Intra-domain Source Address Validation (SAVNET) Architecture
draft-ietf-savnet-intra-domain-architecture-00
| Document | Type | Active Internet-Draft (savnet WG) | |
|---|---|---|---|
| Authors | Dan Li , Jianping Wu , Lancheng Qin , Nan Geng , Li Chen | ||
| Last updated | 2024-04-12 | ||
| Replaces | draft-li-savnet-intra-domain-architecture | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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| Additional resources | Mailing list discussion | ||
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draft-ietf-savnet-intra-domain-architecture-00
SAVNET D. Li
Internet-Draft J. Wu
Intended status: Informational L. Qin
Expires: 14 October 2024 Tsinghua University
N. Geng
Huawei
L. Chen
Zhongguancun Laboratory
12 April 2024
Intra-domain Source Address Validation (SAVNET) Architecture
draft-ietf-savnet-intra-domain-architecture-00
Abstract
This document proposes the intra-domain SAVNET architecture, which
achieves accurate source address validation (SAV) in an intra-domain
network by an automatic way. Compared with uRPF-like SAV mechanisms
that only depend on routers' local routing information, SAVNET
routers generate SAV rules by using both local routing information
and SAV-specific information exchanged among routers, resulting in
more accurate SAV validation in asymmetric routing scenarios.
Compared with ACL rules that require manual efforts to accommodate to
network dynamics, SAVNET routers learn the SAV rules automatically in
a distributed way.
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
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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 14 October 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Intra-domain SAVNET Architecture . . . . . . . . . . . . . . 5
3.1. Overview . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Roles of SAVNET Routers . . . . . . . . . . . . . . . . . 7
3.2.1. Source Entity . . . . . . . . . . . . . . . . . . . . 7
3.2.2. Validation Entity . . . . . . . . . . . . . . . . . . 7
3.2.3. SAV-specific Information Communication Mechanism . . 8
3.3. SAV-related Information . . . . . . . . . . . . . . . . . 9
3.3.1. SAV-specific Information . . . . . . . . . . . . . . 9
3.3.2. Routing Information . . . . . . . . . . . . . . . . . 9
3.4. SAV Rule Generation . . . . . . . . . . . . . . . . . . . 9
3.5. Data-plane Considerations . . . . . . . . . . . . . . . . 11
4. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.1. Use Case 1: SAV at Host-facing or Customer-facing
Routers . . . . . . . . . . . . . . . . . . . . . . . . . 12
4.2. Use Case 2: SAV at AS Border Routers . . . . . . . . . . 13
5. Meeting the Design Requirements of Intra-domain SAVNET . . . 14
5.1. Accurate Validation . . . . . . . . . . . . . . . . . . . 14
5.2. Automatic Update . . . . . . . . . . . . . . . . . . . . 15
5.3. Incremental/Partial Deployment . . . . . . . . . . . . . 15
5.4. Convergence . . . . . . . . . . . . . . . . . . . . . . . 16
5.5. Security . . . . . . . . . . . . . . . . . . . . . . . . 16
6. Manageability Considerations . . . . . . . . . . . . . . . . 17
7. Privacy Considerations . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 18
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 18
11.1. Normative References . . . . . . . . . . . . . . . . . . 18
11.2. Informative References . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
Source address validation (SAV) is important for mitigating source
address spoofing and thus contributes to the Internet security. In
the Source Address Validation Architecture (SAVA) [RFC5210], SAV is
divided into three checking levels, i.e., access-network SAV, intra-
domain SAV, and inter-domain SAV. When an access network does not
deploy SAV (such as SAVI [RFC7039][RFC7513], Cable Source Verify
[cable-verify], and IP Source Guard [IPSG]), intra-domain SAV helps
block spoofed packets from an access network as close to the source
as possible [I-D.ietf-savnet-intra-domain-problem-statement].
