Network Working Group H. Chen
Internet-Draft M. McBride
Intended status: Standards Track Futurewei
Expires: August 25, 2021 A. Wang
China Telecom
G. Mishra
Verizon Inc.
Y. Liu
China Mobile
Y. Fan
Casa Systems
L. Liu
Fujitsu
X. Liu
Volta Networks
February 21, 2021
BIER Egress Protection
draft-chen-bier-egress-protect-01
Abstract
This document describes a mechanism for fast protection against the
failure of an egress node of a "Bit Index Explicit Replication"
(BIER) domain. It does not have any per-flow state in the core of
the domain. For a multicast packet to an egress node of the domain,
when the egress node fails, its upstream hop as a PLR sends the
packet to the egress' backup node once the PLR detects the failure.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown here.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 25, 2021.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Overview of BIER Egress Protection . . . . . . . . . . . . . 4
3. Protocol Extensions . . . . . . . . . . . . . . . . . . . . . 5
3.1. Extensions to OSPF . . . . . . . . . . . . . . . . . . . 5
3.2. Extensions to IS-IS . . . . . . . . . . . . . . . . . . . 6
4. BIER Extensions . . . . . . . . . . . . . . . . . . . . . . . 7
4.1. Egress Protection Bit Index Routing Tables . . . . . . . 7
4.2. Egress Protection Bit Index Forwarding Tables . . . . . . 9
4.3. Updated Forwarding Procedure . . . . . . . . . . . . . . 9
4.4. Switching between EP and Normal Forwarding . . . . . . . 10
5. Example Application of BIER Egress Protection . . . . . . . . 11
5.1. Example BIER Topology . . . . . . . . . . . . . . . . . . 11
5.2. BIRT and BIFT on a BFR . . . . . . . . . . . . . . . . . 12
5.3. EP-BIRTs and EP-BIFTs on a BFR . . . . . . . . . . . . . 13
5.4. Forwarding using EP-BIFT . . . . . . . . . . . . . . . . 15
6. Security Considerations . . . . . . . . . . . . . . . . . . . 17
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
[RFC8279] specifies "Bit Index Explicit Replication" (BIER). It
provides optimal forwarding of multicast data packets through a
"multicast/BIER domain". It does not require the use of a protocol
for explicitly building multicast distribution trees, and it does not
require intermediate nodes to maintain any per-flow state.
This document describes a mechanism for fast protection against the
failure of an egress node of a "Bit Index Explicit Replication"
(BIER) domain, which is called BIER Egress Protection.
This BIER Egress Protection does not require intermediate nodes to
maintain any per-flow state for fast protection against the failure
of an egress node of the flow.
1.1. Terminology
BFR: Bit-Forwarding Router.
BFIR: Bit-Forwarding Ingress Router.
BFER: Bit-Forwarding Egress Router.
BFR-id: BFR Identifier. It is a number in the range [1,65535].
BFR-NBR: BFR Neighbor.
F-BM: Forwarding Bit Mask.
BFR-prefix: An IP address (either IPv4 or IPv6) of a BFR.
BIRT: Bit Index Routing Table. It is a table that maps from the BFR-
id (in a particular sub-domain) of a BFER to the BFR-prefix of
that BFER, and to the BFR-NBR on the path to that BFER.
BIFT: Bit Index Forwarding Table.
FRR: Fast Re-Route.
PLR: Point of Local Repair.
LFA: Loop-Free Alternate.
RLFA: Remote LFA.
DLFA: Remote LFA with Directed forwarding.
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IGP: Interior Gateway Protocol.
LSDB: Link State DataBase.
SPF: Shortest Path First.
SPT: Shortest Path Tree.
OSPF: Open Shortest Path First.
IS-IS: Intermediate System to Intermediate System.
LSA: Link State Advertisement in OSPF.
LSP: Link State Protocol Data Unit (PDU) in IS-IS.
SPT-old(R): The SPT rooted at node R using LSDB before X fails
(i.e., old LSDB).
SPT-new(R, X): The SPT rooted at node R using LSDB without X after X
fails (i.e., new LSDB).
