Segmented MVPN Using IP Lookup for BIER
draft-xie-bier-mvpn-segmented-04
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| Authors | Jingrong Xie , Liang Geng , Lei Wang , Mike McBride , Gang Yan | ||
| Last updated | 2018-10-20 | ||
| Replaced by | draft-xie-bess-mvpn-segmented-updates | ||
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draft-xie-bier-mvpn-segmented-04
Network Working Group J. Xie
Internet-Draft Huawei Technologies
Intended status: Standards Track L. Geng
Expires: April 23, 2019 L. Wang
China Mobile
M. McBride
G. Yan
Huawei
October 20, 2018
Segmented MVPN Using IP Lookup for BIER
draft-xie-bier-mvpn-segmented-04
Abstract
This document specifies an alternative of the control plane and data
plane procedures that allow segmented MVPN using the more efficient
LIR-pF explicit-tracking when BIER is used as the upstream or
downstream or both segments. It requires a segmentation point BFR
doing an IP header lookup, which is common for the forwarding
procedure on BFER, or the forwarding procedure on ABR with local VPN
CEs connected. This document updates [I-D.ietf-bier-mvpn].
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
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Drafts is at https://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 April 23, 2019.
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Copyright Notice
Copyright (c) 2018 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement and Considerations . . . . . . . . . . . . 5
3.1. Problem Statement . . . . . . . . . . . . . . . . . . . . 5
3.2. Considerations . . . . . . . . . . . . . . . . . . . . . 5
4. Upstream BIER and Downstream BIER (BIER-BIER) . . . . . . . . 6
4.1. Explicit Tracking using LIR-pF . . . . . . . . . . . . . 6
4.2. Forwarding using IP lookup on Segmentation Point . . . . 8
5. Upstream P2MP and Downstream BIER (P2MP-BIER) . . . . . . . . 9
5.1. Explicit Tracking using LIR-pF . . . . . . . . . . . . . 9
5.2. Forwarding using IP lookup on Segmentation Point . . . . 10
6. Upstream BIER and Downstream P2MP (BIER-P2MP) . . . . . . . . 11
6.1. Explicit Tracking using LIR-pF . . . . . . . . . . . . . 11
6.2. Forwarding on Segmentation Point . . . . . . . . . . . . 12
7. Summary and Recommendations . . . . . . . . . . . . . . . . . 12
8. Appendix A - Comparison of Solutions . . . . . . . . . . . . 13
9. Security Considerations . . . . . . . . . . . . . . . . . . . 15
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 15
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
12.1. Normative References . . . . . . . . . . . . . . . . . . 16
12.2. Informative References . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
When using BIER to transport an MVPN data packet through a BIER
domain, an ingress PE functions as a BFIR (see [RFC8279]). The BFIR
must determine the set of BFERs to which the packet needs to be
delivered. This can be done through an explicit-tracking function
using a LIR and/or LIR-pF flag in BGP MVPN routes, per the
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[RFC6513],[RFC6514],[RFC6625],[I-D.ietf-bess-mvpn-expl-track], and
[I-D.ietf-bier-mvpn].
Using a LIR-pF Flag will bring some extra benefits, as [I-D.ietf-
bier-mvpn] and [I-D.ietf-bess-mvpn-expl-track] have stated. But
unfortunately, the LIR-pF explicit tracking for a segmented MVPN
deployment is not allowed in the current draft [I-D.ietf-bier-mvpn],
because the draft requires a per-flow upstream-assigned label to do
the data-plane per-flow lookup on the segmentation point BFR.
This document specifies an alternative of the control plane and data
plane procedures that allow segmented MVPN using the more efficient
LIR-pF explicit-tracking when BIER is used as the upstream or
downstream or both segments. It requires a segmentation point BFR
doing an IP header lookup, which is common for the forwarding
procedure on BFER, or the forwarding procedure on ABR with local VPN
CEs connected. This will bring some significant benefits to the
segmented MVPN deployment, including:
o Getting a much better multicast join latency by eliminating the
round trip interaction of S-PMSI AD routes and Leaf AD routes.
