Network Working Group T. Eckert, Ed.
Internet-Draft Futurewei
Intended status: Standards Track G. Cauchie
Expires: May 4, 2020 Bouygues Telecom
M. Menth
University of Tuebingen
November 1, 2019
Traffic Engineering for Bit Index Explicit Replication (BIER-TE)
draft-ietf-bier-te-arch-05
Abstract
This memo introduces per-packet stateless strict and loose path
engineered replication and forwarding for Bit Index Explicit
Replication packets ([RFC8279]). This is called BIER-TE.
BIER-TE leverages the BIER architecture ([RFC8279]) and extends it
with a new semantic for bits in the bitstring. BIER-TE can leverage
BIER forwarding engines with little or no changes.
In BIER, the BitPositions (BP) of the packets bitstring indicate BIER
Forwarding Egress Routers (BFER), and hop-by-hop forwarding uses a
Routing Underlay such as an IGP.
In BIER-TE, BitPositions indicate adjacencies. The BIFT of each BFR
are only populated with BPs that are adjacent to the BFR in the BIER-
TE topology. The BIER-TE topology can consist of layer 2 or remote
(route) adjacencies. The BFR then replicates and forwards BIER
packets to those adjacencies. This results in the aforementioned
strict and loose path forwarding.
BIER-TE can co-exist with BIER forwarding in the same domain, for
example by using separate sub-domains. In the absence of routed
adjacencies, BIER-TE does not require a BIER routing underlay, and
can then be operated without requiring an IGP routing protocol.
BIER-TE operates without explicit in-network tree-building and
carries the multicast distribution tree in the packet header. It can
therefore be a good fit to support multicast path steering in Segment
Routing (SR) networks.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Basic Examples . . . . . . . . . . . . . . . . . . . . . 4
1.2. BIER-TE Topology and adjacencies . . . . . . . . . . . . 7
1.3. Comparison with BIER . . . . . . . . . . . . . . . . . . 8
1.4. Requirements Language . . . . . . . . . . . . . . . . . . 8
2. Components . . . . . . . . . . . . . . . . . . . . . . . . . 8
2.1. The Multicast Flow Overlay . . . . . . . . . . . . . . . 9
2.2. The BIER-TE Controller Host . . . . . . . . . . . . . . . 9
2.2.1. Assignment of BitPositions to adjacencies of the
network topology . . . . . . . . . . . . . . . . . . 10
2.2.2. Changes in the network topology . . . . . . . . . . . 10
2.2.3. Set up per-multicast flow BIER-TE state . . . . . . . 10
2.2.4. Link/Node Failures and Recovery . . . . . . . . . . . 11
2.3. The BIER-TE Forwarding Layer . . . . . . . . . . . . . . 11
2.4. The Routing Underlay . . . . . . . . . . . . . . . . . . 11
3. BIER-TE Forwarding . . . . . . . . . . . . . . . . . . . . . 11
3.1. The Bit Index Forwarding Table (BIFT) . . . . . . . . . . 11
3.2. Adjacency Types . . . . . . . . . . . . . . . . . . . . . 13
3.2.1. Forward Connected . . . . . . . . . . . . . . . . . . 13
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3.2.2. Forward Routed . . . . . . . . . . . . . . . . . . . 13
3.2.3. ECMP . . . . . . . . . . . . . . . . . . . . . . . . 13
3.2.4. Local Decap . . . . . . . . . . . . . . . . . . . . . 14
3.3. Encapsulation considerations . . . . . . . . . . . . . . 14
3.4. Basic BIER-TE Forwarding Example . . . . . . . . . . . . 14
3.5. Forwarding comparison with BIER . . . . . . . . . . . . . 17
3.6. Requirements . . . . . . . . . . . . . . . . . . . . . . 17
4. BIER-TE Controller Host BitPosition Assignments . . . . . . . 18
4.1. P2P Links . . . . . . . . . . . . . . . . . . . . . . . . 18
4.2. BFER . . . . . . . . . . . . . . . . . . . . . . . . . . 18
4.3. Leaf BFERs . . . . . . . . . . . . . . . . . . . . . . . 18
4.4. LANs . . . . . . . . . . . . . . . . . . . . . . . . . . 19
4.5. Hub and Spoke . . . . . . . . . . . . . . . . . . . . . . 20
4.6. Rings . . . . . . . . . . . . . . . . . . . . . . . . . . 20
4.7. Equal Cost MultiPath (ECMP) . . . . . . . . . . . . . . . 21
4.8. Routed adjacencies . . . . . . . . . . . . . . . . . . . 24
4.8.1. Reducing BitPositions . . . . . . . . . . . . . . . . 24
4.8.2. Supporting nodes without BIER-TE . . . . . . . . . . 24
4.9. Reuse of BitPositions (without DNR) . . . . . . . . . . . 24
4.10. Summary of BP optimizations . . . . . . . . . . . . . . . 26
5. Avoiding loops and duplicates . . . . . . . . . . . . . . . . 27
5.1. Loops . . . . . . . . . . . . . . . . . . . . . . . . . . 27
5.2. Duplicates . . . . . . . . . . . . . . . . . . . . . . . 27
6. BIER-TE Forwarding Pseudocode . . . . . . . . . . . . . . . . 27
7. Managing SI, subdomains and BFR-ids . . . . . . . . . . . . . 30
7.1. Why SI and sub-domains . . . . . . . . . . . . . . . . . 31
7.2. Bit assignment comparison BIER and BIER-TE . . . . . . . 32
7.3. Using BFR-id with BIER-TE . . . . . . . . . . . . . . . . 32
7.4. Assigning BFR-ids for BIER-TE . . . . . . . . . . . . . . 33
7.5. Example bit allocations . . . . . . . . . . . . . . . . . 34
7.5.1. With BIER . . . . . . . . . . . . . . . . . . . . . . 34
7.5.2. With BIER-TE . . . . . . . . . . . . . . . . . . . . 35
7.6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 36
8. BIER-TE and Segment Routing (SR) . . . . . . . . . . . . . . 36
9. Security Considerations . . . . . . . . . . . . . . . . . . . 37
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 38
12. Change log [RFC Editor: Please remove] . . . . . . . . . . . 38
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 42
13.1. Normative References . . . . . . . . . . . . . . . . . . 42
13.2. Informative References . . . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 43
1. Introduction
BIER-TE shares architecture, terminology and packet formats with BIER
as described in [RFC8279] and [RFC8296]. This document describes
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BIER-TE in the expectation that the reader is familiar with these two
documents.
In BIER-TE, BitPositions (BP) indicate adjacencies. The BIFT of each
BFR is only populated with BP that are adjacent to the BFR in the
BIER-TE Topology. Other BPs are left without adjacency. The BFR
replicate and forwards BIER packets to adjacent BPs that are set in
the packet. BPs are normally also reset upon forwarding to avoid
duplicates and loops. This is detailed further below.
Note that related work, [I-D.ietf-roll-ccast] uses bloom filters to
represent leaves or edges of the intended delivery tree. Bloom
filters in general can support larger trees/topologies with fewer
addressing bits than explicit bitstrings, but they introduce the
heuristic risk of false positives and cannot reset bits in the
bitstring during forwarding to avoid loops. For these reasons, BIER-
TE uses explicit bitstrings like BIER. The explicit bitstrings of
BIER-TE can also be seen as a special type of bloom filter, and this
is how related work [ICC] describes it.
1.1. Basic Examples
BIER-TE forwarding is best introduced with simple examples.
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BIER-TE Topology:
Diagram:
p5 p6
--- BFR3 ---
p3/ p13 \p7
BFR1 ---- BFR2 BFR5 ----- BFR6
p1 p2 p4\ p14 /p10 p11 p12
--- BFR4 ---
p8 p9
(simplified) BIER-TE Bit Index Forwarding Tables (BIFT):
BFR1: p1 -> local_decap
p2 -> forward_connected to BFR2
BFR2: p1 -> forward_connected to BFR1
p5 -> forward_connected to BFR3
p8 -> forward_connected to BFR4
BFR3: p3 -> forward_connected to BFR2
p7 -> forward_connected to BFR5
p13 -> local_decap
BFR4: p4 -> forward_connected to BFR2
p10 -> forward_connected to BFR5
p14 -> local_decap
BFR5: p6 -> forward_connected to BFR3
p9 -> forward_connected to BFR4
p12 -> forward_connected to BFR6
BFR6: p11 -> forward_connected to BFR5
p12 -> local_decap
Figure 1: BIER-TE basic example
Consider the simple network in the above BIER-TE overview example
picture with 6 BFRs. p1...p14 are the BitPositions (BP) used. All
BFRs can act as ingress BFR (BFIR), BFR1, BFR3, BFR4 and BFR6 can
also be egress BFR (BFER). Forward_connected is the name for
adjacencies that are representing subnet adjacencies of the network.
Local_decap is the name of the adjacency to decapsulate BIER-TE
packets and pass their payload to higher layer processing.
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Assume a packet from BFR1 should be sent via BFR4 to BFR6. This
requires a bitstring (p2,p8,p10,p12). When this packet is examined
by BIER-TE on BFR1, the only BitPosition from the bitstring that is
also set in the BIFT is p2. This will cause BFR1 to send the only
copy of the packet to BFR2. Similarly, BFR2 will forward to BFR4
because of p8, BFR4 to BFR5 because of p10 and BFR5 to BFR6 because
of p12. p12 also makes BFR6 receive and decapsulate the packet.