P-Space P(R,X): The set of nodes that are reachable from R without
going through X. In other words, it is the set of nodes that
are not downstream of X in SPT-old(R).
Extended P-Space P'(R,X): The set of nodes that are reachable from R
or a neighbor of R, without going through X.
Q-Space Q(D,X): The set of nodes that do not use X to reach
destination D using the old LSDB.
PQ node(R,X): A member of both the P-Space P(R, X) (or the extended
P-Space P'(R, X)) and the Q-Space (D, X).
2. Overview of BIER Egress Protection
For fast protecting an egress node of a BIER domain, a backup egress
node is configured on the egress node. After the configuration, the
egress node distributes the information about the backup egress to
its direct neighbors.
For clearly distinguishing between an egress node and a backup egress
node, an egress node is called a primary egress node sometimes.
For a multicast packet to a primary egress node of the domain, when
the primary egress node fails, its upstream hop as a point of local
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repair (PLR) sends the packet to the backup egress node configured to
protect the primary egress node once the PLR detects the failure.
A Bit-Forwarding Router (BFR) in a BIER sub-domain builds and
maintains an "Egress Protection Bit Index Routing Table" (EP-BIRT)
for each of its BFR Neighbors (BFR-NBRs) that are egress nodes of the
domain to provide fast protection against the failure of an egress
node. The BFR builds each EP-BIRT based on a BIRT defined in
[RFC8279]. An "Egress Protection Bit Index Forwarding Table" (EP-
BIFT) is derived from an EP-BIRT in a way that is similar to the way
in which a BIFT is derived from a BIRT, which is defined in
[RFC8279].
Once the BFR as a PLR detects the failure of its BFR-NBR X that is a
primary egress node of the domain, for a multicast packet targeting
to the primary egress node, the PLR uses the EP-BIFT for X to send
the packet to the backup egress node configured to protect the
primary egress node.
3. Protocol Extensions
This section defines extensions to OSPF and IS-IS for advertising the
backup information (including the backup egress node for protecting a
primary egress node) to its direct neighbors.
3.1. Extensions to OSPF
When a node P (as a primary egress node) has a backup egress node
configured to protect against its failure, node P advertises the
information about the backup egress node to its neighbors in its
router information opaque LSA of LS type 9 or 10. The information is
included in a backup egress node TLV. The format of the TLV is shown
in Figure 1.
After each of the neighbors receives the backup egress node TLV, it
knows that node P as a primary egress node will be protected by the
backup egress node in the TLV. Once detecting the failure of node P,
it sends the packet targeting to node P towards the backup egress
node.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD1) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved | BFR-id of backup egress node |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sub-TLVs (Optional) |
: :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: OSPF Backup Egress TLV
Type: 2 octets, its value (TBD1) is to be assigned by IANA.
Length: 2 octets, its value is 4 plus the length of the Sub-TLVs
included. If no Sub-TLV is included, its value is 4.
Reserved: 2 octets, it MUST be set to zero when sending and be
ignored while receiving.
BFR-id of backup egress node: 2 octets, its value is the BFR-id of
the backup egress node configured to protect against the failure of
the primary egress node.
Sub-TLVs (Optional): No Sub-TLV is defined now.
3.2. Extensions to IS-IS
For supporting fast protection against the failure of a primary
egress node in a BIER domain, a new IS-IS TLV, called IS-IS backup
egress node TLV, is defined. It contains the BFR-id of a backup
egress node.
When a node P (as a primary egress node) has a backup egress node
configured to protect against its failure, node P advertises the
information about the backup egress node to its neighbors using a IS-
IS backup egress node TLV.
This TLV may be advertised in IS-IS Hello (IIH) PDUs, LSPs, or in
Circuit Scoped Link State PDUs (CS-LSP) [RFC7356]. The format of the
TLV is shown in Figure 2.
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type (TBD2) | Length | BFR-id of backup egress node |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Sub-TLVs (Optional) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: IS-IS Backup Egress TLV
Type: 1 octet, its value (TBD2) is to be assigned by IANA.
Length: 1 octet, its value is 2 plus the length of the Sub-TLVs
included. If no Sub-TLV is included, its value is 2.
