BGP Failure Propagation (BGP-FP) for Enhancing Control-Plane Convergence
draft-li-idr-bgp-failure-propagation-convergence-01
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| Authors | Yuhang Li , Yahui Li , Xia Yin , Zhang Han , Xingang Shi | ||
| Last updated | 2026-02-28 (Latest revision 2026-02-10) | ||
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draft-li-idr-bgp-failure-propagation-convergence-01
IDR Y. Li
Internet-Draft Y. Li
Intended status: Standards Track X. Yin
Expires: 1 September 2026 H. Zhang
X. Shi
Tsinghua University
28 February 2026
BGP Failure Propagation (BGP-FP) for Enhancing Control-Plane Convergence
draft-li-idr-bgp-failure-propagation-convergence-01
Abstract
This document specifies BGP Failure Propagation (BGP-FP), an
infrastructure and protocol that improves inter-domain routing
convergence by accelerating the removal of stale (invalid) routes.
BGP-FP uses (1) an Agent deployed per Autonomous System (AS) to
detect inter-AS reachability changes and to configure local routers,
(2) a logically centralized Repository to store and selectively
forward AS reachability state, and (3) BGP Large Communities as a
"route freshness" marker. Agents validate and apply Repository
updates to filter routes that traverse AS pairs whose reachability
has been lost or that violate the originating AS's forwarding intent,
reducing route-flap propagation in the control plane.
This document clarifies that "AS reachability" refers to the
reachability between two ASes, not to the state of individual
physical or logical links within an AS. If multiple links exist
between two ASes, the failure of a single link that does not break
overall AS-to-AS reachability does not trigger the BGP-FP mechanism.
A new Repository deployment model is introduced, suggesting that the
Repository be operated by a newly established organization composed
of Tier-1 ASes and Regional Internet Registries (RIRs), using a
distributed deployment with Byzantine fault-tolerant consensus and
rotating leadership.
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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This Internet-Draft will expire on 1 September 2026.
Copyright Notice
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document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 4
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 5
3. Architecture and Operational Overview . . . . . . . . . . . . 5
3.1. Components . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Information Model: AS Reachability State Entries . . . . 6
3.3. Route Freshness Marking with BGP Large Communities . . . 6
4. Protocol Overview . . . . . . . . . . . . . . . . . . . . . . 7
5. BGP-FP Message Encoding . . . . . . . . . . . . . . . . . . . 8
5.1. Common Header . . . . . . . . . . . . . . . . . . . . . . 8
5.2. Attributes (TLV) . . . . . . . . . . . . . . . . . . . . 8
5.3. Defined Attributes . . . . . . . . . . . . . . . . . . . 9
5.3.1. Batch Counter (0x01) . . . . . . . . . . . . . . . . 9
5.3.2. Function (0x02) . . . . . . . . . . . . . . . . . . . 9
5.3.3. Merkle Root (0x03) . . . . . . . . . . . . . . . . . 9
5.3.4. Signature (0x04) . . . . . . . . . . . . . . . . . . 10
5.3.5. AS Reachability State List (0x05) . . . . . . . . . . 10
5.3.6. Subscribed ASes (0x06) . . . . . . . . . . . . . . . 10
5.3.7. Merkle Proof (0x07) . . . . . . . . . . . . . . . . . 11
6. Agent-to-Repository Protocol . . . . . . . . . . . . . . . . 11
6.1. Message Types . . . . . . . . . . . . . . . . . . . . . . 11
6.2. Mandatory/Optional Attributes . . . . . . . . . . . . . . 11
6.3. Agent Procedures . . . . . . . . . . . . . . . . . . . . 11
7. Repository-to-Agent Protocol . . . . . . . . . . . . . . . . 12
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7.1. Message Types . . . . . . . . . . . . . . . . . . . . . . 12
7.2. Mandatory/Optional Attributes . . . . . . . . . . . . . . 12
7.3. Repository Procedures . . . . . . . . . . . . . . . . . . 13
8. Router Policy Behavior . . . . . . . . . . . . . . . . . . . 13
8.1. Inbound Filtering Rule . . . . . . . . . . . . . . . . . 13
8.2. Outbound Marking Rule . . . . . . . . . . . . . . . . . . 14
9. AS-Internal Propagation of Failure Information . . . . . . . 14
10. Deployment Considerations . . . . . . . . . . . . . . . . . . 15
10.1. Repository Organization . . . . . . . . . . . . . . . . 15
10.2. Distributed Deployment . . . . . . . . . . . . . . . . . 15
10.3. Consensus and Trust . . . . . . . . . . . . . . . . . . 16
10.4. Integration with RPKI Infrastructure . . . . . . . . . . 16
10.5. Incremental Deployment . . . . . . . . . . . . . . . . . 17
11. Example of Operation . . . . . . . . . . . . . . . . . . . . 17
11.1. Topology and Customer-Provider Relationships . . . . . . 18
11.2. Loss of AS Reachability Between AS1 and AS2 . . . . . . 19
11.3. BGP-FP Operation . . . . . . . . . . . . . . . . . . . . 19
12. Privacy Considerations . . . . . . . . . . . . . . . . . . . 20
13. Operational Considerations . . . . . . . . . . . . . . . . . 20
14. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20
14.1. TCP Service Name and Port . . . . . . . . . . . . . . . 21
14.2. "BGP-FP Message Types" Registry . . . . . . . . . . . . 21
14.3. "BGP-FP Attribute Types" Registry . . . . . . . . . . . 21
15. Security Considerations . . . . . . . . . . . . . . . . . . . 22
16. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
16.1. Normative References . . . . . . . . . . . . . . . . . . 22
16.2. Informative References . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
BGP-4 [RFC4271] is a path-vector inter-domain routing protocol.
