Internet DRAFT - draft-sr-bess-evpn-dpath
draft-sr-bess-evpn-dpath
BESS Workgroup J. Rabadan, Ed.
Internet-Draft S. Sathappan
Intended status: Standards Track M. Gautam
Expires: 25 April 2024 Nokia
P. Brissette
Cisco Systems
W. Lin
Juniper
B. Wen
Comcast
23 October 2023
Domain Path (D-PATH) for Ethernet VPN (EVPN) Interconnect Networks
draft-sr-bess-evpn-dpath-04
Abstract
The BGP Domain PATH (D-PATH) attribute is defined for Inter-Subnet
Forwarding (ISF) BGP Sub-Address Families that advertise IP prefixes.
When used along with EVPN IP Prefix routes or IP-VPN routes, it
identifies the domain(s) through which the routes have passed and
that information can be used by the receiver BGP speakers to detect
routing loops or influence the BGP best path selection. This
document extends the use of D-PATH so that it can also be used along
with other EVPN route types.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on 25 April 2024.
Copyright Notice
Copyright (c) 2023 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
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. D-PATH to Prevent Loops for EVPN Routes . . . . . . . . . 3
1.2. Add Path Visibility and Influence Best Path Selection for
EVPN Routes . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions used in this document . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Use of Domain Path Attribute (D-PATH) with EVPN routes . . . 6
4.1. D-PATH and Best Path Selection for MAC/IP Advertisement
routes . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2. D-PATH and Best Path Selection for Ethernet A-D per EVI
routes . . . . . . . . . . . . . . . . . . . . . . . . . 9
4.3. D-PATH and Best Path Selection for Inclusive Multicast
Ethernet Tag routes . . . . . . . . . . . . . . . . . . . 10
4.4. Loop Detection . . . . . . . . . . . . . . . . . . . . . 10
4.5. Error Handling . . . . . . . . . . . . . . . . . . . . . 11
5. Use-Case Examples . . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 13
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 13
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 13
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2. Informative References . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Introduction
The BGP Domain PATH (D-PATH) attribute
[I-D.ietf-bess-evpn-ipvpn-interworking] is defined for Inter-Subnet
Forwarding (ISF) BGP Sub-Address Families that advertise IP prefixes.
When used along with EVPN IP Prefix routes or IP-VPN routes, it
identifies the domain(s) through which the routes have passed and
that information can be used by the receiver BGP speakers to detect
routing loops or influence the BGP best path selection. This
document extends the use of D-PATH so that it can also be used along
with other EVPN route types.
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The D-PATH attribute can be used to prevent control plane loops for
EVPN routes, or to provide full path visibility of all the EVPN
Interconnect Gateways through which a route has gone and modify the
best path selection based on it. Some use cases in which D-PATH can
be used along with (non-IP Prefix) EVPN routes follow, but the use
cases are not limited to the ones described in this section.
1.1. D-PATH to Prevent Loops for EVPN Routes
Figure 1 illustrates an EVPN Interconnect case where EVPN MAC/IP
Advertisement routes can be looped indefinitely. The three Gateways
(GW1, GW2 and GW3) and PE1 in the diagram are attached to the same
EVPN Broadcast Domain (BD1). However, BD1 is extended throughout
three different domains that are interconnected by the Gateways,
which follow [RFC9014] procedures. Suppose a host with MAC address
M1 is learned on GW1 and GW1 advertises an EVPN MAC/IP Advertisement
route for M1 into Domain-1 and Domain-2. When the route gets
imported by GW2 and GW3 and later exported into Domain-3, GW2 and GW3
may redistribute each other's route for M1 back into Domain-1 and
Domain-2, respectively, creating a loop. D-PATH can be used by the
Gateways when redistributing the route between Domains, to identify
the Domains through which the route for M1 has gone. When GW1
receives an EVPN MAC/IP Advertisement route for M1 that contains a
D-PATH with a domain-id locally assigned, GW1 identifies the route as
"looped".
