Internet DRAFT - draft-malhotra-bess-evpn-centralized-anycast-gw
draft-malhotra-bess-evpn-centralized-anycast-gw
BESS WorkGroup N. Malhotra, Ed.
Internet-Draft K. Ananthamurthy
Intended status: Standards Track A. Sajassi
Expires: 5 September 2024 L. Krattiger
Cisco Systems
J. Rabadan
Nokia
4 March 2024
Centralized Anycast Gateway in Ethernet VPN(EVPN)
draft-malhotra-bess-evpn-centralized-anycast-gw-01
Abstract
EVPN Integrated Routing and Bridging (IRB) fabrics provide a flexible
and extensible method for Layer-2 and Layer-3 overlay network
connectivity. [EVPN-IRB] defines operation for symmetric and
asymmetric EVPN IRB using distributed anycast gateway architecture
(DAG). In a DAG architecture, both bridging and first-hop routing
functions for overlay subnets are located on leaf PEs, with first-hop
routing provided by a distributed anycast gateway provisioned across
the leaf PEs. This document describes an architecture and operation
for EVPN Centralized Anycast Gateway (CAG), which allows the first-
hop routing function for overlay subnets to be centralized on
designated IRB GWs while the bridging function is still located on
the leaf PEs. The documents also covers trade-offs of deploying a
CAG as compared with DAG. It further describes operation for inter-
op between CAG and DAG based EVPN-IRB network overlays.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 5 September 2024.
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Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements Language and Terminology . . . . . . . . . . . . 5
3. Control Plane Operation . . . . . . . . . . . . . . . . . . . 5
3.1. Requirements for L2 PE . . . . . . . . . . . . . . . . . 5
3.2. Requirements for CAG PE . . . . . . . . . . . . . . . . . 6
4. Data Plane Operation . . . . . . . . . . . . . . . . . . . . 7
4.1. Intra-Subnet Bridging . . . . . . . . . . . . . . . . . . 7
4.2. Inter-Subnet Routing . . . . . . . . . . . . . . . . . . 7
5. MAC/IP Mobility . . . . . . . . . . . . . . . . . . . . . . . 8
6. CAG deployment models . . . . . . . . . . . . . . . . . . . . 8
6.1. CAG Placement as an Interconnect . . . . . . . . . . . . 8
6.1.1. Control Plane . . . . . . . . . . . . . . . . . . . . 10
6.1.2. Tunnel Adjacencies . . . . . . . . . . . . . . . . . 10
6.1.3. Split Horizon domains . . . . . . . . . . . . . . . . 11
6.1.4. Data Plane . . . . . . . . . . . . . . . . . . . . . 11
6.1.4.1. Inter-subnet - L2 fabric to Symmetric IRB
fabric . . . . . . . . . . . . . . . . . . . . . . 11
6.1.4.2. Inter-subnet - Symmetric IRB fabric to L2
fabric . . . . . . . . . . . . . . . . . . . . . . 11
6.1.4.3. Intra-subnet - Symmetric IRB fabric to L2 fabric
unicast . . . . . . . . . . . . . . . . . . . . . . 12
6.1.4.4. Intra-subnet - L2 fabric to Symmetric IRB fabric
unicast . . . . . . . . . . . . . . . . . . . . . . 12
6.1.4.5. Intra-subnet - Symmetric IRB fabric to L2 fabric
BUM . . . . . . . . . . . . . . . . . . . . . . . . 12
6.1.4.6. Intra-subnet - L2 fabric to Symmetric IRB fabric
BUM . . . . . . . . . . . . . . . . . . . . . . . . 12
6.2. CAG Placement on DAG L2/L3PEs . . . . . . . . . . . . . . 12
6.2.1. Dual role of DAGs . . . . . . . . . . . . . . . . . . 14
6.2.2. Operation on CAG as L2/L3 GW . . . . . . . . . . . . 14
6.2.3. FHG Load-sharing and resiliency . . . . . . . . . . . 14
6.2.4. FHG Localization . . . . . . . . . . . . . . . . . . 14
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6.2.5. Comparison between the approaches . . . . . . . . . . 14
6.2.5.1. Operational simplicity . . . . . . . . . . . . . 14
6.2.5.2. Scalability . . . . . . . . . . . . . . . . . . . 15
7. Operational Considerations . . . . . . . . . . . . . . . . . 15
8. Security Considerations . . . . . . . . . . . . . . . . . . . 15
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 15
12. Normative References . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
In a CAG routing architecture, overlay endpoints connect to Layer-2
EVPN gateways that provide VPN bridging function for overlay subnets.
