BIER Workgroup H. Bidgoli, Ed.
Internet Draft A. Dolganow
Intended status: Standard Track J. Kotalwar
Nokia
Fengman Xu
Verizon
IJ. Wijnand
Cisco Systems, Inc.
Mankamana Mishra
Cisco System, Inc.
Expires: August 11, 2018 February 7, 2018
PIM Signaling Through BIER Core
draft-hfa-bier-pim-signaling-01
Abstract
Bit Index Explicit Replication (BIER) is an architecture that
provides multicast forwarding through a "BIER domain" without
requiring intermediate routers to maintain multicast related per-flow
state. Neither does BIER require an explicit tree-building protocol
for its operation. A multicast data packet enters a BIER domain at a
"Bit-Forwarding Ingress Router" (BFIR), and leaves the BIER domain at
one or more "Bit-Forwarding Egress Routers" (BFERs). The BFIR router
adds a BIER header to the packet. Such header contains a bit-string
in which each bit represents exactly one BFER to forward the packet
to. The set of BFERs to which the multicast packet needs to be
forwarded is expressed by the according set of bits switched on in
BIER packet header.
This document describes the procedure needed for PIM Joins and Prunes
to be signaled through a BIER core. Allowing PIM routers to run
traditional PIM multicast services through a BIER core.
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), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on October 8, 2017.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . . 3
2.1. Definitions . . . . . . . . . . . . . . . . . . . . . . . . 4
3. PIM Signaling Through BIER domain . . . . . . . . . . . . . . . 5
3.1. Ingress BBR procedure . . . . . . . . . . . . . . . . . . . 6
3.1.1. BIER packet construction at IBBR . . . . . . . . . . . 7
3.2. Signaling PIM through the BIER domain procedure . . . . . . 8
3.3 Procedure to determine EBBR on IBBR . . . . . . . . . . . . 8
3.3.1 EBBR identification via next-hop . . . . . . . . . . . . 8
3.3.1.1 Static Route . . . . . . . . . . . . . . . . . . . . 8
3.3.1.2 Interior Border Gateway Protocol (iBGP) . . . . . . 8
3.3.2 Route summarization at EBBR . . . . . . . . . . . . . . 9
3.3.4 Constrain shortest path first . . . . . . . . . . . . . 9
3.4. EBBR procedure . . . . . . . . . . . . . . . . . . . . . . 9
4. Datapath Forwarding . . . . . . . . . . . . . . . . . . . . . . 10
4.1. BFIR tracking of (S,G) . . . . . . . . . . . . . . . . . . 10
4.2. Datapath traffic flow . . . . . . . . . . . . . . . . . . . 10
5. PIM-ASM behavior . . . . . . . . . . . . . . . . . . . . . . . 10
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6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . . 11
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
8.1. Normative References . . . . . . . . . . . . . . . . . . . 11
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Greenfield deployment of BIER might not be possible for some large
network. These networks deploy traditional PIM multicast services in
GRT or in mvpns such as multicast vpns rfc 6037. Typically, each
portion of these large networks have their own mandates and
requirements.
Consider the case of converged core, where single core is used for
fixed, business and wireless services. In this case there is a desire
for next generation "lean" core. Where a single IGP protocol or SDN
controller could enable unicast and multicast services. BIER is a
natural fit for this core. That said because of cost and operational
complexity the migration to BIER might fall into below categories:
1.Gradual migration of the network to BIER, starting with the
"lean" core and eventually to access networks.
2.Migrating only the core to BIER and keeping traditional pim
services in access. As an example, in wireless networks where there
are thousands of cell site routers. Each cell site router is a leaf
as such for scaling and cost it might be desired to keep
traditional PIM multicast services in the access network.
This draft explains the procedure to signal PIM joins and prunes
through a BIER core, as such enable provisioning of traditional pim
services through a BIER core.
It should be noted that this "lean" core is usually a single IGP
area. As such the procedures in this draft is concentrating on a
single BIER IGP area.
2. Conventions used in this document
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 RFC 2119 [RFC2119].
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2.1. Definitions
Some of the terminology specified in [I-D. rfc8279] is replicated
here and extended by necessary definitions:
BIER:
Bit Index Explicit Replication (The overall architecture of
forwarding multicast using a Bit Position).
BFR:
Bit Forwarding Router (A router that participates in Bit Index
Multipoint Forwarding).A BFR is identified by a unique BFR-
prefix in a BIER domain.