Especially, the S-PMSI A-D routes may need a data-driven procedure
to trigger, and make the multicast join latency even worse.
o Greatly reducing the number of S-PMSI A-D routes that BFIR and
BFERs need to save.
o Consolidated forwarding procedure of IP lookup for every BIER
Overlay functioning routers, such as BFIR, BFER, segmentation
point BFR, and segmentation point BFR with BFER function.
2. Terminology
Readers of this document are assumed to be familiar with the
terminology and concepts of the documents listed as Normative
References.
This document uses the term "P2MP" for "mLDP P2MP, RSVP-TE P2MP, or
IR P2MP".
Some other important terms introduced by this document is listed
below.
BIER-MVPN tunnel: An unidirectional tunnel indicated by an upstream-
assigned VpnLabel and the according context such as the RootIP where
the VpnLabel is generated. In control plane the BIER-MVPN tunnel is
the PTA of type<BIER> including the MPLS Label of the PTA. One BIER-
MVPN tunnel is always bound to an BGP-MVPN SPMSI route. There is no
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two BGP-MVPN SPMSI routes of different VPN has the same BIER-MVPN
tunnel, but there is possibly two BGP-MVPN SPMSI routes of the same
VPN has the same BGP-MVPN tunnel.
P2MP tunnel: An unidirectional tunnel indicated by an downstream
label. In control plane the P2MP tunnel is the PTA of type<mLDP> or
type <RSVP-TE> or type <IR>. The MPLS Label of the PTA is zero in
real implementation. One P2MP tunnel is always bound to an BGP-MVPN
SPMSI route. There are no two BGP-MVPN SPMSI routes in different
VPNs with the same BIER-MVPN tunnel bound, but there are possibly two
BGP-MVPN SPMSI routes in the same VPN with the same P2MP tunnel
bound.
BGP-MVPN FEC: Either a (OrigIP, RD) tuple indicating by an
SPMS(OrigIP, RD, *, *), or a (OrigIP, RD, S, G) tuple indicating by
an SPMSI(OrigIP, RD, S, G). The BGP-MVPN FEC is used for control
plane to build some form of forwarding state on an segment point ABR
node. One example of such forwarding state is to use the upstream
P2MP tunnel bound to an SPMSI route, and the downstream P2MP
tunnel(s) bound to an SPMSI route, with the same BGP-MVPN FEC.
Another example of such forwarding state is to use the upstream BIER-
MVPN tunnel bound to an SPMSI route, and the downstream P2MP
tunnel(s) and/or BIER-MVPN tunnel(s).
VRF: Virtual Routing Forwarding. It is usually a number to indicate
a VPN/MVPN instance locally when L3VPN is configured. It is also
called local VRF.
Pseudo VRF: a Pseudo VRF indicates a VPN/MVPN instance locally on the
segment point ABR when downstream BIER forwarding using IP lookup is
required. The segment point ABR can be PE of a VPN/MVPN instance at
the same time, and then there would have VRF and Pseudo VRF(s)
simultaneously. Note that the Pseudo VRF(s) is per the tunnel (BIER-
MVPN tunnel or P2MP tunnel). Numbers of RootIP per a VPN/MVPN, and
numbers of tunnels per a VPN/MVPN and a RootIP, in the BIER-MVPN
FEC(s), will cause numbers of the Pseudo VRF allocated.
Local VpnLabel: a Local VpnLabel indicates a upstream-assigned MPLS
Label locally on the segment point ABR when downstream BIER
forwarding using IP lookup is required. Local VpnLabel is 1:1 to
Pseudo VRF, and it is assumed that a Pseudo VRF always indicates a
Local VpnLabel within it.
o Getting a much better multicast join latency by eliminating the
round trip interaction of S-PMSI AD routes and Leaf AD routes.
Especially, the S-PMSI A-D routes may need a data-driven procedure
to trigger, and make the multicast join latency even worse.