Internet operators have long observed BGP instability and route-flap
propagation [RFC2439]. A key contributor is that routes that have
become invalid (e.g., because the reachability between two ASes is
lost) can persist and propagate until withdrawals and path
exploration complete.
BGP-FP addresses this by disseminating authenticated AS reachability
changes and by marking routes with a per-AS freshness indicator.
Upon learning that reachability between AS X and AS Y has been lost,
downstream ASes can proactively reject stale routes whose AS_PATH
traverses that AS pair, reducing control-plane churn and improving
eBGP convergence. This document focuses on eBGP control-plane
convergence. Terminology related to convergence benchmarking is
aligned with [RFC4098].
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"AS reachability" in this document refers to the ability of one AS to
reach another AS via at least one eBGP session, not to the state of
individual links or routers inside an AS. If multiple parallel links
or sessions exist between two ASes, the failure of a single component
that does not break the overall AS-to-AS reachability does not
trigger the BGP-FP mechanisms.
2. Conventions and Definitions
2.1. Terminology
eBGP: As defined in [RFC4271].
Agent: A server deployed per AS that (1) receives router logs, (2)
reads local routing state (e.g., RIB/Adj-RIB-In/Adj-RIB-Out), (3)
communicates with a Repository using BGP-FP messages, and (4)
configures local routers’ import/export policies to apply BGP-FP.
Repository: A network service with a well-known reachability method
(discovery is out of scope) that stores per-AS BGP-FP state and
forwards updates on-demand to subscribed ASes.
AS Reachability: The property that two ASes have at least one usable
eBGP session and forwarding relationship between them. It is a
pairwise AS-level property, not a link-level property.
AS Reachability State: The status of reachability between a pair of
ASes, represented as a tuple (Local ASN, Peer ASN, Scope, Status).
Scope and Status are defined in Section 3.2.
Invalid (Stale) BGP Route: A route whose AS_PATH includes an AS pair
whose reachability has been lost, or whose propagation violates a
policy/prefix condition expressed by the originating AS. For
example, if the AS reachability between AS X and AS Y is down, but a
route's AS_PATH still contains "... X Y ...", the route is considered
stale and is expected to be withdrawn or replaced.
Local AS: The AS in which a given Agent is deployed.
Subscribed ASes: The set of ASNs that appear in AS_PATH attributes of
routes in the Local AS routing state (e.g., Loc-RIB). The Local AS
subscribes to BGP-FP updates originating from those ASes.
NOTE: The terms "route", "BGP route", "AS_PATH", "BGP Neighbor", "BGP
Peer", "MRAI", and "RIB" are used consistent with [RFC4098] where
applicable.
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2.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Architecture and Operational Overview
3.1. Components
BGP-FP consists of:
* Agent (per AS): detects local AS reachability changes, maintains a
per-AS freshness counter, reports state to the Repository, and
configures routers to (a) attach freshness markers to outbound
routes and (b) filter stale routes upon receiving Repository
updates.
* Repository: stores per-AS reported AS reachability state and
forwards BGP-FP updates to ASes that have subscribed to the source
AS. The Repository is logically centralized but can be physically
distributed.