BFIR:
Bit Forwarding Ingress Router (The ingress border router that
inserts the BM into the packet). Each BFIR must have a valid
BFR-id assigned. In this draft BIER will be used for
forwarding and tunneling of control plain packet (i.e. PIM)
and forwarding dataplane packets. BFIR is term used for
dataplane packet forwarding.
BFER:
Bit Forwarding Egress Router. A router that participates in
Bit Index Forwarding as leaf. Each BFER must be a BFR. Each
BFER must have a valid BFR-id assigned. In this draft BIER
will be used for forwarding and tunneling of control plain
packet (i.e. PIM) and forwarding dataplain packets. BFIR is
term used for dataplain packet forwarding.
BBR:
BIER Boundary router. The router between the PIM domain and
BIER domain. Maintains PIM adjacency for all routers attached
to it on the PIM domain and terminates the PIM adjacency
toward the BIER domain.
IBBR:
Ingress BIER Boundary Router. The ingress router from
signaling point of view. It maintains PIM adjacency toward the
PIM domain and determines if PIM joins and prunes arriving
from PIM domain need to be signaled across the BIER domain. If
so it terminates the PIM adjacency toward the BIER domain and
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signals the PIM joins/prunes through the BIER core.
EBBR:
Egress BIER Boundary Router. The egress router in BIER domain
from signaling point of view. It terminates the BIER packet
and forwards the signaled joins and prunes into PIM Domain.
BFT:
Bit Forwarding Tree used to reach all BFERs in a domain.
BIFT:
Bit Index Forwarding Table.
BIER sub-domain:
A further distinction within a BIER domain identified by its
unique sub-domain identifier. A BIER sub-domain can support
multiple BitString Lengths.
BFR-id:
An optional, unique identifier for a BFR within a BIER sub-
domain.
3. PIM Signaling Through BIER domain
bbr bbr
|--pim Domain--|-----bier domain-----|--pim domain--|
S--( A )----------( B ) ---- ( C ) ---- ( D )----------( E )--h
ebbr ibbr
Sig <-----PIM-----|<--Bier Tunneling----|<----PIM------
(new)
bfir bfer
------------->|--------BIER-------->|-------------> Datapatah
(no change)
Figure 1: bier boundary router
As per figure 1, the procedures of PIM signaling is done at the BIER
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boundary router. The BIER boundary router (BBR) are connected to PIM
capable routers toward the pim domain and BIER routers toward the
bier domain. PIM routers in pim domain continue to send PIM state
messages to the BBR. The BBR will create pim adjacency between all
the PIM routers attach to it on the pim domain. That said the BBR
does not propagate all PIM packets natively into the BIER domain.
Instead when it determines that the PIM join or prune messages needs
to be signaled through the BIER domain it will tunnel the PIM packet
through BIER network. This tunneling is only done for signaling
purposes and not for creating a PIM adjacency between the two
disjoint pim domains through the bier domain.
The terminology ingress BBR (ibbr) and egress BBR (ebbr) are relative
from signaling point of view.
The ingress BBR will determine if an arriving pim join or prune needs
to be signaled across the bier domain. While the egress BBR will
determine if the bier packet is a signaling packet and propagate the
packet to its attach pim domain.
The BFER and BFIR are BBR from datapath point of view. It should be
noted the new procedures in this draft are only applicable to
signaling and there are no changes from datapath point of view.
3.1. Ingress BBR procedure
IBBR will create pim adjacency to all pim routers attach to it toward
the pim domain.
When a PIM join or prune for certain (S,G) arrives, the IBBR first
determines weather the join or prune is meant for a source that is
reachable through the bier domain. As an example, this source is
located on a disjoint PIM domain that is reachable through the BIER
domain. If so the ibbr will try to resolve the source via an ebbr
closest to the source.
The procedure to find the ebbr (BFIR from datapath point of view) can
be via many mechanisms explained in more detail in upcoming sections.
It should be noted that in most cases the BIER domain is a single IGP
area. The PIM domains are part of the same IGP area as BIER
domain(single area) or are stitched to the BIER domain via an ABR or
ASBR. in either case the BBRs are all located in the same area as
bier domain. Below are two examples of resolving ebbrs:
1.The ebbr can be an ABR or ASBR router in the same IGP area as bier
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domain. In this case the ebbr summarizes the route to the source,
and as such the ebbr is the IGP source of this route. The IGP
source information can be used for identifying the ebbr and
resolving it.
2.If source and ebbr are within a single IGP area, the ebbr can be
resolved via SPF calculation. As an example, the closest ebbr to
the source. The ebbr BFR-ID is signaled via IGP to all BFRs, as
such making it possible to do SFP calculation.