BFR-id of backup egress node: 2 octets, its value is the BFR-id of
the backup egress node configured to protect against the failure of
the primary egress node.
Sub-TLVs (Optional): No Sub-TLV is defined now.
4. BIER Extensions
4.1. Egress Protection Bit Index Routing Tables
If a BFR is a direct neighbor of an egress node in a BIER sub-domain,
it builds and maintains a number of "Egress Protection Bit Index
Routing Tables" (EP-BIRTs). There is an EP-BIRT for each of the
BFR's neighbors that are egress nodes of the domain. The BFR builds
each EP-BIRT based on its BIRT. Comparing to the BIRT, an EP-BIRT
has a piece of new backup information for each BFER.
The new backup information for a BFER indicates if the BFER as an
egress node is protected by the BFR. If so, the information further
includes the backup egress node configured to protect the BFER.
In one implementation, the new backup information is represented by
{EP, BE-BFER}. EP (short for Egress Protection) is a flag,
indicating whether the BFER as an egress node is protected. EP = 1
means that the BFER is protected. EP = 0 means that the BFER is not
protected. BE-BFER (short for Backup Egress BFER) is the BFER (i.e.,
BFER-id) of the backup egress node when EP = 1. BE-BFER is NULL (0)
when EP = 0.
In the EP-BIRT for BFR-NBR X that is an egress node, the row having X
as BFER and as its next hop BFR-NBR contains the new backup
information {EP = 1, BE-BFER}, where BE-BFER is the BFER (i.e., BFER-
id) of backup egress node for protecting the egress node. Each of
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the other rows in the EP-BIRT contains the new backup information {EP
= 0, BE-BFER = NULL}.
When the egress node fails, for a multicast packet targeting to the
primary egress node BFER (PE-BFER), the BFR sends the packet to the
BE-BFER through using the route to the backup egress node. The BFR
clears the bit for PE-BFER and adds the bit for BE-BFER in the
packet's BitString first, and then forwards the packet according to
the forwarding entry for BE-BFER.
The EP-BIRT for BFR-NBR X that is an egress node considers the
failure of X. It has a route or say a next hop (i.e., BFR-NBR N on
the path, where N is not X) to every BFER except for X.
The BFR may build the EP-BIRT for BFR-NBR X by copying its BIRT to
the EP-BIRT and sets the new information for each BFER to empty such
as {EP = 0, BE-BFER = NULL} first. And then it updates each of the
rows in the EP-BIRT that has X as BFER or next hop BFR-NBR X.
For the BFR-id of a BFER in the EP-BIRT for egress node X, when the
next hop BFR-NBR on the path to the BFER is X, the BFR checks whether
the BFER is X. If the BFER is not X, the BFR changes next hop BFR-
NBR X to a backup next hop (BNH) when there is a BNH on a backup path
to the BFER without going through X and the link from the BFR to X.
If the BFER is X, the BFR adds the new backup information {EP = 1,
BE-BFER} for the BFER as PE-BFER.
If there is not any BNH to a BFER to protect against the failure of
X, the next hop BFR-NBR X to the BFER in the EP-BIRT for BFR-NBR X is
changed to NULL. For a multicast packet having the BFER as one of
its destinations, if the next hop BFR-NBR to the BFER is NULL, the
BFR does not send the packet to the next hop BFR-NBR NULL but drops
it when X fails.
Note: In another option, the next hop BFR-NBR X to the BFER in the
EP-BIRT for BFR-NBR X keeps unchanged when there is not any BNH to
the BFER to protect against the failure of X. In this case, for a
multicast packet having the BFER as one of its destinations, the BFR
sends the packet to X when X fails.
In one implementation, the BNH is the Loop-Free Node-Protecting
Alternate defined in [RFC5286] to protect against the failure of X
and link from the BFR to X. In another implementation, the BNH is
the virtual Loop-Free Alternate (LFA), i.e., PQ node, defined in
[RFC7490]. In a special case, a PQ node is a Loop-Free Node-
Protecting Alternate defined in [RFC5286].
