Internet DRAFT - draft-eckert-bier-te-arch
draft-eckert-bier-te-arch
Network Working Group T. Eckert, Ed.
Internet-Draft Huawei
Intended status: Standards Track G. Cauchie
Expires: May 20, 2018 Bouygues Telecom
W. Braun
M. Menth
University of Tuebingen
November 16, 2017
Traffic Engineering for Bit Index Explicit Replication BIER-TE
draft-eckert-bier-te-arch-06
Abstract
This document proposes an architecture for BIER-TE: Traffic
Engineering for Bit Index Explicit Replication (BIER).
BIER-TE shares part of its architecture with BIER as described in
[I-D.ietf-bier-architecture]. It also proposes to share the packet
format with BIER.
BIER-TE forwards and replicates packets like BIER based on a
BitString in the packet header but it does not require an IGP. It
does support traffic engineering by explicit hop-by-hop forwarding
and loose hop forwarding of packets. It does support Fast ReRoute
(FRR) for link and node protection and incremental deployment.
Because BIER-TE like BIER operates without explicit in-network tree-
building but also supports traffic engineering, it is more similar to
SR than RSVP-TE.
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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 20, 2018.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Layering . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. The Multicast Flow Overlay . . . . . . . . . . . . . . . 5
2.2. The BIER-TE Controller Host . . . . . . . . . . . . . . . 5
2.2.1. Assignment of BitPositions to adjacencies of the
network topology . . . . . . . . . . . . . . . . . . 6
2.2.2. Changes in the network topology . . . . . . . . . . . 6
2.2.3. Set up per-multicast flow BIER-TE state . . . . . . . 6
2.2.4. Link/Node Failures and Recovery . . . . . . . . . . . 6
2.3. The BIER-TE Forwarding Layer . . . . . . . . . . . . . . 7
2.4. The Routing Underlay . . . . . . . . . . . . . . . . . . 7
3. BIER-TE Forwarding . . . . . . . . . . . . . . . . . . . . . 7
3.1. The Bit Index Forwarding Table (BIFT) . . . . . . . . . . 7
3.2. Adjacency Types . . . . . . . . . . . . . . . . . . . . . 8
3.2.1. Forward Connected . . . . . . . . . . . . . . . . . . 8
3.2.2. Forward Routed . . . . . . . . . . . . . . . . . . . 9
3.2.3. ECMP . . . . . . . . . . . . . . . . . . . . . . . . 9
3.2.4. Local Decap . . . . . . . . . . . . . . . . . . . . . 9
3.3. Encapsulation considerations . . . . . . . . . . . . . . 10
3.4. Basic BIER-TE Forwarding Example . . . . . . . . . . . . 10
3.5. Forwarding comparison with BIER . . . . . . . . . . . . . 12
4. BIER-TE Controller Host BitPosition Assignments . . . . . . . 13
4.1. P2P Links . . . . . . . . . . . . . . . . . . . . . . . . 13
4.2. BFER . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.3. Leaf BFERs . . . . . . . . . . . . . . . . . . . . . . . 14
4.4. LANs . . . . . . . . . . . . . . . . . . . . . . . . . . 14
4.5. Hub and Spoke . . . . . . . . . . . . . . . . . . . . . . 15
4.6. Rings . . . . . . . . . . . . . . . . . . . . . . . . . . 15
4.7. Equal Cost MultiPath (ECMP) . . . . . . . . . . . . . . . 16
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4.8. Routed adjacencies . . . . . . . . . . . . . . . . . . . 18
4.8.1. Reducing BitPositions . . . . . . . . . . . . . . . . 18
4.8.2. Supporting nodes without BIER-TE . . . . . . . . . . 18
5. Avoiding loops and duplicates . . . . . . . . . . . . . . . . 18
5.1. Loops . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.2. Duplicates . . . . . . . . . . . . . . . . . . . . . . . 19
6. BIER-TE Forwarding Pseudocode . . . . . . . . . . . . . . . . 19
7. Managing SI, subdomains and BFR-ids . . . . . . . . . . . . . 20
7.1. Why SI and sub-domains . . . . . . . . . . . . . . . . . 21
7.2. Bit assignment comparison BIER and BIER-TE . . . . . . . 22
7.3. Using BFR-id with BIER-TE . . . . . . . . . . . . . . . . 22
7.4. Assigning BFR-ids for BIER-TE . . . . . . . . . . . . . . 23
7.5. Example bit allocations . . . . . . . . . . . . . . . . . 24
7.5.1. With BIER . . . . . . . . . . . . . . . . . . . . . . 24
7.5.2. With BIER-TE . . . . . . . . . . . . . . . . . . . . 25
7.6. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 26
8. BIER-TE and Segment Routing . . . . . . . . . . . . . . . . . 26
9. Security Considerations . . . . . . . . . . . . . . . . . . . 27
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 27
12. Change log [RFC Editor: Please remove] . . . . . . . . . . . 27
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 29
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 29
1. Introduction
1.1. Overview
This document specifies the architecture for BIER-TE: traffic
engineering for Bit Index Explicit Replication BIER.
