| Internet-Draft | Per multicast flow Designated Forwarder | July 2023 |
| Sajassi, et al. | Expires 11 January 2024 | [Page] |
[RFC7432] describes mechanism to elect designated forwarder (DF) at the granularity of (ESI, EVI) which is per VLAN (or per group of VLANs in case of VLAN bundle or VLAN-aware bundle service). However, the current level of granularity of per-VLAN is not adequate for some applications.[RFC8584] improves base line DF election by introducing HRW DF election. [RFC9251] introduces applicability of EVPN to Multicast flows, routes to sync them and a default DF election. This document is an extension to HRW base draft [RFC8584] and further enhances HRW algorithm for the Multicast flows to do DF election at the granularity of (ESI, VLAN, Mcast flow).¶
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EVPN based All-Active multi-homing is becoming the basic building block for providing redundancy in next generation data center deployments as well as service provider access/aggregation networks. [RFC7432] defines the role of a designated forwarder as the node in the redundancy group that is responsible to forward Broadcast, Unknown unicast, Multicast (BUM) traffic on that Ethernet Segment (CE device or network) in All-Active multi-homing.¶
The default DF election mechanism allows selecting a DF at the granularity of (ES, VLAN) or (ES, VLAN bundle) for BUM traffic. While [RFC8584] improve on the default DF election procedure, some service provider residential applications require a finer granularity, where whole multicast flows are delivered on a single VLAN.¶
(Multicast sources)
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+---+
|CE4|
+---+
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+-----+-----+
+------------| PE-1 |------------+
| | | |
| +-----------+ |
| |
| EVPN |
| |
| |
| (DF) (NDF)|
+-----------+ +-----------+
| |EVI-1| | | |EVI-1| |
| PE-2 |------------------------| PE-3 |
+-----------+ +-----------+
AC1 \ / AC2
\ /
\ ESI-1 /
\ /
\ /
+---------------+
| CE2 |
+---------------+
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(Multiple receivers)
Figure 1: Multi-homing Network of EVPN
for IPTV deployments
¶
Consider the above topology, which shows a typical residential deployment scenario, where multiple receivers are behind an all-active multihoming segments. All of the multicast traffic is provisioned on EVI-1. Assume PE-2 get elected as DF. According to [RFC7432], PE-2 will be responsible for forwarding multicast traffic to that Ethernet segment.¶
In this document, we propose an extension to the HRW base draft to allow DF election at the granularity of (ESI, VLAN, Mcast flow) which would allow multicast flows to be better distributed among redundancy group PEs to share the load.¶
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119] .¶
With respect to EVPN, this document follows the terminology that has been defined in [RFC7432] and [RFC4601] for multicast terminology.¶
[RFC8584] defines an extended community, which would be used for PEs in redundancy group to reach a consensus as to which DF election procedure is desired. A PE can notify other participating PEs in redundancy group about its willingness to support Per multicast flow base DF election capability by signaling a DF election extended community along with Ethernet-Segment Route (Type-4). The current proposal extends the existing extended community defined in [RFC8584]. This draft defines new a DF type.¶
DF type (1 octet) - Encodes the DF Election algorithm values (between 0 and 255) that the advertising PE desires to use for the ES.¶
When a PE receives the ES Routes from all the other PEs for the ES, it checks if all of other PEs have advertised their desire to proceed by Per multicast flow DF election. If all peering PEs have done so, it performs DF election based on Per multicast flow procedure. But if:¶
it MUST be considered as an indication to support of only Default DF election [RFC7432] and DF election procedure in [RFC7432] MUST be used.¶
This document is an extension of [RFC8584], so this draft does not repeat the description of HRW algorithm itself.¶
EVPN PE does the discovery of redundancy groups based on [RFC7432]. If redundancy group consists of N peering EVPN PE nodes, after the discovery all PEs build an unordered list of IP address of all the nodes in the redundancy group. The procedure defined in this draft does not require the list of PEs to be ordered. Address [i] denotes the IP address of the [i]th EVPN PE in redundancy group where (0 < i <= N ).¶
The DF is the PE who has maximum weight for (S, G, V, Es) where¶
Address[i] is address of the ith PE. The PEs IP address length does not matter as only the lower-order 31 bits are modulo significant.¶
Weight¶
Digest¶
The DF is the PE who has maximum weight for (G, V, Es) where¶
Address[i] is address of the ith PE. The PEs IP address length does not matter as only the lower-order 31 bits are modulo significant.¶
Weight¶
Digest¶
Per multicast DF election procedure would be applicable only when host behind Attachment Circuit (of the Es) start sending IGMP membership requests. Membership requests are synced using procedure defined in [RFC9251], and each of the PE in redundancy group can use per flow DF election and create DF state per multicast flow. The HRW DF election "Type 1" procedure defined in [RFC8584] MUST be used for the Es DF election and SHOULD be performed on Es even before learning multicast membership request state. This default election procedure MUST be used at port level but will be overwritten by Per flow DF election as and when new membership request state are learnt.¶
Multicast Source
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+---------+
+--------------+ PE-4 +--------------+
| | | |
| +---------+ |
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| EVPN CORE |
| |
| |
| |
+---------+ +---------+ +---------+
| PE-1 +--------+ PE-2 +---------+ PE-3 |
| EVI-1 | | EVI-1 | | EVI-1 |
+---------+ +---------+ +---------+
|__________________|___________________|
AC-1 ESI-1 | AC-2 AC-3
+---------+
| CE-1 |
| |
+---------+
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Multicast Receivers
Figure-2 : Multihomed network
¶
Figure-2 shows multihomed network. Where EVPN PE-1, PE-2, PE-3 are multihomed to CE-1. Multiple multicast receivers are behind all active multihoming segment.¶
When a receiver starts sending membership requests for (s1,g1), where s1 is multicast source address and g1 is multicast group address, CE-1 could hash membership request (IGMP join) to any of the PEs in redundancy group. Let's consider it is hashed to PE-2. [RFC9251] defines a procedure to sync IGMP join state among redundancy group of PEs. Now each of the PE would have information about membership request (s1,g1) and each of them run DF election procedure Section 4.1 to elect DF among participating PEs in redundancy group. Consider PE-2 gets elected as DF for multicast flow (s1,g1).¶
There are multiple triggers which can cause DF re-election. Some of the triggers could be¶
This document does not provide any new mechanism to handle DF re-election procedure. It uses the existing mechanism defined in [RFC7432]. Whenever either of the triggers occur, a DF re-election would be done. and all of the flows would be redistributed among existing PEs in redundancy group for ES.¶
The same Security Considerations described in [RFC7432] are valid for this document.¶
Allocation of DF type in DF extended community for EVPN.¶
Authors would like to acknowledge helpful comments and contributions of Luc Andre Burdet.¶