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4.2. Egress Protection Bit Index Forwarding Tables
From each EP-BIRT on the BFR, an "Egress Protection Bit Index
Forwarding Table" (EP-BIFT) is derived. In addition to having a
route to a BFER in each row of the EP-BIFT which is the same as the
EP-BIRT, it has a "Forwarding Bit Mask" (F-BM) in its each row. For
the rows in the EP-BIRT that have the same SI and the same BFR-NBR
and the same new backup information {EP, BE-BFER}, the F-BM for each
of these rows in the EP-BIFT is the logical OR of the BitStrings of
these rows.
This EP-BIFT is programmed into the data plane and is not used to
forward any packet in normal operations. It is activated to forward
a packet with a BIER header once the BFR detects the failure of BFR-
NBR. The header contains SI, BitString, BitStringLength, and sub-
domain.
4.3. Updated Forwarding Procedure
The forwarding procedure defined in [RFC8279] is updated/enhanced for
an EP-BIFT to consider the egress protection (i.e., the new
information {EP, BE-BFER} in the EP-BIFT). For a multicast packet
with the BitString indicating a BFER as one of its destinations, the
updated forwarding procedure sends the packet towards the backup
egress node of the BFER if the BFER is protected. It checks whether
EP = 1 in the forwarding entry for the BFER. If EP = 1, the
procedure clears the bit for the BFER as PE-BFER and adds the bit for
BE-BFER in the packet's BitString first, and then forwards the packet
using the row (i.e., forwarding entry) for BE-BFER.
The updated procedure is described in Figure 3. It is used with an
EP-BIFT for BFR-NBR X as egress node on a BFR to forward multicast
packets when X fails. It can also be used with a BIFT on the BFR to
forward multicast packets in normal operations if the new backup
information in each row of the BIFT is empty such as {EP = 0, BE-BFER
= NULL}.
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Packet = the packet received by BFR;
FOR each BFER k (from the rightmost in Packet's BitString) {
IF BFER k is the BFR itself {
copies Packet, sends the copy to the multicast
flow overlay and clears bit k in Packet's BitString
} ELSE {
finds the row in the EP-BIFT for the sub-domain using
Packet's SI and BitString as the key/index
IF EP == 1 {
clears bit k in Packet's BitString; //BFER k is PE-BFER
adds bit j in Packet's BitString; //BFER j is BE-BFER
} ELSE {
IF BFR-NBR in the row is not NULL {
Copies Packet, updates the copy's BitString by ANDing
it with F-BM in the row,sends updated copy to BFR-NBR
} // BFR-NBR == NULL, not sent Packet to BFR-NBR
updates Packet's BitString by ANDing it with the INVERSE
of the F-BM in the row
}
}
}
Figure 3: Updated Forwarding Procedure
4.4. Switching between EP and Normal Forwarding
The EP-BIFTs will be pre-computed and installed ready for activation
when an egress node failure is detected. Once the BFR detects the
failure of its BFR-NBR X as an egress, it activates the EP-BIFT for X
to forward packets with BIER headers and de-activates its BIFT.
After activation of the EP-BIFT, it remains in effect until it is no
longer required.
In general, when the routing protocol has re-converged on the new
topology taking into account the failure of X, the BIRT is re-
computed using the updated LSDB and the BIFT is re-derived from the
BIRT. Once the BIFT is installed ready for activation, it is
activated to forward packets with BIER headers and the EP-BIFT for X
is de-activated.
From the new topology, the BFR computes/re-computes the EP-BIRT for
each BFR-NBR Y as an egress of the BFR and the EP-BIFT for Y is
derived/re-derived from the EP-BIRT for Y. The EP-BIFT is installed/
re-installed ready for activation when Y fails.
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5. Example Application of BIER Egress Protection
This section illustrates an example application of BIER Egress
Protection on a BFR in a BIER topology in Figure 4.
5.1. Example BIER Topology
An example BIER topology for a BIER sub-domain is shown in Figure 4.
It has 8 nodes/BFRs A, B, C, D, E, F, G and H. Each of the links
connecting these nodes/BFRs has a cost. The link cost of 1 is
default and is not indicated in the figure. The link costs of other
values such as 2 and 3 are indicated in the figure.