This VPN bridging function enables intra-subnet flows across the
overlay while routing function between end-points in different
subnets and to/from end-points external to the fabric is located on
designated L2+L3 (IRB) gateways.
First-hop routing for each overlay subnet is deployed using a subnet
Anycast GW that is hosted on one or more designated IRB GW nodes. A
key attribute that defines this architecture is that the first-hop
routing function for an overlay subnet is decoupled from the EVPN
leaf that only provides intra-subnet bridging service for that
subnet. This decoupling in-turn results in first-hop routing for
overlay endpoints being "centralized" on designated IRB nodes. Note
that the Anycast GW for each subnet is still distributed across these
"centralized" IRB GW nodes.
It is common to deploy first-hop Anycast routing for all overlay
subnets in a fabric on the same set of IRB nodes. While not
necessarily required, as is covered later in the document, this is
often done for operational simplicity and optimal routing. It is
also common for this first-hop routing function to be hosted on
border nodes that also act as interconnect GWs to external L2 or L2/
L3 domains. Optionally, the CAG IRB nodes may also have directly
connected end-points.
CAG architecture essentially uses a Layer-2 EVPN overlay and first-
hop routing operation on CAG is identical to asymmetric routing as
defined in [EVPN-IRB]. Figure below shows a reference L2 fabric with
CAG topology that is also used to illustrate the procedures specified
in later sections.
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+-----------------------------------------------------------------+
| L2/L3 Interconnect to external domains |
| | |
| | |
| | |
| | CAGs with Anycast IP |
| +-----------------------+ |
| | +------+ +------+ | IRB1: [IP10, M10] |
| | | CAG1 | | CAG2 | | IRB2: [IP20, M20] |
| | +------+ +------+ | IRB3: [IP30, M30] |
| +-----------------------+ |
| |
| |
| |
| +---------------+ |
| | | |
| | EVPN | |
| | | |
| +---------------+ |
| |
| |
| |
| |
| +------+ +------+ +------+ +------+ +------+ +------+ |
| |L2 PE1| |L2 PE2| |L2 PE3| |L2 PE4| |L2 PE5| |L2 PE6| |
| +------+ +------+ +------+ +------+ +------+ +------+ |
| \ / \ / \ / |
| \ / \ / \ / |
| \ / \ / \ / |
| +\---/+ +\---/+ +\---/+ |
| | \ / | | \ / | | \ / | |
| +--+--+ +--+--+ +--+--+ |
| | | | |
| | | | |
+-----------------------------------------------------------------+
| | |
EVI1 H11:[IP11, M11] H13:[IP13, M13]
EVI2 H21:[IP21, M21] H22:[IP22, M22]
EVI3 H31:[IP31, M31] H33:[IP33, M33]
Figure 1
* L2 PE1..L2 PE6 are L2-Only GWs.
* IRB1/IRB2/IRB3 are IRB interfaces on CAGs for EVI1, EVI2 and EVI3.
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* Hosts H11/H13 are in EVI1, H21/H22 are in EVI2 and H31/H33 are in
EVI3.
* CAG1 and CAG2 form a redundant anycast CAG pair for EVI1, EVI2,
and EVI3.
2. Requirements Language and Terminology
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].
* CAG: Centralized Anycast Gateway
* DAG: Distributed Anycast Gateway
* EVI: An EVPN instance spanning the Provider Edge (PE) devices
participating in that EVPN
* FHR: First Hop Router
* IRB: Integrated Routing and Bridging
* L2-GW: Layer-2 Only Gateway
* L2-Only GW: Layer-2 Only Gateway
3. Control Plane Operation
This section defines control plane procedures required on L2 PE and
CAG PE for a CAG architecture based deployment.
3.1. Requirements for L2 PE
* ARP/ND snooping MUST be enabled on L2-PEs. Locally connected host
IP and MAC is learnt by L2 PE via ARP/ND snooping and advertised
using EVPN RT-2 with a single label that represents the EVI. This
enables a significant simplification in CAG operation to avoid the
need for data plane learning and syncing of ARP/ND tables across
redundant CAGs.