+----------------+ GW2
| EVPN +-------+
| Domain-1 | +---+ |
| | |BD1| |---------------+
| | +---+ | |
GW1 | +-------+ | PE1
+-------+ | | EVPN +-------+
| +---+ |---------------+ | Domain-3 | +---+ |
| |BD1| | | | |BD1| |
| +---+ |---------------+ | | +---+ |
+---|---+ | GW3 | +---|---+
| | EVPN +-------+ | |
M1--+ | Domain-2 | +---+ | | +--M2
| | |BD1| |---------------+
| | +---+ |
| +-------+
+----------------+
Figure 1: Loops for EVPN routes
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Similar examples are possible with EVPN VPWS services on the Gateways
and PEs, where loop prevention for the redistributed A-D per EVI
routes is needed. D-PATH provides the end to end path visibility
that is required to prevent the loop.
1.2. Add Path Visibility and Influence Best Path Selection for EVPN
Routes
Figure 2 illustrates another [RFC9014] EVPN Interconnect case where,
in addition to using D-PATH to prevent EVPN MAC/IP Advertisement
route loops when redistributing routes between domains, the D-PATH
attribute can also influence the best path selection for the routes.
For example, if all the Gateways in the diagram are attached to the
same BD1, an EVPN MAC/IP Advertisement route for MAC address M1
advertised by GW1 is advertised into Domain-1 and Domain-4. Two
routes for M1 will arrive at GW3 with different route distinguishers
and BGP Next Hops. If D-PATH is used by all the Gateways, the two
routes arriving at GW3 will have a different sequence of domain-ids
in the D-PATH attribute. GW3 can use the length of the D-PATH as a
way of influencing the selection (i.e., the shortest D-PATH route is
selected). D-PATH improves the path visibility of the route since it
provides information about all the Domains through which the route
has passed.
+----------+ GW11 +----------+ GW2 +----------+
| EVPN +-------+ EVPN +-------+ EVPN |
| Domain-1 | +---+ | Domain-2 | +---+ | Domain-3 |
| | |BD1| | | |BD1| | |
| | +---+ | | +---+ | |
GW1 | +-------+ +-------+ | GW3
+-------+ | | | | +-------+
| +---+ |---------+ +----------+ +---------| +---+ |
| |BD1| | | |BD1| |
| +---+ |---------+ +----------------------------| +---+ |
+---|---+ | GW12 | +---|---+
| | EVPN +-------+ EVPN | |
M1--+ | Domain-4 | +---+ | Domain-5 | +--M2
| | |BD1| | |
| | +---+ | |
| +-------+ |
+----------+ +-----------------------------+
Figure 2: Influence Best Path Selection for EVPN routes
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2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Terminology
This section summarizes the terminology that is used throughout the
rest of the document.
* AC: Attachment Circuit or logical interface associated to a given
Broadcast Domain. To determine the AC on which a packet arrived,
the PE examines the combination of a physical port and VLAN tags
(where the VLAN tags can be individual c-tags, s-tags or ranges of
both).
* BD and BT: a Broadcast Domain and Bridge Table, as defined in
[I-D.ietf-bess-rfc7432bis]. A BD is a group of PEs attached to
the same EVPN layer-2 multipoint service. A BT is the
instantiation of a Broadcast Domain in a PE. When there is a
single Broadcast Domain in a given EVI, the MAC-VRF in each PE
contains a single BT. When there are multiple BTs within the same
MAC-VRF, each BT is associated to a different Ethernet Tag. The
EVPN routes specific to a BT indicate which Ethernet Tag the route
corresponds to. This document does not distinguish between a
"Broadcast Domain" and a "Bridge Table", and will use the terms
interchangeably (or will use the acronym "BD" to refer to either).
Also, the way the BDs are grouped into MAC-VRFs depending on the
service model (VLAN-based versus VLAN Bundle or VLAN-aware Bundle)
is not relevant to the procedures specified in this document.
* BUM: Broadcast, Unknown unicast and Multicast traffic.
* ES and ESI: Ethernet Segment and Ethernet Segment Identifier, as
defined in [I-D.ietf-bess-rfc7432bis].
* EVPN Domain: two PEs are in the same EVPN Domain if they are
attached to the same service and the packets between them do not
require a data path lookup of the inner frame (e.g., in the BD of
a MAC-VRF) in any intermediate router. An EVPN Domain Gateway PE
is always configured with multiple Domain identifiers (EVPN
Domain-ID) in the MAC-VRF or VPWS that connects those EVPN
Domains, each EVPN Domain-ID representing an EVPN Domain.