To send in addition to BFR6 via BFR4 also a copy to BFR3, the
bitstring needs to be (p2,p5,p8,p10,p12,p13). When this packet is
examined by BFR2, p5 causes one copy to be sent to BFR3 and p8 one
copy to BFR4. When BFR3 receives the packet, p13 will cause it to
receive and decapsulate the packet.
If instead the bitstring was (p2,p6,p8,p10,p12,p13), the packet would
be copied by BFR5 towards BFR3 because p6 instead of BFR2 to BFR5
because of p6 in the prior case. This is showing the ability of the
shown BIER-TE Topology to make the traffic pass across any possible
path and be replicated where desired.
BIER-TE has various options to minimize BP assignments, many of which
are based on assumptions about the required multicast traffic paths
and bandwidth consumption in the network.
The following picture shows a modified example, in which Rtr2 and
Rtr5 are assumed not to support BIER-TE, so traffic has to be unicast
encapsulated across them. Unicast tunneling of BIER-TE packets can
leverage any feasible mechanism such as MPLS or IP, these
encapsulations are out of scope of this document. To emphasize non-
native forwarding of BIER-TE packets, these adjacencies are called
"forward_routed", but otherwise there is no difference in their
processing over the aforementioned "forward_connected" adjacencies.
In addition, bits are saved in the following example by assuming that
BFR1 only needs to be BFIR but not BFER or transit BFR.
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BIER-TE Topology:
Diagram:
p1 p3 p7
....> BFR3 <.... p5
........ ........>
BFR1 (Rtr2) (Rtr5) BFR6
........ ........>
....> BFR4 <.... p6
p2 p4 p8
(simplified) BIER-TE Bit Index Forwarding Tables (BIFT):
BFR1: p1 -> forward_routed to BFR3
p2 -> forward_routed to BFR4
BFR3: p3 -> local_decap
p5 -> forward_routed to BFR6
BFR4: p4 -> local_decap
p6 -> forward_routed to BFR6
BFR6: p5 -> local_decap
p6 -> local_decap
p7 -> forward_routed to BFR3
p8 -> forward_routed to BFR4
Figure 2: BIER-TE basic overlay example
To send a BIER-TE packet from BFR1 via BFR3 to BFR6, the bitstring is
(p1,p5). From BFR1 via BFR4 to BFR6 it is (p2,p6). A packet from
BFR1 to BFR3,BFR4 and BFR6 can use (p1,p2,p3,p4,p5) or
(p1,p2,p3,p4,p6), or via BFR6 (p2,p3,p4,p6,p7) or (p1.p3,p4,p5,p8).
1.2. BIER-TE Topology and adjacencies
The key new component in BIER-TE to control where replication can or
should happens and how to minimize the required BP for segments is -
as shown in these two examples - the BIER-TE topology.
The BIER-TE Topology effectively consists of the BIFT of all the BFR
and can also be expressed in a diagram as a graph where the edges are
the adjacencies between the BFR. Adjacencies are naturally
unidirectional. BP can be reused across multiple adjacencies as long
as this does not lead to undesired duplicates or loops as explained
further down in the text.
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If the BIER-TE topology represents the underlying (layer 2) topology
of the network, this is called "native" BIER-TE as shown in the first
example. This can be freely mixed with "overlay" BIER-TE, in
"forward_routed" adjacencies are used.
1.3. Comparison with BIER
The key differences over BIER are:
o BIER-TE replaces in-network autonomous path calculation by
explicit paths calculated off-path by the BIER-TE controller host.
o In BIER-TE every BitPosition of the BitString of a BIER-TE packet
indicates one or more adjacencies - instead of a BFER as in BIER.
o BIER-TE in each BFR has no routing table but only a BIER-TE
Forwarding Table (BIFT) indexed by SI:BitPosition and populated
with only those adjacencies to which the BFR should replicate
packets to.
BIER-TE headers use the same format as BIER headers.
BIER-TE forwarding does not require/use the BFIR-ID. The BFIR-ID can
still be useful though for coordinated BFIR/BFER functions, such as
the context for upstream assigned labels for MPLS payloads in MVPN
over BIER-TE.
If the BIER-TE domain is also running BIER, then the BFIR-ID in BIER-
TE packets can be set to the same BFIR-ID as used with BIER packets.
If the BIER-TE domain is not running full BIER or does not want to
reduce the need to allocate bits in BIER bitstrings for BFIR-ID
values, then the allocation of BFIR-ID values in BIER-TE packets can
be done through other mechanisms outside the scope of this document,
as long as this is appropriately agreed upon between all BFIR/BFER.
1.4. 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 RFC 2119 [RFC2119].
2. Components
End to end BIER-TE operations consists of four mayor components: The
"Multicast Flow Overlay", the "BIER-TE control plane" consisting of
the "BIER-TE Controller Host" and its signaling channels to the BFR,
the "Routing Underlay" and the "BIER-TE forwarding layer". The Bier-
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TE Controller Host is the new architectural component in BIER-TE
compared to BIER.
Picture 2: Components of BIER-TE
<------BGP/PIM----->
|<-IGMP/PIM-> multicast flow <-PIM/IGMP->|
overlay
[BIER-TE Controller Host] <=> [BIER-TE Topology]
BIER-TE control plane
^ ^ ^
/ | \ BIER-TE control protocol
| | | e.g. Netconf/Restconf/Yang
v v v
Src -> Rtr1 -> BFIR-----BFR-----BFER -> Rtr2 -> Rcvr
|<----------------->|
BIER-TE forwarding layer
|<- BIER-TE domain->|
|<--------------------->|
Routing underlay
Figure 3: BIER-TE architecture
2.1. The Multicast Flow Overlay
The Multicast Flow Overlay operates as in BIER. See [RFC8279].
Instead of interacting with the BIER forwarding layer (as in BIER),
it interacts with the BIER-TE Controller Host.
2.2. The BIER-TE Controller Host
The BIER-TE controller host is representing the control plane of
BIER-TE. It communicates two sets of information with BFRs:
During initial provisioning or modifications of the network topology,
the controller discovers the network topology and creates the BIER-TE
topology from it: determine which adjacencies are required/desired
and assign BitPositions to them. Then it signals the resulting of
BitPositions and their adjacencies to each BFR to set up their BIER-
TE BIFTs.
During day-to-day operations of the network, the controller signals
to BFIRs what multicast flows are mapped to what BitStrings.
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Communications between the BIER-TE controller host to BFRs is ideally
via standardized protocols and data-models such as Netconf/Restconf/
Yang. This is currently outside the scope of this document. Vendor-
specific CLI on the BFRs is also a possible stopgap option (as in
many other SDN solutions lacking definition of standardized data
model).
For simplicity, the procedures of the BIER-TE controller host are
described in this document as if it is a single, centralized
automated entity, such as an SDN controller. It could equally be an
operator setting up CLI on the BFRs. Distribution of the functions
of the BIER-TE controller host is currently outside the scope of this
document.
2.2.1. Assignment of BitPositions to adjacencies of the network
topology
The BIER-TE controller host tracks the BFR topology of the BIER-TE
domain. It determines what adjacencies require BitPositions so that
BIER-TE explicit paths can be built through them as desired by
operator policy.
The controller then pushes the BitPositions/adjacencies to the BIFT
of the BFRs, populating only those SI:BitPositions to the BIFT of
each BFR to which that BFR should be able to send packets to -
adjacencies connecting to this BFR.
2.2.2. Changes in the network topology
If the network topology changes (not failure based) so that
adjacencies that are assigned to BitPositions are no longer needed,
the controller can re-use those BitPositions for new adjacencies.
First, these BitPositions need to be removed from any BFIR flow state
and BFR BIFT state, then they can be repopulated, first into BIFT and
then into the BFIR.
2.2.3. Set up per-multicast flow BIER-TE state
The BIER-TE controller host interacts with the multicast flow overlay
to determine what multicast flow needs to be sent by a BFIR to which
set of BFER. It calculates the desired distribution tree across the
BIER-TE domain based on algorithms outside the scope of this document
(e.g. CSFP, Steiner Tree, ...). It then pushes the calculated
BitString into the BFIR.
See [I-D.ietf-bier-multicast-http-response] for a solution describing
this interaction.
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2.2.4. Link/Node Failures and Recovery
When link or nodes fail or recover in the topology, BIER-TE can
quickly respond with the optional FRR procedures described in [I-
D.eckert-bier-te-frr]. It can also more slowly react by
recalculating the BitStrings of affected multicast flows. This
reaction is slower than the FRR procedure because the controller
needs to receive link/node up/down indications, recalculate the
desired BitStrings and push them down into the BFIRs. With FRR, this
is all performed locally on a BFR receiving the adjacency up/down
notification.
2.3. The BIER-TE Forwarding Layer
When the BIER-TE Forwarding Layer receives a packet, it simply looks
up the BitPositions that are set in the BitString of the packet in
the Bit Index Forwarding Table (BIFT) that was populated by the BIER-
TE controller host. For every BP that is set in the BitString, and
that has one or more adjacencies in the BIFT, a copy is made
according to the type of adjacencies for that BP in the BIFT. Before
sending any copy, the BFR resets all BP in the BitString of the
packet for which the BFR has one or more adjacencies in the BIFT,
except when the adjacency indicates "DoNotReset" (DNR, see
Section 3.2.1). This is done to inhibit that packets can loop.
