



BESS WG                                                       S. Dikshit
Internet-Draft                                                Aruba, HPE
Intended status: Standards Track                                V. Joshi
Expires: 28 January 2026                            Oracle India Pvt Ltd
                                                            27 July 2025


                             All PEs as DF
                  draft-saumvinayak-bess-all-df-bum-09

Abstract

   The Designated forwarder concept is leveraged to prevent looping of
   BUM traffic into tenant network sourced across NVO fabric for
   multihoming deployments.  [RFC7432] defines a preliminary approach to
   select the DF for an ES,VLAN or ES,Vlan Group, panning across
   multiple NVE's.  [RFC8584] makes the election logic more robust and
   fine grained by inculcating fair election of DF handling most of the
   prevalent use-cases.  This document presents a deployment problem and
   a corresponding solution which cannot be easily resolve by rules
   mentioned in [RFC7432] and [RFC8584].  It involves redundant firewall
   deployment on disparate overlay sites connected over WAN.  The
   requirement is to allow reachability, ONLY, to the local firewall,
   unless there is an outage.  In case of outage the reachability can be
   extended to remote site's firewall over WAN.

Status of This Memo

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   This Internet-Draft will expire on 28 January 2026.

Copyright Notice

   Copyright (c) 2025 IETF Trust and the persons identified as the
   document authors.  All rights reserved.




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   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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Table of Contents

   1.  Important Terms . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Requirements Language . . . . . . . . . . . . . . . . . . . .   3
   4.  Problem Description . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Problem Example . . . . . . . . . . . . . . . . . . . . .   4
   5.  Solution(s) . . . . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Sending All PEs are DF mode . . . . . . . . . . . . . . .   5
     5.2.  Receive All PEs are DF mode . . . . . . . . . . . . . . .   5
     5.3.  Example of algorithm  . . . . . . . . . . . . . . . . . .   6
   6.  Interoperability with other Algos . . . . . . . . . . . . . .   6
   7.  Backward Compatibility  . . . . . . . . . . . . . . . . . . .   6
   8.  Impact on Local Bias  . . . . . . . . . . . . . . . . . . . .   6
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   11. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   7
     12.2.  Informative References . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Important Terms

   DF: Designated Forwarder as defined in [RFC7432].

   VTEP: Virtual Tunnel End Point or Vxlan Tunnel End Point

2.  Introduction

   The Designated forwarder concept is leveraged to prevent looping of
   BUM traffic into tenant network sourced across NVO fabric for
   multihoming deployments.  [RFC7432] defines a preliminary approach to
   select the DF for an ES,VLAN or ES,Vlan Group, panning across
   multiple NVE's.  [RFC8584] makes the election logic more robust and
   fine grained by inculcating fair election of DF handling most of the
   prevalent use-cases.  This document presents a deployment problem and
   a corresponding solution which cannot be easily resolve by rules
   mentioned in [RFC7432] and [RFC8584].  It involves redundant firewall



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   deployment on disparate overlay sites connected over WAN.  The
   requirement is to allow reachability, ONLY, to the local firewall,
   unless there is an outage.  In case of outage the reachability can be
   extended to remote site's firewall over WAN.

3.  Requirements Language

   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].

   When used in lowercase, these words convey their typical use in
   common language, and they are not to be interpreted as described in
   [RFC2119].

4.  Problem Description

   It's a typical deployment case of Firewall devices, also configured
   as default gateway for NVO fabric.  The default gateways inturn
   redirects traffic to firewalls over a shared vlan.  This example, for
   simplicity, assumes the former case wherein firewall is also
   configured as default gateway for all VLANs on the site (SITE-1 and
   SITE-2).

   All PEs(Vtep1 and Vtep2 in below example) in the diagram are attached
   to same ES and both intend to act act as DF for the broadcast domain
   (BD-1) for their respective sites.  As already mentioned, this is a
   typical case of firewall-gateways (active/active) across fabrics
   (sites).  The preferred firewall-gateway is the one local to the
   site.  All ARP broadcast request generated for the gateway are
   directed to the local firewall and NOT to the remote one.

   Whereas, upon failure of the local firewall, all packets orginating
   from the affected site, including broadcast packets like ARP
   requests, need to be redirected (over WAN, via DCI/VPN) towards the
   remote site firewall.  The firewall-device is connected to it's
   first-hop vtep over the same bridge-domain and same ESI across all
   sites.