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Example: Figure 3 illustrates an example where PE1 and PE2 belong
to different EVPN Domains since packets between them (for flows
between hosts with MAC addresses M1 and M2) require a MAC lookup
in two of the gateways that are connecting the three EVPN Domains.
E.g., if frames from M1 to M2 go through PE1, GW1, GW3 and PE2, a
MAC lookup is performed at GW1 and GW3.
GW1------------GW3
+------+ +------+
+-------------| BD1 | | BD1 |-------------+
PE1 +------+ +------+ PE2
+------+ | | +------+
M1-| BD1 | EVPN | EVPN | EVPN | BD1 |-M2
+------+ GW2 GW4 +---+--+
| +------+ +------+ |
+-------------| BD1 | | BD1 |-------------+
+------+ +------+
+--------------+
EVPN Domain 1 EVPN Domain 2 EVPN Domain 3
<---------------> <------------> <---------------->
Figure 3: EVPN Domain Interconnect Example
* EVPN Domain Gateway: a PE where a service (BD or VPWS instance) is
instantiated and is attached to two or more EVPN Domains. This
document uses the term "EVPN Domain Gateway" or simply "Gateway".
An example of EVPN Domain Gateway is a PE following the procedures
in section 4.4 or section 4.6 of [RFC9014]. In the example in
Figure 3, GW1 and GW2 connect EVPN Domains 1 and 2, whereas GW3
and GW4 connect EVPN Domains 2 and 3. GW1 and GW2 import the MAC/
IP Advertisement route for M1 coming from the EVPN Domain 1 into
the MAC-VRF for BD1, and redistribute it into EVPN Domain 2.
Likewise, GW3 and GW4 import the route into their MAC-VRF and re-
advertise it into EVPN Domain 3.
* MAC-VRF: a MAC Virtual Routing and Forwarding table, as defined in
[I-D.ietf-bess-rfc7432bis]. It is also the instantiation of an
EVI (EVPN Instance) in a PE.
4. Use of Domain Path Attribute (D-PATH) with EVPN routes
This document extends the use of the D-PATH attribute specified in
[I-D.ietf-bess-evpn-ipvpn-interworking] so that D-PATH can be
advertised and processed along with the following EVPN route types:
* EVPN MAC/IP Advertisement routes that are not used for Inter-
Subnet Forwarding (ISF). Note that if the EVPN MAC/IP
Advertisement route is used for Inter-Subnet Forwarding as in
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[RFC9135], the procedures for the D-PATH advertisement and
processing are described in
[I-D.ietf-bess-evpn-ipvpn-interworking].
* EVPN A-D per EVI routes that are used for EVPN VPWS [RFC8214].
Advertised A-D per EVI routes not used for EVPN VPWS SHOULD NOT
contain D-PATH.
* EVPN Inclusive Multicast Ethernet Tag routes
[I-D.ietf-bess-rfc7432bis].
As discussed, the use of D-PATH with EVPN IP Prefix routes is
specified in [I-D.ietf-bess-evpn-ipvpn-interworking]. When used
along with EVPN routes other than IP Prefix routes, the D-PATH
attribute is characterized as follows:
1. D-PATH is composed of a sequence of Domain segments following the
format specified in [I-D.ietf-bess-evpn-ipvpn-interworking] where
each Domain is represented as <DOMAIN-ID:ISF_SAFI_TYPE>. In this
specification, DOMAIN-ID is an EVPN Domain identifier configured
in an EVPN Domain Gateway and ISF_SAFI_TYPE is set to either 70
(EVPN) or 0 (local route). To simplify the explanation, this
document represents the domains for EVPN routes as <Domain-
ID:TYPE>.
2. D-PATH identifies the sequence of EVPN Domains the route has gone
through, with the last <Domain-ID:TYPE> entry (rightmost)
identifying the first PE or EVPN Domain Gateway that added the
D-PATH attribute.