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o Greatly reducing the number of S-PMSI A-D routes that BFIR and
BFERs need to save.
o Consolidated forwarding procedure of IP lookup for every BIER
Overlay functioning routers, such as BFIR, BFER, segmentation
point BFR, and segmentation point BFR with BFER function.
3. Problem Statement and Considerations
3.1. Problem Statement
BIER is a stateless multicast forwarding by introducing a multicast-
specific BIER header in the data plane. The maximal number of BFERs
a packet can reach is limited by the bit string length of a BIER
header. For a network with many routers in multiple IGP areas
(typically an Inter-Area network), it may be expected to use a
segmented MVPN when deploying BIER because operators don't want to
replicate packets to many BIER Sets. It is also possible for an
incremental deployment of BIER on one area (e.g. one Metro network
area) while keeping the P2MP in other areas (e.g. the Core network
area, and the other Metro network areas).
However, it is not allowed in the [I-D.ietf-bier-mvpn] to use a LIR-
pF explicit-tracking when deploying a segmented MVPN. This will lead
to a low efficiency of explicit-tracking, and cause a worse multicast
join latency. Here we first take a scenario of inter-area segmented
MVPN with both segments using BIER in section 4 for a generic
description. The second scenario is inter-area segmented MVPN with
upstream segment using P2MP and downstream segment using BIER in
section 5. The third scenario is inter-area segmented MVPN with
upstream segment using BIER and downstream segment using P2MP in
section 6.
3.2. Considerations
A BFIR always need to know the BFERs interested in a specific flow.
This is a function of a BIER overlay defined in [RFC8279]. A
segmentation point BFR in a segmented MVPN deployment, saying ABR,
will play similar roles of both BFIR and BFER. It needs to do a
disposition of a BIER Header, and then do an imposition of a new BIER
Header. It requires the ABR router to maintain per-flow states, and
especially, such per-flow states always include a set of BFERs who
are intrested in a specific flow by using an explicit-tracking
procedure.
This behavior is completely different from a traditional segmented
MVPN deployment, e.g, with both of the two segments using P2MP label
switch. In a traditional segmented MVPN with both segments using
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P2MP label switch, it is expected to receive a MPLS packet and
replicate to downstream routers after swap the MPLS Label. A lookup
of IP packet is not expected. Also, in a traditional segmented MVPN
deployment, an MPLS label represents a P-tunnel, which may carry one,
many or even all multicast flow(s) of a VPN, so it is not always a
per-flow state on the segmentation point router.
In conclusion, the pattern of forwarding packets on segmentation
points only by lookup of MPLS label mapped from multicast flow(s) is
significantly unnecessary when BIER is introduced. Instead, doing a
per-flow lookup of IP header on segmentation points is more efficient
and consolidated.
4. Upstream BIER and Downstream BIER (BIER-BIER)
4.1. Explicit Tracking using LIR-pF
In a scenario of Inter-area Segmented MVPN with both segments using
BIER, the determination of the set of BFERs that need to receive a
specific multicast flow of (C-S1,C-G1) in each segment, can be
obtained by using a LIR-pF flag.
Suppose a topology of this:
(Ingress PE)PE1-------P1-------ABR-------P2------PE2(Egress PE)
| | |
| Ingress Area | Egress Area |
| ( BIER SD<X> ) | ( BIER SD<Y> ) |
Figure 1: Example topology
PE1 is Ingress PE, and the area of { PE1 -- P1 -- ABR } is called an
Ingress Area.
PE2 is Egress PE, and the area of { ABR -- P2 -- PE2 } is called an
Egress Area.
The Ingress PE is configured to use a BIER tunnel type for a MVPN
instance for the Ingress Area, and the ABR is configured to use a
BIER tunnel type for the MVPN instance for the Egress Area.
The Ingress PE originates a wildcard S-PMSI A-D route (C-*,C-*) and
the PTA of that route has the following settings:
o The LIR-pF and LIR flags be set.
o The tunnel type be set to "BIER".
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o A non-zero MPLS label be specified.