The main purpose of the intra-domain SAV mechanism for an AS A, is to
protect the outgoing packets of a subnet of AS A from forging their
source addresses as other subnets' addresses or other ASes'
addresses, as well as protect the incoming packets to AS A from
forging their source addresses as AS A's addresses. The main task of
the intra-domain SAV mechanism is to generate the correct mapping
relationship between a source address (prefix) and the valid incoming
interface(s), called SAV rules. The core challenge of the intra-
domain SAV mechanism is how to efficiently and accurately learn the
mapping relationship. Although many existing intra-domain SAV
mechanisms (such as ACL-based filtering [RFC2827], strict uRPF
[RFC3704], and loose uRPF [RFC3704]) have been proposed, they suffer
from either inaccurate mapping in asymmetric routing scenraios, or
high operational overhead in dynamic networks. The key cause is that
exsiting mechanisms generate the SAV rules by a router's local
routing information or by manual inputs. In
[I-D.ietf-savnet-intra-domain-problem-statement], five requirements
for a new intra-domain SAVNET architecture are proposed.
This document introduces the intra-domain SAVNET architecture to meet
the five requirements. The key idea of intra-domain SAVNET is to
generate SAV rules in routers based on SAV-specific information
exchanged among routers, instead of depending on local routing
information like in existing mechanisms. It achieves accurate SAV
validation, because SAV-specific information is specialized for SAV
and thus helps generate more accurate SAV rules than solely using
local routing information. It achieves automatic SAV rule update,
because SAV-specific information exchange is triggered when there is
topology change or prefix change. In the incremental/partial
deployment scenario where only part of intra-domain routers support
the intra-domain SAVNET, it provides incremental benefits by using
SAV-specific information provided by routers that support the intra-
domain SAVNET, and/or local routing information to generate SAV
rules.
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The reader is encouraged to be familiar with
[I-D.ietf-savnet-intra-domain-problem-statement] and
[huang-savnet-sav-table].
1.1. 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.
2. Terminology
Local Routing Information: The information in a router's local RIB or
FIB that can be used to infer SAV rules.
SAV-specific Information: The information specialized for SAV rule
generation, which is exchanged among routers.
SAV-related Information: The information used by a router to make SAV
decisions. For intra-domain SAV, SAV-related information includes
both local routing information and SAV-specific information.
SAV-specific Information Communication Mechanism: The mechanism for
exchanging SAV-specific information between routers. It can be
either a new protocol or an extension to an existing protocol.
SAV Information Base: A table or data structure in a router which
stores SAV-specific information and local routing information.
SAV Rule: The rule in a router that describes the mapping
relationship between a source address (prefix) and the valid incoming
interface(s). It is used by a router to make SAV decisions and is
inferred from the SAV Information Base.
SAVNET Router: An intra-domain router which runs intra-domain SAVNET.
SAVNET Agent: The agent in a SAVNET router that is responsible for
communicating SAV-specific information, processing SAV-related
information, and generating SAV rules.
Host-facing Router: An intra-domain router of an AS which is
connected to a host network (i.e., a layer-2 network).
Customer-facing Router: An intra-domain router of an AS which is
connected to an intra-domain customer network running the routing
protocol (i.e., a layer-3 network).
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AS Border Router: An intra-domain router of an AS which is connected
to other ASes.
Improper Block: The validation results that the packets with
legitimate source addresses are blocked improperly due to inaccurate
SAV rules.
Improper Permit: The validation results that the packets with spoofed
source addresses are permitted improperly due to inaccurate SAV
rules.
3. Intra-domain SAVNET Architecture
3.1. Overview
Figure 1 illustrates intra-domain SAVNET architecture in an intra-
domain network. In the intra-domain network, host-facing routers,
customer-facing routers, and AS border routers are required to
perform SAV filtering on specific interfaces (i.e., interfaces '#' in
Figure 1):
* Host-facing routers (e.g., Router C) generate SAV rules on
interfaces facing a layer-2 host network and block data packets
with source addresses not belonging to the host network receiving
from that interface.
* Customer-facing routers (e.g., Routers A and B) generate SAV rules
on interfaces facing a layer-3 customer network and block data
packets with source addresses not belonging to the customer
network receiving from that interface.
* AS border routers (e.g., Routers D or E) generate SAV rules on
interfaces facing another AS and block data packets with source
addresses belonging to the local AS receiving from that interface.