3. For non-Inter Subnet Forwarding EVPN MAC/IP Advertisement routes
or EVPN A-D per EVI routes [I-D.ietf-bess-rfc7432bis], D-PATH
SHOULD be added/modified by a EVPN Domain Gateway that
redistributes the route between EVPN Domains and MAY be added by
a PE or EVPN Domain Gateway that originates the route, as
follows:
a. An EVPN Domain Gateway that connects two EVPN Domains "X" and
"Y", and receives a route on a EVPN Domain identified by a
Domain-ID "X" SHOULD append a domain <X:EVPN> to the existing
(or newly added) D-PATH attribute when redistributing the
route to EVPN Domain "Y". The route is redistributed if it
is first imported in a MAC-VRF (or VPWS instance), the MAC
(or Ethernet Tag) is active, and policy allows the re-export
of the route to a BGP neighbor.
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b. An EVPN Domain Gateway MAY also add the D-PATH attribute for
locally learned MACs or MAC/IP pairs. In this case, the
domain added would be <A:0>, where "A" is the Domain-ID
configured on the Gateway's MAC-VRF that is specific to local
routes (MAC/IP learned via local AC), and "0" is the TYPE of
the EVPN Domain and indicates that the route is locally
originated and not redistributed after receiving it from a
BGP-EVPN neighbor. The EVPN Domain-ID for local routes MAY
be shared by all the EVPN Domain Gateways of the same
redundancy group for local routes, or each EVPN Domain
Gateway of the redundancy group can use its own Domain-ID.
c. A PE that is connected to a single EVPN Domain (therefore the
PE is not an EVPN Domain Gateway) MAY add the D-PATH with a
domain <B:0>, where "B" is the Domain-ID configured on the
PE's MAC-VRF (or VPWS) for locally learned MAC/IPs (or
Ethernet Tag IDs for VPWS). "0" is the TYPE that indicates
the route is not re-advertised, but originated in the PE.
4. For EVPN Inclusive Multicast Ethernet Tag routes, an EVPN Domain
Gateway must not redistribute routes between Domains as specified
in [RFC9014]. An EVPN Domain Gateway originates an EVPN
Inclusive Multicast Ethernet Tag route per Domain to which the
Gateway is attached, so that BUM traffic can be attracted from
one Domain to the rest. Therefore, only the above point 3.b.
applies to EVPN Domain Gateways. That is, an EVPN Domain Gateway
MAY add a <A:0> D-PATH attribute for the Inclusive Multicast
Ethernet Tag routes generated for the EVPN Domains, where "A" is
the configured local Domain-ID, and "0" is the TYPE that
indicates the route is locally originated and not redistributed
across EVPN Domains. When two or more EVPN Domain Gateways of
the same redundancy group connect two EVPN Domains "X" and "Y"
and D-PATH is used for EVPN Inclusive Multicast Ethernet Tag
routes, it is RECOMMENDED to add the D-PATH attribute with the
same local Domain-ID and only on "X" or "Y" but not on both
Domains. In this case, all Gateways under the same redundancy
group MUST choose the same Domain in which the D-PATH attribute
is used.
5. On received EVPN routes, D-PATH is processed and used for loop
detection (Section 4.4) as well as to influence the best path
selection (Section 4.1, Section 4.2 and Section 4.3).
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4.1. D-PATH and Best Path Selection for MAC/IP Advertisement routes
When two (or more) MAC/IP Advertisement routes with the same route
key (and same or different RDs) are received, a best path selection
algorithm is used to select and install only one route. The best
path selection for MAC/IP Advertisement routes is specified in
[I-D.ietf-bess-rfc7432bis], in section 7.13.1, and this document
modifies the algorithm by including the D-PATH comparison across EVPN
MAC/IP Advertisement routes after tie-breaking rule 5 in
[I-D.ietf-bess-rfc7432bis] section 7.13.1, which removes from
consideration routes that are not tied for higher degree of
preference.
If none of the tie-breaking rules up to (and including) rule 5
produces a single route, the router compares the D-PATH attribute in
the remaining candidate routes:
1. The routes with the shortest D-PATH are preferred, hence routes
not tied for the shortest D-PATH are removed. Routes without
D-PATH are considered zero-length D-PATH.