2.4. The Routing Underlay
BIER-TE is sending BIER packets to directly connected BIER-TE
neighbors as L2 (unicasted) BIER packets without requiring a routing
underlay. BIER-TE forwarding uses the Routing underlay for
forward_routed adjacencies which copy BIER-TE packets to not-
directly-connected BFRs (see below for adjacency definitions).
If the BFR intends to support FRR for BIER-TE, then the BIER-TE
forwarding plane needs to receive fast adjacency up/down
notifications: Link up/down or neighbor up/down, e.g. from BFD.
Providing these notifications is considered to be part of the routing
underlay in this document.
3. BIER-TE Forwarding
3.1. The Bit Index Forwarding Table (BIFT)
The Bit Index Forwarding Table (BIFT) exists in every BFR. For every
subdomain in use, it is a table indexed by SI:BitPosition and is
populated by the BIER-TE control plane. Each index can be empty or
contain a list of one or more adjacencies.
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BIER-TE can support multiple subdomains like BIER. Each one with a
separate BIFT
In the BIER architecture, indices into the BIFT are explained to be
both BFR-id and SI:BitString (BitPosition). This is because there is
a 1:1 relationship between BFR-id and SI:BitString - every bit in
every SI is/can be assigned to a BFIR/BFER. In BIER-TE there are
more bits used in each BitString than there are BFIR/BFER assigned to
the bitstring. This is because of the bits required to express the
(traffic engineered) path through the topology. The BIER-TE
forwarding definitions do therefore not use the term BFR-id at all.
Instead, BFR-ids are only used as required by routing underlay, flow
overlay of BIER headers. Please refer to Section 7 for explanations
how to deal with SI, subdomains and BFR-id in BIER-TE.
------------------------------------------------------------------
| Index: | Adjacencies: |
| SI:BitPosition | <empty> or one or more per entry |
==================================================================
| 0:1 | forward_connected(interface,neighbor{,DNR}) |
------------------------------------------------------------------
| 0:2 | forward_connected(interface,neighbor{,DNR}) |
| | forward_connected(interface,neighbor{,DNR}) |
------------------------------------------------------------------
| 0:3 | local_decap({VRF}) |
------------------------------------------------------------------
| 0:4 | forward_routed({VRF,}l3-neighbor) |
------------------------------------------------------------------
| 0:5 | <empty> |
------------------------------------------------------------------
| 0:6 | ECMP({adjacency1,...adjacencyN}, seed) |
------------------------------------------------------------------
...
| BitStringLength | ... |
------------------------------------------------------------------
Bit Index Forwarding Table
Figure 4: BIFT adjacencies
The BIFT is programmed into the data plane of BFRs by the BIER-TE
controller host and used to forward packets, according to the rules
specified in the BIER-TE Forwarding Procedures.
Adjacencies for the same BP when populated in more than one BFR by
the controller does not have to have the same adjacencies. This is
up to the controller. BPs for p2p links are one case (see below).
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3.2. Adjacency Types
3.2.1. Forward Connected
A "forward_connected" adjacency is towards a directly connected BFR
neighbor using an interface address of that BFR on the connecting
interface. A forward_connected adjacency does not route packets but
only L2 forwards them to the neighbor.
Packets sent to an adjacency with "DoNotReset" (DNR) set in the BIFT
will not have the BitPosition for that adjacency reset when the BFR
creates a copy for it. The BitPosition will still be reset for
copies of the packet made towards other adjacencies. This can be
used for example in ring topologies as explained below.
3.2.2. Forward Routed
A "forward_routed" adjacency is an adjacency towards a BFR that is
not a forward_connected adjacency: towards a loopback address of a
BFR or towards an interface address that is non-directly connected.
Forward_routed packets are forwarded via the Routing Underlay.
If the Routing Underlay has multiple paths for a forward_routed
adjacency, it will perform ECMP independent of BIER-TE for packets
forwarded across a forward_routed adjacency. This is independent of
BIER-TE ECMP described in Section 3.2.3.
If the Routing Underlay has FRR, it will perform FRR independent of
BIER-TE for packets forwarded across a forward_routed adjacency.
3.2.3. ECMP
The ECMP mechanisms in BIER are tied to the BIER BIFT and are
therefore not directly useable with BIER-TE. The following
procedures describe ECMP for BIER-TE that we consider to be
lightweight but also well manageable. It leverages the existing
entropy parameter in the BIER header to keep packets of the flows on
the same path and it introduces a "seed" parameter to allow
engineering traffic to be polarized or randomized across multiple
hops.
An "Equal Cost Multipath" (ECMP) adjacency has a list of two or more
adjacencies included in it. It copies the BIER-TE to one of those
adjacencies based on the ECMP hash calculation. The BIER-TE ECMP
hash algorithm must select the same adjacency from that list for all
packets with the same "entropy" value in the BIER-TE header if the
same number of adjacencies and same seed are given as parameters.
Further use of the seed parameter is explained below.
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3.2.4. Local Decap
A "local_decap" adjacency passes a copy of the payload of the BIER-TE
packet to the packets NextProto within the BFR (IPv4/IPv6,
Ethernet,...). A local_decap adjacency turns the BFR into a BFER for
matching packets. Local_decap adjacencies require the BFER to
support routing or switching for NextProto to determine how to
further process the packet.
3.3. Encapsulation considerations
Specifications for BIER-TE encapsulation are outside the scope of
this document. This section gives explanations and guidelines.
Because a BFR needs to interpret the BitString of a BIER-TE packet
differently from a BIER packet, it is necessary to distinguish BIER
from BIER-TE packets. This is subject to definitions in BIER
encapsulation specifications.
MPLS encapsulation [RFC8296] for example assigns one label by which
BFRs recognizes BIER packets for every (SI,subdomain) combination.
If it is desirable that every subdomain can forward only BIER or
BIER-TE packets, then the label allocation could stay the same, and
only the forwarding model (BIER/BIER-TE) would have to be defined per
subdomain. If it is desirable to support both BIER and BIER-TE
forwarding in the same subdomain, then additional labels would need
to be assigned for BIER-TE forwarding.
"forward_routed" requires an encapsulation permitting to unicast
BIER-TE packets to a specific interface address on a target BFR.
With MPLS encapsulation, this can simply be done via a label stack
with that addresses label as the top label - followed by the label
assigned to (SI,subdomain) - and if necessary (see above) BIER-TE.
With non-MPLS encapsulation, some form of IP tunneling (IP in IP,
LISP, GRE) would be required.
The encapsulation used for "forward_routed" adjacencies can equally
support existing advanced adjacency information such as "loose source
routes" via e.g. MPLS label stacks or appropriate header extensions
(e.g. for IPv6).
3.4. Basic BIER-TE Forwarding Example
[RFC Editor: remove this section.]
THIS SECTION TO BE REMOVED IN RFC BECAUSE IT WAS SUPERCEEDED BY
SECTION 1.1 EXAMPLE - UNLESS REVIEWERS CHIME IN AND EXPRESS DESIRE TO
KEEP THIS ADDITIONAL EXAMPLE SECTION.
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Step by step example of basic BIER-TE forwarding. This does not use
ECMP or forward_routed adjacencies nor does it try to minimize the
number of required BitPositions for the topology.
[Bier-Te Controller Host]
/ | \
v v v
| p13 p1 |
+- BFIR2 --+ |
| | p2 p6 | LAN2
| +-- BFR3 --+ |
| | | p7 p11 |
Src -+ +-- BFER1 --+
| | p3 p8 | |
| +-- BFR4 --+ +-- Rcv1
| | | |
| |
| p14 p4 |
+- BFIR1 --+ |
| +-- BFR5 --+ p10 p12 |
LAN1 | p5 p9 +-- BFER2 --+
| +-- Rcv2
|
LAN3
IP |..... BIER-TE network......| IP
Figure 5: BIER-TE Forwarding Example
pXX indicate the BitPositions number assigned by the BIER-TE
controller host to adjacencies in the BIER-TE topology. For example,
p9 is the adjacency towards BFR5 on the LAN connecting to BFER2.
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BIFT BFIR2:
p13: local_decap()
p2: forward_connected(BFR3)
BIFT BFR3:
p1: forward_connected(BFIR2)
p7: forward_connected(BFER1)
p8: forward_connected(BFR4)
BIFT BFER1:
p11: local_decap()
p6: forward_connected(BFR3)
p8: forward_connected(BFR4)
Figure 6: BIER-TE Forwarding Example Adjacencies
...and so on.
For example, we assume that some multicast traffic seen on LAN1 needs
to be sent via BIER-TE by BFIR2 towards Rcv1 and Rcv2. The
controller determines it wants it to pass this traffic across the
following paths:
-> BFER1 ---------------> Rcv1
BFIR2 -> BFR3
-> BFR4 -> BFR5 -> BFER2 -> Rcv2
Figure 7: BIER-TE Forwarding Example Paths
These paths equal to the following BitString: p2, p5, p7, p8, p10,
p11, p12.
This BitString is assigned by BFIR2 to the example multicast traffic
received from LAN1.
Then BFIR2 forwards this multicast traffic with BIER-TE based on that
BitString. The BIFT of BFIR2 has only p2 and p13 populated. Only p2
is in the BitString and this is an adjacency towards BFR3. BFIR2
therefore resets p2 in the BitString and sends a copy towards BFR2.
BFR3 sees a BitString of p5,p7,p8,p10,p11,p12. It is only interested
in p1,p7,p8. It creates a copy of the packet to BFER1 (due to p7)
and one to BFR4 (due to p8). It resets p7, p8 before sending.