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+----------------------------------+
| Other ASes |
+----------------------------------+
| |
+------------------|----------------------------|--------------+
| Intra-domain | SAV-specific | |
| | message from | |
| | Router A | |
| +----+#+---+ --------------> +----+#+---+ |
| | Router D | | Router E | |
| +-----/\---+ <-------------- +-----/\---+ |
| SAV-specific | SAV-specific | SAV-specific |
| message from | message from | message from |
| Router A | Router C | Router C |
| +----------------------------------------+ |
| | Other intra-domain routers | |
| +-/\-------------------------------/\----+ |
| SAV-specific / \ SAV-specific | SAV-specific |
| message from/ \ message from | message from |
| Router A / \Router A | Router C |
| +----------+ +----\/----+ +----------+ |
| | Router A | | Router B | | Router C | |
| +---+#+----+ +------+#+-+ +----+#+---+ |
| \ / | |
+------------\------------/---------------------|--------------+
\ / |
+--------------+ +--------------+
| Customer | | Host |
| Network | | Network |
+--------------+ +--------------+
Figure 1: Overview of intra-domain SAVNET architecture
To generate more accurate SAV rules, intra-domain SAVNET requires
routers to automatically exchange SAV-specific information. For
example, a host-facing (or customer-facing) router can contain its
locally-known prefixes of the host network (or customer network) in
its SAV-specific information. The router can choose to only provide
this information to specific routers or provide this information to
all routers in the intra-domain network. The arrows in Figure 1
indicate the direction of SAV-specific information flows originated
from Router A and Router C. SAV-specific information flows
originated from other routers are omitted for brevity.
After receiving SAV-specific information provided by other routers,
routers can generate more accurate SAV rules by using SAV-specific
information provided by other routers, its own SAV-specific
information, and/or routing information in the local FIB/RIB. For
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example, in Figure 1, Router B can identify all prefixes in the
customer network by using its own SAV-specific information and SAV
specific information provided by Router A, even if there is an
asymmetric routing between Router B and the customer network.
Routers F and G can identify all prefixes in the local AS by using
SAV-specific inforamtion provided by Routers A, B, and C.
3.2. Roles of SAVNET Routers
A SAVNET router can be a host-facing router, a customer-facing
router, an AS border router, or other routers. Every SAVNET router
has a SAVNET Agent that is responsible for actions related to SAV.
As shown in Figure 2, a SAVNET router can act as one or two roles in
the intra-domain SAVNET architecture, namely, source entity to
provide its SAV-specific information to other SAVNET routers, or/and
validation entity to receive SAV-specific information from other
SAVNET routers.
3.2.1. Source Entity
When a SAVNET router acts as source entity, the information provider
of its SAVNET Agent provides its SAV-specific information to other
SAVNET routers that act as validation entity. For example, a host-
facing router acting as source entity can obtain its SAV-specific
information related to the host network to which it is connected and
selectively provide this information to other SAVNET routers.
3.2.2. Validation Entity
When a SAVNET router acts as validation entity, the information
receiver of its SAVNET Agent receives SAV-specific information from
other SAVNET routers that act as source entity. Then, its SAVNET
Agent processes SAV-specific information provided by other SAVNET
routers, its own SAV-specific information, and/or its local routing
information to generate SAV rules on corresponding interfaces. As
mentioned above, host-facing routers perform SAV filtering on
interfaces facing the host network, customer-facing routers perform
SAV filtering on interfaces facing the customer network, and AS
border routers perform SAV filtering on interfaces facing another AS.
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+---------------------+ +---------------------+
| Source Entity | | Validation Entity |
| (Router A) | | (Router B) |
| | | |
| +-----------------+ | | +-----------------+ |
| | SAVNET Agent | | SAV-specific | | SAVNET Agent | |
| | +-------------+ | | Information | | +-------------+ | |
| | | Information +----------------------> Information | | |
| | | Provider | | | | | | Receiver | | |
| | +-------------+ | | | | +-------------+ | |
| +-----------------+ | | +-----------------+ |
| | | |
+---------------------+ +---------------------+
Figure 2: Roles of SAVNET routers
3.2.3. SAV-specific Information Communication Mechanism
New intra-domain SAV solutions should design a SAV-specific
communication mechanism to propagate SAV-specific information from
source entity to validation entity. It can be a new protocol or an
extension to an existing protocol. This document does not present
the details of the protocol design or protocol extensions, but lists
necessary features of SAV-specific communication mechanism in the
following.
