SAVI J. Bi
Internet-Draft J. Wu
Intended status: Standards Track G. Yao
Expires: November 7, 2013 Tsinghua Univ.
F. Baker
Cisco
May 6, 2013
SAVI Solution for DHCP
draft-ietf-savi-dhcp-16
Abstract
This document specifies the procedure for creating a binding between
a DHCPv4/DHCPv6 assigned IP address and a binding anchor on a SAVI
(Source Address Validation Improvements) device. The bindings set up
by this procedure can be used to filter out packets with forged
source IP address in DHCP scenario. This mechanism is proposed as a
complement to ingress filtering to provide finer-grained source IP
address validation.
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 http://datatracker.ietf.org/drafts/current/.
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 November 7, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
Bi, et al. Expires November 7, 2013 [Page 1]
Internet-Draft SAVI DCHP May 2013
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
This document may contain material from IETF Documents or IETF
Contributions published or made publicly available before November
10, 2008. The person(s) controlling the copyright in some of this
material may not have granted the IETF Trust the right to allow
modifications of such material outside the IETF Standards Process.
Without obtaining an adequate license from the person(s) controlling
the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
Bi, et al. Expires November 7, 2013 [Page 2]
Internet-Draft SAVI DCHP May 2013
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 5
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Deployment Scenario and Configuration . . . . . . . . . . . . 7
4.1. Elements and Scenario . . . . . . . . . . . . . . . . . . 7
4.2. Attribute . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2.1. Trust Attribute . . . . . . . . . . . . . . . . . . . 9
4.2.2. DHCP-Trust Attribute . . . . . . . . . . . . . . . . . 10
4.2.3. DHCP-Snooping Attribute . . . . . . . . . . . . . . . 10
4.2.4. Data-Snooping Attribute . . . . . . . . . . . . . . . 10
4.2.5. Validating Attribute . . . . . . . . . . . . . . . . . 11
4.2.6. Table of Mutual Exclusions . . . . . . . . . . . . . . 11
4.3. Perimeter . . . . . . . . . . . . . . . . . . . . . . . . 12
5. Binding State Table (BST) . . . . . . . . . . . . . . . . . . 13
6. DHCP Snooping Process . . . . . . . . . . . . . . . . . . . . 14
6.1. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 14
6.2. Binding States Description . . . . . . . . . . . . . . . . 15
6.3. Events . . . . . . . . . . . . . . . . . . . . . . . . . . 15
6.3.1. Timer Expiration Event . . . . . . . . . . . . . . . . 15
6.3.2. Control Message Arriving Events . . . . . . . . . . . 15
6.4. State Machine of DHCP Packet Snooping . . . . . . . . . . 17
6.4.1. From NO_BIND to Other States . . . . . . . . . . . . . 17
6.4.1.1. Trigger Event . . . . . . . . . . . . . . . . . . 17
6.4.1.2. Following Actions . . . . . . . . . . . . . . . . 18
6.4.2. From INIT_BIND to Other States . . . . . . . . . . . . 20
6.4.2.1. Trigger Event . . . . . . . . . . . . . . . . . . 20
6.4.2.2. Following Actions . . . . . . . . . . . . . . . . 20
6.4.3. From BOUND to Other States . . . . . . . . . . . . . . 22
6.4.3.1. Trigger Event . . . . . . . . . . . . . . . . . . 22
6.4.3.2. Following Actions . . . . . . . . . . . . . . . . 22
6.5. Table of State Machine . . . . . . . . . . . . . . . . . . 22
7. Data Snooping Process . . . . . . . . . . . . . . . . . . . . 24
7.1. Scenario . . . . . . . . . . . . . . . . . . . . . . . . . 24
7.2. Rationale . . . . . . . . . . . . . . . . . . . . . . . . 25
7.3. Additional Binding States Description . . . . . . . . . . 25
7.4. Events . . . . . . . . . . . . . . . . . . . . . . . . . . 26
7.5. State Machine of Binding Recovery Process . . . . . . . . 26
7.5.1. From NO_BIND to Other States . . . . . . . . . . . . . 27
7.5.1.1. Trigger Event . . . . . . . . . . . . . . . . . . 27
7.5.1.2. Following Actions . . . . . . . . . . . . . . . . 27
7.5.2. From DETECTION to Other States . . . . . . . . . . . . 28
7.5.2.1. Trigger Event . . . . . . . . . . . . . . . . . . 28
7.5.2.2. Following Actions . . . . . . . . . . . . . . . . 28
7.5.3. From RECOVERY to Other States . . . . . . . . . . . . 29
7.5.3.1. Trigger Event . . . . . . . . . . . . . . . . . . 29
7.5.3.2. Following Actions . . . . . . . . . . . . . . . . 29
Bi, et al. Expires November 7, 2013 [Page 3]
Internet-Draft SAVI DCHP May 2013
7.5.4. After BOUND . . . . . . . . . . . . . . . . . . . . . 29
7.5.4.1. Trigger Event . . . . . . . . . . . . . . . . . . 30
7.5.4.2. Following Action . . . . . . . . . . . . . . . . . 30
7.6. Table of State Machine . . . . . . . . . . . . . . . . . . 30