+------------------------------+
| Repository (logically one, |
| physically distributed) |
+---------------+--------------+
^
| BGP-FP over TCP
v
+---------------+--------------+
| Agent (per AS) |
| - receives router logs |
| - reads routing state |
| - configures import/export |
+---------------+--------------+
^
| logs / RIB / config channels
v
+--------+--------+
| BGP Routers |
| (border routers |
| in the AS) |
+-----------------+
Figure 1: The Architecture of BGP-FP
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3.2. Information Model: AS Reachability State Entries
An Agent reports "AS Reachability State" information as a list of
entries. Each entry is a UTF-8 string formatted as:
"peer-asn ":" scope ":" status"
where:
* peer-asn: The 4-octet ASN of the eBGP neighbor.
* scope: Either "*" or a prefix/identifier that indicates the
affected traffic scope. This document uses "prefix" in the broad
sense and permits "*" to indicate all prefixes.
* status: "Established" or "Failure".
The following classes are distinguished:
* (1) Policy failure (prefix scoped to a peer):
"PeerASN:Prefix:Failure" . The Local AS indicates that it will not
forward the indicated prefix toward PeerASN.
* (2) AS reachability failure (all prefixes to a peer):
"PeerASN:*:Failure" . The Local AS indicates that its overall
reachability to PeerASN is lost (i.e., no usable eBGP session or
forwarding relationship exists for any prefixes).
* (3) Prefix withdrawal/denial (all peers for a prefix):
"*:Prefix:Failure". The Local AS indicates that it will not
accept or propagate the indicated prefix (or has withdrawn it).
If multiple parallel links or sessions exist between two ASes, the
failure of a single link or session that does not break overall AS-
to-AS reachability MUST NOT be reported as a "PeerASN:*:Failure"
entry. Only when the Local AS determines that it has no usable path
to PeerASN for any prefixes does it report such a failure.
3.3. Route Freshness Marking with BGP Large Communities
BGP-FP uses the BGP Large Communities attribute [RFC8092].
Operational guidance for organizing Large Communities is discussed in
[RFC8195].
Each AS maintains a monotonically increasing 32-bit Batch Counter.
The Agent configures routers to attach a Large Community of the form.
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+======================+===============+
| RFC8092 | this document |
+======================+===============+
| Global Administrator | Source ASN |
+----------------------+---------------+
| Local Data Part 1 | Function |
+----------------------+---------------+
| Local Data Part 2 | Batch Counter |
+----------------------+---------------+
Table 1: Field Mapping
The table above shows a mapping table between the fields in BGP Large
Communities [RFC8092] and this document.
* Source ASN is the AS performing the marking (the Local AS).
* Function is an operator-chosen 32-bit value; this document uses
1234 as a default example.
* Batch Counter is the current freshness value for the Local AS.
A route MAY carry multiple Large Communities. BGP-FP requires that
routers preserve existing Large Communities and that each AS that
deploys BGP-FP adds (at least) its own freshness community.
4. Protocol Overview
BGP-FP defines a simple message protocol carried over TCP [RFC793]
between Agents and the Repository. The protocol MUST support 4-octet
ASNs as specified in [RFC6793]. High-level operation:
* Subscription: Each Agent computes its Subscribed ASes from local
routing state and reports subscription deltas to the Repository.
* Failure reporting: Upon local events (loss of AS reachability,
policy change, prefix withdrawal/restore), an Agent increments its
Batch Counter and reports updated AS Reachability State entries to
the Repository
* On-demand forwarding: The Repository forwards Source-AS updates
only to Agents whose Local AS has subscribed to that Source ASN.
* Filtering: Receiving Agents validate updates and install import
policy rules to reject stale routes that traverse AS pairs with
lost reachability or that violate reported policy/prefix
constraints.
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5. BGP-FP Message Encoding
All multi-octet fields are in network byte order (big-endian).
5.1. Common Header
Each BGP-FP message begins with the following header:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source ASN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Attributes (TLVs) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
* Message Length (32 bits): Number of octets following this field
(i.e., header remainder and TLVs). Implementations MUST reject
messages whose length exceeds the remaining TCP segment stream
availability.
* Type (8 bits): Message type (Agent-to-Repository in Section 6;
Repository-to-Agent in Section 7).
* Reserved (24 bits): Reserved for future use. The sender MUST set
these bits to zero. The receiver MUST ignore them.
* Source ASN (32 bits): The originating AS for the state carried in
the message.
5.2. Attributes (TLV)
Following the common header is a sequence of zero or more attributes,
each encoded as a TLV:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attr Type | Attr Length | (value...) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attr Value (variable) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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* Attr Type (8 bits): Attribute identifier.
* Attr Length (16 bits): Length in octets of Attr Value.
* Attr Value (variable): Attribute content. Unknown Attr Type
values MUST be ignored (skipped using Attr Length).