ABR receives the S-PMSI A-D route from the Ingress PE, and re-
advertises the route to the Egress PE, with a PTA type "BIER", and
PTA flags of LIR and LIR-pF, and a new non-zero upstream-assigned
MPLS label allocated by ABR per-VPN.
Egress PE receives the S-PMSI A-D route from the ABR, and checks if
it need to response with a Leaf A-D route to this S-PMSI A-D route
using the process of the "match for reception" and "match for
tracking" as defined in [I-D.bess-mvpn-expl-track]. In this example,
for a C-flow of (C-S1, C-G1), the checking result of "matched for
tracking" is the S-PMSI(C-*, C-*), and the checking result of
"matched for reception" is also the S-PMSI(C-*, C-*). Egress PE will
then send a Leaf A-D route (RD, C-S1, C-G1, Root=PE1, Leaf=PE2) to
the ABR with a PTA flag LIR-pF, and a Leaf A-D route (RD, C-*, C-*,
Root=PE1, Leaf=PE2) without a PTA flag LIR-pF.
ABR then has an explicit-tracking result of a new per-flow
information of (RD, C-S1, C-G1, Root=PE1) with Egress PE as its leaf
or BFER. ABR's "matched for tracking" result to this flow(RD, C-S1,
C-G1, PE1) will then be updated with a new record, and ABR then sends
a Leaf A-D route (RD, C-S1, C-G1, Root=PE1, Leaf=ABR) to Ingress PE.
Ingress PE then has an explicit-tracking result of a new per-flow
information of (RD, C-S1, C-G1, Root=PE1) with ABR as its leaf or
BFER.
From this procedure description one can see that:
1. The S-PMSI A-D(C-*, C-*) route is functioning as a per-VPN anchor
of the upstream and the downstream(s), which can be called an
BGP-MVPN FEC in this document, saying BGP-MVPN FEC(OrigIP, RD).
2. The Leaf A-D(S,G) routes are functioning as a per-flow anchor of
the downstream(s) and the upstream, which are also BGP-MVPN FECs
accordingly, saying BGP-MVPN FEC(OrigIP, RD, S,G).
3. The Tuple of (Root=PE1, RD) in S-PMSI (C-*, C-*) or Leaf AD(C-*,
C-*) or Leaf AD(C-S, C-G) represents an VRF on the ABR
implicitly.
ABR knows the per-vpn infmation of a (Root=PE1, RD) tuple when
receiving and re-advertising the S-PMSI A-D(*,*) route bound with a
PTA, where:
o Inbound SD (InSD): in PTA of the received S-PMSI(*,*) route.
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o Inbound VpnLabel (InVpnLabel): in PTA of the received S-PMSI(*,*)
route.
o Inbound BfirId (InBfirId): in PTA of the received S-PMSI(*,*)
route.
o Outbound SD(OutSD): in PTA of the re-advertised S-PMSI(*,*) route.
o Outbound VpnLabel (OutVpnLabel): in PTA of the re-advertised
S-PMSI(*,*) route.
o Outbound BfirId (OutBfirId): in PTA of the re-advertised
S-PMSI(*,*) route.
ABR establishs a per-flow control-plane state accordingly like this:
o Per-flow upstream state, according to the Leaf A-D (C-S, C-G)
route send to the Ingress PE: (PE1, RD, C-S1, C-G1, InSD,
InBfirId, InVpnLabel).
o Per-flow downstream state(s), according to the Leaf A-D(C-S, C-G)
route(s) received by the ABR from Egress PE(s): (PE1, RD, C-S1,
C-G1, Leaf, OutSD, OutBfirId, OutVpnLabel).
