BESS W. Lin
Internet-Draft Z. Zhang
Intended status: Standards Track J. Drake
Expires: September 18, 2016 Juniper Networks, Inc.
J. Rabadan
Nokia
March 17, 2016
EVPN Inter-subnet Multicast Forwarding
draft-lin-bess-evpn-irb-mcast-02
Abstract
This document describes inter-subnet multicast forwarding procedures
for Ethernet VPNs (EVPN).
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.
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
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 18, 2016.
Copyright Notice
Copyright (c) 2016 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
(http://trustee.ietf.org/license-info) in effect on the date of
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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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. EVPN-aware Solution . . . . . . . . . . . . . . . . . . . . . 4
2.1. IGMP/MLD Snooping Consideration . . . . . . . . . . . . . 5
2.2. Receiver sites not connected to a source subnet . . . . . 5
2.3. Receiver sites without IRB . . . . . . . . . . . . . . . 6
2.4. Multi-homing Support . . . . . . . . . . . . . . . . . . 7
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
6.1. Normative References . . . . . . . . . . . . . . . . . . 8
6.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
EVPN offers an efficient L2 VPN solution with all-active multi-homing
support for intra-subnet connectivity over MPLS/IP network. EVPN
also provides an integrated L2 and L3 service. When forwarding among
Tenant Systems (TS) across different IP subnets is required,
Integrated Routing and Bridging (IRB) can be used [ietf-bess-evpn-
inter-subnet-forwarding].
An network virtualization endpoint (NVE) device supporting IRB is
called a L3 Gateway. In a centralized approach, a centralized
gateway provides all L3 routing functionality, and even two tenant
systems on two subnets connected to the same NVE need to go through
the central gateway, which is inefficient. In a distributed
approach, each NVE has IRB configured, and inter-subnet traffic will
be locally routed without having to go through a central gateway.
Inter-subnet multicast forwarding is more complicated and not covered
in [ietf-bess-evpn-inter-subnet-forwarding]. This document describes
the procedures for inter-subnet multicast forwarding.
For multicast traffic sourced from a TS in subnet 1, EVPN Broadcast,
Unknow unicast, Multicast (BUM) forwarding based on RFC 7432, will
deliver it to all sites in subnet 1. When IRBs in subnet 1 receive
the mulitcast traffic, they deliver to other corresponding IRBs in
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other subnets at L3. From L3 point of view, those NVEs are routers
connected to the subnet via the IRB interfaces and the source is
locally attached. Nothing is different from a traditional LAN and
regular IGMP/MLD/PIM procedures kick in.
If a TS is a multicast receiver, it uses IGMP/MLD to signal its
interest in some multicast flows. One of the gateways is the IGMP/
MLD querier for a given subnet. It sends queries out the IRB for
that subnet, which in turn causes the queries to be forwarded
throughout the subnet following the EVPN BUM procedures. TS's send
IGMP/MLD joins via multicast, which are also forwarded throughout the
subnet via EVPN BUM procedure. The gateways receive the joins via
their IRB interfaces. From layer 3 point of view, again it is
nothing different from a traditional LAN.
On a traditional LAN, only one router can send multicast to the LAN.
That is either the PIM Designated Router (DR) or IGMP/MLD querier
(when PIM is not needed - e.g., the LAN is a stub network). On the
source subnet, PIM is typically needed so that traffic can be
delivered to other subnets via other routers. For example, in case
of PIM-SM, the DR on the source network encapsulates the initial
packets for a particular flow in PIM Register messages and unicasts
the Register messages to the Rendezvous Point (RP) for that flow,
triggering necessary states for that flow to be built throughout the
network.
That also works in the EVPN scenario, although not efficiently.
Consider the example depicted in Figure 1, where a tenant has two
subnets corresponding to two VLANs realized by two EVPN Instances
(EVIs) at three sites. The VLAN1 and VLAN 2 shown in Figure 1
correspond to subnet 1 and subnet 2 respectively. A multicast source
is located at site 1 on subnet 1 and three receivers are located at
site 2 on subnet 1, site 1 and 2 on subnet 2 respectively. On subnet
1, NVE1 is the PIM DR while on subnet 2, NVE3 is the PIM DR. The
connection drawn in Figure 1 among NVEs are L3 connections.
Multicast traffic from the source at site 1 on subnet 1 is forwarded
to all three sites on VLAN 1 following EVPN BUM procedure. Rcvr1
gets the traffic when NVE2 sends it out of its local Attachment
Circuit (AC). The three gateways for EVI1 also receive the traffic
on their IRB interfaces to potentially route to other subnets. NVE3
is the DR on subnet 2 so it routes the local traffic (from L3 point
of view) to subnet 2 while NVE1/2 is not the DR on subnet 2 so they
don't. Once traffic gets onto subnet 2, it is forwarded back to
NVE1/2 and delivered to rcvr2/3 following the EVPN BUM procedures.