   All in all, it's an emulated multi-homing scenario.  This is a
   scenario of firewall devices hosting same(IP and MAC) credentials.










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4.1.  Problem Example

   The following details out the problem further.  There are two sites,
   SITE-1 and SITE-2 in the below diagram.  Traffic (including BUM)
   generated by Host1 (in SITE-1) (for a bridge-domain) should run
   through site-local firewall instance (firewall_1) preferably and
   should not be leaked to the remote sites.

   Only in case of local-outage, the traffic should be send across over
   WAN to the remote firewall (firewall_2).  Same should apply to
   traffic generated by Host2 (in SITE-2), wherein, it should ONLY run
   through the local firewall (firewall_2), unless there is local-
   firewall.  In that case should go over the WAN towards remote sites
   firewall, firewall_1.

   Vtep1 and/or Vtep2 learn the firewall MAC (MAC_F) as a local host
   learning and also from the remote vteps, Vtep2 and Vtep1,
   respectively.  But since both the learnings are over the same ESI, it
   should not lead to MAC move.  Cometh the local firewall failure,
   Vtep1 or Vtep2 should start redirecting the traffic to remote SITE
   firewall, firewall_2 and firewall_1, respectively.  Any ARP request
   (BUM traffic) for firewall credentials landing at either Vtep1 or
   Vtep2 from the remote fabric, should then be flooded to network or
   LAN towards the locally connected firewall.

            SITE-1          |          SITE-2
   ------------------------------------------------------
         Host1                            Host2
          \                                 /
           \                               /
   Vtep_host1                             Vtep_host2
            |                             |
            |       [ EVPN-fabric ]       |
            |                             |
        Vtep1============WAN==============Vtep2
           /                                 \
          /                                   \
   Firewall _1                           Firewall_2
     (MAC_F)                              (MAC_F)


          Figure 1: Figure 1: Active-Active Firewall Across Sites









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5.  Solution(s)

   The control plane part of the solution can be leveraged from the 'DF
   Election Extended Community' described in [RFC8584].  Since the
   requirement is to ensure all the PEs attached to ESI, forward the BUM
   traffic arriving from hosts connected to local NVO fabric towards the
   Attachment circuits (ACs), that are configured over the ES for a BD
   (broadcast or bridge domain) mapped to Vlan or bundle of Vlans.  As
   explained in the above section, that this is a case, where PEs are in
   disparate networks and the ACs behind them are not connected to
   common physical device, even though they are part of the same ES.
   The diagram gives an overview of the network or deployment in
   contention.

   This document proposes a new mode of DF-election called 'ALL-PEs-DF',
   where-in, all the pariticipating PEs, intend to play DF role for
   subset of vlan(s) enabled on an ESI.  This requires "DF Election
   Extended Community" to carry this information with the ES route to
   indicate it to remote PEs.  This ensures all PEs receiving BUM
   traffic over NVO fabric destined to ESI, BD, SHOULD flood it on the
   associated ES on the access/tenant side.  A PE device MAY be
   explicitly configured to choose the ALL-PEs-DF mode.

5.1.  Sending All PEs are DF mode

   The All-PEs-DF mode is used as follows:

   (1)  PEs configured to use ALL-PEs-DF mode SHOULD set "DF Alg"
        algorithm field in 'DF Election Extended Community' to
        appropriate value.

   (2)  This document proposes value TBD for All-PEs-DF mode, as values
        '0', '1' and '2' are already reserved for usage.

   (3)  This algorithm is agnostic to the values carried in 'Bitmap' but
        does not discounts any use-case(s) in future which may need
        extra information carried in 'Bitmap' along with All-PEs-DF
        mode.

5.2.  Receive All PEs are DF mode

   When a PE receives the ES routes from all the other PEs, for the ES
   in question, carrying the ALL-PEs-DF mode set, in 'DF Election
   Extended Community', it SHOULD, check to see if all the
   advertisements have the Extended Community with 'All-DF-mode' set as
   'DF Algo'.  If yes, then PE SHOULD ignore the 'Bitmap' and 'Rsvd'
   field in the extended community.  As also mentioned in [RFC8584] ,
   even if, a single advertisement for Route Type 4 is received without



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   the locally configured DF Alg and capability, the default DF election
   algorithm MUST be used as mandated in [RFC7432].