5.3. Defined Attributes
This document defines the following attribute types:
* 0x01 Batch Counter
* 0x02 Function
* 0x03 Merkle Root
* 0x04 Signature
* 0x05 AS Reachability State List
* 0x06 Subscribed ASes
* 0x07 Merkle Proof
5.3.1. Batch Counter (0x01)
A 32-bit unsigned integer. Each Agent maintains its own counter.
When an Agent reports any change affecting AS reachability (including
loss of overall AS-to-AS reachability, policy changes, and prefix
events), it MUST increment the counter by 1.
5.3.2. Function (0x02)
A 32-bit unsigned integer chosen by operator policy. The default
example value is 1234.
5.3.3. Merkle Root (0x03)
A 32-octet value computed using SHA-256 over the current dataset of
(a) AS Reachability State List and (b) Subscribed ASes. The Merkle
tree and inclusion proof model is aligned with the Merkle tree
approach used in Certificate Transparency [RFC9162]. The exact leaf
canonicalization is to be specified in a future revision.
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5.3.4. Signature (0x04)
A digital signature computed by the Source ASN's private key over the
Merkle Root value. The signature algorithm and encoding follow the
DigitallySigned conventions used in [RFC9162], unless otherwise
profiled by an implementation profile. The Signature attribute MUST
NOT appear unless a Merkle Root attribute is present in the same
message.
5.3.5. AS Reachability State List (0x05)
Encodes a list of AS reachability state entries:
* Entry Count (16 bits), followed by Entry Count entries: Entry
Length (16 bits) + Entry (UTF-8 string)
* Each Entry string MUST follow this ABNF:
as-reachability-entry = peer-asn ":" scope ":" status
peer-asn = 1*10DIGIT ; decimal ASN, MUST fit in 32 bits
scope = "*" / prefix
status = "Established" / "Failure"
The "prefix" syntax is deployment-specific; implementations SHOULD use CIDR textual forms.
ABNF is specified per [RFC5234].
5.3.6. Subscribed ASes (0x06)
Carries two ASN lists:
* Add List: ASNs newly subscribed
* Remove List: ASNs unsubscribed
Encoding:
* Add Count (16 bits), followed by Add Count ASNs (each 32 bits)
* Remove Count (16 bits), followed by Remove Count ASNs (each 32
bits)
For an INIT message, Remove Count MUST be zero.
For a Update message, Add List SHOULD be the set of all ASNs
appearing in AS_PATH attributes of BGP routes in the Local AS routing
state.
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5.3.7. Merkle Proof (0x07)
Provides hashes necessary to verify inclusion of disseminated data,
aligned with [RFC9162]. Encoding:
* Proof Count (16 bits), followed by Proof Count tuples
* Each tuple: ASN (32 bits) + Hash (32 octets)
6. Agent-to-Repository Protocol
6.1. Message Types
Agent messages use the Type field as follows:
* Type = 0 KEEPALIVE Message
* Type = 1 INIT Message
* Type = 2 UPDATE Message
INIT is sent when an Agent is first deployed and informs the
Repository that the Local AS participates in BGP-FP. INIT conveys a
full snapshot. UPDATE conveys incremental changes after a successful
INIT.
6.2. Mandatory/Optional Attributes
For Agent messages:
* KEEPALIVE (Type=0): no attributes.
* INIT (Type=1): MUST include: Batch Counter (0x01), Function
(0x02), Merkle Root (0x03), Signature (0x04) MAY include: AS
Reachability State List (0x05), Subscribed ASes (0x06)
* UPDATE (Type=2): MUST include: Batch Counter (0x01), Merkle Root
(0x03), Signature (0x04) MAY include: Function (0x02),AS
Reachability State List (0x05), Subscribed ASes (0x06)
6.3. Agent Procedures
Initialization:
* Set Batch Counter to 0.
* Choose Function (default example: 1234).
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* Collect current AS Reachability State from logs.
* Collect Subscribed ASes from routing state.
* Configure outbound marking (Section 8.2).
* Send INIT with required attributes.
Subscription change:
* Compute Add/Remove deltas.
* Batch Counter SHOULD NOT change for subscription-only updates.
* Send UPDATE carrying Subscribed ASes.
AS Reachability/policy/prefix events:
* Upon detecting a failure or restoration, Agent MUST increment the
Batch Counter by 1 and MUST refresh outbound marking.
* Send UPDATE carrying affected AS Reachability State List entries.