4 (0:01000)
/--------( G )--------- ( H ) Backup Egress for D
2/ 2\______ / \
/ _____)____/ \
/ / (____ (CE) Receiver
/ / \ /
/ / \ /
( A )----------( B )-----------( C )----------( D ) Primary Egress
5 (0:10000) \ \ 1 (0:00001)
3\ \
\ \
( E )-----------( F )
3 (0:00100) 2 (0:00010)
Figure 4: Example BIER Topology
Nodes/BFRs D, F, E, H and A are BFERs and have BFR-ids 1, 2, 3, 4,
and 5 respectively. For simplicity, these BFR-ids are represented by
(SI:BitString), where SI = 0 and BitString is of 5 bits. BFR-ids 1,
2, 3, 4, and 5 are represented by (0:00001), (0:00010), (0:00100),
(0:01000) and (0:10000) respectively.
BFER H is configured to protect BFER D on BFR D. Suppose that this
information is distributed to BFR D's neighbors BFR C and BFR G by
IGP. BFR C and BFR G know that H is the backup egress to protect the
primary egress D.
CE is a multicast traffic Receiver, which is dual homed to primary
egress node D and backup egress node H for protecting primary egress
D. During normal operations, there is no multicast traffic to CE
from backup egress node H and CE receives the multicast traffic only
from primary egress node D. There is no duplicated traffic to
receiver CE. This is different from MoFRR in [RFC7431], where the
same traffic is sent through two separated paths/trees to both
primary egress node D and backup egress node H, to which the receiver
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CE is dual homed. When primary egress node D fails, the multicast
traffic is sent to CE from backup egress node H.
The fast egress protection mechanism in this document will use less
network resources such as link bandwidth than MoFRR in [RFC7431].
5.2. BIRT and BIFT on a BFR
Every BFR in a BIER sub-domain/topology builds and maintains a Bit
Index Routing Table (BIRT). For the BIER topology in Figure 4, each
of 8 nodes/BFRs A, B, C, D, E, F, G and H builds and maintains a BIRT
using the LSDB for the topology.
The BIRT built on BFR C (i.e. node C) is shown in Figure 5.
+----------------+--------------+------------+
| BFR-id | BFR-Prefix | BFR-NBR |
| (SI:BitString) | of Dest BFER | (Next Hop) |
+================+==============+============+
| 1 (0:00001) | D | D |
+----------------+--------------+------------+
| 2 (0:00010) | F | F |
+----------------+--------------+------------+
| 3 (0:00100) | E | F |
+----------------+--------------+------------+
| 4 (0:01000) | H | H |
+----------------+--------------+------------+
| 5 (0:10000) | A | B |
+----------------+--------------+------------+
Figure 5: Bit Index Routing Table on BFR C
The 1st row in the BIRT indicates that the next hop BFR-NBR on the
shortest path to BFER D with BFR-id 1 is BFR D.
The 2nd row in the BIRT indicates that the next hop BFR-NBR on the
shortest path to BFER F with BFR-id 2 is BFR F.
The 3rd row in the BIRT indicates that the next hop BFR-NBR on the
shortest path to BFER E with BFR-id 3 is BFR F.
The 4-th row in the BIRT indicates that the next hop BFR-NBR on the
shortest path to BFER H with BFR-id 4 is BFR H.
The 5-th row in the BIRT indicates that the next hop BFR-NBR on the
shortest path to BFER A with BFR-id 5 is BFR B.
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From this BIRT on BFR C, a Bit Index Forwarding Table (BIFT) is
derived. This BIFT is shown in Figure 6.
The 2nd and 3-th rows in the BIRT have the same SI = 0 and next hop
BFR-NBR = F. The F-BM for each of these two rows in the BIFT is the
logical OR of the BitStrings of these rows, which is 00110 (00010 OR
00100 = 00110).
The F-BM for 1st row in the BIFT is 00001.
The F-BM for 4-th row in the BIFT is 01000.
The F-BM for 5-th row in the BIFT is 10000.