ABR knows the BIER Label(s) it allocated for InSD and OutSD, saying
InBierLabel for InSD<X> and OutBierLabel for OutSD<Y>, and thus it
can establish the per-flow forwarding state:
o Per-flow upstream forwarding state: (InBierLabel, InBfirId,
InVpnLabel, C-S1, C-G1).
o Per-flow downstream(s) forwarding state: (InBierLabel, InBfirId,
InVpnLabel, C-S1, C-G1, Leaf, OutBfirId, OutVpnLabel,
OutBitString)
4.2. Forwarding using IP lookup on Segmentation Point
The Forwarding procedure of a segmentation point, ABR, have the
following steps:
1. Do a disposition of MVPN-BIER tunnel to get the Pseudo-VRF, and a
following IP lookup in the Pseudo-VRF to get the appropriate BIER
encapsulation for Area<Y>, including the Local-VpnLabel indicated
by the Pseudo-VRF.
2. Do a disposition of MVPN-BIER tunnel to get the VRF, and a
following IP lookup to get the appropriate local VRF interfaces
if ABR has local VPN CEs.
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3. The said "disposition of MVPN-BIER tunnel" requires a lookup of
upstream-assigned VpnLabel in special context.
For Step 1 and step 2, One can think them as one-to-many swapping of
a big 'BIER header' instead of a small 'Label' in P2MP case:
o swapping the InBierLabel with an OutBierLabel.
o swapping the InBfirId with an OutBfirId.
o swapping the InVpnLabel with an OutVpnLabel.
o swapping the InBitString with an OutBitString.
The key of a per-flow lookup on ABR is a tuple of (InBierLabel,
InBfirId, InVpnLabel) and a tuple of (C-S1, C-G1), representing a VRF
and a flow respectively. All the elements are from a BIER packet,
and such an IP lookup is very similar to an MFIB lookup, if the
(InBierLabel, InBfirId, InVpnLabel) tuple is mapped to a Pseudo-VRF
locally on the ABR per the BGP-MVPN FEC(OrigIP, RD). The ABR can be
configured as PE of an MVPN instance as well, and then there would
have an MFIB lookup of the real VRF, and an MFIB lookup of the
Pseudo-VRF, independently, to not impact each other when
configuration is changed.
5. Upstream P2MP and Downstream BIER (P2MP-BIER)
5.1. Explicit Tracking using LIR-pF
The procedures described in chapter 4.1 is also suitable for this
case, provided the LIR-pF explicit-tracking is used appropriately.
Suppose a topology of this:
| Egress Area<Z> |
| (P2MP) |
| |
+-------P3------PE3(Egress PE)
/
(Ingress PE)PE1-------P1-------ABR
| \
| +-------P2------PE2(Egress PE)
| | |
| Ingress Area<X> | Egress Area<Y> |
| ( P2MP ) | ( BIER SD<Y> ) |
Figure 2: Example topology
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The Ingress PE is configured to use an P2MP tunnel type for a MVPN
instance for the Ingress Area<X>, and the ABR is configured to use a
BIER tunnel type for the MVPN instance for the Egress Area <Y>, and
ABR may be configured to use a P2MP tunnel type for another Egress
Area<Z>.
Example 1: Use Inclusive P-tunnel for traditional areas.
PE1 may configure to use one SPMSI (*,*,PTA<mLDP, Flag=LIR+LIRpF>)
route , for one Unidirectional Inclusive mLDP P2MP tunnel.
ABR may configure to reflect only the SPMSI(*,*) route with the PTA
type changed to BIER for Area<Y>, and reflect the SPMSI(*,*) route
with the PTA type changed to mLDP, RSVP-TE or IR for Area<Z>.
Example 2: Use Selective P-tunnel for traditional areas.
PE1 may configure to use one SPMSI (*,*,PTA<mLDP, Flag=LIR+LIRpF>)
route and a number of SPMSI (S,G,PTA<mLDP, Flag=LIR+LIFpF>) routes,
for one Unidirectional Inclusive mLDP P2MP tunnel and a number of
Selective mLDP P2MP tunnels respectively.
ABR may configure to reflect only the SPMSI(*,*) route with the PTA
type changed to BIER for Area<Y>, and reflect the SPMSI(*,*) route
and SPMSI(S,G) routes with the PTA type changed to mLDP, RSVP-TE or
IR for Area<Z>.