BIER-TE shares architecture and packet formats with BIER as described
in [I-D.ietf-bier-architecture].
BIER-TE forwards and replicates packets like BIER based on a
BitString in the packet header but it does not require an IGP. It
does support traffic engineering by explicit hop-by-hop forwarding
and loose hop forwarding of packets. It does support incremental
deployment and a Fast ReRoute (FRR) extension for link and node
protection is given in [I-D.eckert-bier-te-frr]. Because BIER-TE
like BIER operates without explicit in-network tree-building but also
supports traffic engineering, it is more similar to Segment Routing
(SR) than RSVP-TE.
The key differences over BIER are:
o BIER-TE replaces in-network autonomous path calculation by
explicit paths calculated offpath by the BIER-TE controller host.
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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.
1.2. 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. Layering
End to end BIER-TE operations consists of four components: The
"Multicast Flow Overlay", the "BIER-TE Controller Host", the "Routing
Underlay" and the "BIER-TE forwarding layer".
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Picture 2: Layers of BIER-TE
<------BGP/PIM----->
|<-IGMP/PIM-> multicast flow <-PIM/IGMP->|
overlay
[Bier-TE Controller Host]
^ ^ ^
/ | \ BIER-TE control protocol
| | | eg.: Netconf/Restconf/Yang
v v v
Src -> Rtr1 -> BFIR-----BFR-----BFER -> Rtr2 -> Rcvr
|--------------------->|
BIER-TE forwarding layer
|<- BIER-TE domain-->|
|<--------------------->|
Routing underlay
2.1. The Multicast Flow Overlay
The Multicast Flow Overlay operates as in BIER. See
[I-D.ietf-bier-architecture]. Instead of interacting with the BIER
layer, 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 bring-up or modifications of the network topology, the
controller discovers the network topology, assigns BitPositions to
adjacencies and signals the resulting mapping of BitPositions to
adjacencies to each BFR connecting to the adjacency.
During day-to-day operations of the network, the controller signals
to BFIRs what multicast flows are mapped to what BitStrings.
Communications between the BIER-TE controller host to BFRs is ideally
via standardized protocols and data-models such as Netconf/Retconf/
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).
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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 tracks 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
(eg.: CSFP, Steiner Tree,...). It then pushes the calculated
BitString into the BFIR.
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
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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 BitPositions in the BitString of
the packet to which it can create a copy. 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, eg.: 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.
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
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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
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 do not have to have the same adjacencies. This is up
to the controller. BPs for p2p links are one case (see below).
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
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copies of the packet made towards other adjacencies. The 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.
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 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.
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.
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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 [I-D.ietf-bier-mpls-encapsulation] 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 eg: MPLS label stacks or appropriate header extensions
(eg: for IPv6).
3.4. Basic BIER-TE Forwarding Example
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.
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Picture 1: Forwarding Example
[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
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 BFR9 on the LAN connecting to BFER2.
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)
...and so on.
Traffic needs to flow from BFIR2 towards Rcv1, Rcv2. The controller
determines it wants it to pass across the following paths:
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-> BFER1 ---------------> Rcv1
BFIR2 -> BFR3
-> BFR4 -> BFR5 -> BFER2 -> Rcv2
These paths equal to the following BitString: p2, p5, p7, p8, p10,
p11, p12.
This BitString is set up in BFIR2. Multicast packets arriving at
BFIR2 from Src are assigned this BitString.
BFIR2 forwards based on that BitString. It has p2 and p13 populated.
Only p13 is in BitString which has an adjacency towards BFR3. BFIR2
resets p2 in 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
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. Like BIER, the core of BIER-TE forwarding are BIFTs with
bitstring size number of entries: One for each bit of the bitstring
in the processed packet (consider that 256 is the most common size).
When a packet is received, the BIFT to process needs to be selected.
This is based on SI and subdomain like in BIER. How SI and subdomain
are indicated is subject to the BIER-TE encapsulation, but not BIER-T
itself. It is expected that the mechanisms for encapsulation will be
very similar if not the same to BIER, but this is subject to followup
work.