* L2-PEs MUST handle ARP refreshes when MAC ages out or ARP ages out
in order to relearn the host MAC and IP to avoid traffic loss. If
a host does not respond to an ARP refresh, then the previously
advertised EVPN RT-2 by the L2-PE MUST be withdrawn. If the host
responds to host MAC/IP, then ARP MUST be refreshed. EVPN RT-2
SHOULD NOT be re-advertised
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* L2-PEs on receiving GW MAC/IP RT-2 from CAG, in addition to
installing the MAC in the MAC-VRF, MUST also install a GW MAC/IP
entry in the ARP/ND suppression cache. This enables L2-PEs to act
as a proxy for CAG by using the entry in the suppression cache to
respond to ARP requests from hosts for GW MAC/IP. If enabled,
this avoids flooding of ARP/ND requests across the fabric and
avoids duplicate ARP responses from redundant CAGs.
3.2. Requirements for CAG PE
* A set of redundant CAG PEs that act as the FHR for the same subnet
MUST be provisioned with the same anycast GW IP and MAC.
* For each subnet for which CAG is an FHR, CAG MUST advertise
Anycast GW MAC/IP using EVPN RT-2 with Default Gateway Extended
Community as defined in [RFC7432]. In Figure 1, CAG1/2 advertise
IRB1/2/3 MAC and IP using EVPN RT-2 with Default Gateway Extended
Community with nexthop as anycast IP.
* In case of VXLAN encapsulation, set of redundant CAG PEs
provisioned as FHR for a common set of subnets MAY advertise the
anycast GW MAC/IP RT-2 with an anycast VTEP IP as the next-hop.
This enables the GW MAC to be installed with a single BGP path on
L2 PEs and hence enables interworking with low end L2 devices that
may not be capable of MAC multi-pathing. It also results in a
much simplified solution that avoids a need for virtual ESI
provisioning on CAG PE as well as a need for MAC multi-pathing and
fast convergence procedures on CAG and L2 PEs. Note that this
anycast VTEP IP is solely for the purpose of GW MAC/IP RT-2
advertisement and all directly connected end-points (single-homed
or multi-homed) will continue to be advertised with a non-anycast
VTEP IP as the next-hop. ESI multi-homing procedures specified in
[RFC7432] apply as-is to directly connected end-points multi-homed
via ESI LAG.
* Upon receiving RT-2 advertisements from Egress EVPN L2-PE, CAG
MUST import MACs into MAC-VRFs, thus establishing Host MAC
reachability via Layer-2 EVPN encapsulation and tunnel to Egress
L2 PE. In Figure 1, L2-GW1/2 advertise RT-2 for hosts H11, H21
and H31. CAG MUST import M11, M21 and M31 in corresponding MAC-
VRFs. CAG will perform the Asymmetric IRB procedures defined in
[RFC9135] with IP-to-MAC binding resolved via respective
adjacency/next-hop table entry.
* It should be noted that reachability to a remote host layer-3
adjacency is still resolved by host MAC reachability via a Layer-2
VPN tunnel to the Egress L2-PE.
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4. Data Plane Operation
4.1. Intra-Subnet Bridging
Intra-subnet host to host flow is identical to that in symmetric or
asymmetric distributed anycast GW based IRB deployments as defined in
[EVPN-IRB]. When the ingress L2 PE receives a packet from its
locally attached host, it does a destination MAC lookup in its VLAN
which yields an L2 VPN and tunnel encapsulation towards the egress L2
PE. The ingress L2 PE then encapsulates the original packet and
sends to the egress L2 PE. Egress L2 PE decapsulates the packet and
does a destination MAC lookup in the local VLAN (MAC VRF) table
identified by the received L2 VPN label. This yields a local VLAN
Port. The egress L2GW then sends the decapsulated packet to the
port.
4.2. Inter-Subnet Routing
Inter-subnet host to host flow destined to default GW MAC is bridged
to CAG PE with the L2 VPN encapsulation learnt via default GW RT-2
from the CAG PE. CAG decapsulates the packet and does a destination
MAC lookup in the local MAC VRF identified by the received L2 VPN
encapsulation that results in my MAC. This yields the local IRB
interface. CAG then does a destination IP lookup in IP VRF attached
to the IRB interface. If the destination subnet is local/attached to
the CAG node, IP lookup yields a local host adjacency on the
destination subnet IRB interface. This results in host MAC rewrite,
followed by host MAC lookup that results in the packet being bridged
to the egress L2 PE with L2 VPN and tunnel encapsulation learnt via
RT-2 from egress L2 PE. On the egress L2 PE, packet is decapsulated,
local MAC VRF is resolved by the received L2 VPN encapsulation. The
packet is then bridged to the local host via local MAC VRF lookup.