After discovering the EBBR and its BFR-ID (flooded via IGP BIER
extension), the IBBR will construct the BIER header via the BIFT. The
signaling packet, in this case the PIM join/prune packet, is
encapsulated in the BIER header and transported through BIER domain
to EBBR.
On forwarding plane the IBBR will track all the PIM interfaces on the
attach pim domain which are interested in a certain (S,G). It creates
multicast states for arriving (S,G)s from pim domain, with incoming
interface (RPF) as BIER "tunnel" interface and outgoing interface as
the pim domain interface(s) on which PIM Join(s) were received on. If
there is another PIM Join for the same multicast (S,G) entry on
another interface arriving from pim domain, that interface gets added
in the outgoing interface list as well.
3.1.1. BIER packet construction at IBBR
The BIER header will be encoded with the BFR-id of the IBBR(with
appropriate bit set in the bitstring) and the PIM signaling packet is
then encapsulated in the packet.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BIFT-id | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Nibble | Ver | BSL | Entropy |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|OAM|Rsv| DSCP | Proto | BFIR-id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| BitString (first 32 bits) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ BitString (last 32 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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BIERHeader.Proto = IPv4 or IPv6
BIERHeader.BitString= Bit corresponding to the BFR-ID of the EBBR
BIERHeader.BFIR-id = BFR-Id of the BER originating the encapsulated
PIM packet, i.e. the IBBR.
Rest of the values in the BIER header are determined based on the
network (MPLS/non-MPLS), capabilities (BSL), and network
configuration.
3.2. Signaling PIM through the BIER domain procedure
Throughout the BIER domain the BIER forwarding procedure is in par
with RFC 8279. No BIER router will examine the BIER packet
encapsulating the PIM signaling packet. As such there is no multicast
state build in the BIER domain.
The packet will be forwarded through the BIER domain until it reaches
the BER with matching BFR-ID as in the BIERHeader.Bitstring. This BER
(EBBR) will remove the BIER header and examine the PIM IPv4 or IPv6
signaling packet farther.
3.3 Procedure to determine EBBR on IBBR
As it was explained in previous section, IBBR needs to determine the
EBBR closest to the source. This is needed to encode the BIER header
BitString field for forwarding of the signaling packet. There can be
many mechanism to determine the EBBR. This section explain some
routing methods that can be used to achieve this.
3.3.1 EBBR identification via next-hop
Assuming on the IBBR the source is resolved via EBBR bier prefix-id
as its next-hop, the next-hop can be used to lookup the EBBR bit-
index via the BIFT. In most cases the bier prefix-id is a loopback
address. The next-hop of the source on IBBR can be set to EBBR via
multiple methods, including Static Route and BGP.
3.3.1.1 Static Route
On IBBR there can be a static route configured for the source, with
source next-hop set as EBBR BIER prefix id.
3.3.1.2 Interior Border Gateway Protocol (iBGP)
Consider the following topology:
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bbr bbr
ebbr ibbr
|--pim Domain--|-----bier domain-----|--pim domain--|
S--( A )----------( B ) ---- ( C ) ---- ( D )----------( E )--h
Figure 2
Suppose BGP is enable between EBBR (B) and IBBR (D) and the PIM
Domain routes are redistributed to the BIER domain via BGP. This
would include the Multicast Source IP address (S), which resides in
the PIM Domain. In such case BGP should use the same loopback
interface as its next-hop as the BBR prefix-id. This will ensure that
all PIM domain routes, including the Multicast Source IP address (S)
are resolve via BBR's bier prefix id as thier next-hop. When the host
(h) triggers a PIM join message to IBBR (D), IBBR tries to resolve
(S). It resolves (S) via BGP installed route and realizes its next-
hop is EBBR (B). IBBR will use this next-hop (B) to do a lookup in
the BIFT and find its corresponding BIER bit index in the BIFT. Next
IBBR will build the BIER header with corresponding EBBR bit index and
tunnel the PIM signaling message toward EBBR. This procedure is
inline with RFC6826 mLDP in-band signaling section 2.
3.3.2 Route summarization at EBBR
The BIER domain can be an IGP area, in this case the EBBRs and IBBRs
would act as an area boundary router (ABR). ABR could summarize
routes and/or generate new routes with advertising router field set
to EBBR bier prefix-id. When IBBR resolves the Source it can use the
advertising router field to generate the BIER BitString Header for
the EBBR closest to the source.