The SAV-specific Information communication mechanism SHOULD define
the data structure or format of SAV-specific information, and the
operations of communication (such as communication establishment and
communication termination). In addition, the mechanism SHOULD
require source entity to inform validation entity of the updates of
SAV-specific information in a timely manner, so that validation
entity can update SAV rules based on the latest information.
In order to ensure the convergence and security of the communication,
the session of the SAV-specific communication mechanism SHOULD meet
the following requirements:
* The session can be a long-time session or a temporary one, but it
SHOULD provide sufficient assurance of transmission reliability
and timeliness, so that validation entity can update its SAV rules
in time.
* Authentication can be conducted before session establishment.
Authentication is optional but the ability of authentication
SHOULD be available.
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3.3. SAV-related Information
For intra-domain SAV, both SAV-specific information and local routing
information can be used for SAV decisions.
3.3.1. SAV-specific Information
SAV-specific information is specialized for SAV and thus helps
generate more accurate SAV rules. A SAVNET router can obtain its own
SAV-specific information based on local routing information, local
interface configurations, and/or other local configuration
information. In addition, SAVNET routers acting as validation entity
can obtain SAV-specific information of other SAVNET routers that act
as source entity. By using SAV-specific information provided by
other SAVNET routers, the SAVNET router acting as validation entity
can generate more accurate SAV rules than solely using its local
routing information.
For example, customer-facing routers connected to the same multi-
homed customer network can exchange locally-known source prefixes of
the customer network through SAV-specific information communication.
By processing both SAV-specific information of itself and SAV-
specific information of the other customer-facing routers, each of
them can identify all prefixes in the customer network and thus avoid
improper block in case there is an asymmetric routing. Section 4.1
elaborates on this example.
3.3.2. Routing Information
Routing information is used for computing packet forwarding rules,
which is stored in the router's RIB/FIB. Although it is not
specialized for SAV, it is widely used to infer SAV rules in existing
uRPF-based SAV mechanisms, such as strict uRPF and loose uRPF
[RFC3704]. A SAVNET router acting as validation entity can obtain
routing information from its local RIB/FIB to generate SAV rules for
some prefixes, when the corresponding SAV-specific information is
missing.
3.4. SAV Rule Generation
Figure 3 shows the SAV rule generation process of the SAVNET router
acting as validation entity. The SAV Information Manager of SAVNET
Agent consolidates SAV-specific information provided by other
routers, SAV-specific information of the router itself, and local
routing information into the SAV Information Base. Then, it sends
the consolidated information to the SAV Rule Generator. The SAV Rule
Generator should preferentially use SAV-specific information to
generate SAV rules for specific source prefixes. Local routing
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information is only recommended when some SAV-specific information is
missing.
SAV Information Manager also provides the support of diagnosis.
Operators can look up the information in SAV Information Base for
monitoring or troubleshooting purpose.
+--------------------------------------------------------+
| SAVNET Agent |
| |
| SAV-specific SAV-specific Routing |
| information information information |
| provided by of the router in local |
| other routers itself FIB/RIB |
| + + + |
| | | | |
| +-v------------------v---------------v-+ |
| | SAV Information Manager | |
| | +------------------------+ | |
| | | SAV Information Base | | |
| | +------------------------+ | |
| +--------------------------------------+ |
| | |
| | SAV-related information |
| | |
| +------------------v--------------------+ |
| | SAV Rule Generator | |
| | +------------------------+ | |
| | | SAV Rules | | |
| | +------------------------+ | |
| +---------------------------------------+ |
+--------------------------------------------------------+
Figure 3: Workflow of SAV rule generation
The basic workflow of different kinds of SAVNET routers is summarized
below:
* For a host-facing router (or a customer-facing router), it
processes SAV-related information to identify prefixes in the host
network (or customer network) it connected to, and then generate
SAV rules on the interface facing to the host network (or customer
network). Data packets coming from that interface will be
considered invalid and should be blocked if they use source
addresses not belonging to the host network (or customer network).
In the incremental/partial deployment scenario when some routers
do not deploy SAV-specific information communication mechanism,
the host-facing router (or customer-facing router) may not be able
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to identify all prefixes in the host network (or customer network)
through SAV-specific information. To avoid improper block in this
case, the router is recommended to use less strict SAV rules. For
example, it can choose to only block packets with non-global or
non-routable source addresses by using its local routing
information.