If the destination subnet is not local to the CAG node, IP lookup
yields the destination subnet prefix that resolves via L3 VPN
encapsulation and tunnel to the next-hop CAG PE that is the FHR for
the destination subnet. Packet is hence routed to another CAG, where
the packet is decapsulated, received L3 VPN encapsulation resolves
the local IP VRF, and IP lookup now yields a local host adjacency on
the destination subnet IRB interface. Packet is then bridged to the
destination L2 PE with the L2 VPN encapsulation as described above.
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5. MAC/IP Mobility
GW MAC/IP route advertised by CAG MUST follow default gateway best
path selection procedures specified in [RFC7432bis] to ensure that GW
MAC is treated as static and is always preferred over any duplicate
host MAC across the L2 overlay. Beyond BGP best path selection,
forwarding implementations MUST ensure that a locally learnt
duplicate MAC will never overwrite the forwarding entry for the GW
MAC route. Hosts attached to L2-PEs follow existing mobility
procedures as defined in [RFC7432].
6. CAG deployment models
Fabrics with symmetric IRB are widely deployed. This section
discusses how a CAG architecture discussed in the earlier sections
may be deployed together with a symmetric IRB fabric with L2 and L3
overlays that extend across symmetric IRB and CAG based fabrics. Two
deployment models are discussed:
* CAG Placement as an Interconnect
* CAG Placement on DAG L2/L3PEs
6.1. CAG Placement as an Interconnect
In this model, CAG is placed as an interconnect or hub between the
Layer-2 fabric consisting of L2-PEs and the symmetric IRB fabric
consisting of L2/L3 PEs. CAG device essentially performs the CAG
function for hosts connected to L2 only fabric and in addition, also
performs an L2/L3 overlay interconnect function between the L2 only
fabric and the symmetric IRB fabric.
EVI1 H24:[IP24 M24]
EVI2 H14:[IP14,M14] H25:[IP25, M25] H15:[IP15]
| | |
+-----------------------------------------------------------------+
| | | | |
| | | | |
| +--+--+ +--+--+ | |
| | / \ | | / \ | | |
| +-----+ +-----+ | |
| / \ / \ | |
| / \ / \ | |
| / \ / \ | |
| +-----+ +-----+ +-----+ +-----+ +-----+ |
| | PE7 | | PE8 | | PE9 | | PE10| | PE11| |
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| +-----+ +-----+ +-----+ +-----+ +-----+ |
| |
| IRB1: [IP10, M10] |
| IRB2: [IP20, M20] |
| |
+-----------------------------------------------------------------+
Symmetric IRB Fabric
+-----------------------+ CAGs with Anycast IP as Interconnect
| +------+ +------+ | IRB1: [IP10, M10]
| | CAG1 | | CAG2 | | IRB2: [IP20, M20]
| +------+ +------+ | IRB3: [IP30, M30]
+-----------------------+
Layer-2 EVPN Fabric
+-----------------------------------------------------------------+
| |
| +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ |
| | PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 | |
| +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ |
| \ / \ / \ / |
| \ / \ / \ / |
| \ / \ / \ / |
| +\---/+ +\---/+ +\---/+ |
| | \ / | | \ / | | \ / | |
| +--+--+ +--+--+ +--+--+ |
| | | | |
| | | | |
+-----------------------------------------------------------------+
| | |
EVI1 H11:[IP11, M11] H13:[IP13, M13]
EVI2 H21:[IP21, M21] H22:[IP22, M22]
EVI3 H31:[IP31, M31] H33:[IP33, M33]
Figure 2
* IRB1/IRB2 are IRB interfaces on L2/L3 PEs PE7- PE10.
* PE11 is L3-only PE
* CAG pair consisting of CAG1/CAG2 is placed an Interconnect between
Layer-2 only and Symmetric IRB fabric.
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6.1.1. Control Plane
In addition to the control plane operation described in Section 3,
the following operations must be done at CAG to enable seamless
interworking between the fabrics.