BFER1 sees a BitString of p5,p10,p11,p12. It is only interested in
p6,p7,p8,p11 and therefore considers only p11. p11 is a "local_decap"
adjacency installed by the BIER-TE controller host because BFER1
should pass packets to IP multicast. The local_decap adjacency
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instructs BFER1 to create a copy, decapsulate it from the BIER header
and pass it on to the NextProtocol, in this example IP multicast. IP
multicast will then forward the packet out to LAN2 because it did
receive PIM or IGMP joins on LAN2 for the traffic.
Further processing of the packet in BFR4, BFR5 and BFER2 accordingly.
3.5. Forwarding comparison with BIER
Forwarding of BIER-TE is designed to allow common forwarding hardware
with BIER. In fact, one of the main goals of this document is to
encourage the building of forwarding hardware that can not only
support BIER, but also BIER-TE - to allow experimentation with BIER-
TE and support building of BIER-TE control plane code.
The pseudocode in Section 6 shows how existing BIER/BIFT forwarding
can be amended to support basic BIER-TE forwarding, by using BIER
BIFT's F-BM. Only the masking of bits due to avoid duplicates must
be skipped when forwarding is for BIER-TE.
Whether to use BIER or BIER-TE forwarding can simply be a configured
choice per subdomain and accordingly be set up by a BIER-TE
controller host. The BIER packet encapsulation [RFC8296] too can be
reused without changes except that the currently defined BIER-TE ECMP
adjacency does not leverage the entropy field so that field would be
unused when BIER-TE forwarding is used.
3.6. Requirements
Basic BIER-TE forwarding MUST support to configure Subdomains to use
basic BIER-TE forwarding rules (instead of BIER). With basic BIER-TE
forwarding, every bit MUST support to have zero or one adjacency. It
MUST support the adjacency types forward_connected without DNR flag,
forward_routed and local_decap. All other BIER-TE forwarding
features are optional. These basic BIER-TE requirements make BIER-TE
forwarding exactly the same as BIER forwarding with the exception of
skipping the aforementioned F-BM masking on egress.
BIER-TE forwarding SHOULD support the DNR flag, as this is highly
useful to save bits in rings (see Section 4.6).
BIER-TE forwarding MAY support more than one adjacency on a bit and
ECMP adjacencies. The importance of ECMP adjacencies is unclear when
traffic engineering is used because it may be more desirable to
explicitly steer traffic across non-ECMP paths to make per-path
traffic calculation easier for controllers. Having more than one
adjacency for a bit allows further savings of bits in hub&spoke
scenarios, but unlike rings it is less "natural" to flood traffic
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across multiple links unconditional. Both ECMP and multiple
adjacencies are forwarding plane features that should be possible to
support later when needed as they do not impact the basic BIER-TE
replication loop. This is true because there is no inter-copy
dependency through resetting of F-BM as in BIER.
4. BIER-TE Controller Host BitPosition Assignments
This section describes how the BIER-TE controller host can use the
different BIER-TE adjacency types to define the BitPositions of a
BIER-TE domain.
Because the size of the BitString is limiting the size of the BIER-TE
domain, many of the options described exist to support larger
topologies with fewer BitPositions (4.1, 4.3, 4.4, 4.5, 4.6, 4.7,
4.8).
4.1. P2P Links
Each P2p link in the BIER-TE domain is assigned one unique
BitPosition with a forward_connected adjacency pointing to the
neighbor on the p2p link.
4.2. BFER
Every non-Leaf BFER is given a unique BitPosition with a local_decap
adjacency.
4.3. Leaf BFERs
BFR1(P) BFR2(P) BFR1(P) BFR2(P)
| \ / | | |
| X | | |
| / \ | | |
BFER1(PE) BFER2(PE) BFER1(PE)----BFER2(PE)
Leaf BFER / Non-Leaf BFER /
PE-router PE-router
Figure 8: Leaf vs. non-Leaf BFER Example
Leaf BFERs are BFERs where incoming BIER-TE packets never need to be
forwarded to another BFR but are only sent to the BFER to exit the
BIER-TE domain. For example, in networks where PEs are spokes
connected to P routers, those PEs are Leaf BFERs unless there is a
U-turn between two PEs. Consider how redundant disjoint traffic can
reach BFER1/BFER2 in above picture: When BFER1/BFER2 are Non-Leaf
BFER as shown on the right hand side, one traffic copy would be
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forwarded to BFER1 from BFR1, but the other one could only reach
BFER1 via BFER2, which makes BFER2 a non-Leaf BFER. Likewise BFER1
is a non-Leaf BFER when forwarding traffic to BFER2.
Note that the BFERs in the left hand picture are only guaranteed to
be leaf-BFER by fitting routing configuration that prohibits transit
traffic to pass through the BFERs, which is commonly applied in these
topologies.
All leaf-BFER in a BIER-TE domain can share a single BitPosition.
This is possible because the BitPosition for the adjacency to reach
the BFER can be used to distinguish whether or not packets should
reach the BFER.
This optimization will not work if an upstream interface of the BFER
is using a BitPosition optimized as described in the following two
sections (LAN, Hub and Spoke).
4.4. LANs
In a LAN, the adjacency to each neighboring BFR on the LAN is given a
unique BitPosition. The adjacency of this BitPosition is a
forward_connected adjacency towards the BFR and this BitPosition is
populated into the BIFT of all the other BFRs on that LAN.
BFR1
|p1
LAN1-+-+---+-----+
p3| p4| p2|
BFR3 BFR4 BFR7
Figure 9: LAN Example
If Bandwidth on the LAN is not an issue and most BIER-TE traffic
should be copied to all neighbors on a LAN, then BitPositions can be
saved by assigning just a single BitPosition to the LAN and
populating the BitPosition of the BIFTs of each BFRs on the LAN with
a list of forward_connected adjacencies to all other neighbors on the
LAN.
This optimization does not work in the case of BFRs redundantly
connected to more than one LANs with this optimization because these
BFRs would receive duplicates and forward those duplicates into the
opposite LANs. Adjacencies of such BFRs into their LANs still need a
separate BitPosition.
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4.5. Hub and Spoke
In a setup with a hub and multiple spokes connected via separate p2p
links to the hub, all p2p links can share the same BitPosition. The
BitPosition on the hub's BIFT is set up with a list of
forward_connected adjacencies, one for each Spoke.
This option is similar to the BitPosition optimization in LANs:
Redundantly connected spokes need their own BitPositions.
This type of optimized BP could be used for example when all traffic
is "broadcast" traffic (very dense receiver set) such as live-TV or
situation-awareness (SA). This BP optimization can then be used to
explicitly steer different traffic flows across different ECMP paths
in Data-Center or broadband-aggregation networks with minimal use of
BPs.
4.6. Rings
In L3 rings, instead of assigning a single BitPosition for every p2p
link in the ring, it is possible to save BitPositions by setting the
"Do Not Reset" (DNR) flag on forward_connected adjacencies.
For the rings shown in the following picture, a single BitPosition
will suffice to forward traffic entering the ring at BFRa or BFRb all
the way up to BFR1:
On BFRa, BFRb, BFR30,... BFR3, the BitPosition is populated with a
forward_connected adjacency pointing to the clockwise neighbor on the
ring and with DNR set. On BFR2, the adjacency also points to the
clockwise neighbor BFR1, but without DNR set.
Handling DNR this way ensures that copies forwarded from any BFR in
the ring to a BFR outside the ring will not have the ring BitPosition
set, therefore minimizing the chance to create loops.
v v
| |
L1 | L2 | L3
/-------- BFRa ---- BFRb --------------------\
| |
\- BFR1 - BFR2 - BFR3 - ... - BFR29 - BFR30 -/
| | L4 | |
p33| p15|
BFRd BFRc
Figure 10: Ring Example
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Note that this example only permits for packets to enter the ring at
BFRa and BFRb, and that packets will always travel clockwise. If
packets should be allowed to enter the ring at any ring BFR, then one
would have to use two ring BitPositions. One for clockwise, one for
counterclockwise.
Both would be set up to stop rotating on the same link, e.g. L1.
When the ingress ring BFR creates the clockwise copy, it will reset
the counterclockwise BitPosition because the DNR bit only applies to
the bit for which the replication is done. Likewise for the
clockwise BitPosition for the counterclockwise copy. In result, the
ring ingress BFR will send a copy in both directions, serving BFRs on
either side of the ring up to L1.
4.7. Equal Cost MultiPath (ECMP)
The ECMP adjacency allows to use just one BP per link bundle between
two BFRs instead of one BP for each p2p member link of that link
bundle. In the following picture, one BP is used across L1,L2,L3.
--L1-----
BFR1 --L2----- BFR2
--L3-----
BIFT entry in BFR1:
------------------------------------------------------------------
| Index | Adjacencies |
==================================================================
| 0:6 | ECMP({forward_connected(L1, BFR2), |
| | forward_connected(L2, BFR2), |
| | forward_connected(L3, BFR2)}, seed) |
------------------------------------------------------------------
BIFT entry in BFR2:
------------------------------------------------------------------
| Index | Adjacencies |
==================================================================
| 0:6 | ECMP({forward_connected(L1, BFR1), |
| | forward_connected(L2, BFR1), |
| | forward_connected(L3, BFR1)}, seed) |
------------------------------------------------------------------
Figure 11: ECMP Example
This document does not standardize any ECMP algorithm because it is
sufficient for implementations to document their freely chosen ECMP
algorithm. This allows the BIER-TE controller host to calculate ECMP
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paths and seeds. The following picture shows an example ECMP
algorithm:
forward(packet, ECMP(adj(0), adj(1),... adj(N-1), seed)):
i = (packet(bier-header-entropy) XOR seed) % N
forward packet to adj(i)
Figure 12: ECMP algorithm Example
In the following example, all traffic from BFR1 towards BFR10 is
intended to be ECMP load split equally across the topology. This
example is not meant as a likely setup, but to illustrate that ECMP
can be used to share BPs not only across link bundles, and it
explains the use of the seed parameter.