* For an AS border router, it processes SAV-related information to
identify prefixes in the local AS, and then generate SAV rules on
the interface facing to another AS. Data packets coming from that
interface will be considered invalid and should be blocked if they
use source addresses belonging to the local AS. In the
incremental/partial deployment scenario, the AS border router may
only identify partial prefixes in the local AS through SAV-
specific information. In this case, the AS border router can
still block data packets with source addresses in learned
prefixes.
In addition, if the AS border router also implements inter-domain
SAVNET, its intra-domain SAVNET Agent SHOULD send the intra-domain
SAV-specific information to its inter-domain SAVNET Agent, helping
the inter-domain SAVNET Agent generate inter-domain SAV rules or
inter-domain SAV-specific information.
3.5. Data-plane Considerations
This document mainly focuses on SAV rule generation process on
control plane, including exchanging SAV-specific information,
consolidating SAV-related information, and generating SAV rules. As
for data-plane SAV filtering, SAVNET routers check source addresses
of incoming data packets against local SAV rules and drop those that
are identified as using spoofing source addresses. Therefore, the
accuracy of data-plane SAV filtering depends entirely on the accuracy
of generated SAV rules. More data-plane considerations can be found
in [huang-savnet-sav-table].
4. Use Cases
This section uses two use cases to illustrate that intra-domain
SAVNET can achieve more accurate and efficient SAV than existing
intra-domain SAV mechanisms. The two use cases have already been
described in [I-D.ietf-savnet-intra-domain-problem-statement] to show
that existing intra-domain SAV mechanisms have problems of improper
block or high operational overhead.
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4.1. Use Case 1: SAV at Host-facing or Customer-facing Routers
Figure 4 shows an asymmetric routing in a multi-homed host/customer
network scenario. Router 1 and Router 2 adopt intra-domain SAV to
block spoofing data packets with source addresses not belonging to
Network 1 (e.g., a host network or a customer network) receiving from
interface '#'.
Network 1 has prefix 10.0.0.0/15 and is connected to two routers
(i.e., Router 1 and Router 2) in the intra-domain network. Due to
the inbound load balance strategy of Network 1, Router 1 only learns
the route to sub prefix 10.1.0.0/16 from Network 1, while Router 2
only learns the route to the other sub prefix 10.0.0.0/16 from
Network 1. After that, Router 1 or Router 2 learns the route to the
other sub prefix through the intra-domain routing protocol. The FIBs
of Router 1 and Router 2 are shown in the figure. Assume Network 1
may send outbound packets with source addresses in sub prefix
10.0.0.0/16 to Router 1 for outbound load balance. The arrows in
Figure 4 indicate the direction of traffic.
+-------------------------------------------------------------+
| AS |
| +----------+ |
| | Router 3 | |
| FIB on Router 1 +----------+ FIB on Router 2 |
| Dest Next_hop /\ \ Dest Next_hop |
| 10.1.0.0/16 Network 1 / \ 10.0.0.0/16 Network 1 |
| 10.0.0.0/16 Router 3 / \/ 10.1.0.0/16 Router 3 |
| +----------+ +----------+ |
| | Router 1 | | Router 2 | |
| +-----+#+--+ +-+#+------+ |
| /\ / |
| Outbound traffic with \ / Inbound traffic with |
| source IP addresses \ / destination IP addresses |
| of 10.0.0.0/16 \ \/ of 10.0.0.0/16 |
| +---------------+ |
| | Host/Customer | |
| | Network 1 | |
| | (10.0.0.0/15) | |
| +---------------+ |
| |
+-------------------------------------------------------------+
Figure 4: A use case of outbound SAV
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In this case, strict uRPF at Router 1 will improperly block
legitimate packets with source addresses in prefix 10.0.0.0/16 from
Network 1 on interface '#', because it only accepts data packets with
source addresses in prefix 10.1.0.0/16 from Router 1's interface '#'
according to its local routing information.
If intra-domain SAVNET is implemented in the intra-domain network,
Router 2 can inform Router 1 that prefix 10.0.0.0/16 also belongs to
Network 1 by providing its SAV-specific information to Router 1.