There are some key difference between the BIFT in BIER and BIER-TE:
In BIER-TE, each entry in the BIFT can have a list of 0 or more
adjacencies. A separate copy of the packet is made for each
adjacency. In BIER, each BIFT entry has at most one adjacency (BFR-
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NBR). In BIER, different bits can not be processed independently
directly: Only one packet copy is to be sent for all bits in the
packet with the same adjacency, which is why the forwarding procedure
specifies how to sequentially identify those bits and avoid
duplication. In BIER-TE there are no mutual dependencies between bit
adjacencies, so all bits of a BIER-TE bitstring could be procssed
independently in parallel.
In BIER the BIFT has adjacencies for all BFR-ids assigned to BFER and
reachable in the IGP. In BIER-TE the BIFT only has adjacencies for
bits that are adjacent hops - intermediate or BFER. In forwarding,
this can be treated via the same lookup logic except that in BIER-TE
there is no step modifyin the original packet and the packet copy
bitstring with the FBM. Instead, all the bits locally processed are
reset in the original packet before looking up bits in the BIFT
(~MyBitsOfInterest). Only for an adjacency with the "DNR" (Do Not
Reset) bit set would the bit in the bitstring not be set again as
part of processing of the adjacency.
In summary, implementations of BIER forwarding that are to be
extended to also support BIER-TE forwarding primarily need to
consider how they can ensure that individual bit lookups can result
in a sequence of more than one copy to be made (as opposed to one in
BIER), and they need to see that they can accordingly reset bits in
the bitstring differently for BIER (per-packet) vs. BIER-TE (per-
paket-copy).
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.
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4.2. BFER
Every BFER is given a unique BitPosition with a local_decap
adjacency.
4.3. Leaf BFERs
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 BFIRs unless there is a
U-turn between two PEs.
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
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 face 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 hubs 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.
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
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, eg: L1. When
the ingress ring BFR creates the clockwise copy, it will reset the
counterclockwise BitPosition because the DNR bit only applies to the
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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 and
BFR1/BFR2 have for the BP
--L1-----
BFR1 --L2----- BFR2
--L3-----
BIFT entry in BFR1:
------------------------------------------------------------------
| Index | Adjacencies |
==================================================================
| 0:6 | ECMP({L1-to-BFR2,L2-to-BFR2,L3-to-BFR2}, seed) |
------------------------------------------------------------------
BIFT entry in BFR2:
------------------------------------------------------------------
| Index | Adjacencies |
==================================================================
| 0:6 | ECMP({L1-to-BFR1,L2-to-BFR1,L3-to-BFR1}, seed) |
------------------------------------------------------------------
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 mean 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.
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BFR1
/ \
/L11 \L12
BFR2 BFR3
/ \ / \
/L21 \L22 /L31 \L32
BFR4 BFR5 BFR6 BFR7
\ / \ /
\ / \ /
BFR8 BFR9
\ /
\ /
BFR10
BIFT entry in BFR1:
------------------------------------------------------------------
| 0:6 | ECMP({L11-to-BFR2,L12-to-BFR3}, seed) |
------------------------------------------------------------------
BIFT entry in BFR2:
------------------------------------------------------------------
| 0:6 | ECMP({L21-to-BFR4,L22-to-BFR5}, seed) |
------------------------------------------------------------------
BIFT entry in BFR3:
------------------------------------------------------------------
| 0:6 | ECMP({L31-to-BFR6,L32-to-BFR7}, seed) |
------------------------------------------------------------------
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 a list of 2 adjacencies: link
L11-to-BFR2. When forwarding in BFR2 performs again an ECMP with two
adjacencies on that subset of traffic, then it will again select the
first of its two adjacencies to it: L21-to-BFR4. And therefore L22
and BFR5 sees no traffic.
To resolve this issue, the ECMP adjacency on BFR1 simply needs to be
set up with a different seed than the ECMP adjacencies on BFR2/BFR3
This issue is called polarization. It depends on the ECMP hash. It
is possible to build ECMP that does not have polarization, for
example by taking entropy from the actual adjacency members into
account, but that can make it harder to achieve evenly balanced load-
splitting on all BFR without making the ECMP hash algorithm
potentially too complex for fast forwarding in the BFRs.
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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.
............... ...............
BFR1--... Redundant ...--L1-- BFR2... Redundant ...---
\--... Network ...--L2--/ ... Network ...---
BFR4--... Segment 1 ...--L3-- BFR3... Segment 2 ...---
............... ...............