2. Then routes with the numerically lowest left-most Domain-ID are
preferred, hence routes not tied for the numerically lowest left-
most Domain-ID are removed from consideration.
If the steps above do not produce a single route, then the rest of
the rules in [I-D.ietf-bess-rfc7432bis] follow.
4.2. D-PATH and Best Path Selection for Ethernet A-D per EVI routes
When two (or more) EVPN A-D per EVI routes with the same route key
(and same or different RDs) are received for a Virtual Private Wire
Service (VPWS), a best path selection algorithm is used. The best
path selection for EVPN A-D per EVI routes is specified in
[I-D.ietf-bess-rfc7432bis], in section 7.13.2, and this document
modifies the algorithm by including the D-PATH comparison across EVPN
A-D per EVI routes in the same way Section 4.1 does it for EVPN MAC/
IP Advertisement routes. That is, rules 1 and 2 of Section 4.1 are
interleaved between rules 5 and 6 of [I-D.ietf-bess-rfc7432bis].
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4.3. D-PATH and Best Path Selection for Inclusive Multicast Ethernet
Tag routes
When two (or more) EVPN Inclusive Multicast Ethernet Tag routes with
the same route key (and same or different RDs) are received for a
MAC-VRF, a best path selection algorithm is used and only one of them
is programmed. The selection algorithm follows
[I-D.ietf-bess-rfc7432bis] the same D-PATH comparison steps as in
Section 4.1 interleaved between rules 5 and 6 of
[I-D.ietf-bess-rfc7432bis].
4.4. Loop Detection
An EVPN route received by a PE with a D-PATH attribute that contains
one or more of its locally associated Domain-IDs for the MAC-VRF or
VPWS instance is considered to be a looped route. A looped route
MUST NOT be redistributed to a different domain and SHOULD be flagged
as "looped".
EVPN Inclusive Multicast Ethernet Tag looped routes MUST NOT be
installed, where "install" in this document means "create forwarding
state". An EVPN MAC/IP Advertisement looped route or an A-D per EVI
looped route (in EVPN VPWS services) MAY be installed if selected as
the best route.
For instance, in the example of Figure 3, assuming PE1 advertises
M1's MAC/IP and does not add the D-PATH attribute, the EVPN Domain
Gateway GW1 receives two MAC/IP Advertisement routes for M1's MAC/IP:
* A MAC/IP Advertisement route with next hop PE1 and no D-PATH.
* A MAC/IP Advertisement route with next hop GW2 and
D-PATH={length=1,<6500:1:EVPN>}, assuming that the Domain-ID for
EVPN Domain 1 is 6500:1.
In this case, EVPN Domain Gateway GW1 flags the MAC/IP Advertisement
route with D-PATH as "looped", and does not install the MAC in the
BD, and does not redistribute the route back to EVPN Domain 1 (since
the route includes one of GW1's Domain-IDs). In case the MAC/IP
Advertisement route with next hop PE1 is withdrawn, GW1 may install
the route with next hop GW2 and D-PATH <6500:1:EVPN>; this may help
speed up convergence in case of failures.
The procedures described in this section, based on D-PATH, can be
used along with the Ethernet Segment Identifier of the received
routes as a way to detect looped routes on EVPN domain gateways
attached to an Interconnect Ethernet Segment as in [RFC9014]. An
EVPN domain gateway MUST NOT redistribute a received EVPN MAC/IP
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route or EVPN A-D per EVI route with an Ethernet Segment Identifier
value that matches the value of a local Ethernet Segment,
irrespective of the D-PATH Domain-IDs.
4.5. Error Handling
The error handling for the D-PATH attribute is described in
[I-D.ietf-bess-evpn-ipvpn-interworking]. This document extends the
use of D-PATH to non-Inter Subnet Forwarding (non-ISF) EVPN routes.
5. Use-Case Examples
This section illustrates the use of D-PATH in EVPN routes with
examples.
Figure 4 and Figure 5 illustrate an integrated interconnect solution
for an EVPN BD, as described in section 4.4 and section 4.6 of
[RFC9014]. GW1 and GW2 are EVPN Domain Gateways connecting two EVPN
Domains identified by D-PATH domain {1:1:EVPN} and {1:2:EVPN},
respectively. Received Ethernet A-D routes, ES routes, and Inclusive
Multicast routes from the routers in one EVPN Domain are consumed and
processed by GW1 and GW2, but not redistributed to the other EVPN
Domain. However, MAC/IP Advertisement routes received by GW1 and GW2
in one EVPN Domain are processed and, if installed, redistributed
into the other EVPN Domain.