5.3.  Example of algorithm

   The BGP-EVPN control plane extension, as mentioned in this document,
   helps in resolving the problem decsribed in Section 4.  If PEs, Vtep1
   and Vtep2 are configured to use ALL-PEs-DF mode, then any BUM traffic
   from respective local hosts Host1/Host2 connected to the EVPN fabric,
   SHOULD get redirected towards the AC for the ESI,Vlan to which the
   firewall_1/firewall_2 (respectively) is attached.  For example the
   arp-request for the Firewall IP will be honored by the Firewall_1
   behind the Vtep1 which receives the ARP-request.  Whereas, when Vtep2
   receives the arp-request it will be honored by Firewall_2.  Vtep1 and
   Vtep2 will publish the arp-request in their respective ACs attached
   to the firewall on which Vlan,ESI is configured and enabled

6.  Interoperability with other Algos

   Since All-DF-algo is special mode and not exactly an algorithm, which
   requires the participation of all PEs for an ESI, VLAN.  Hence, even
   if one PE publishes an algo which is NOT "All-DF-mode", other PEs
   SHOULD revert back to default algorithm.  The reason being that, if
   there are PE1, PE2, PE3 and PE4 in contention.  PE1 and PE2 publishes
   DF Algo 'ALL-PEs-DF', PE3 publishes '0' and PE4 publishes '1'.  Once
   this mismatch is perceived, all PEs SHOULD try and converge towards
   the default mode.  An admin intervention may be required to achieve
   the same or to converge on any other supported 'DF Algo'.

7.  Backward Compatibility

   As prescribed in [RFC8584], PEs not supporting (hence not publishing)
   'ALL-PEs-DF', SHOULD ignore the processing of the 'DF Election
   Extended Community' and SHOULD indulge in DF-election using the
   default aglorithm mentioned in [RFC7432].  The PEs configured with
   this new alogrithm (hence publishing it), if receive Route Type 4
   without 'DF Election Extended Community', SHOULD also revert back to
   default algorithm.  If PEs receive Route Type 4 with another
   algorithm published in 'DF Election Extended Community', then it
   should follow procedures prescribed in Section 6.

8.  Impact on Local Bias

   There is no impact on the local-bias handling, as the PE receiving
   the BUM from access side over {ESI, VLAN} and relays it to other PEs
   that published {ESI, VLAN} in Route Type 4; the receiving side PEs
   will not relay it to EVPN fabric nor will they redirect it to same
   ESI configured with same VLAN on the access/tenant side.



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9.  Security Considerations

   This document inherits all the security considerations discussed in
   [RFC7432] and [RFC8584].

10.  IANA Considerations

   IANA considerations yet to be concluded as the value of mode proposed
   here is still under discussion.

11.  Acknowledgements

   The authors want to thank Jorge Rabadan and Luc Andre for their
   valuable comment.  They also advised on other potential solution
   while helping in paraphrasing the problem statement.

12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997,
              <http://www.rfc-editor.org/rfc/rfc2119.txt>.

12.2.  Informative References

   [RFC7348]  Mahalingam, M., "Virtual eXtensible Local Area Network
              (VXLAN): A Framework for Overlaying Virtualized Layer 2
              Networks over Layer 3 Networks", RFC 7348, August 2014,
              <http://www.rfc-editor.org/rfc/rfc7348.txt>.

   [RFC7432]  Sajassi, A., "BGP MPLS-Based Ethernet VPN", RFC 7432,
              February 2015,
              <http://www.rfc-editor.org/rfc/rfc7432.txt>.

   [RFC8584]  Rabadan, J., "Framework for Ethernet VPN Designated
              Forwarder Election Extensibility", RFC 8584, April 2019,
              <http://www.rfc-editor.org/rfc/rfc8584.txt>.

   [RFC9014]  Rabadan, J., "Interconnect Solution for Ethernet VPN
              (EVPN) Overlay Networks", RFC 9014, May 2021,
              <http://www.rfc-editor.org/rfc/rfc9014.txt>.

Authors' Addresses

   Saumya Dikshit
   Aruba Networks, HPE
   Mahadevpura



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   Bangalore 560 048
   Karnataka
   India
   Email: saumya.dikshit@hpe.com


   Vinayak Joshi
   Oracle India Pvt Ltd
   Bangalore
   Karnataka
   India
   Email: vinayak.j.joshi@oracle.com







































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