* MAC/IP RT-2s learnt on CAGs from L2 PEs in the Layer-2 only EVPN
Fabric MUST be re-originated by all CAGs towards the L2/L3 PEs and
L3-only PEs in the Symmetric IRB Fabric with CAG as the tunnel
next-hop.
* MAC/IP RT-2s learnt on CAGs from L2 PEs in the Layer-2 only EVPN
Fabric MUST be re-originated by all CAGs towards the L2/L3 PEs and
L3-only PEs in the Symmetric IRB Fabric in symmetric IRB format
with both L2 and L3 VPN local labels. Essentially, these MAC-IP
routes are learnt from L2 PEs with only L2 label and re-originated
with locally provisioned or allocated L2 and L3 labels.
* MAC/IP RT-2s learnt from L2/L3 PEs in the Symmetric IRB fabric
MUST be re-originated towards the Layer-2 only fabric with CAG as
the tunnel next-hop.
* MAC/IP RT-2s learnt from L2/L3 PEs in the Symmetric IRB fabric and
re-originated towards the L2 PEs MAY have L3 label and L3 RTs
removed resulting in re-origination with only locally assigned L2
VPN label and L2 RTs. L2 PEs in the Layer-2 only fabric ignore
the L3 label and RTs if they are present.
6.1.2. Tunnel Adjacencies
This results in the following overlay tunnel adjacencies at CAG:
* L2 and L3 VPN tunnel adjacencies between CAG and L2/L3 PEs in
symmetric IRB fabric. In above topology, Layer-2 and Layer-3
tunnel adjacencies are formed between L2/L3 PEs PE7-PE10 and CAG.
* L3 VPN tunnel adjacencies between CAG and L3 only PEs in symmetric
IRB fabric. In above topology, Layer-3 tunnel adjacencies are
formed between L3-only PE11 and CAG.
* L2 VPN tunnel adjacencies between CAG and L2 PEs in L2 fabric. In
above topology, Layer-3 tunnel adjacencies are formed between L2
PEs PE1-PE6 and CAG.
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6.1.3. Split Horizon domains
CAG MUST consider the two fabrics as separate split horizon domains
and hence apply split-horizon procedures specified in [RFC9014]. As
a result, The BUM traffic from one domain is distributed to the other
domain. For e.g. ARP requests from symmetric IRB domain are
distributed to the Layer-2 domain and vice versa.
6.1.4. Data Plane
In addition to the data plane operation described in Section 4, the
following operations must be done at CAG to enable seamless
interworking between the fabrics.
6.1.4.1. Inter-subnet - L2 fabric to Symmetric IRB fabric
Intersubnet traffic is sent from host in the Layer-2 only fabric
destined to host IP attached to the symmetric IRB fabric and GW MAC
on CAG. The L2 PE performs a Gateway MAC lookup in MAC-VRF and
tunnels traffic to CAG with L2 VPN label and tunnel encapsulation to
CAG. CAG performs a GW MAC lookup in the MAC-VRF followed by an IP
lookup in IP-VRF. This results a route to the L2/L3 PE next-hop.
CAG tunnels the packet to L2/L3 PE with L3 VPN label and tunnel
encapsulation to L2/L3 PE. L2/L3 PE performs a lookup in the IP-VRF
which results in an adjacency to the destination host, using which
traffic is routed to the attached destination host.
In the topology above, traffic sourced from H11 destined to H24 is
sent to M10 and IP24. PE1/2 perform a lookup of M10 and tunnel
traffic to CAG1/2. CAG1/2 perform a lookup of M10 in the MAC-VRF,
followed by lookup of IP24 in IP-VRF, which results in a route to
PE7/8. CAG1/2 tunnel Layer-3 traffic to PE7/8. PE7/8 perform a
lookup of IP24 in IP-VRF, which results in adjacency to H24. PE7/8
bridge traffic to H24 destined to M24.
6.1.4.2. Inter-subnet - Symmetric IRB fabric to L2 fabric
Intersubnet traffic is sent from host in symmetric IRB fabric
destined to host IP attached to Layer-2 only fabric and DAG MAC on
L2/L3 PE. L2/L3 PE performs GW MAC lookup in MAC-VRF followed by an
IP lookup in the IP-VRF. This results in a route to the CAG next-
hop. L2/L3 PE tunnels the packet to the CAG with L3 VPN label and
tunnel encapsulation to CAG. CAG performs destination IP lookup in
IP-VRF resolved by L3 VPN label, which results in an adjacency to the
destination host. CAG performs a MAC lookup of destination host MAC
and tunnels traffic to L2 PE next-hop with L2 label and tunnel
encapsulation to L2 PE. L2-only PE performs a MAC lookup in the MAC-
VRF and bridges the packet to the destination host.