+----EVPN Domain-1---+ +----EVPN Domain-2--+
| 1:1:EVPN | GW1 | 1:2:EVPN |
| +---------+ |
| | +-----+ | |
| | | BD1 | X <-+ |
PE1 | +-----+ | | PE2
+---------+ +---------+ | +---------+
| +-----+ | | | | | +-----+ |
M1-----| BD1 | | | | | | | BD1 |-----M2
| +-----+ | -------> | | | | +-----+ |
+---------+ (RT2)M1/IP1 | | | +---------+
| +---------+ | |
| | +-----+ | |(RT2)M1/IP1 |
| | | BD1 | | --+ <1:1:EVPN> |
| | +-----+ | |
| +---------+ |
| | GW2 | |
+---------------------+ +-------------------+
Figure 4: EVPN Interconnect
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Consider the example of Figure 4, where PE1 advertises a MAC/IP
Advertisement route for M1/IP1. The route is processed and installed
by GW1 and GW2 in BD1, and both redistribute the routes into the EVPN
Domain-2. By using D-PATH in GW1 and GW2, when the route is received
on PE2, PE2 has the visibility of the EVPN Domains through which the
route has gone, and can also use the D-PATH for best path selection.
In addition, GW1 and GW2 can compare the D-PATH of the incoming
routes with their local list of EVPN Domain-IDs, and detect looped
routes if any of the local EVPN Domain-IDs matches a domain in the
received D-PATH. This procedure prevents the redistribution of the
route back into EVPN Domain-1. For example, when GW1 receives the
MAC/IP Advertisement route for M1/IP1 with D-PATH <1:1:EVPN>, GW1
identifies the route as looped and it does not redistribute it back
to Domain-1. The M1/IP1 route with Next Hop PE1 is installed. If
M1/IP1 with Next Hop PE1 is withdrawn, GW1 MAY install the route M1/
IP1 with Next Hop GW2, as specified in Section 4.4.
The example of Figure 5 illustrates how GW1 and GW2 can also have
local ACs in BD1 and learn local MAC (or MAC/IP) addresses from
devices connected to the ACs.
+----EVPN Domain-1---+ +----EVPN Domain-2--+
| 1:1:EVPN | GW1 | 1:2:EVPN |
| +---------+ |
| | +-----+ | |
| +-->X| | BD1 | |X<--+ |
PE1 | | +-----+ | | PE2
+---------+ | +---------+ | +---------+
| +-----+ | | | | | | +-----+ |
M1-----| BD1 | | | | | +---> | | BD1 |-----M2
| +-----+ | | | | | | +-----+ |
+---------+ | | | | +---------+
| | | GW2 | | |
| <---+-- +---------+ (RT2)M3/IP3 |
| (RT2)M3/IP3 | +-----+ | {1:3:0} |
| {1:3:0} | | BD1 | | | |
| | +-----+ | ---+ |
| +----|----+ |
| | | | |
+---------------------+ | +-------------------+
+
M3
Figure 5: EVPN Interconnect local AC
Assuming GW2 learns M3/IP3 via local AC, GW2 advertises a MAC/IP
Advertisement route for M3/IP3 into each of the EVPN Domains that GW2
is connected to. As described in Section 4, GW2 can advertise these
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two MAC/IP Advertisement routes with a configured EVPN Domain-ID for
local MAC/IPs routes that can be shared with GW1. Consider this EVPN
Domain-ID is 1:3 and it is configured on both, GW1 and GW2. When GW2
advertises the route into each EVPN Domain, it adds the D-PATH
attribute with a domain {1:3:0}. These routes are flagged by GW1 as
"looped" since 1:3 is configured as a local EVPN Domain-ID in GW1.
In addition, PE1 and PE2 receive the routes with the D-PATH and they
have the visibility of the origin of the routes, in this case local
EVPN Domain Gateway routes. This information can be used to
influence the best path selection in case of multiple routes for M3/
IP3 are received on PE1 or PE2 for BD1.