5.2. Forwarding using IP lookup on Segmentation Point
The Forwarding procedure of a segmentation point, ABR, have 3
conditions:
1. Do a disposition of P2MP tunnel to get the Pseudo-VRF, and a
following IP lookup in Pseudo-VRF to get the appropriate BIER
encapsulation for Area<Y>, including the Local-VpnLabel indicated
by the Pseudo-VRF.
2. Do a lookup of P2MP tunnel to get the appropriate P2MP
downstreams for Area<Z>.
3. Do a disposition of P2MP tunnel to get the VRF, and a following
IP lookup to get the appropriate local VRF interfaces if ABR has
local VPN CEs.
4. The said "lookup/disposition of P2MP tunnel" requires a lookup of
downstream-assigned P2MP Label lookup.
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6. Upstream BIER and Downstream P2MP (BIER-P2MP)
6.1. Explicit Tracking using LIR-pF
The procedures described in chapter 4.1 is also suitable for this
case, provided the LIR-pF explicit-tracking is used appropriately.
Suppose a topology of this:
| Egress Area<Z> |
| (P2MP) |
| |
+-------P3------PE3(Egress PE)
/
(Ingress PE)PE1-------P1-------ABR
| \
| +-------P2------PE2(Egress PE)
| | |
| Ingress Area<X> | Egress Area<Y> |
| ( BIER SD<X> ) | ( BIER SD<Y> ) |
Figure 3: Example topology
The Ingress PE is configured to use a BIER tunnel type for a MVPN
instance for the Ingress Area<X>, and the ABR is configured to use a
BIER tunnel type for the MVPN instance for the Egress Area <Y>, and
ABR may be configured to use a P2MP tunnel type for another Egress
Area<Z>.
Example 1: Use Inclusive P-tunnel for traditional areas.
PE1 may configure to use one SPMSI (*,*,PTA<BIER, Flag=LIR+LIRpF>)
route , for one BIER tunnel.
ABR may configure to reflect only the SPMSI(*,*) route with the PTA
type unchanged for Area<Y>, and reflect the SPMSI(*,*) route with the
PTA type changed to mLDP, RSVP-TE or IR for Area<Z>.
Example 2: Use Selective P-tunnel for traditional areas.
PE1 may configure to use one SPMSI (*,*,PTA<BIER, Flag=LIR+LIRpF,
VpnLabel1>) route and a number of SPMSI (S,G,PTA<BIER,
Flag=LIR+LIFpF>, VpnLabelX) routes. They include the same BIER
tunnel type with different VpnLabels, and the SPMSI(S,G) routes are
used to initialize the many Inter-area BGP-MVPN FECs with MVPN-BIER
tunnels, and thus enable the ABR to initialize many SPMSI tunnels for
Area<Z> per the upstream MVPN-BIER tunnels.
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ABR may configure to reflect only the SPMSI(*,*) route with the PTA
type changed to BIER for Area<Y>, and reflect the SPMSI(*,*) route
and SPMSI(S,G) routes with the PTA type changed to mLDP, RSVP-TE or
IR for Area<Z>.
6.2. Forwarding on Segmentation Point
The Forwarding procedure of a segmentation point, ABR, have the
following conditions:
1. Do a disposition of MVPN-BIER tunnel to get the Pseudo-VRF, and a
following IP lookup in the Pseudo-VRF to get the appropriate BIER
encapsulation for Area<Y>, including the Local-VpnLabel indicated
by the Pseudo-VRF.
2. Do a disposition of MVPN-BIER tunnel to get the appropriate P2MP
downstreams for Area<Z>.
3. Do a disposition of MVPN-BIER tunnel to get the VRF, and a
following IP lookup to get the appropriate local VRF interfaces
if ABR has local VPN CEs.
4. The said "disposition of MVPN-BIER tunnel" requires a lookup of
upstream-assigned VpnLabel in special context.
7. Summary and Recommendations
Traditional P2MP forwarding on an router can be simple if it is not
the Bud router case. Only a one shot Label lookup is enough to get
the outgoing P2MP interfaces to replicate. The same benefit is also
available by a pure 'ABR' node for segmented MVPN scenario.