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In the topology above, traffic sourced from H24 destined to H11 is
sent to M20 and IP11. PE7/8 perform a lookup of M20 followed by IP11
lookup in IP-VRF and tunnels Layer-3 traffic to CAG. CAG performs a
lookup of IP11 in IP-VRF, which results in adjacency to H11. CAG
perform lookup M11 and tunnels traffic to PE1/2. PE1/2 perform
lookup of M11 and bridge traffic to H11.
6.1.4.3. Intra-subnet - Symmetric IRB fabric to L2 fabric unicast
6.1.4.4. Intra-subnet - L2 fabric to Symmetric IRB fabric unicast
6.1.4.5. Intra-subnet - Symmetric IRB fabric to L2 fabric BUM
6.1.4.6. Intra-subnet - L2 fabric to Symmetric IRB fabric BUM
6.2. CAG Placement on DAG L2/L3PEs
In this placement approach, all L2/L3 PEs in the Symmetric IRB fabric
that locally host an EVI assume an additional role of a CAG for hosts
in that EVI that are attached to L2 only fabric.
EVI1 H14:[IP14 M14]
EVI2 H24:[IP24,M24] H25:[IP25, M25]
| |
+----------------------------------------------------------------+
| | | |
| | | |
| +--+--+ +--+--+ |
| | / \ | | / \ | |
| +-----+ +-----+ |
| / \ / \ |
| / \ / \ |
| / \ / \ |
| +-----+ +-----+ +-----+ +-----+ |
| | PE7 | | PE8 | | PE9 | | PE10| |
| | CAG | | CAG | | CAG | | CAG | |
| +-----+ +-----+ +-----+ +-----+ |
| |
| IRB1: [IP10, M10] |
| IRB2: [IP20, M20] |
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| IP-VRF |
+----------------------------------------------------------------+
Symmetric IRB Fabric/CAG pair
+---------------+
| |
| EVPN |
| |
+---------------+
Layer-2 EVPN Fabric
+------------------------------------------------------------------------+
| |
| +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ |
| | PE1 | | PE2 | | PE3 | | PE4 | | PE5 | | PE6 | |
| +-----+ +-----+ +-----+ +-----+ +-----+ +-----+ |
| \ / \ / \ / |
| \ / \ / \ / |
| \ / \ / \ / |
| +\---/+ +\---/+ +\---/+ |
| | \ / | | \ / | | \ / | |
| +--+--+ +--+--+ +--+--+ |
| | | | |
| | | | |
+------------------------------------------------------------------------+
| | |
EVI1 H11:[IP11, M11] H13:[IP13, M13]
EVI2 H21:[IP21, M21] H22:[IP22, M22]
Figure 3
* Symmetric IRB Fabric is EVPN fabric consisting of L2/L3 PEs and
L3-only PEs operating in Symmetric IRB mode.
* PE7- PE10 are L2/L3 PEs and participate in EVI/EVI2 and host IP-
VRF which has subnets for EVI1/EVI2.
* PE7 - PE10 are L2/L3 PEs and also CAG to Layer-2 only fabric.
* IRB1/IRB2 are IRB interfaces on PE7/CAG - PE10/CAG.
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6.2.1. Dual role of DAGs
In this placement method, each DAG in the symmetric IRB fabric plays
a dual role of DAG and CAG. Thus, the CAG for an EVI comprises of
each L2/L3 PE DAG node in the symmetric IRB fabric that hosts the
EVI. Such a placement results in forming a full mesh of tunnels
between the L2-only PEs and every DAG/CAG.
6.2.2. Operation on CAG as L2/L3 GW
The operation on the CAG remains the same as described in section FIX
and MUST be performed by each member of the CAG pair that hosts the
EVI.