8. Filtering Specification . . . . . . . . . . . . . . . . . . . 31
8.1. Data Packet Filtering . . . . . . . . . . . . . . . . . . 31
8.2. Control Packet Filtering . . . . . . . . . . . . . . . . . 32
9. State Restoration . . . . . . . . . . . . . . . . . . . . . . 32
9.1. Attribute Configuration Restoration . . . . . . . . . . . 33
9.2. Binding State Restoration . . . . . . . . . . . . . . . . 33
10. Constants . . . . . . . . . . . . . . . . . . . . . . . . . . 33
11. MLD Consideration . . . . . . . . . . . . . . . . . . . . . . 34
12. Security Considerations . . . . . . . . . . . . . . . . . . . 34
12.1. Security Problem about Binding Setup Triggered by
EVE_DHCP_REPLY_NULL . . . . . . . . . . . . . . . . . . . 34
12.2. Security Problems about the Data Snooping Process . . . . 35
12.3. Issues about Leaving Clients . . . . . . . . . . . . . . . 35
12.4. Duplicate Bindings of the Same Address . . . . . . . . . . 36
12.5. Compatibility with DNA (Detecting Network Attachment) . . 36
12.6. Bogus DHCP Server Threat . . . . . . . . . . . . . . . . . 37
12.7. Authentication in DHCPv6 Leasequery . . . . . . . . . . . 38
12.8. Binding Number Limitation . . . . . . . . . . . . . . . . 38
12.9. Residual Threats . . . . . . . . . . . . . . . . . . . . . 38
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39
14. Acknowledgment . . . . . . . . . . . . . . . . . . . . . . . . 39
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
15.1. Informative References . . . . . . . . . . . . . . . . . . 40
15.2. Normative References . . . . . . . . . . . . . . . . . . . 40
Appendix A. change log . . . . . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 43
Bi, et al. Expires November 7, 2013 [Page 4]
Internet-Draft SAVI DCHP May 2013
1. Introduction
This document describes a fine-grained source IP address validation
mechanism. This mechanism creates bindings between addresses
assigned to network attachment points by DHCP and suitable binding
anchors (refer to Section 3) of the attachments. Then the bindings
are used to identify and filter out packets originated from these
attachments with forged source IP addresses. In this way, this
mechanism can prevent hosts from spoofing IP addresses assigned to
the other attachment points. Compared with [BCP38], which provides
prefix granularity source IP address validity, this mechanism can
benefit the network with finer-grained validity and traceability of
source IP addresses.
This mechanism primarily performs DHCP snooping to set up bindings
between IP addresses assigned by DHCP and corresponding binding
anchors. This binding process is inspired by the work of [BA2007].
Different from [BA2007], which designs specifications about DHCPv4,
this mechanism covers the DHCPv6 snooping process, the data snooping
process (refer to Section 7), as well as a number of other technical
details. Specially, the data snooping process is a data-triggered
binding setup procedure designed to avoid permanent block of valid
address in case that DHCP snooping is insufficient to set up all the
valid bindings.
This mechanism is designed for the stateful DHCP scenario [rfc2131],
[rfc3315]. In the stateless DHCP scenario [rfc3736], a client
obtains its addresses through some other mechanisms and so the
addresses of the client MUST be bound based on other SAVI solutions,
for example, SAVI FCFS[savi-fcfs]. Besides, this mechanism is
primarily designed for pure DHCP scenarios in which only addresses
assigned through DHCP are allowed. However, it does not block any
link-local address. It is because link-local addresses are used by
DHCPv6 clients before the clients are assigned a DHCPv6 address.
Considering that link-local addresses are generally self-generated,
and the spoofing of link local address may disturb this mechanism, it
is RECOMMENDED to enable a SAVI solution for link-local addresses,
e.g., the SAVI-FCFS [savi-fcfs].
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [rfc2119].
Bi, et al. Expires November 7, 2013 [Page 5]
Internet-Draft SAVI DCHP May 2013
3. Terminology
Binding anchor: A "binding anchor" is defined to be a link layer
property of network attachment in [savi-framework]. A list of proper
binding anchors can be found in Section 3.2 of [savi-framework].
Attribute: A configurable property of each network attachment which
indicates the actions to be performed on packets received from the
network attachment.
DHCP address: An IP address assigned to an interface via DHCP.
SAVI-DHCP: The name of this SAVI function for DHCP address.
SAVI device: A network device on which this SAVI function is enabled.
Non-SAVI device: A network device on which this SAVI function is not
enabled.