7. Repository-to-Agent Protocol
7.1. Message Types
Repository messages use the Type field as follows:
* Type = 0 KEEPALIVE
* Type = 1 UPDATE
A Repository UPDATE broadcasts the BGP-FP state of a given Source ASN
to ASes that have subscribed to that Source ASN.
7.2. Mandatory/Optional Attributes
For Repository messages:
KEEPALIVE (Type=0): no attributes.
UPDATE (Type=1): MUST include: Batch Counter (0x01), Function (0x02),
Merkle Root (0x03), Signature (0x04), Merkle Proof (0x07) MAY
include: AS Reachability State List (0x05), Subscribed ASes (0x06)
The Repository MUST forward the Source ASN’s Signature without
modification.
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7.3. Repository Procedures
Validation: Repository SHOULD validate Agent messages by verifying
the signature over the Merkle Root and by recomputing the Merkle Root
from the carried dataset.
Storage and maintenance: Maintain per-Source-ASN state:
R_BatchCounter, R_Function, R_MerkleRoot, R_Signature,
R_AS_Reachability State, and subscription mappings.
On-demand forwarding: Forward Source-ASN updates only to Local ASes
that have subscribed to that Source ASN. Repository UPDATE messages
MUST include a Merkle Proof sufficient for the receiver to validate
inclusion of the forwarded elements.
8. Router Policy Behavior
8.1. Inbound Filtering Rule
Upon receiving a Repository UPDATE, an Agent MUST:
1. Obtain the Source ASN public key via the configured PKI mechanism
(in Section 12), verify Signature over Merkle Root, and verify
the Merkle Proof.
2. For each failure entry affecting (Source ASN, Peer ASN, scope),
install an import policy rule on routers such that a route r is
rejected if ALL of the following hold:
* r’s AS_PATH contains the adjacent pair "... SourceASN PeerASN ..."
(i.e., r traverses the AS pair whose reachability is lost), OR the
failure scope indicates a prefix withdrawal that matches r.
* r contains a BGP Large Community whose Global Administrator is
SourceASN and whose Local Data Part 1 matches Function.
* Let r_bc be Local Data Part 2 of that community. The route is
considered stale if r_bc < BatchCounter carried in the Repository
UPDATE for that Source ASN.
Filtering MUST be applied to Adj-RIB-In (or equivalently as close as
possible to route import) so that the BGP decision process does not
select stale routes.
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8.2. Outbound Marking Rule
Routers in a BGP-FP-enabled AS MUST attach the Large Community
(SourceASN, Function, BatchCounter) to all outbound eBGP
announcements. The Large Communities attribute is an optional
transitive attribute [RFC8092] ;implementations MUST NOT strip
communities unrelated to the Local AS’s own marking.
When BatchCounter changes, the Agent MUST refresh the export policy
so subsequent updates carry the new freshness value.
9. AS-Internal Propagation of Failure Information
Within an AS, there may be multiple BGP routers, including multiple
border routers participating in eBGP. The Agent is responsible for
propagating AS reachability changes and related filtering policies to
all relevant BGP routers inside the AS.
The Agent connects to the AS's border BGP routers using existing
management and configuration channels, such as:
* BGP Monitoring Protocol (BMP) [RFC7854] to receive BGP session
state updates and routing information.
* Network Configuration Protocol (NETCONF) [RFC6241] or RESTCONF
with YANG [RFC7950] models to configure import/export policies.
When the Agent detects a change in AS reachability, it:
1. Updates the Batch Counter and refreshes outbound marking on all
eBGP sessions (Section 8.2).
2. Computes new import filtering rules based on the received
Repository updates (Section 8.1).
3. Installs these rules on all border routers using the configured
management interface.
Internal routers that are not directly connected to the Agent learn
about stale routes via normal BGP mechanisms:
* If a route is rejected at a border router's Adj-RIB-In, the border
router will not advertise it via iBGP to internal routers. In
topologies where route reflectors or Confederations are used,
internal routers will simply not see the stale route or will see
its withdrawal.
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* If the filtering is applied at the point of import, internal
routers receive fewer or no stale routes, reducing churn in the
AS-internal control plane.
The Agent itself does not directly propagate BGP withdrawals or
updates; it only influences the policies applied by the border
routers. This design minimizes changes to existing BGP
implementations and operational practices.
10. Deployment Considerations
The introduction of a logically centralized Repository raises
questions about its deployment, operation, and governance. This
section provides guidance on how BGP-FP could be deployed in the
global Internet.
10.1. Repository Organization
It is RECOMMENDED that a new organization be established to operate
the Repository, with participation from:
* Tier-1 ASes, which have broad visibility into inter-domain routing
, play a crucial role in global route convergence..