BFR1 (BFIR)
/L11 \L12
/ \
BFR2 BFR3
/L21 \L22 /L31 \L32
/ \ / \
BFR4 BFR5 BFR6 BFR7
\ / \ /
\ / \ /
BFR8 BFR9
\ /
\ /
BFR10 (BFER)
BIFT entry in BFR1:
------------------------------------------------------------------
| 0:6 | ECMP({forward_connected(L11, BFR2), |
| | forward_connected(L12, BFR3)}, seed1) |
------------------------------------------------------------------
BIFT entry in BFR2:
------------------------------------------------------------------
| 0:7 | ECMP({forward_connected(L21, BFR4), |
| | forward_connected(L22, BFR5)}, seed1) |
------------------------------------------------------------------
BIFT entry in BFR3:
------------------------------------------------------------------
| 0:7 | ECMP({forward_connected(L31, BFR6), |
| | forward_connected(L32, BFR7)}, seed1) |
------------------------------------------------------------------
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BIFT entry in BFR4, BFR5:
------------------------------------------------------------------
| 0:8 | forward_connected(Lxx, BFR8) |xx differs on BFR4/BFR5|
------------------------------------------------------------------
BIFT entry in BFR6, BFR7:
------------------------------------------------------------------
| 0:8 | forward_connected(Lxx, BFR9) |xx differs on BFR6/BFR7|
------------------------------------------------------------------
BIFT entry in BFR8, BFR9:
------------------------------------------------------------------
| 0:9 | forward_connected(Lxx, BFR10) |xx differs on BFR8/BFR9|
------------------------------------------------------------------
Figure 13: Polarization Example
Note that for the following discussion of ECMP, only the BIFT ECMP
adjacencies on BFR1, BFR2, BFR3 are relevant. The re-use of BP
across BFR in this example is further explained in Section 4.9 below.
With the setup of ECMP in above topology, traffic would not be
equally load-split. Instead, links L22 and L31 would see no traffic
at all: BFR2 will only see traffic from BFR1 for which the ECMP hash
in BFR1 selected the first adjacency in the list of 2 adjacencies
given as parameters to the ECMP. It is link L11-to-BFR2. BFR2
performs again ECMP with two adjacencies on that subset of traffic
using the same seed1, and will therefore again select the first of
its two adjacencies: L21-to-BFR4. And therefore L22 and BFR5 sees no
traffic. Likewise for L31 and BFR6.
This issue in BFR2/BFR3 is called polarization. It results from the
re-use of the same hash function across multiple consecutive hops in
topologies like these. To resolve this issue, the ECMP adjacency on
BFR1 can be set up with a different seed2 than the ECMP adjacencies
on BFR2/BFR3. BFR2/BFR3 can use the same hash because packets will
not sequentially pass across both of them. Therefore, they can also
use the same BP 0:7.
Note that ECMP solutions outside of BIER often hide the seed by auto-
selecting it from local entropy such as unique local or next-hop
identifiers. The solutions choosen for BIER-TE to allow the
controller to explicitly set the seed maximizes the ability of the
controller to choose the seed, independent of such seed source that
the controller may not be able to control well, and even calculate
optimized seeds for multi-hop cases.
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4.8. Routed adjacencies
4.8.1. Reducing BitPositions
Routed adjacencies can reduce the number of BitPositions required
when the traffic engineering requirement is not hop-by-hop explicit
path selection, but loose-hop selection. Routed adjacencies can also
allow to operate BIER-TE across intermediate hop routers that do not
support BIER-TE.
...............
...BFR1--... ...--L1-- BFR2...
... .Routers. ...--L2--/
...BFR4--... ...------ BFR3...
............... |
LO
Network Area 1
Figure 14: Routed Adjacencies Example
Assume the requirement in the above picture is to explicitly steer
traffic flows that have arrived at BFR1 or BFR4 via a shortest path
in the routing underlay "Network Area 1" to one of the following
three next segments: (1) BFR2 via link L1, (2) BFR2 via link L2, (3)
via BFR3.
To enable this, both BFR1 and BFR4 are set up with a forward_routed
adjacency BitPosition towards an address of BFR2 on link L1, another
forward_routed BitPosition towards an address of BFR2 on link L2 and
a third forward_routed Bitposition towards a node address LO of BFR3.
4.8.2. Supporting nodes without BIER-TE
Routed adjacencies also enable incremental deployment of BIER-TE.
Only the nodes through which BIER-TE traffic needs to be steered -
with or without replication - need to support BIER-TE. Where they
are not directly connected to each other, forward_routed adjacencies
are used to pass over non BIER-TE enabled nodes.
4.9. Reuse of BitPositions (without DNR)
BitPositions can be re-used across multiple BFR to minimize the
number of BP needed. This happens when adjacencies on multiple BFR
use the DNR flag as described above, but it can also be done for non-
DNR adjacencies. This section only discussses this non-DNR case.
Because BP are reset after passing a BFR with an adjacency for that
BP, reuse of BP across multiple BFR does not introduce any problems
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with duplicates or loops that do not also exist when every adjacency
has a unique BP: Instead of setting one BP in a BitString that is
reused in N-adjacencies, one would get the same or worse results if
each of these adjacencies had a unique BP and all of them where set
in the BitString. Instead, based on the case, BPs can be reused
without limitation, or they introduce fewer path engineering choices,
or they do not work.
BP cannot be reused across two BFR that would need to be passed
sequentially for some path: The first BFR will reset the BP, so those
paths cannot be built. BP can be set across BFR that would (A) only
occur across different paths or (B) across different branches of the
same tree.
An example of (A) was given in Figure 13, where BP 0:7, BP 0:8 and BP
0:9 are each reused across multiple BFR because a single packet/path
would never be able to reach more than one BFR sharing the same BP.
Assume the example was changed: BFR1 has no ECMP adjacency for BP
0:6, but instead BP 0:5 with forward_connected to BFR2 and BP 0:6
with forward_connected to BFR3. Packets with both BP 0:5 and BP 0:6
would now be able to reach both BFR2 and BFR3 and the still existing
re-use of BP 0:7 between BFR2 and BFR3 is a case of (B) where reuse
of BP is perfect because it does not limit the set of useful path
choices:
If instead of reusing BP 0:7, BFR3 used a separate BP 0:10 for its
ECMP adjacency, no useful additional path engineering would be
enabled. If duplicates at BFR10 where undesirable, this would be
done by not setting BP 0:5 and BP 0:6 for the same packet. If the
duplicates where desirable (e.g.: resilient transmission), the
additional BP 0:10 would also not render additional value.
Reuse may also save BPs in larger topologies. Consider the topology
shown in Figure 17, but only the following explanations: A BFIR/
sender (e.g.: video headend) is attached to area 1, and area 2...6
contain receivers/BFER. Assume each area had a distribution ring,
each with two BPs to indicate the direction (as explained in before).
These two BPs could be reused across the 5 areas. Packets would be
replicated through other BPs to the desired subset of areas, and once
a packet copy reaches the ring of the area, the two ring BPs come
into play. This reuse is a case of (B), but it limits the topology
choices: Packets can only flow around the same direction in the rings
of all areas. This may or may not be acceptable based on the desired
traffic engineering: If resilient transmission is the traffic
engineering goal, then it is likely a good optimization, if the
bandwidth of each ring was to be optimized separately, it would not
be a good limitation.
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4.10. Summary of BP optimizations
This section reviewed a range of techniques by which a controller can
create a BIER-TE topology in a way that minimizes the number of
necessary BPs.
Without any optimization, a controller would attempt to map the
network subnet topology 1:1 into the BIER-TE topology and every
subnet adjacent neighbor requires a forward_connected BP and every
BFER requires a local_decap BP.
The optimizations described are then as follows:
o P2p links require only one BP (Section 4.1).
o All leaf-BFER can share a single local_decap BP (Section 4.3).
o A LAN with N BFR needs at most N BP (one for each BFR). It only
needs one BP for all those BFR tha are not redundanty connected to
multiple LANs (Section 4.4).
o A hub with p2p connections to multiple non-leaf-BFER spokes can
share one BP to all spokes if traffic can be flooded to all
spokes, e.g.: because of no bandwidth concerns or dense receiver
sets (Section 4.5).
o Rings of BFR can be built with just two BP (one for each
direction) except for BFR with multiple ring connections - similar
to LANs (Section 4.6).
o ECMP adjacencies to N neighbors can replace N BP with 1 BP.
Multihop ECMP can avoid polarization through different seeds of
the ECMP algorithm (Section 4.7).
o Routed adjacencies allow to "tunnel" across non-BIER-TE capable
routers and across BIER-TE capable routers where no traffic-
steering or replications are required (Section 4.8).
o BP can generally be reused across nodes that do not need to be
consecutive in paths, but depending on scenario, this may limit
the feasible traffic engineering options (Section 4.9).
Note that the described list of optimizations is not exhaustive.