3.3.4 Constrain shortest path first
In the BIER domain the edge BIER routers use IGP or BGP to advertise
BIER extension TLVs. As such the routing protocols have a view of the
EBBR closest to the source in PIM domain. To find the EBBR, IBBR can
do a lookup for the source and ask for the closest EBBR on the path
to the source. This look up can be a CSPF lookup. The IGP should
return the EBBR closest to the source as part of this lookup.
3.4. EBBR procedure
After receiving the BIER packet and determining this packet is a
signaling packet. As such the EBBR will remove the BIER header from
PIM packet and does a route lookup for the source of the pim packet,
if the source is on a local attach pim domain, it forwards the PIM
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packet toward the source.
With same token the EBBR creates a multicast state with incoming
interface as same interface that PIM join packet was forwarded and
outgoing interfaces of BIER tunnel with BIER-Header.BFIR-id as one of
the BFER of the tunnel.
The EBBR will also build a BIER reverse path forwarding table, using
the BIERHeader.BFIR-id and the arriving PIM packet (S,G). This is
explained in section 4.1.
It should be noted EBBR will maintain PIM adjacency toward the PIM
domain and all PIM routers which are connected to it.
At this point the end-to-end multicast traffic flow setup is
complete.
4. Datapath Forwarding
4.1. BFIR tracking of (S,G)
For a specific Source and Group, BFIR (EBBR)should track all the
interested BFERs via arriving PIM signaling from BIER Domain. BFIR
should build its multicast tree with incoming interface (IIF) as PIM
interface (in PIM domain) and out going interfaces OIFs set as the
<SD, BFR-ID> of the interested BFERs (in BIER Domain).
4.2. Datapath traffic flow
When the multicast data traffic arrives on the BFIR (EBBR) the router
will find all the interested BFERs for that specific (S,G). The
router then constructs the BIERHeader.BitString with all the BFER
interested in the group and will forward the packet to the BIER
domain. The BFER(s) will accept the packets and remove the BIER
header and forward the multicast packet as per pre-build multicast
state for (G) and its outgoing interfaces.
5. PIM-ASM behavior
In case of PIM ASM the procedure for LEAFs joining RP is same as
above. The unicast (source registration) traffic from source to RP
will be flooded throughout the BIER domain as regular unicast traffic
without BIER involvement.
6. IANA Considerations
This document contains no actions for IANA.
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7. Security Considerations
TBD
8. References
8.1. Normative References
[BIER_ARCH] Wijnands, IJ., Rosen, E., Dolganow, A., Przygienda, T.,
and S. Aldrin, "Multicast using Bit Index Explicit Replication", rfc
8279, October 2016.
8.2. Informative References
[BIER_MVPN] Rosen, E., Ed., Sivakumar, M., Wijnands, IJ., Aldrin, S.,
Dolganow, A., and T. Przygienda, "Multicast VPN Using Bier",
internet-draft draft-ietf-bier-mvpn-08, January 2017.
[ISIS_BIER_EXTENSIONS] Ginsberg, L., Przygienda, T., Aldrin, S., and
Z. Zhang, "BIER Support via ISIS", internet-draft draft-ietf-bier-
isis-extensions-06.txt, March 2017.
[OSPF_BIER_EXTENSIONS] Psenak, P., Kumar, N., Wijnands, IJ.,
Dolganow, A., Przygienda, T., Zhang, Z., and S. Aldrin, "OSPF
Extensions for Bit Index Explicit Replication", internet-draft draft-
ietf-ospf-bier-extensions-09.txt, March 2017.
7. Acknowledgments <Add any acknowledgements>
Authors' Addresses
Hooman Bidgoli (editor)
Nokia
600 March Rd.
Ottawa, Ontario K2K 2E6
Canada
Email: hooman.bidgoli@nokia.com
Fengman Xu
Verizon
400 International PKWY
Richardson, Tx 75081
US
Email: fengman.xu@verizon.com
Jayant Kotalwar
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Nokia
380 N Bernardo Ave,
Mountain View, CA 94043
US
Email: jayant.kotalwar@nokia.com
Andrew Dolganow
Nokia
750D Chai Chee Rd
06-06, Viva Business Park
Singapore 469004
Email: Andrew.dolganow@nokia.com
IJsbrand Wijnands
Cisco Systems, Inc.
De Kleetlaan 6a
Diegem 1831
Belgium
Email: ice@cisco.com
Mankamana Mishra
mankamis@cisco.com
821 alder drive,
Milpitas California
USA
Email: mankamis@cisco.com
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