* Regional Internet Registries (RIRs), which already operate
critical infrastructure such as RPKI repositories and have
established trust relationships with network operators.
This organization would be responsible for:
* Operating the distributed Repository infrastructure.
* Defining policies for access control, data retention, and privacy.
* Coordinating with existing RPKI and routing security efforts.
10.2. Distributed Deployment
The Repository SHOULD be deployed in a distributed manner across
multiple locations and administrative domains. This distribution
serves several purposes:
* Reducing latency for Agents in different regions.
* Improving resilience against failures and attacks.
* Avoiding a single point of failure or control.
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A possible architecture is similar to that of RPKI repositories
[RFC6480] or distributed logs in Certificate Transparency [RFC9162],
but tailored for AS reachability state.
10.3. Consensus and Trust
To ensure consistency and integrity across distributed Repository
nodes, it is RECOMMENDED to use a Byzantine fault-tolerant (BFT)
consensus protocol, such as variants of Practical Byzantine Fault
Tolerance (PBFT) or similar algorithms. This allows the Repository
to tolerate malicious or faulty nodes while maintaining a consistent
view of the AS reachability state.
A rotating leadership model can be used to:
* Distribute the load of ordering and committing updates.
* Reduce the risk of any single party gaining long-term control over
the consensus process. The precise choice of consensus protocol
and governance structure is left to the organization operating the
Repository and may be specified in separate deployment documents.
10.4. Integration with RPKI Infrastructure
The architecture of BGP-FP shares significant similarities with the
Resource Public Key Infrastructure (RPKI) [RFC6480]. RPKI employs
origin validation to filter routes with invalid source assertions,
whereas BGP-FP disseminates AS reachability failure states to filter
stale routes. Both mechanisms rely on cryptographic validation to
secure routing information. Consequently, it is RECOMMENDED that
BGP-FP deployment leverage the existing RPKI infrastructure to
minimize deployment overhead and capitalize on established
operational trust models. This approach requires specific extensions
to existing RPKI components:
* *Repository Enhancements*: RPKI Repository systems SHOULD be
extended to support BGP-FP data objects. This includes
implementing capabilities for the active push of AS reachability
updates to subscribed local Relying Party (RP) software.
Furthermore, repositories MUST support Merkle verification
mechanisms and the generation of Merkle proofs to ensure the
integrity and authenticity of the propagated state.
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* *RP Software Extensions*: Local RPKI Relying Party software SHOULD
be extended to assume the functionality of the BGP-FP Agent. This
involves monitoring local BGP routers to detect the reachability
status between the Local AS and its neighbors. The RP software
MUST be capable of uploading this state information to the
repository and performing local Merkle root calculation and
verification.
* *Protocol Extensions*: The RPKI-to-Router (RTR) protocol [RFC8210]
MUST be extended to convey AS reachability failure lists to
routers. This allows routers to filter stale routes based on BGP-
FP data, similar to how they currently filter routes with invalid
RPKI Route Origin Authorizations (ROAs).
10.5. Incremental Deployment
BGP-FP is designed to allow incremental deployment:
* An AS can deploy BGP-FP unilaterally to filter stale routes from
other participating ASes, without requiring global adoption.
* Early deployment can focus on monitoring and verification of AS
reachability state, with optional enforcement of route filtering.
* As more ASes adopt BGP-FP, the benefits of faster convergence and
reduced route-flap propagation increase.
11. Example of Operation
This section illustrates the operation of BGP-FP using a simplified
topology with six ASes. The example demonstrates how loss of AS
reachability between AS1 and AS2 leads to multiple rounds of path
exploration in the worst case, and how BGP-FP could accelerate
convergence by preventing the propagation of stale routes.
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+---------+ +---------+
| | | |
+->| AS5 +------->| AS6 |
| | +-+ +---+ |
| +---------+ | | +-------+-+
| | | |
| | | |
| v v v
+---------+ +-----+---+ +---------+ +---------+
| Agent | | | | Agent | | |
| AS1 +------->| AS2 +----->| AS3 |<---+ AS4 |
|prefix p | | | | | | |
+---------+ +---------+ +---------+ +---------+
route：<2,1>
customer --> provider <5,2,1>
<6,5,2,1>
<4,6,5,2,1>
Figure 2: An Example topology with 6 ASes
11.1. Topology and Customer-Provider Relationships
Consider the following ASes: AS1, AS2, AS3, AS4, AS5,AS6.