+----------------+---------+------------+
| BFR-id | F-BM | BFR-NBR |
| (SI:BitString) | | (Next Hop) |
+================+=========+============+
| 1 (0:00001) | 00001 | D |
+----------------+---------+------------+
| 2 (0:00010) | 00110 | F |
+----------------+---------+------------+
| 3 (0:00100) | 00110 | F |
+----------------+---------+------------+
| 4 (0:01000) | 01000 | H |
+----------------+---------+------------+
| 5 (0:10000) | 10000 | B |
+----------------+---------+------------+
Figure 6: Bit Index Forwarding Table on BFR C
5.3. EP-BIRTs and EP-BIFTs on a BFR
Each of the BFRs that are neighbors of egress nodes (i.e., BFERs) in
a BIER sub-domain/topology builds and maintains a number of Egress
Protection Bit Index Routing Tables (EP-BIRTs).
For the BIER topology in Figure 4,
BFR B is the neighbor of BFERs A and E;
BFR C is the neighbor of BFERs D, F and H;
BFR E is the neighbor of BFER F;
BFR F is the neighbor of BFER E;
BFR G is the neighbor of BFERs D and H.
Each of 5 nodes/BFRs B, C, E, F and G builds and maintains a number
of EP-BIRTs using the LSDB for the topology for its every BFR-NBR as
an egress node.
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For example, BFR C (i.e., node C) in the BIER topology builds and
maintains three EP-BIRTs for its three BFR-NBRs (BFERs D, F and H)
that are egress nodes respectively.
The EP-BIRT for BEFR D built by BFR C based on the BIRT on BFR C
(refer to Figure 5) is shown in Figure 7.
The BIRT is copied to the EP-BIRT for BFER D (i.e., the first three
columns of the EP-BIRT). The new backup information (i.e., the 4-th
column) for every row in the EP-BIRT is initialized to {EP = 0, BE-
BFER = 0/NULL}.
+--------------+--------------+----------+----------------+
| BFR-id | BFR-Prefix | BFR-NBR | {EP,BE-BFER} |
|(SI:BitString)| of Dest BFER |(Next Hop)| (Backup Info) |
+==============+==============+==========+================+
| 1 (0:00001) | D | D/NULL |EP=1, BE-BFER=H |
+--------------+--------------+----------+----------------+
| 2 (0:00010) | F | F |EP=0, BE-BFER=0 |
+--------------+--------------+----------+----------------+
| 3 (0:00100) | E | F |EP=0, BE-BFER=0 |
+--------------+--------------+----------+----------------+
| 4 (0:01000) | H | H |EP=0, BE-BFER=0 |
+--------------+--------------+----------+----------------+
| 5 (0:10000) | A | B |EP=0, BE-BFER=0 |
+--------------+--------------+----------+----------------+
Figure 7: EP-BIRT for BFER D on BFR C
In the EP-BIRT for BFER D, the row that has BFR-NBR == D is the 1st
row. This row has the new backup information {EP = 1, BE-BFER = H},
which indicates that BFER D (i.e., primary egress node D) is
protected by BFER H (i.e., backup egress node H). Each of the other
rows has the new backup information {EP = 0, BE-BFER = 0/NULL}.
The 1st row in the EP-BIRT indicates that the next hop BFR-NBR on the
path to BFER D with BFR-id 1 is NULL (changed to NULL from D). There
is no backup next hop (BNH) to D when D fails.
The 2nd row in the EP-BIRT indicates that the next hop BFR-NBR on the
path to BFER F with BFR-id 2 is BFR F.
The 3rd row in the EP-BIRT indicates that the next hop BFR-NBR on the
path to BFER E with BFR-id 3 is BFR F.
The 4-th row in the EP-BIRT indicates that the next hop BFR-NBR on
the path to BFER H with BFR-id 4 is BFR H.
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The 5-th row in the EP-BIRT indicates that the next hop BFR-NBR on
the path to BFER A with BFR-id 5 is BFR B.
From this EP-BIRT for BFER D on BFR C, an Egress Protection Bit Index
Forwarding Table (EP-BIFT) is derived. This EP-BIFT for BFER D is
shown in Figure 8.
The 2nd and 3rd rows in the EP-BIRT have the same SI = 0, the same
next hop BFR-NBR = E and the same backup information {EP=0, BE-
BFER=0}. The F-BM for each of these two rows in the EP-BIFT is the
logical OR of the BitStrings of these rows, which is 00110 (00010 OR
00100 = 00110).