Notice that both NVE1 and NVE2 receive the multicast traffic from
subnet 1 on their IRB interfaces for subnet 1, but they do not route
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to subnet 2 where they are not the PIM DRs. Instead, they wait to
receive traffic at L2 from NVE3. For example, for receiver 3
connected to NVE1 but on different IP subnet as the multicast source,
the multicast traffic from source has to go from NVE1 to NVE3 and
then back to NVE1 before it is being delivered to the receiver 3.
This is similar to the hairpinning issue with centralized approach,
here the multicast forwarding is centralized via the DR, even though
distributed approach is being used for unicast (in that each NVE is
supporting IRB and routing inter-subnet unicast traffic locally).
site 1 . site 2 . site 3
. .
src . rcvr1 .
| . | .
-------------------------------------------- VLAN 1 (EVI1)
| . | . |
IRB1| DR . IRB1| . IRB1|
NVE1------------NVE2-----------------NVE3---RP
IRB2| . IRB2| . IRB2| DR
| . | . |
-------------------------------------------- VLAN 2 (EVI2)
| . | .
rcvr3 . rcvr2 .
. .
site 1 . site 2 . site 3
Figure 1 - EVPN IRB multicast scenario
2. EVPN-aware Solution
This multicast hairpinning can be avoided if the following procedures
are followed:
o On the IRB interface, the gateway receives multicast traffic from
a source subnet, it sends the traffic on its IRB interfaces to any
other subnets that have receivers for the traffic, regardless
whether the gateway is DR for that subnet or not.
o On the IRB interface, if a gateway receives Membership Reports
from one of its ACs, it sends PIM joins towards the RP or source
regardless if it is DR/querier or not.
o Multicast data traffic sent out of the IRB interfaces is forwarded
to local ACs only and not to other EVPN sites.
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Essentially, each router on an IRB interface behaves as a DR/querier
for receivers (but only the true DR behaves as a DR for sources), and
multicast data traffic from IRB interfaces is limited to local
receivers.
Note that link local multicast traffic (e.g. addressed to 224.0.0.x
in case of IPv4)), typically use for protocols, is not subject to the
above procedures and still forwarded to remote sites following EVPN
procedures.
In the example in Figure 1, when NVE1 gets traffic on its IRB1
interface it will route the traffic out of its IRB2 and deliver to
local rcvr3. It also sends register messages to the RP, since it is
the DR on the source network. Both NVE2 and NVE3 will receive the
traffic on IRB1 but neither sends register messages to the RP, since
they are not the DR on the source subnet. NVE2 will route the
traffic out of its IRB2 and deliver to local rcvr2. NVE3 will also
route the traffic out of IRB2 even though there is no receiver at the
local site, because the IGMP/MLD joins from rcvr2/3 are also received
by NVE3.
2.1. IGMP/MLD Snooping Consideration
In the example in Figure 1, NVE3 receives IGMP/MLD joins from rcvr2/3
and will route packets out of IRB2, even though there are no
receivers at the local site. IGMP/MLD snooping on NVE3 can prevent
the traffic from actually being sent out of ACs but at L3 there will
still be related states and processing/forwarding (e.g., IRB2 will be
in the downstream interface list for PIM join states and forwarding
routes).
To prevent NVE3 from learning those remote receivers at all, IGMP/MLD
snooping on NVE3 could optionally suppress the joins from remote
sites being sent to its IRB interface. With that, in the example in
Figure 1, NVE3 will not learn of rcvr2/3 on IRB2 and will not try to
route packets out of IRB2 at all.
2.2. Receiver sites not connected to a source subnet
In the example in Figure 1, the source subnet is connected to all
NVEs that has receiver sites, and there are no receivers outside the
EVPN network. As a result, PIM is not really needed and each NVE can
just route multicast traffic locally. In that case, IGMP/MLD querier
will be responsible to send traffic to a subnet.
If there is a receiver subnet connected to an NVE that is not
connected to the source subnet, then there must exist layer 3
multicast paths between them. This could be over an L3VPN core (in
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this revision it is assumed that the subnets realized by EVPN are
stub only and not transit) and normal PIM and MVPN procedures will be
followed.
The L3VPN routes can be propagated either per RFC 4364 procedures or
per EVPN Type 5 procedures [bess-evpn-prefix-advertisement]. BGP-
MVPN [RFC 6514] requires that the routes used for RPF checking carry
two extended communities (ECs) - VRF Route Import EC and Source AS
EC. That must be applied to EVPN Prefix Advertisement (Type 5)
routes as well.
2.3. Receiver sites without IRB
It is possible that a particular NVE may not have an IRB interface
for its l2 domain. In that case, for traffic from another l2 domain,
receivers need to receive from another NVE following EVPN procedures.
The obvious choice is that it receives from the DR of that subnet.