The customer-provider relationships are:
* AS1 -> AS2 (AS1 is a customer of AS2)
* AS2 -> AS3 , AS2 -> AS5
* AS4->AS3
* AS5->AS6, AS5->AS3
* AS6->AS4, AS6->AS3
These relationships determine the allowed directions of route
advertisement. For simplicity, this example assumes that AS1
announces a single prefix P to its providers. Under normal
conditions, AS3 would learn the following paths to prefix P, ordered
by AS_PATH length:
* Path 1: <2,1>
* Path 2: <5,2,1>
* Path 3: <6,5,2,1>
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* Path 4: <4,6,5,2,1>
11.2. Loss of AS Reachability Between AS1 and AS2
Suppose the overall AS reachability between AS1 and AS2 is lost. In
a plain BGP deployment without BGP-FP, AS2 will withdraw its route to
prefix P from AS3 and AS5. However, routes learned via other ASes
(AS5, AS6, AS4) may still be considered valid until their own
withdrawals propagate.
In the worst case, AS3 would perform path exploration as follows:
1. *Path 1 Withdrawal*: AS2 withdraws the path <2,1> from AS3. AS3
removes this path.
2. *Path 2 Exploration*: AS3 may then select the next best path
<5,2,1>. It sends a withdrawal for this path to AS5. AS5, upon
processing the withdrawal, removes the route and propagates it to
AS6 and AS3.
3. *Path 3 Exploration*: AS3 may then select the next best path
<6,5,2,1>. It sends a withdrawal for this path to AS6. AS6
processes and propagates the withdrawal to AS4 and AS3.
4. *Path 4 Exploration*: Finally, AS3 may select the last known path
<4,6,5,2,1>. It sends a withdrawal to AS4. AS4 processes it.
After multiple rounds of propagation and MRAI timers, AS3 converges
to having no valid route to prefix P. The root cause is that the
critical information, “AS1 is no longer reachable from AS2”, did not
propagate in time to AS3. AS3 continued to accept routes whose
AS_PATH traversed the failed AS pair (AS1, AS2), assuming they were
still valid.
11.3. BGP-FP Operation
With BGP-FP deployed:
* *Failure Detection & Reporting*: The Agent in AS1 detects the loss
of reachability to AS2. It increments its Batch Counter and
reports an AS Reachability State entry “AS2:*:Failure” to the
Repository.
* *State Dissemination*: The Repository securely forwards this
authenticated state to all Agents subscribed to AS1, including the
Agent in AS3.
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* *Proactive Filtering*: Upon receiving and validating the update,
the Agent in AS3 installs an import policy rule on its border
routers. This rule rejects *any* route whose:
1. AS_PATH contains the adjacent pair “… AS1 AS2 …”, AND
2. Carries a freshness community from AS1 with a Batch Counter
value older than the new one reported in the Repository
update.
Consequently, when AS3 receives the updates or withdrawals for paths
like <5,2,1> or <6,5,2,1>, it can immediately recognize them as stale
because they traverse the failed link between AS1 and AS2. The
routes are filtered at the edge, preventing them from being
considered in the BGP decision process.
This mechanism breaks the chain of path exploration. AS3 converges
to “no route” state as soon as the withdrawal for the direct path
<2,1> is processed, without exploring alternative stale paths. This
example highlights how BGP-FP’s authenticated AS reachability
propagation can drastically reduce control-plane churn and
convergence time.
12. Privacy Considerations
Subscribed ASes may reveal portions of an AS’s observed AS_PATHs and
thus aspects of routing visibility. Deployments SHOULD minimize
unnecessary subscription disclosure (e.g., aggregate subscriptions,
policy-based suppression) and secure transport and storage.
13. Operational Considerations
* Repository discovery, redundancy, and anycast/distribution are out
of scope, but are expected to be critical for availability.
* Operators should carefully stage deployment, starting with
monitoring-only mode before enforcing route rejection.
* Interaction with existing route flap damping [RFC2439] should be
evaluated; BGP-FP is intended to reduce the need for aggressive
damping by removing stale routes earlier.
14. IANA Considerations
Following the guidance of [RFC8126], this document requests IANA
actions to support interoperable deployment:
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14.1. TCP Service Name and Port
IANA is requested to allocate a TCP port for the "bgpfp" service (BGP
Failure Propagation). The port number is TBD.
14.2. "BGP-FP Message Types" Registry
Create a new registry for the 8-bit Type field in the BGP-FP common
header.
Initial allocations:
* 0 KEEPALIVE
* 1 INIT (Agent-to-Repository only)
* 2 UPDATE (Agent-to-Repository only)
* 3 UPDATE (Repository-to-Agent)
NOTE: If IANA prefers separate registries for Agent vs Repository
message spaces, this can be revised.