+----------------+---------+------------+----------------+
| BFR-id | F-BM | BFR-NBR | {EP,BE-BFER} |
| (SI:BitString) | | (Next Hop) | (Backup Info) |
+================+=========+============+================+
| 1 (0:00001) | 00001 | NULL |EP=1, BE-BFER=H |
+----------------+---------+------------+----------------+
| 2 (0:00010) | 00110 | F |EP=0, BE-BFER=0 |
+----------------+---------+------------+----------------+
| 3 (0:00100) | 00110 | F |EP=0, BE-BFER=0 |
+----------------+---------+------------+----------------+
| 4 (0:01000) | 01000 | H |EP=0, BE-BFER=0 |
+----------------+---------+------------+----------------+
| 5 (0:10000) | 10000 | B |EP=0, BE-BFER=0 |
+----------------+---------+------------+----------------+
Figure 8: EP-BIFT for BFER D on BFR C
The F-BM for 1st row in the EP-BIFT is 00001.
The F-BM for 4-th row in the EP-BIFT is 01000.
The F-BM for 5-th row in the EP-BIFT is 10000.
5.4. Forwarding using EP-BIFT
Suppose that there is a multicast traffic from BFR A as ingress/BFIR
to egresses/BFERs D, F and E. For every packet of the traffic, after
receiving it, BFR A adds a BIER header into the packet and sends the
packet with the BIER header to BFR B, which sends the packet BFR C.
The BIER header contains (SI:BitString) = (0:00111) for egresses/
BFERs D, F and E.
In normal operations, after receiving the packet from BFR B, BFR C
copies, updates and sends the packet to BFR D and BFR F using the
BIFT on BFR C according to the forwarding procedure defined in
[RFC8279].
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Once BFR C detects the failure of its BFR-NBR D, which is a BFER,
after receiving the packet from BFR B, BFR C copies, updates and
sends the packet using the EP-BIFT for BFER D on BFR C according to
the updated forwarding procedure.
For the packet targeting to BFER D (i.e., primary egress node), BFR C
sends it towards BFER H (i.e., backup egress node), which is
configured to protect BFER D.
For example, once BFR C detects the failure of its BFR-NBR D, after
receiving the packet from BFR B, BFR C copies, updates and sends the
packet to BFR H and BFR F using the EP-BIFT for BFER D on BFR C.
The packet received by BFR C from BFR B contains (SI:BitString) =
(0:00111). The rightmost one bit in BitString is bit 1. For BFER 1
(0:00001) (i.e., BFR D as BFER), BFR C gets the 1st row (i.e.,
forwarding entry) in the EP-BIFT for BFER D. EP = 1 in the row
indicates that BFER D is protected against the failure of D. BFR C
clears bit 1 in Packet's BitString and sets bit 4 (i.e., the bit for
BE-BFER = H) in Packet's BitString to one. The BitString in Packet
is 01110 now. This lets BFR C send Packet to BE-BFER H.
For the packet containing BitString = 01110, the rightmost one bit in
BitString is bit 2. For BFER 2 (0:00010) (i.e., BFR F as BFER), BFR
C gets the 2nd row (i.e., forwarding entry) in the EP-BIFT for BFER
D. EP = 0 and the next hop BFR-NBR is F in the row. BFR C copies,
updates and sends the packet to F.
The packet sent to F contains the updated BitString = 00110, which is
01110 & F-BM in the 2nd row = 01110 & 00110 = 00110.
After sending the packet to F, BFR C updates the original packet by
ANDing its BitString with the INVERSE of the F-BM in the 2nd row.
The updated BitString = 01000, which is 01110 & ~F-BM in the row =
01110 & 11001 = 01000.
For the packet containing BitString = 01000, the rightmost one bit in
BitString is bit 4. For BFER 4 (0:01000) (i.e., BFR H as BFER), BFR
C gets the 4-th row (i.e., forwarding entry) in the EP-BIFT for BFER
D. EP = 0 and the next hop BFR-NBR is H in the row. BFR C copies,
updates and sends the packet to H. The packet sent to H contains
BitString = 01000.