Because an NVE does not deliver traffic out of IRBs to remote sites
with IRB, the DR needs to use a separate provider tunnel to deliver
traffic only to sites that do not have IRB interfaces. The tunnel is
advertised in new EVPN route type that is analogous to the MVPN
"S-PMSI A-D" route [RFC6514]. This route will carry an EVPN Non-IRB
Extended Community, indicating that a PE attached to the EVI
identified in the route should join the advertised tunnel only if it
does not have an IRB for that EVI. The routes could be either be a
(*,*) wildcard S-PMSI A-D routes if an inclusive tunnel is used (but
only for all sites without IRBs), or individual (*,g)/(s,*) S-PMSI
A-D routes if selective tunnels are used per [draft-zzhang-bess-evpn-
bum-procedure-updates]. The (*,*) wildcard S-PMSI A-D route may be
advertised by the NVE carrying Non-IRB Site extended community for
each of its BD to deliver multicast traffic routed out of the IRB
interface to remote sites that do not have IRBs. Different RDs MUST
be used for this (*, *) S-PMSI A-D route in the following case: if
instead of an inclusive multicast Ethernet tag route, the NVE also
uses (*,*) S-PMSI to deliver BUM traffic received from local ACs to
remote PEs.
If [draft-sajassi-bess-evpn-igmp-mld-proxy] procedures are used, then
routes from those non-IRB sites MUST also carry the EVPN non-IRB
extended community, so that the DR will only forward traffic to those
non-IRB NVEs.
The EVPN non-IRB Extended Community is a new EVPN extended community.
EVPN extended communities are transitive extended community with a
Type field of 6. The subtype of this new EVPN extended community
will be assigned by IANA, and with the following 8-octet encoding:
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=0x06 | Sub-Type TBD | Flag(Octet) | Reserved=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved=0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The lower-order bit of the Flag is defined as non-IRB bit. A value
one indicates non-IRB NVE. The rest of the undefined bits are set to
zero.
2.4. Multi-homing Support
The solution works equally well in multi-homing situations, as long
as the multi-homed PEs attached to the same Ethernet segment have the
same IRB capability, which is expected to be the normal deployment.
As shown in Figure 2, both rcvr4 and rcvr5 are active-active multi-
homed to NVE2 and NVE3. Receiver 4 is on subnet VLAN 1 and receiver
5 is on VLAN 2. When IRBs on NVE1 and NVE2 forward multicast traffic
to its local attached access interface(s) based on EVPN BUM
procedure, only DF for the ES deliveries multicast traffic to its
multi-homed receiver. Hence no duplicated multicast traffic will be
forwarded to receiver 4 or receiver 5.
.
src . +-------- rcvr4-----+
| . | . |
-------------------------------------------- VLAN 1 (EVI1)
| . | . |
IRB1| DR . IRB1| . IRB1|
NVE1------------NVE2-----------------NVE3---RP
IRB2| . IRB2| . IRB2| DR
| . | . |
-------------------------------------------- VLAN 2 (EVI2)
| . | . |
rcvr3 . +-------- rcvr5-----+
.
Figure 2 - EVPN IRB multicast and multi-homing
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3. IANA Considerations
This document requests the following IANA assignments:
o A "Non-IRB Site" Sub-Type in "EVPN Extended Community Sub-Types"
registry for the EVPN Non-IRB Extended Community.
o A "non-IRB" flag bit in the EVPN Non-IRB Extended Community.
4. Security Considerations
This document does not introduce new security risks.
5. Acknowledgements
The authors would like to thank Eric Rosen for his detailed review
and valuable comments.
6. References
6.1. Normative References
[I-D.sajassi-bess-evpn-igmp-mld-proxy]
Sajassi, A., Patel, K., Thoria, S., Yeung, D., Drake, J.,
and W. Lin, "IGMP and MLD Proxy for EVPN", draft-sajassi-
bess-evpn-igmp-mld-proxy-00 (work in progress), October
2015.
[I-D.zzhang-bess-evpn-bum-procedure-updates]
Zhang, J., Lin, W., Rabadan, J., and K. Patel, "Updates on
EVPN BUM Procedures", draft-zzhang-bess-evpn-bum-
procedure-updates-01 (work in progress), December 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://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, <http://www.rfc-editor.org/info/rfc7432>.
6.2. Informative References
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[I-D.ietf-bess-evpn-inter-subnet-forwarding]
Sajassi, A., Salam, S., Thoria, S., Rekhter, Y., Drake,
J., Yong, L., and L. Dunbar, "Integrated Routing and
Bridging in EVPN", draft-ietf-bess-evpn-inter-subnet-
forwarding-00 (work in progress), November 2014.
[I-D.ietf-bess-evpn-prefix-advertisement]
Rabadan, J., Henderickx, W., Palislamovic, S., Balus, F.,
and A. Isaac, "IP Prefix Advertisement in EVPN", draft-
ietf-bess-evpn-prefix-advertisement-01 (work in progress),
March 2015.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <http://www.rfc-editor.org/info/rfc4364>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<http://www.rfc-editor.org/info/rfc6514>.
Authors' Addresses
Wen Lin
Juniper Networks, Inc.
EMail: wlin@juniper.net
Zhaohui Zhang
Juniper Networks, Inc.
EMail: zzhang@juniper.net
John Drake
Juniper Networks, Inc.
EMail: jdrake@juniper.net
Jorge Rabadan
Nokia
EMail: jorge.rabadan@nokia.com
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