6.2.3. FHG Load-sharing and resiliency
As the CAG pair is comprised of all L2/L3 PEs that host the EVI, the
FHG function can be load-shared across a larger number of CAGs. As
all members of the pair advertise the GW MAC/IP to all the L2-only
PEs, this opens up an opportunity on the L2-only PEs for creating a
scheme optimal load-sharing, load-balancing, failure resiliency and
achieving faster convergence during failure events. As an example,
the L2-only PEs may choose to pick one CAG per EVI as the FHG,
resulting in load-sharing traffic across the pair or the L2-only PEs
may pick a subset of CAGs for per EVI as FHGs which provides failure
resiliency, faster convergence in failure events while providing
load-sharing across the members of the CAG pair.
6.2.4. FHG Localization
If the use case requires FHG function to be localized on a subset of
members of the CAG pair for a given EVI, only this subset MUST be
configured to advertise the GW MAC/IP to the L2-only PEs. Thus
forming two sub-clusters within the CAG cluster. The subset which
does not advertise the GW MAC/IP form a CAG non-FHG sub-cluster
whereas, the other cluster forms a CAG FHG sub-cluster. As the non-
FHG cluster does not advertise GW MAC/IP, it does not attract inter-
subnet traffic from L2-only PEs. Both sub-clusters MUST perform the
operations as described in section FIX.
6.2.5. Comparison between the approaches
6.2.5.1. Operational simplicity
In the full mesh placement approach, the operation on CAGs is largely
simplified as re-origination of routes as described in section FIX is
not required and thus, does not require and additional functionality
on the CAG for seamless interworking between the fabrics.
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6.2.5.2. Scalability
The interconnect placement approach requires re-origination of routes
by CAG between the two fabrics. This results in logically separated
domains. As a result, segregated tunnel domains are be created, thus
making this approach more scalable. In the full mesh placement, as a
full mesh of tunnels is formed between the L2-only PEs and CAG, thus
making this approach less scalable.
7. Operational Considerations
None
8. Security Considerations
Security considerations discussed in [RFC7432] and [RFC9135] apply to
this document.
9. IANA Considerations
10. Acknowledgements
Authors would like to thank Aparna Pattekar for spending considerable
time on and contributing multiple sections to rev0 of this draft.
11. Contributors
Aparna Pattekar
Cisco Systems
Email: apjoshi@cisco.com
12. Normative References
[EVPN-IRB] Sajassi, A., Salam, S., Samil, S., Drake, J., Rabadan, J.,
and , "Integrated Routing and Bridging in EVPN", Work in
Progress, Internet-Draft, Integrated Routing and Bridging
in EVPN, 26 July 2021,
<https://www.rfc-editor.org/info/rfc9135>.
[EXTENDED-MOBILITY-EVPN-IRB]
Malhotra, N., Sajassi, A., Pattekar, A., Rabadan, J.,
Lingala, A., Drake, J., and , "Extended Mobility
Procedures for EVPN-IRB", Work in Progress, Internet-
Draft, draft-ietf-bess-evpn-irb-extended-mobility-17, 16
October 2023, <https://www.ietf.org/archive/id/draft-ietf-
bess-evpn-irb-extended-mobility-17.txt>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC7432] Sajassi, A., Ed., Aggarwal, R., Bitar, N., Isaac, A.,
Uttaro, J., Drake, J., and W. Henderickx, "BGP MPLS-Based
Ethernet VPN", RFC 7432, DOI 10.17487/RFC7432, February
2015, <https://www.rfc-editor.org/info/rfc7432>.
[RFC7432bis]
Sajassi, A., Brudet, L.A., Rabadan, J., Drake, J., and ,
"BGP MPLS-Based Ethernet VPN", Work in Progress, Internet-
Draft, draft-ietf-bess-rfc7432bis-08, 13 February 2024,
<https://www.ietf.org/archive/id/draft-ietf-bess-
rfc7432bis-08.txt>.
[RFC9014] Rabadan, J., Sathappan, S., Henderickx, W., Sajassi, A.,
Drake, J., and , "Interconnect Solution for Ethernet VPN
(EVPN) Overlay Networks", 26 May 2021,
<https://www.rfc-editor.org/rfc/rfc9014.txt>.
Authors' Addresses
Neeraj Malhotra (editor)
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: nmalhotr@cisco.com
Krishnaswamy Ananthamurthy
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: kriswamy@cisco.com
Ali Sajassi
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: sajassi@cisco.com
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Lukas Krattiger
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
United States of America
Email: lkrattig@cisco.com
Jorge Rabadan
Nokia
777 E. Middlefield Road
Mountain View, CA 94043
United States of America
Email: jorge.rabadan@nokia.com
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