After sending the packet to H, BFR C updates the original packet by
ANDing its BitString with the INVERSE of the F-BM in the 4-th row.
The updated BitString = 00000, which is 01000 & ~F-BM in the row =
01000 & 10111 = 00000.
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The updated packet has BitString without any one bit. BFR C finishes
forwarding the packet to F and H (backup for D). BFR F will sends
the packet to E.
6. Security Considerations
TBD.
7. IANA Considerations
No requirements for IANA.
8. Acknowledgements
The authors would like to thank people for their comments to this
work.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
[RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250,
July 2008, <https://www.rfc-editor.org/info/rfc5250>.
[RFC5286] Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
IP Fast Reroute: Loop-Free Alternates", RFC 5286,
DOI 10.17487/RFC5286, September 2008,
<https://www.rfc-editor.org/info/rfc5286>.
[RFC5714] Shand, M. and S. Bryant, "IP Fast Reroute Framework",
RFC 5714, DOI 10.17487/RFC5714, January 2010,
<https://www.rfc-editor.org/info/rfc5714>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
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[RFC7356] Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
Scope Link State PDUs (LSPs)", RFC 7356,
DOI 10.17487/RFC7356, September 2014,
<https://www.rfc-editor.org/info/rfc7356>.
[RFC7490] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
RFC 7490, DOI 10.17487/RFC7490, April 2015,
<https://www.rfc-editor.org/info/rfc7490>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
[RFC8556] Rosen, E., Ed., Sivakumar, M., Przygienda, T., Aldrin, S.,
and A. Dolganow, "Multicast VPN Using Bit Index Explicit
Replication (BIER)", RFC 8556, DOI 10.17487/RFC8556, April
2019, <https://www.rfc-editor.org/info/rfc8556>.
9.2. Informative References
[I-D.ietf-rtgwg-segment-routing-ti-lfa]
Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B.,
and D. Voyer, "Topology Independent Fast Reroute using
Segment Routing", draft-ietf-rtgwg-segment-routing-ti-
lfa-05 (work in progress), November 2020.
[I-D.ietf-spring-segment-protection-sr-te-paths]
Hegde, S., Bowers, C., Litkowski, S., Xu, X., and F. Xu,
"Segment Protection for SR-TE Paths", draft-ietf-spring-
segment-protection-sr-te-paths-00 (work in progress),
September 2020.
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[RFC7431] Karan, A., Filsfils, C., Wijnands, IJ., Ed., and B.
Decraene, "Multicast-Only Fast Reroute", RFC 7431,
DOI 10.17487/RFC7431, August 2015,
<https://www.rfc-editor.org/info/rfc7431>.
[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>.
[RFC8401] Ginsberg, L., Ed., Przygienda, T., Aldrin, S., and Z.
Zhang, "Bit Index Explicit Replication (BIER) Support via
IS-IS", RFC 8401, DOI 10.17487/RFC8401, June 2018,
<https://www.rfc-editor.org/info/rfc8401>.
[RFC8444] Psenak, P., Ed., Kumar, N., Wijnands, IJ., Dolganow, A.,
Przygienda, T., Zhang, J., and S. Aldrin, "OSPFv2
Extensions for Bit Index Explicit Replication (BIER)",
RFC 8444, DOI 10.17487/RFC8444, November 2018,
<https://www.rfc-editor.org/info/rfc8444>.
Authors' Addresses
Huaimo Chen
Futurewei
Boston, MA
USA
Email: Huaimo.chen@futurewei.com
Mike McBride
Futurewei
Email: michael.mcbride@futurewei.com
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing, 102209
China
Email: wangaj3@chinatelecom.cn
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Gyan S. Mishra
Verizon Inc.
13101 Columbia Pike
Silver Spring MD 20904
USA
Phone: 301 502-1347
Email: gyan.s.mishra@verizon.com
Yisong Liu
China Mobile
Email: liuyisong@chinamobile.com
Yanhe Fan
Casa Systems
USA
Email: yfan@casa-systems.com
Lei Liu
Fujitsu
USA
Email: liulei.kddi@gmail.com
Xufeng Liu
Volta Networks
McLean, VA
USA
Email: xufeng.liu.ietf@gmail.com
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