Especially when the set of required path engineering choices is
limited and the set of possible subsets of BFER that should be able
to receive traffic is limited, further optimizations of BP are
possible. The hub & spoke optimization is a simple example of such
traffic pattern dependent optimizations.
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5. Avoiding loops and duplicates
5.1. Loops
Whenever BIER-TE creates a copy of a packet, the BitString of that
copy will have all BitPositions cleared that are associated with
adjacencies on the BFR. This inhibits looping of packets. The only
exception are adjacencies with DNR set.
With DNR set, looping can happen. Consider in the ring picture that
link L4 from BFR3 is plugged into the L1 interface of BFRa. This
creates a loop where the rings clockwise BitPosition is never reset
for copies of the packets traveling clockwise around the ring.
To inhibit looping in the face of such physical misconfiguration,
only forward_connected adjacencies are permitted to have DNR set, and
the link layer port unique unicast destination address of the
adjacency (e.g. MAC address) protects against closing the loop.
Link layers without port unique link layer addresses should not be
used with the DNR flag set.
5.2. Duplicates
Duplicates happen when the topology of the BitString is not a tree
but redundantly connecting BFRs with each other. The controller must
therefore ensure to only create BitStrings that are trees in the
topology.
When links are incorrectly physically re-connected before the
controller updates BitStrings in BFIRs, duplicates can happen. Like
loops, these can be inhibited by link layer addressing in
forward_connected adjacencies.
If interface or loopback addresses used in forward_routed adjacencies
are moved from one BFR to another, duplicates can equally happen.
Such re-addressing operations must be coordinated with the
controller.
6. BIER-TE Forwarding Pseudocode
The following simplified pseudocode for BIER-TE forwarding is using
BIER forwarding pseudocode of [RFC8279], section 6.5 with the one
modification necessary to support basic BIER-TE forwarding. Like the
BIER pseudo forwarding code, for simplicity it does hide the details
of the adjacency processing inside PacketSend() which can be
forward_connected, forward_routed or local_decap.
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void ForwardBitMaskPacket_withTE (Packet)
{
SI=GetPacketSI(Packet);
Offset=SI*BitStringLength;
for (Index = GetFirstBitPosition(Packet->BitString); Index ;
Index = GetNextBitPosition(Packet->BitString, Index)) {
F-BM = BIFT[Index+Offset]->F-BM;
if (!F-BM) continue;
BFR-NBR = BIFT[Index+Offset]->BFR-NBR;
PacketCopy = Copy(Packet);
PacketCopy->BitString &= F-BM; [2]
PacketSend(PacketCopy, BFR-NBR);
// The following must not be done for BIER-TE:
// Packet->BitString &= ~F-BM; [1]
}
}
Figure 15: Simplified BIER-TE Forwarding Pseudocode
The difference is that in BIER-TE, step [1] must not be performed,
but is replaced with [2] (when the forwarding plane algorithm is
implemented verbatim as shown above).
In BIER, the F-BM of a BP has all BP set that are meant to be
forwarded via the same neighbor. It is used to reset those BP in the
packet after the first copy to this neighbor has been made to inhibit
multiple copies to the same neighbor.
In BIER-TE, the F-BM of a particular BP with an adjacency is the list
of all BPs with an adjacency on this BFR except the particular BP
itself if it has an adjacency with the DNR bit set. The F-BM is used
to reset the F-BM BPs before creating copies.
In BIER, the order of BPs impacts the result of forwarding because of
[1]. In BIER-TE, forwarding is not impacted by the order of BPs. It
is therefore possible to further optimize forwarding than in BIER.
For example, BIER-TE forwarding can be parallelized such that a
parallel instance (such as an egres linecard) can process any subset
of BPs without any considerations for the other BPs - and without any
prior, cross-BP shared processing.
The above simplified pseudocode is elaborated further as follows:
o This pseudocode eliminates per-bit F-BM, therefore reducing state
by BitStringLength^2*SI and eliminating the need for per-packet-
copy masking operation except for adjacencies with DNR flag set:
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* AdjacentBits[SI] are bits with a non-empty list of adjacencies.
This can be computed whenever the BIER-TE controller host
updates the adjacencies.
* Only the AdjacentBits need to be examined in the loop for
packet copies.
* The packets BitString is masked with those AdjacentBits on
ingress to avoid packets looping.
o The code loops over the adjacencies because there may be more than
one adjacency for a bit.
o When an adjacency has the DNR bit, the bit is set in the packet
copy (to save bits in rings for example).
o The ECMP adjacency is shown. Its parameters are a
ListOfAdjacencies from which one is picked.
o The forward_local, forward_routed, local_decap adjacencies are
shown with their parameters.
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void ForwardBitMaskPacket_withTE (Packet)
{
SI=GetPacketSI(Packet);
Offset=SI*BitStringLength;
AdjacentBitstring = Packet->BitString &= ~AdjacentBits[SI];
Packet->BitString &= AdjacentBits[SI];
for (Index = GetFirstBitPosition(AdjacentBits); Index ;
Index = GetNextBitPosition(AdjacentBits, Index)) {
foreach adjacency BIFT[Index+Offset] {
if(adjacency == ECMP(ListOfAdjacencies, seed) ) {
I = ECMP_hash(sizeof(ListOfAdjacencies),
Packet->Entropy, seed);
adjacency = ListOfAdjacencies[I];
}
PacketCopy = Copy(Packet);
switch(adjacency) {
case forward_connected(interface,neighbor,DNR):
if(DNR)
PacketCopy->BitString |= 2<<(Index-1);
SendToL2Unicast(PacketCopy,interface,neighbor);
case forward_routed({VRF},neighbor):
SendToL3(PacketCopy,{VRF,}l3-neighbor);
case local_decap({VRF},neighbor):
DecapBierHeader(PacketCopy);
PassTo(PacketCopy,{VRF,}Packet->NextProto);
}
}
}
}
Figure 16: BIER-TE Forwarding Pseudocode
7. Managing SI, subdomains and BFR-ids
When the number of bits required to represent the necessary hops in
the topology and BFER exceeds the supported bitstring length,
multiple SI and/or subdomains must be used. This section discusses
how.
BIER-TE forwarding does not require the concept of BFR-id, but
routing underlay, flow overlay and BIER headers may. This section
also discusses how BFR-ids can be assigned to BFIR/BFER for BIER-TE.
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7.1. Why SI and sub-domains
For BIER and BIER-TE forwarding, the most important result of using
multiple SI and/or subdomains is the same: Packets that need to be
sent to BFER in different SI or subdomains require different BIER
packets: each one with a bitstring for a different (SI,subdomain)
combination. Each such bitstring uses one bitstring length sized SI
block in the BIFT of the subdomain. We call this a BIFT:SI (block).
For BIER and BIER-TE forwarding itself there is also no difference
whether different SI and/or sub-domains are chosen, but SI and
subdomain have different purposes in the BIER architecture shared by
BIER-TE. This impacts how operators are managing them and how
especially flow overlays will likely use them.
By default, every possible BFIR/BFER in a BIER network would likely
be given a BFR-id in subdomain 0 (unless there are > 64k BFIR/BFER).
If there are different flow services (or service instances) requiring
replication to different subsets of BFER, then it will likely not be
possible to achieve the best replication efficiency for all of these
service instances via subdomain 0. Ideal replication efficiency for
N BFER exists in a subdomain if they are split over not more than
ceiling(N/bitstring-length) SI.
If service instances justify additional BIER:SI state in the network,
additional subdomains will be used: BFIR/BFER are assigned BFIR-id in
those subdomains and each service instance is configured to use the
most appropriate subdomain. This results in improved replication
efficiency for different services.
Even if creation of subdomains and assignment of BFR-id to BFIR/BFER
in those subdomains is automated, it is not expected that individual
service instances can deal with BFER in different subdomains. A
service instance may only support configuration of a single subdomain
it should rely on.
To be able to easily reuse (and modify as little as possible)
existing BIER procedures including flow-overlay and routing underlay,
when BIER-TE forwarding is added, we therefore reuse SI and subdomain
logically in the same way as they are used in BIER: All necessary
BFIR/BFER for a service use a single BIER-TE BIFT and are split
across as many SI as necessary (see below). Different services may
use different subdomains that primarily exist to provide more
efficient replication (and for BIER-TE desirable traffic engineering)
for different subsets of BFIR/BFER.
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7.2. Bit assignment comparison BIER and BIER-TE
In BIER, bitstrings only need to carry bits for BFER, which leads to
the model that BFR-ids map 1:1 to each bit in a bitstring.
In BIER-TE, bitstrings need to carry bits to indicate not only the
receiving BFER but also the intermediate hops/links across which the
packet must be sent. The maximum number of BFER that can be
supported in a single bitstring or BIFT:SI depends on the number of
bits necessary to represent the desired topology between them.
"Desired" topology because it depends on the physical topology, and
on the desire of the operator to allow for explicit traffic
engineering across every single hop (which requires more bits), or
reducing the number of required bits by exploiting optimizations such
as unicast (forward_route), ECMP or flood (DNR) over "uninteresting"
sub-parts of the topology - e.g. parts where different trees do not
need to take different paths due to traffic-engineering reasons.
The total number of bits to describe the topology vs. the BFER in a
BIFT:SI can range widely based on the size of the topology and the
amount of alternative paths in it. The higher the percentage, the
higher the likelihood, that those topology bits are not just BIER-TE
overhead without additional benefit, but instead that they will allow
to express desirable traffic-engineering path alternatives.