Then, by combining both its own SAV-specific information and SAV-
specific information provided by Router 2, Router 1 learns that
Network 1 have both prefix 10.1.0.0/16 and prefix 10.0.0.0/16.
Therefore, Router 1 will accept data packets with source addresses in
prefix 10.1.0.0/16 and prefix 10.0.0.0/16 on interface '#', so
improper block can be avoided.
4.2. Use Case 2: SAV at AS Border Routers
Figure 5 shows a scenario of inbound SAV at AS border routers.
Router 3 and Router 4 adopt intra-domain SAV to block spoofing data
packets with internal source addresses receiving from interface '#'.
The arrows in Figure 5 indicate the direction of spoofing traffic.
Packets with + Packets with +
spoofed P1/P2| spoofed P1/P2|
+-------------|---------------------------|---------+
| AS \/ \/ |
| +--+#+-----+ +---+#+----+ |
| | Router 3 +---------------+ Router 4 | |
| +----------+ +----+-----+ |
| / \ | |
| / \ | |
| / \ | |
| +----------+ +----------+ +----+-----+ |
| | Router 1 | | Router 2 | | Router 5 | |
| +----------+ +----------+ +----+-----+ |
| \ / | |
| \ / | |
| \ / | |
| +---------------+ +-------+-------+ |
| | Host | | Customer | |
| | Network | | Network | |
| | (P1) | | (P2) | |
| +---------------+ +---------------+ |
| |
+---------------------------------------------------+
Figure 5: A use case of inbound SAV
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If Router 3 and Router 4 deploy ACL-based ingress filtering, the
operator needs to manually generate and update ACL rules at Router 3
and Router 4 when internal source prefixes change. The operational
overhead of manually maintaining and updating ACL rules will be
extremely high, especially when there are multiple inbound validation
interfaces '#'.
If intra-domain SAVNET is implemented in the intra-domain network,
Router 1, Router 2, and Router 5 will automatically inform Router 3
and Router 4 of prefixes in the host network and customer network by
providing SAV-specific information. After receiving SAV-specific
information from other routers, Router 3 and Router 4 can identify
all internal source prefixes. The SAV-specific information
communication will be triggered if topology or prefix related to the
host network or customer network changes. For example, if the
customer network has a new source prefix P3, Router 5 will inform
Router 3 and Router 4 of the new source prefix immediately through
SAV-specific information communication mechanism. In this way,
Router 3 and Router 4 can automatically generate and update SAV rules
on interface '#'.
5. Meeting the Design Requirements of Intra-domain SAVNET
Intra-domain SAVNET architecture is proposed to meet the five design
requirements defined in
[I-D.ietf-savnet-intra-domain-problem-statement].
5.1. Accurate Validation
In the asymmetric routing scenario shown in Figure 4, the host-facing
router (or customer-facing router) cannot identify all prefixes in
its host network (or customer network) solely using its local routing
information. As a result, existing intra-domain SAV mechanisms
(e.g., strict uRPF) solely using local routing information to
generate SAV rules will have improper block problems in the case of
asymmetric routing.
Intra-domain SAVNET requires routers to exchange SAV-specific
information among each other. The SAVNET router can use SAV-specific
information provided by other routers as well as its own SAV-specific
information to generate more accurate SAV rules. The use case in
Figure 4 has shown that intra-domain SAVNET can achieve more accurate
SAV filtering compared with strict uRPF in asymmetric routing
scenarios.
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5.2. Automatic Update
In real intra-domain networks, the topology or prefixes of networks
may change dynamically. The SAV mechanism MUST automatically update
SAV rules as the network changes. However, ACL-based SAV mechanism
requires manual efforts to accommodate to network dynamics, resulting
in high operational overhead.
Intra-domain SAVNET allows SAVNET routers to exchange the changes of
SAV-specific information among each other automatically. After
receiving updated SAV-specific information from source entity, SAVNET
routers acting as validation entity can generate and update their SAV
rules accordingly. The use case in Section 4.2 has shown that intra-
domain SAVNET can achieve automatic update.
5.3. Incremental/Partial Deployment
Although an intra-domain network mostly has one administration,
incremental/partial deployment may still exist due to phased
deployment or multi-vendor supplement. In phased deployment
scenarios, SAV-specific information of non-deploying routers is not
available.