But for a Bud router, the forwarding of an MPLS P2MP packet must
include a label lookup to find the outgoing P2MP interfaces, and a
further IP lookup for the local overlay forwarding. The same
challenge is same to a ABR node who has local VPN CEs connected.
For a segmented MVPN deployment with BIER, there are much more
ingredients different from the simple P2MP label lookup and swap.
1. When BIER is used as the tunnel of the upstream segment, then a
upstream-assigned VpnLabel lookup in a special context is
required, instead of a downstream-assigned label lookup.
2. When BIER is used as the tunnel of the downstream segment, then a
per-flow lookup is required to get the BIER encapsulation, beside
the normal 1:1 mapping of one MVPN-BIER tunnel to one tunnel
(MVPN-BIER tunnel or P2MP tunnel).
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3. It is possible to require a per-flow VpnLabel allocation for the
whole Segmented MVPN, then a per-flow lookup can be the same
result as the VpnLabel lookup, and then one can optimize not to
use IP lookup. While this may not be allowed when BIER-P2MP or
P2MP-BIER are deployed and the P2MP part can not support per-flow
tunnels. One obvious example is when the P2MP segment use
Inclusive P2MP tunnel for all or for part of the multicast flows.
Also this does not hinder the use of LIR-pF explicit-tracking.
4. An IP lookup following a VpnLabel lookup in special context is a
mandatory capability for a BFER function, and an IP lookup
following a P2MP label lookup is a mandatory capability for a
P2MP BUD function, so they did not hinder the use of IP lookup on
ABR in case when downstream segment deploying BIER.
Recommendations are:
1. that implementations support the IP lookup for Segmented MVPN
when downstream segment using BIER.
2. that implementations support the optimization of not using IP
lookup when end to end distinct tunnels (P2MP tunnels or MVPN-
BIER tunnels) to distinct C-flows is not a limit.
3. that implementations support the LIR-pF explicit tracking for
Segmented MVPN if it support LIR-pF explicit tracking for
unsegmented MVPN already.
4. that implementations support the LIR-pF explicit tracking for
Segmented MVPN if one want to gain better multicast join latency
and tolerate the unnecessary LeafAD routes in P2MP segment(s)
cased by the enabling of LIR-pF explicit tracking.
8. Appendix A - Comparison of Solutions
The table below provides a side-by-side comparison of explicit
tracking recommended, for unsegmented MVPN and segmented MVPN cases.
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+------------------+-------------------------+-----------------------+
| <Expl-tracking> | draft-ietf-bier-mvpn | this draft |
+------------------+-------------------------+-----------------------+
| Unsegmented MVPN | LIR-pF | LIR-pF |
| | Per-flow Label NotReq | Per-flow Label NotReq |
+------------------+-------------------------+-----------------------+
| | LIR | LIR-pF |
| Segmented MVPN | Per-flow Label Required | Per-flow Label NotReq |
+------------------+-------------------------+-----------------------+
| (BIER-BIER) | LIR | LIR-pF |
+------------------+-------------------------+-----------------------+
| (BIER-P2MP) | Not specified | LIR-pF |
+------------------+-------------------------+-----------------------+
| (BIER-BIER) | Not specified | LIR-pF |
+------------------+-------------------------+-----------------------+
Figure 4: Comparison of Segmented and unsegmented MVPN
The table below provides a side-by-side comparison of forwarding
procedure on BFER/segmentation point ABR about whether to use IP
Lookup, for BFER, BIER-BIER, P2MP-BIER and BIER-P2MP cases.