7.3. Using BFR-id with BIER-TE
Because there is no 1:1 mapping between bits in the bitstring and
BFER, BIER-TE cannot simply rely on the BIER 1:1 mapping between bits
in a bitstring and BFR-id.
In BIER, automatic schemes could assign all possible BFR-ids
sequentially to BFERs. This will not work in BIER-TE. In BIER-TE,
the operator or BIER-TE controller host has to determine a BFR-id for
each BFER in each required subdomain. The BFR-id may or may not have
a relationship with a bit in the bitstring. Suggestions are detailed
below. Once determined, the BFR-id can then be configured on the
BFER and used by flow overlay, routing underlay and the BIER header
almost the same as the BFR-id in BIER.
The one exception are application/flow-overlays that automatically
calculate the bitstring(s) of BIER packets by converting BFR-id to
bits. In BIER-TE, this operation can be done in two ways:
"Independent branches": For a given application or (set of) trees,
the branches from a BFIR to every BFER are independent of the
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branches to any other BFER. For example, shortest part trees have
independent branches.
"Interdependent branches": When a BFER is added or deleted from a
particular distribution tree, branches to other BFER still in the
tree may need to change. Steiner tree are examples of dependent
branch trees.
If "independent branches" are sufficient, the BIER-TE controller host
can provide to such applications for every BFR-id a SI:bitstring with
the BIER-TE bits for the branch towards that BFER. The application
can then independently calculate the SI:bitstring for all desired
BFER by OR'ing their bitstrings.
If "interdependent branches" are required, the application could call
a BIER-TE controller host API with the list of required BFER-id and
get the required bitstring back. Whenever the set of BFER-id
changes, this is repeated.
Note that in either case (unlike in BIER), the bits in BIER-TE may
need to change upon link/node failure/recovery, network expansion and
network load by other traffic (as part of traffic engineering goals).
Interactions between such BFIR applications and the BIER-TE
controller host do therefore need to support dynamic updates to the
bitstrings.
7.4. Assigning BFR-ids for BIER-TE
For a non-leaf BFER, there is usually a single bit k for that BFER
with a local_decap() adjacency on the BFER. The BFR-id for such a
BFER is therefore most easily the one it would have in BIER: SI *
bitstring-length + k.
As explained earlier in the document, leaf BFERs do not need such a
separate bit because the fact alone that the BIER-TE packet is
forwarded to the leaf BFER indicates that the BFER should decapsulate
it. Such a BFER will have one or more bits for the links leading
only to it. The BFR-id could therefore most easily be the BFR-id
derived from the lowest bit for those links.
These two rules are only recommendations for the operator or BIER-TE
controller assigning the BFR-ids. Any allocation scheme can be used,
the BFR-ids just need to be unique across BFRs in each subdomain.
It is not currently determined if a single subdomain could or should
be allowed to forward both BIER and BIER-TE packets. If this should
be supported, there are two options:
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A. BIER and BIER-TE have different BFR-id in the same subdomain.
This allows higher replication efficiency for BIER because their BFR-
id can be assigned sequentially, while the bitstrings for BIER-TE
will have also the additional bits for the topology. There is no
relationship between a BFR BIER BFR-id and BIER-TE BFR-id.
B. BIER and BIER-TE share the same BFR-id. The BFR-id are assigned
as explained above for BIER-TE and simply reused for BIER. The
replication efficiency for BIER will be as low as that for BIER-TE in
this approach. Depending on topology, only the same 20%..80% of bits
as possible for BIER-TE can be used for BIER.
7.5. Example bit allocations
7.5.1. With BIER
Consider a network setup with a bitstring length of 256 for a network
topology as shown in the picture below. The network has 6 areas,
each with ca. 170 BFR, connecting via a core with some larger (core)
BFR. To address all BFER with BIER, 4 SI are required. To send a
BIER packet to all BFER in the network, 4 copies need to be sent by
the BFIR. On the BFIR it does not make a difference how the BFR-id
are allocated to BFER in the network, but for efficiency further down
in the network it does make a difference.
area1 area2 area3
BFR1a BFR1b BFR2a BFR2b BFR3a BFR3b
| \ / \ / |
................................
. Core .
................................
| / \ / \ |
BFR4a BFR4b BFR5a BFR5b BFR6a BFR6b
area4 area5 area6
Figure 17: Scaling BIER-TE bits by reuse
With random allocation of BFR-id to BFER, each receiving area would
(most likely) have to receive all 4 copies of the BIER packet because
there would be BFR-id for each of the 4 SI in each of the areas.
Only further towards each BFER would this duplication subside - when
each of the 4 trees runs out of branches.
If BFR-id are allocated intelligently, then all the BFER in an area
would be given BFR-id with as few as possible different SI. Each
area would only have to forward one or two packets instead of 4.
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Given how networks can grow over time, replication efficiency in an
area will also easily go down over time when BFR-id are network wide
allocated sequentially over time. An area that initially only has
BFR-id in one SI might end up with many SI over a longer period of
growth. Allocating SIs to areas with initially sufficiently many
spare bits for growths can help to alleviate this issue. Or renumber
BFR-id after network expansion. In this example one may consider to
use 6 SI and assign one to each area.
This example shows that intelligent BFR-id allocation within at least
subdomain 0 can even be helpful or even necessary in BIER.
7.5.2. With BIER-TE
In BIER-TE one needs to determine a subset of the physical topology
and attached BFER so that the "desired" representation of this
topology and the BFER fit into a single bitstring. This process
needs to be repeated until the whole topology is covered.
Once bits/SIs are assigned to topology and BFER, BFR-id is just a
derived set of identifiers from the operator/BIER-TE controller as
explained above.
Every time that different sub-topologies have overlap, bits need to
be repeated across the bitstrings, increasing the overall amount of
bits required across all bitstring/SIs. In the worst case, random
subsets of BFER are assigned to different SI. This is much worse
than in BIER because it not only reduces replication efficiency with
the same number of overall bits, but even further - because more bits
are required due to duplication of bits for topology across multiple
SI. Intelligent BFER to SI assignment and selecting specific
"desired" subtopologies can minimize this problem.
To set up BIER-TE efficiently for above topology, the following bit
allocation methods can be used. This method can easily be expanded
to other, similarly structured larger topologies.
Each area is allocated one or more SI depending on the number of
future expected BFER and number of bits required for the topology in
the area. In this example, 6 SI, one per area.
In addition, we use 4 bits in each SI: bia, bib, bea, beb: bit
ingress a, bit ingress b, bit egress a, bit egress b. These bits
will be used to pass BIER packets from any BFIR via any combination
of ingress area a/b BFR and egress area a/b BFR into a specific
target area. These bits are then set up with the right
forward_routed adjacencies on the BFIR and area edge BFR:
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On all BFIR in an area j, bia in each BIFT:SI is populated with the
same forward_routed(BFRja), and bib with forward_routed(BFRjb). On
all area edge BFR, bea in BIFT:SI=k is populated with
forward_routed(BFRka) and beb in BIFT:SI=k with
forward_routed(BFRkb).
For BIER-TE forwarding of a packet to some subset of BFER across all
areas, a BFIR would create at most 6 copies, with SI=1...SI=6, In
each packet, the bits indicate bits for topology and BFER in that
topology plus the four bits to indicate whether to pass this packet
via the ingress area a or b border BFR and the egress area a or b
border BFR, therefore allowing path engineering for those two
"unicast" legs: 1) BFIR to ingress are edge and 2) core to egress
area edge. Replication only happens inside the egress areas. For
BFER in the same area as in the BFIR, these four bits are not used.
7.6. Summary
BIER-TE can like BIER support multiple SI within a sub-domain to
allow re-using the concept of BFR-id and therefore minimize BIER-TE
specific functions in underlay routing, flow overlay methods and BIER
headers.
The number of BFIR/BFER possible in a subdomain is smaller than in
BIER because BIER-TE uses additional bits for topology.
Subdomains can in BIER-TE be used like in BIER to create more
efficient replication to known subsets of BFER.
Assigning bits for BFER intelligently into the right SI is more
important in BIER-TE than in BIER because of replication efficiency
and overall amount of bits required.
8. BIER-TE and Segment Routing (SR)
Segment Routing (SR ([RFC8402])) aims to enable lightweight path
engineering via loose source routing. Compared to its more heavy-
weight predecessor RSVP-TE ([RFC3209]), SR does for example not
require per-path signaling to each of these hops.
BIER-TE supports the same design philosophy for multicast. Like in
SR, it relies on source-routing - via the definition of a BitString.
Like SR, it only requires to consider the "hops" on which either
replication has to happen, or across which the traffic should be
steered (even without replication). Any other hops can be skipped
via the use of routed adjacencies.
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BIER-TE BitPosition (BP) can be understood as the BIER-TE equivalent
of "forwarding segments" in SR, but they have a different scope than
SR forwarding segments. Whereas forwarding segments in SR are global
or local, BPs in BIER-TE have a scope that is the group of BFR(s)
that have adjacencies for this BP in their BIFT. This can be called
"adjacency" scoped forwarding segments.
Adjacency scope could be global, but then every BFR would need an
adjacency for this BP, for example a forward_routed adjacency with
encapsulation to the global SR SID of the destination. Such a BP
would always result in ingress replication though. The first BFR
encountering this BP would directly replicate to it. Only by using
non-global adjacency scope for BPs can traffic be steered and
replicated on non-ingress BFR.
SR can naturally be combined with BIER-TE and help to optimize it.