Registration policy: IETF Review.
14.3. "BGP-FP Attribute Types" Registry
Create a new registry for the 8-bit Attr Type field.
Initial allocations:
* 0x01 Batch Counter
* 0x02 Function
* 0x03 Merkle Root
* 0x04 Signature
* 0x05 AS Reachability State List
* 0x06 Subscribed ASes
* 0x07 Merkle Proof
Registration policy: IETF Review. Range 0x80-0xFF is RESERVED for
Private Use.
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15. Security Considerations
BGP-FP can cause large-scale route rejection if updates are forged or
mishandled. The protocol therefore requires authenticity and
integrity of Repository updates and of Source-AS-originated state.
Key requirements:
* Agents MUST verify signatures on Repository UPDATE messages.
* The system MUST provide a trustworthy mapping from ASN to public
key. RPKI [RFC6480] is one candidate infrastructure for
distributing authenticated resource-linked keys/certificates; the
detailed certificate profile and distribution procedure are out of
scope.
* Merkle proofs help receivers detect tampering with forwarded
subsets of state.
Additional threats include replay of old updates, Repository
compromise, denial of service against Agents/Repository, and privacy
leakage via subscription information. Implementations SHOULD provide
replay protection (e.g., track per-Source-ASN BatchCounter
monotonicity) and rate limiting.
16. References
16.1. Normative References
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/rfc/rfc4271>.
[RFC8092] Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas,
I., and N. Hilliard, "BGP Large Communities Attribute",
RFC 8092, DOI 10.17487/RFC8092, February 2017,
<https://www.rfc-editor.org/rfc/rfc8092>.
[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/rfc/rfc2119>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/rfc/rfc5234>.
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[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/rfc/rfc8174>.
[RFC793] Postel, J., "Transmission Control Protocol", RFC 793,
DOI 10.17487/RFC0793, September 1981,
<https://www.rfc-editor.org/rfc/rfc793>.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793,
DOI 10.17487/RFC6793, December 2012,
<https://www.rfc-editor.org/rfc/rfc6793>.
[RFC9162] Laurie, B., Messeri, E., and R. Stradling, "Certificate
Transparency Version 2.0", RFC 9162, DOI 10.17487/RFC9162,
December 2021, <https://www.rfc-editor.org/rfc/rfc9162>.
[RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
February 2012, <https://www.rfc-editor.org/rfc/rfc6480>.
[RFC8210] Bush, R. and R. Austein, "The Resource Public Key
Infrastructure (RPKI) to Router Protocol, Version 1",
RFC 8210, DOI 10.17487/RFC8210, September 2017,
<https://www.rfc-editor.org/rfc/rfc8210>.
16.2. Informative References
[RFC2439] Villamizar, C., Chandra, R., and R. Govindan, "BGP Route
Flap Damping", RFC 2439, DOI 10.17487/RFC2439, November
1998, <https://www.rfc-editor.org/rfc/rfc2439>.
[RFC8195] Snijders, J., Heasley, J., and M. Schmidt, "Use of BGP
Large Communities", RFC 8195, DOI 10.17487/RFC8195, June
2017, <https://www.rfc-editor.org/rfc/rfc8195>.
[RFC4098] Berkowitz, H., Davies, E., Ed., Hares, S., Krishnaswamy,
P., and M. Lepp, "Terminology for Benchmarking BGP Device
Convergence in the Control Plane", RFC 4098,
DOI 10.17487/RFC4098, June 2005,
<https://www.rfc-editor.org/rfc/rfc4098>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
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[RFC7854] Scudder, J., Ed., Fernando, R., and S. Stuart, "BGP
Monitoring Protocol (BMP)", RFC 7854,
DOI 10.17487/RFC7854, June 2016,
<https://www.rfc-editor.org/rfc/rfc7854>.
[RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
and A. Bierman, Ed., "Network Configuration Protocol
(NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
<https://www.rfc-editor.org/rfc/rfc6241>.
[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language",
RFC 7950, DOI 10.17487/RFC7950, August 2016,
<https://www.rfc-editor.org/rfc/rfc7950>.
Authors' Addresses
Yuhang Li
Tsinghua University
Email: yh-li24@mails.tsinghua.edu.cn
Yahui Li
Tsinghua University
Email: liyahui@tsinghua.edu.cn
Xia Yin
Tsinghua University
Email: yxia@tsinghua.edu.cn
Han Zhang
Tsinghua University
Email: zhhan@tsinghua.edu.cn
Xingang Shi
Tsinghua University
Email: shixg@cernet.edu.cn
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