+---------------+----------------------+-----------------------+
| <Forwarding> | draft-ietf-bier-mvpn | this draft |
+---------------+----------------------+-----------------------+
| BFER | VpnLabel Lookup | VpnLabel Lookup |
| | + IP Lookup | + IP Lookup |
+---------------+----------------------+-----------------------+
| ABR(BIER-BIER)| VpnLabel lookup | VpnLabel lookup |
| | | + IP Lookup |
+---------------+----------------------+-----------------------+
| ABR(P2MP-BIER)| P2MP-Label Lookup | P2MP-Label Lookup |
| | | + IP Lookup |
+---------------+----------------------+-----------------------+
| ABR(BIER-P2MP)| VpnLabel lookup | VpnLabel Lookup |
+---------------+----------------------+-----------------------+
| ABR(P2MP-P2MP)| P2MP-Label lookup | P2MP-Label Lookup |
+---------------+----------------------+-----------------------+
Figure 5: Comparison of Various Forwarding cases
The table below provides a list of the forwarding on ABR in a 3
segments deployment cases.
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+----------------------------------------------+------------+
| Topology Deployed | Forwarding |
| PE1--(Tnl1)--ABR1--(Tnl2)--ABR2--(Tnl3)--PE2 | on ABR1 |
+----------------------------------------------+------------+
| BIER | BIER | ANY | *(1) |
| BIER | IR | ANY | *(2) |
| BIER | MLDP | ANY | *(2) |
| BIER | RSVP-TE | ANY | *(2) |
+----------------------------------------------+------------+
| IR | BIER | ANY | *(3) |
| IR | IR | ANY | P2MP Swap |
| IR | MLDP | ANY | P2MP Swap |
| IR | RSVP-TE | ANY | P2MP Swap |
+----------------------------------------------+------------+
| MLDP | BIER | ANY | *(3) |
| MLDP | IR | ANY | P2MP Swap |
| MLDP | MLDP | ANY | P2MP Swap |
| MLDP | RSVP-TE | ANY | P2MP Swap |
+----------------------------------------------+------------+
| RSVP-TE | BIER | ANY | *(3) |
| RSVP-TE | IR | ANY | P2MP Swap |
| RSVP-TE | MLDP | ANY | P2MP Swap |
| RSVP-TE | RSVP-TE | ANY | P2MP Swap |
+----------------------------------------------+------------+
*(1) VpnLabel Lookup for PseudoVRF, and IP Lookup for per-flow encapsulation.
*(2) VpnLabel Lookup for per-tunnel P2MP downstreams.
*(3) P2MP-Label Lookup for PseudoVRF, and IP Lookup for per-flow encapsulation.
*(4) P2MP-Label Lookup for per-tunnel P2MP downstreams.
Figure 6: Comparison of Various segmented combinations
9. Security Considerations
The procedures of this document do not, in themselves, provide
privacy, integrity, or authentication for the control plane or the
data plane.
10. IANA Considerations
No IANA allocation is required.
11. Acknowledgements
TBD.
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12. References
12.1. Normative References
[I-D.ietf-bess-mvpn-expl-track]
Dolganow, A., Kotalwar, J., Rosen, E., and Z. Zhang,
"Explicit Tracking with Wild Card Routes in Multicast
VPN", draft-ietf-bess-mvpn-expl-track-12 (work in
progress), October 2018.
[I-D.ietf-bier-mvpn]
Rosen, E., Sivakumar, M., Aldrin, S., Dolganow, A., and T.
Przygienda, "Multicast VPN Using BIER", draft-ietf-bier-
mvpn-11 (work in progress), March 2018.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
[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,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC6625] Rosen, E., Ed., Rekhter, Y., Ed., Hendrickx, W., and R.
Qiu, "Wildcards in Multicast VPN Auto-Discovery Routes",
RFC 6625, DOI 10.17487/RFC6625, May 2012,
<https://www.rfc-editor.org/info/rfc6625>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
12.2. Informative 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>.
Authors' Addresses
Jingrong Xie
Huawei Technologies
Email: xiejingrong@huawei.com
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Liang Geng
China Mobile
Beijing 10053
Email: gengliang@chinamobile.com
Lei Wang
China Mobile
Beijing 10053
Email: wangleiyjy@chinamobile.com
Mike McBride
Huawei
Email: mmcbride7@gmail.com
Gang Yan
Huawei
Email: yangang@huawei.com
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