffic forwarding while non-DF devices handle traffic attraction and advertisement. This role segmentation simplifies the overall system complexity while maintaining redundancy, as each device has a clear, simplified function rather than all devices needing to perform all forwarding operations.
Solution Approach 2:
The patent makes PE devices universal by enabling them to perform both traffic attraction (through IGMP processing) and traffic advertisement (through EVPN type-6 routes), while only the elected DF performs actual forwarding. This multi-functionality allows any PE device to participate in redundancy without each device needing complex forwarding logic, simplifying individual device complexity while improving overall network redundancy.
Data Source
AI summary
Embodiments of the present disclosure relate to assisting forwarding of multicast traffic over Ethernet Virtual Private Network (EVPN) from a multicast source to a host multi-homed to multiple provider edge (PE) devices. Embodiments are based on the inclusion of an Ethernet Segment Identification (ESI) to EVPN type-6 routes advertised by PE devices which received a multicast Join message. Other PE devices receiving such routes are able to determine whether they belong to the ES identified by the ESI and to determine whether they are designated forwarders (DFs) for the host. Furthermore, PE devices which are the DFs are configured to re-originate the EVPN type-6 routes, i.e. re-send the advertisements, indicating themselves as DFs. This ensures that a remote PE device associated with the multicast source will also send multicast traffic to such DF PE devices, which, in turn, would allow the multicast traffic to successfully reach the host.