As described in Section 3.4, intra-domain SAVNET can adapt to
incremental/partial deployment. To mitigate the impact of phased
deployment, it is RECOMMENDED that routers connected to the same
host/customer network can simultaneously adopt intra-domain SAVNET so
that all prefixes in the host/customer network can be identified.
For example, in Figure 4, Router 1 and Router 2 are recommended to be
upgraded to SAVNET routers together so that the two routers can
identify all prefixes in Network 1 and generate accurate SAV rules on
interfaces '#'.
In addition, SAVNET routers acting as validation entity are
RECOMMENDED to support flexible validation modes and perform SAV
filtering gradually to smooth the transition from partial to full
deployment:
* SAVNET routers acting as validation entity are RECOMMENDED to
support flexible validation modes such as interface-based prefix
allowlist, interface-based prefix blocklist, and prefix-based
interface allowlist (see [huang-savnet-sav-table]). The first two
modes are interface-scale, and the last one is device-scale.
Under incremental/partial deployment, SAVNET routers SHOULD take
on the proper validation mode according to acquired SAV-specific
information. For example, if a customer-facing router can
identify all prefixes in its customer network by processing
acquired SAV-specific information, an interface-based prefix
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allowlist containing these prefixes can be used on that customer-
facing interface. Otherwise, it should use interface-based prefix
blocklist or prefix-based interface allowlist to avoid improper
block.
* Validation entity is RECOMMENDED to performed SAV-invalid
filtering gradually. The router can first take conservative
actions on the validated data packets. That is to say, the router
will not discard packets with invalid results in the beginning of
deployment. It can conduct sampling action for measurement
analysis at first, and then conducts rate-limiting action or
redirecting action for packets with invalid results. These
conservative actions will not result in serious consequences if
some legitimate packets are mistakenly considered invalid, while
still providing protection for the network. Finally, filtering
action is enabled only after confirming that there are no improper
block problems.
5.4. Convergence
When SAV-related information changes, the SAVNET Agent MUST be able
to detect the changes in time and update SAV rules with the latest
information. Otherwise, outdated SAV rules may cause legitimate data
packets to be blocked or spoofing data packets to be accepted.
Intra-domain SAVNET requires routers to update SAV-specific
information and update SAV rules in a timely manner. Since SAV-
specific information is originated from source entity, it requires
that source entity MUST timely send the updated SAV-specific
information to validation entity. Therefore, the propagation speed
of SAV-specific information is a key factor affecting the
convergence. Consider that routing information and SAV-specific
information can be originated and advertised through a similar way,
SAV-specific information SHOULD at least have a similar propagation
speed as routing information.
5.5. Security
Typically, routers in an intra-domain network can trust each other
because they would not compromise intra-domain control-plane
architectures and protocols.
However, in some unlikely cases, some routers may do harm to other
routers within the same domain. Operators SHOULD be aware of
potential threats involved in deploying the architecture. Some
potential threats and solutions are as follows:
* Entity impersonation.
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- Potential solution: Mutual authentication SHOULD be conducted
before session establishment between two entities.
- Gaps: Impersonation may still exist due to credential theft,
implementation flaws, or entity being compromised. Some other
security mechanisms can be taken to make such kind of
impersonation difficult. Besides, the entities SHOULD be
monitored so that misbehaved entities can be detected.
* Message blocking.
- Potential solution: Acknowledgement mechanisms MUST be provided
in the session between a sender and a receiver, so that message
losses can be detected.
- Gaps: Message blocking may be a result of DoS/DDoS attack, man-
in-the-middle (MITM) attack, or congestion induced by traffic
burst. Acknowledgement mechanisms can detect message losses
but cannot avoid message losses. MITM attacks cannot be
effectively detected by acknowledgement mechanisms.
* Message alteration.
- Potential solution: An authentication field can be carried by
each message so as to ensure message integrity.
- Gaps: More overhead of control plane and data plane will be
induced.
* Message replay.
- Potential solution: Authentication value can be computed by
adding a sequence number or timestamp as input.
- Gaps: More overhead of control plane and data plane will be
induced.
To meet the security requirement, the above security threats SHOULD
be considered when designing the new intra-domain SAV mechanism.