Assume the requirement in above network is to explicitly engineer
paths such that specific traffic flows are passed from segment 1 to
segment 2 via link L1 (or via L2 or via L3).
To achieve this, BFR1 and BFR4 are set up with a forward_routed
adjacency BitPosition towards an address of BFR2 on link L1 (or link
L2 BFR3 via L3).
For paths to be engineered through a specific node BFR2 (or BFR3),
BFR1 and BFR4 are set up up with a forward_routed adjacency
BitPosition towards a loopback address of BFR2 (or 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.
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 in 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.
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To inhibit looping in the face of such physical misconfiguration,
only forward_connected adjacencies are permitted to have DNR set, and
the link layer destination address of the adjacency (eg.: MAC
address) protects against closing the loop. Link layers without port
unique link layer addresses should not 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 sections of Pseudocode are meant to illustrate the
BIER-TE forwarding plane. This code is not meant to be normative but
to serve both as a potentially easier to read and more precise
representation of the forwarding functionality and to illustrate how
simple BIER-TE forwarding is and that it can be efficiently be
implemented.
The following procedure is executed on a BFR whenever the BIFT is
changed by the BIER-TE controller host:
global MyBitsOfInterest
void BIFTChanged()
{
for (Index = 0; Index++ ; Index <= BitStringLength)
if(BIFT[Index] != <empty>)
MyBitsOfInterest != 2<<(Index-1)
}
The following procedure is executed whenever a BIER-TE packet is to
be forwarded:
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void ForwardBierTePacket (Packet)
{
// We calculate in BitMask the subset of BPs of the BitString
// for which we have adjacencies. This is purely an
// optimization to avoid to replicate for every BP
// set in BitString only to discover that for most of them,
// the BIFT has no adjacency.
local BitMask = Packet->BitString
Packet->BitString &= ~MyBitsOfInterest
BitMask &= MyBitsOfInterest
// Replication
for (Index = GetFirstBitPosition(BitMask); Index ;
Index = GetNextBitPosition(BitMask, Index))
foreach adjacency BIFT[Index]
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)
}
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-id 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)
bitstring. 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 lead 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 - eg: 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 in a BIFT:SI can
therefore easily be as low as 20% or as high as 80%. The higher the
percentage, the higher the likelihood, that those topology bits are
not just BIER-TE overhead without additional benefit, but instead
they will allow to express the desired traffic-engineering
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 can not 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 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 BFER 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. 180 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
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.
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
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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:
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
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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
Segment Routing aims to achieve lightweight path engineering via
loose source routing. Compared for example to RSVP-TE, it does not
require per-path signaling to each of these hops.
BIER-TE is 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.
Instead of defining BitPositions for non-replicating hops, it is
equally possible to use segment routing encapsulations (eg: MPLS
label stacks) for "forward_routed" adjacencies.
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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.
10. IANA Considerations
This document requests no action by IANA.
11. Acknowledgements
The authors would like to thank Greg Shepherd, Ijsbrand Wijnands and
Neale Ranns for their extensive review and suggestions.
12. Change log [RFC Editor: Please remove]
draft-eckert-bier-te-arch:
00: 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!.
- Added overview of differences between BIER, BIER-TE forwarding.
draft-eckert-bier-te-arch:
06: Added forwarding comparison with BIER.
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"
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- 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
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.
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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
[I-D.ietf-bier-architecture]
Wijnands, I., Rosen, E., Dolganow, A., Przygienda, T., and
S. Aldrin, "Multicast using Bit Index Explicit
Replication", draft-ietf-bier-architecture-08 (work in
progress), September 2017.
[I-D.ietf-bier-mpls-encapsulation]
Wijnands, I., Rosen, E., Dolganow, A., Tantsura, J.,
Aldrin, S., and I. Meilik, "Encapsulation for Bit Index
Explicit Replication in MPLS and non-MPLS Networks",
draft-ietf-bier-mpls-encapsulation-12 (work in progress),
October 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
Authors' Addresses
Toerless Eckert (editor)
Futurewei Technologies Inc.
2330 Central Expy
Santa Clara 95050
USA
Email: tte+ietf@cs.fau.de
Gregory Cauchie
Bouygues Telecom
Email: GCAUCHIE@bouyguestelecom.fr
Wolfgang Braun
University of Tuebingen
Email: wolfgang.braun@uni-tuebingen.de
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Michael Menth
University of Tuebingen
Email: menth@uni-tuebingen.de
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