As an alternative solution to configuring the same EVPN Domain-ID for
local routes on both EVPN Domain Gateways, GW2 can be configured with
EVPN Domain-ID 1:3 for local routes, and GW1 can use a different EVPN
Domain-ID, e.g., 1:4. In this case, GW2 advertises the route for M3/
IP3 into each EVPN Domain as before, but now GW1 does not flag the
route as "looped" since 1:3 is not on the list of GW1's local EVPN
Domain-IDs. GW1 receives the routes from both EVPN Domains, and GW1
selects the route from e.g., EVPN Domain-1. GW1 then installs the
route in its BD and redistributes the route into EVPN Domain-2 with
D-PATH {1:1:EVPN, 1:3:0}. When PE2 receives two routes for M3/IP3,
one from GW2 with D-PATH {1:3:0} and another from GW1 with D-PATH
{1:1:EVPN, 1:3:0}, PE2 uses best path selection and choose to send
its traffic to GW2. Also GW2 receives the route for M3/IP3 from GW1
and mark it as "looped" since that route conveys its own EVPN Domain-
IDs 1:1 and 1:3.
In a nutshell, the use of D-PATH in MAC/IP Advertisement routes helps
prevent loops and influences the best path selection so that PEs
choose the shortest paths to the destination PEs.
6. Security Considerations
Most of the considerations included in
[I-D.ietf-bess-evpn-ipvpn-interworking] apply to this document.
7. IANA Considerations
None.
8. Acknowledgments
9. Contributors
In addition to the authors included on the front page, the following
people contributed significantly:
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Vinod Prabhu, Nokia
10. References
10.1. Normative References
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[I-D.ietf-bess-evpn-ipvpn-interworking]
Rabadan, J., Sajassi, A., Rosen, E. C., Drake, J., Lin,
W., Uttaro, J., and A. Simpson, "EVPN Interworking with
IPVPN", Work in Progress, Internet-Draft, draft-ietf-bess-
evpn-ipvpn-interworking-09, 9 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-ipvpn-interworking-09>.
[I-D.ietf-bess-rfc7432bis]
Sajassi, A., Burdet, L. A., Drake, J., and J. Rabadan,
"BGP MPLS-Based Ethernet VPN", Work in Progress, Internet-
Draft, draft-ietf-bess-rfc7432bis-07, 13 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
rfc7432bis-07>.
[RFC9014] Rabadan, J., Ed., Sathappan, S., Henderickx, W., Sajassi,
A., and J. Drake, "Interconnect Solution for Ethernet VPN
(EVPN) Overlay Networks", RFC 9014, DOI 10.17487/RFC9014,
May 2021, <https://www.rfc-editor.org/info/rfc9014>.
[RFC8214] Boutros, S., Sajassi, A., Salam, S., Drake, J., and J.
Rabadan, "Virtual Private Wire Service Support in Ethernet
VPN", RFC 8214, DOI 10.17487/RFC8214, August 2017,
<https://www.rfc-editor.org/info/rfc8214>.
10.2. Informative References
[RFC9135] Sajassi, A., Salam, S., Thoria, S., Drake, J., and J.
Rabadan, "Integrated Routing and Bridging in Ethernet VPN
(EVPN)", RFC 9135, DOI 10.17487/RFC9135, October 2021,
<https://www.rfc-editor.org/info/rfc9135>.
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Authors' Addresses
J. Rabadan (editor)
Nokia
520 Almanor Avenue
Sunnyvale, CA 94085
United States of America
Email: jorge.rabadan@nokia.com
S. Sathappan
Nokia
520 Almanor Avenue
Sunnyvale, CA 94085
United States of America
Email: senthil.sathappan@nokia.com
M. Gautam
Nokia
520 Almanor Avenue
Sunnyvale, CA 94085
United States of America
Email: mallika.gautam@nokia.com
P. Brissette
Cisco Systems
Canada
Email: pbrisset@cisco.com
W. Lin
Juniper
United States of America
Email: wlin@juniper.net
B. Wen
Comcast
United States of America
Email: bin_wen@comcast.com
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