6. Manageability Considerations
The architecture provides a general framework for communicating SAV-
specific information between routers and generating SAV rules based
on SAV-specific information and local routing information. Protocol-
independent mechanisms SHOULD be provided for operating and managing
SAV-related configurations. For example, a YANG data model for SAV
configuration and operation is necessary for the ease of management.
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SAV may affect the normal forwarding of data packets. The diagnosis
approach and necessary logging information SHOULD be provided. SAV
Information Base SHOULD store some information that may not be useful
for SAV rule generation but is helpful for management. The SAV-
specific information communication mechanism SHOULD have monitoring
and troubleshooting functions, which are necessary for efficiently
operating the architecture.
7. Privacy Considerations
An intra-domain network is mostly operated by a single organization
or company, and the advertised SAV-specific information is used
within the network. Therefore, the architecture will not import
critical privacy issues in usual cases.
8. IANA Considerations
This document has no IANA requirements.
9. Contributors
Mingqing Huang
Email: huangmq@vip.sina.com
Fang Gao
Email: fredagao520@sina.com
10. Acknowledgements
Many thanks to the valuable comments from: Igor Lubashev, Alvaro
Retana, Aijun Wang, Joel Halpern, Jared Mauch, Kotikalapudi Sriram,
Rüdiger Volk, Jeffrey Haas, Xiangqing Chang, Changwang Lin, Xueyan
Song, etc.
11. References
11.1. Normative References
[I-D.ietf-savnet-intra-domain-problem-statement]
Li, D., Wu, J., Qin, L., Huang, M., and N. Geng, "Source
Address Validation in Intra-domain Networks Gap Analysis,
Problem Statement, and Requirements", Work in Progress,
Internet-Draft, draft-ietf-savnet-intra-domain-problem-
statement-03, 13 February 2024,
<https://datatracker.ietf.org/doc/html/draft-ietf-savnet-
intra-domain-problem-statement-03>.
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[RFC2827] Ferguson, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
May 2000, <https://www.rfc-editor.org/info/rfc2827>.
[RFC3704] Baker, F. and P. Savola, "Ingress Filtering for Multihomed
Networks", BCP 84, RFC 3704, DOI 10.17487/RFC3704, March
2004, <https://www.rfc-editor.org/info/rfc3704>.
[huang-savnet-sav-table]
"General Source Address Validation Capabilities", 2023,
<https://datatracker.ietf.org/doc/draft-huang-savnet-sav-
table/>.
[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>.
[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>.
11.2. Informative References
[RFC5210] Wu, J., Bi, J., Li, X., Ren, G., Xu, K., and M. Williams,
"A Source Address Validation Architecture (SAVA) Testbed
and Deployment Experience", RFC 5210,
DOI 10.17487/RFC5210, June 2008,
<https://www.rfc-editor.org/info/rfc5210>.
[RFC7039] Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed.,
"Source Address Validation Improvement (SAVI) Framework",
RFC 7039, DOI 10.17487/RFC7039, October 2013,
<https://www.rfc-editor.org/info/rfc7039>.
[RFC7513] Bi, J., Wu, J., Yao, G., and F. Baker, "Source Address
Validation Improvement (SAVI) Solution for DHCP",
RFC 7513, DOI 10.17487/RFC7513, May 2015,
<https://www.rfc-editor.org/info/rfc7513>.
[IPSG] "Configuring DHCP Features and IP Source Guard", January
2016, <https://www.cisco.com/c/en/us/td/docs/switches/lan/
catalyst2960/software/release/12-
2_53_se/configuration/guide/2960scg/swdhcp82.html>.
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[cable-verify]
"Cable Source-Verify and IP Address Security", January
2021, <https://www.cisco.com/c/en/us/support/docs/
broadband-cable/cable-security/20691-source-verify.html>.
Authors' Addresses
Dan Li
Tsinghua University
Beijing
China
Email: tolidan@tsinghua.edu.cn
Jianping Wu
Tsinghua University
Beijing
China
Email: jianping@cernet.edu.cn
Lancheng Qin
Tsinghua University
Beijing
China
Email: qlc19@mails.tsinghua.edu.cn
Nan Geng
Huawei
Beijing
China
Email: gengnan@huawei.com
Li Chen
Zhongguancun Laboratory
Beijing
China
Email: lichen@zgclab.edu.cn
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