For example, instead of defining BitPositions for non-replicating
hops, it is equally possible to use segment routing encapsulations
(eg: MPLS label stacks) for the encapsulation of "forward_routed"
adjacencies.
Note that BIER itself can also be seen to be similar to SR. BIER BPs
act as global destination Node-SIDs and the BIER bitstring is simply
a highly optimized mechanism to indicate multiple such SIDS and let
the network take care of effectively replicating the packet hop-by-
hop to each destination Node-SID. What BIER does not allow is to
indicate intermediate hops, or terms of SR the ability to indicate a
sequence of SID to reach the destination. This is what BIER-TE and
its adjacency scoped BP enables.
Both BIER and BIER-TE allow BFIR to "opportunistically" copy packets
to a set of desired BFER on a packet-by-packet basis. In BIER, this
is done by OR'ing the BP for the desired BFER. In BIER-TE this can
be done by OR'ing for each desired BFER a bitstring using the
"independent branches" approach described in Section 7.3 and
therefore also indicating the engineered path towards each desired
BFER. This is the approach that
[I-D.ietf-bier-multicast-http-response] relies on.
9. Security Considerations
The security considerations are the same as for BIER with the
following differences:
BFR-ids and BFR-prefixes are not used in BIER-TE, nor are procedures
for their distribution, so these are not attack vectors against BIER-
TE.
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10. IANA Considerations
This document requests no action by IANA.
11. Acknowledgements
The authors would like to thank Greg Shepherd, Ijsbrand Wijnands,
Neale Ranns, Dirk Trossen, Sandy Zheng and Jeffrey Zhang for their
extensive review and suggestions.
12. Change log [RFC Editor: Please remove]
draft-ietf-bier-te-arch:
05: Review Jeffrey Zhang.
Part 2:
4.3 added note about leaf-BFER being also a propery of routing
setup.
4.7 Added missing details from example to avoid confusion with
routed adjacencies, also compressed explanatory text and better
justification why seed is explicitly configured by controller.
4.9 added section discussing generic reuse of BP methods.
4.10 added section summarizing BP optimizations of section 4.
6. Rewrote/compressed explanation of comparison BIER/BIER-TE
forwarding difference. Explained benefit of BIER-TE per-BP
forwarding being independent of forwarding for other BPs.
Part 1:
Explicitly ue forwarded_connected adjcency in ECMP adjcency
examples to avoid confusion.
4.3 Add picture as example for leav vs. non-leaf BFR in topology.
Improved description.
4.5 Exampe for traffic that can be broadcast -> for single BP in
hub&spoke.
4.8.1 Simplified example picture for routed adjacency, explanatory
text.
Review from Dirk Trossen:
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Fixed up explanation of ICC paper vs. bloom filter.
04: spell check run.
Addded remaining fixes for Sandys (Zhang Zheng) review:
4.7 Enhance ECMP explanations:
example ECMP algorithm, highlight that doc does not standardize
ECMP algorithm.
Review from Dirk Trossen:
1. Added mentioning of prior work for traffic engineered paths
with bloom filters.
2. Changed title from layers to components and added "BIER-TE
control plane" to "BIER-TE controller host" to make it clearer,
what it does.
2.2.3. Added reference to I-D.ietf-bier-multicast-http-response
as an example solution.
2.3. clarified sentence about resetting BPs before sending copies
(also forgot to mention DNR here).
3.4. Added text saying this section will be removed unless IESG
review finds enough redeeming value in this example given how -03
introduced section 1.1 with basic examples.
7.2. Removed explicit numbers 20%/80% for number of topology bits
in BIER-TE, replaced with more vague (high/low) description,
because we do not have good reference material Added text saying
this section will be removed unless IESG review finds enough
redeeming value in this example given how -03 introduced section
1.1 with basic examples.
many typos fixed. Thanks a lot.
03: Last call textual changes by authors to improve readability:
removed Wolfgang Braun as co-authors (as requested).
Improved abstract to be more explanatory. Removed mentioning of
FRR (not concluded on so far).
Added new text into Introduction section because the text was too
difficult to jump into (too many forward pointers). This
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primarily consists of examples and the early introduction of the
BIER-TE Topology concept enabled by these examples.
Amended comparison to SR.
Changed syntax from [VRF] to {VRF} to indicate its optional and to
make idnits happy.
Split references into normative / informative, added references.
02: Refresh after IETF104 discussion: changed intended status back
to standard. Reasoning:
Tighter review of standards document == ensures arch will be
better prepared for possible adoption by other WGs (e.g. DetNet)
or std. bodies.
Requirement against the degree of existing implementations is self
defined by the WG. BIER WG seems to think it is not necessary to
apply multiple interoperating implementations against an
architecture level document at this time to make it qualify to go
to standards track. Also, the levels of support introduced in -01
rev. should allow all BIER forwarding engines to also be able to
support the base level BIER-TE forwarding.
01: Added note comparing BIER and SR to also hopefully clarify
BIER-TE vs. BIER comparison re. SR.
- added requirements section mandating only most basic BIER-TE
forwarding features as MUST.
- reworked comparison with BIER forwarding section to only
summarize and point to pseudocode section.
- reworked pseudocode section to have one pseudocode that mirrors
the BIER forwarding pseudocode to make comparison easier and a
second pseudocode that shows the complete set of BIER-TE
forwarding options and simplification/optimization possible vs.
BIER forwarding. Removed MyBitsOfInterest (was pure
optimization).
- Added captions to pictures.
- Part of review feedback from Sandy (Zhang Zheng) integrated.
00: Changed target state to experimental (WG conclusion), updated
references, mod auth association.
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- Source now on http://www.github.com/toerless/bier-te-arch
- Please open issues on the github for change/improvement requests
to the document - in addition to posting them on the list
(bier@ietf.). Thanks!.
draft-eckert-bier-te-arch:
06: Added overview of forwarding differences between BIER, BIER-
TE.
05: Author affiliation change only.
04: Added comparison to Live-Live and BFIR to FRR section
(Eckert).
04: Removed FRR content into the new FRR draft [I-D.eckert-bier-
te-frr] (Braun).
- Linked FRR information to new draft in Overview/Introduction
- Removed BTAFT/FRR from "Changes in the network topology"
- Linked new draft in "Link/Node Failures and Recovery"
- Removed FRR from "The BIER-TE Forwarding Layer"
- Moved FRR section to new draft
- Moved FRR parts of Pseudocode into new draft
- Left only non FRR parts
- removed FrrUpDown(..) and //FRR operations in
ForwardBierTePacket(..)
- New draft contains FrrUpDown(..) and ForwardBierTePacket(Packet)
from bier-arch-03
- Moved "BIER-TE and existing FRR to new draft
- Moved "BIER-TE and Segment Routing" section one level up
- Thus, removed "Further considerations" that only contained this
section
- Added Changes for version 04
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03: Updated the FRR section. Added examples for FRR key concepts.
Added BIER-in-BIER tunneling as option for tunnels in backup
paths. BIFT structure is expanded and contains an additional
match field to support full node protection with BIER-TE FRR.
03: Updated FRR section. Explanation how BIER-in-BIER
encapsulation provides P2MP protection for node failures even
though the routing underlay does not provide P2MP.
02: Changed the definition of BIFT to be more inline with BIER.
In revs. up to -01, the idea was that a BIFT has only entries for
a single bitstring, and every SI and subdomain would be a separate
BIFT. In BIER, each BIFT covers all SI. This is now also how we
define it in BIER-TE.
02: Added Section 7 to explain the use of SI, subdomains and BFR-
id in BIER-TE and to give an example how to efficiently assign
bits for a large topology requiring multiple SI.
02: Added further detailed for rings - how to support input from
all ring nodes.
01: Fixed BFIR -> BFER for section 4.3.
01: Added explanation of SI, difference to BIER ECMP,
consideration for Segment Routing, unicast FRR, considerations for
encapsulation, explanations of BIER-TE controller host and CLI.
00: Initial version.
13. References
13.1. Normative References
[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>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
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13.2. Informative References
[I-D.ietf-bier-multicast-http-response]
Trossen, D., Rahman, A., Wang, C., and T. Eckert,
"Applicability of BIER Multicast Overlay for Adaptive
Streaming Services", draft-ietf-bier-multicast-http-
response-01 (work in progress), June 2019.
[I-D.ietf-roll-ccast]
Bergmann, O., Bormann, C., Gerdes, S., and H. Chen,
"Constrained-Cast: Source-Routed Multicast for RPL",
draft-ietf-roll-ccast-01 (work in progress), October 2017.
[ICC] Reed, M., Al-Naday, M., Thomos, N., Trossen, D.,
Petropoulos, G., and S. Spirou, "Stateless multicast
switching in software defined networks", IEEE
International Conference on Communications (ICC), Kuala
Lumpur, Malaysia, 2016, May 2016,
<https://ieeexplore.ieee.org/document/7511036>.
[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>.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
<https://www.rfc-editor.org/info/rfc3209>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
Authors' Addresses
Toerless Eckert (editor)
Futurewei Technologies Inc.
2330 Central Expy
Santa Clara 95050
USA
Email: tte+ietf@cs.fau.de
Eckert, et al. Expires May 4, 2020 [Page 43]
Internet-Draft BIER-TE ARCH November 2019
Gregory Cauchie
Bouygues Telecom
Email: GCAUCHIE@bouyguestelecom.fr
Michael Menth
University of Tuebingen
Email: menth@uni-tuebingen.de
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