DHCP Client-Server message: A message that is sent from a DHCP client
to a DHCP server or DHCP servers. Such a message is of one of the
following types:
o DHCPv4 Discover: DHCPDISCOVER [rfc2131]
o DHCPv4 Request: DHCPREQUEST generated during SELECTING state
[rfc2131]
o DHCPv4 Renew: DHCPREQUEST generated during RENEWING state
[rfc2131]
o DHCPv4 Rebind: DHCPREQUEST generated during REBINDING state
[rfc2131]
o DHCPv4 Reboot: DHCPREQUEST generated during INIT-REBOOT state
[rfc2131]
o DHCPv4 Decline: DHCPDECLINE [rfc2131]
o DHCPv4 Release: DHCPRELEASE [rfc2131]
o DHCPv4 Inform: DHCPINFORM [rfc2131]
o DHCPv6 Request: REQUEST [rfc3315]
o DHCPv6 Solicit: SOLICIT [rfc3315]
Bi, et al. Expires November 7, 2013 [Page 6]
Internet-Draft SAVI DCHP May 2013
o DHCPv6 Confirm: CONFIRM [rfc3315]
o DHCPv6 Decline: DECLINE [rfc3315]
o DHCPv6 Release: RELEASE [rfc3315]
o DHCPv6 Rebind: REBIND [rfc3315]
o DHCPv6 Renew: RENEW [rfc3315]
o DHCPv6 Information-Request: INFORMATION-REQUEST [rfc3315]
DHCP Server-Client message: A message that is sent from a DHCP server
to a DHCP client. Such a message is of one of the following types:
o DHCPv4 ACK: DHCPACK [rfc2131]
o DHCPv4 NAK: DHCPNAK [rfc2131]
o DHCPv4 OFFER: DHCPOFFER [rfc2131]
o DHCPv6 Reply: REPLY [rfc3315]
o DHCPv6 Advertise: ADVERTISE [rfc3315]
o DHCPv6 Reconfigure: RECONFIGURE [rfc3315]
Lease time: The lease time in IPv4 [rfc2131] or the valid lifetime in
IPv6 [rfc3315].
Binding entry: An 'permit' rule that defines a valid association
between an IP address and a binding anchor.
Binding State Table: The data structure that contains all the binding
entries.
4. Deployment Scenario and Configuration
4.1. Elements and Scenario
A list of essential elements in a SAVI-DHCP deployment scenario is
given as follows:
Bi, et al. Expires November 7, 2013 [Page 7]
Internet-Draft SAVI DCHP May 2013
(1) DHCP server
(2) DHCP client
(3) SAVI device
And there may be following optional elements in a SAVI-DHCP
deployment scenario:
(1) DHCP relay
(2) Non-SAVI device
Figure 1 shows a deployment scenario that contains these elements.
Note that a physical device can be multiple elements, e.g, a switch
can be both a SAVI device and a DHCP relay. In such cases, the links
are logic links rather than physical links.
+--------+ +------------+
|DHCP |-----| Non-SAVI |
|Server A| | Device 1 |
+--------+ +-----|------+
......................|............................
. | .
. Protection +---|------+ .
. Perimeter | SAVI | .
. | Device C| .
. +---|------+ .
. | .
. +----------+ +---|------+ +----------+ .
downstream . | SAVI | | Non SAVI| | SAVI | .
link +----.-| Device A|----| Device 3|-------| Device B| .
| . +----|--|--+ +----------+ +-|---|----+ .
| . | +----------+ ............ | | .
| '.............. | . . | | .
| | . | . +--------+ | .
+----|-----+ +--|---+ . +----|-+ . +--|---+ . +---|----+ .
| Non-SAVI | |Client| . |DHCP | . |Client| . |DHCP | .
| Device 2 | |A | . |Relay | . |B | . |Server B| .
+----------+ +------+ . +------+ . +------+ . +--------+ .
............ ...............
Figure 1: SAVI-DHCP Scenario
Bi, et al. Expires November 7, 2013 [Page 8]
Internet-Draft SAVI DCHP May 2013
4.2. Attribute
As illustrated in Figure 1, an attachment to a SAVI device can be
from either a DHCP client, or a DHCP relay/server, or a SAVI device,
or a non-SAVI device. Different actions are performed on traffic
originated from different elements. To distinguish different types
of attachments, an attachment property named 'attribute' is
configured on SAVI devices. This section specifies the attributes
used by this mechanism.
Before configuration, an attachment is with no attribute. An
attachment MAY be configured to have one or more compatible
attributes(refer to Section 4.2.6). The attributes of each
attachment MUST be configured before this SAVI-DHCP function is
enabled on the attachment. The procedure performed by SAVI devices
on traffic from each attachment is determined by the attributes set
on the attachment.
Particularly, if an attachment has no attribute, no actions will be
performed by this SAVI function on traffic from such attachments.
For example, in Figure 1, the attachment from the Non-SAVI Device 1
to the SAVI Device B should be configured with no attribute. It
means 1) SAVI devices will neither set up bindings for upstream hosts
nor check traffic from upstream hosts; 2) SAVI devices will not snoop
DHCP messages from upstream devices unless the DHCP-Trust attribute
(refer to Section 4.2.2) is set on the corresponding attachment. The
reason that DHCP messages from upstream devices are not trusted by
default is discussed in Section 12.6.
4.2.1. Trust Attribute
The "Trust Attribute" indicates the packets from the corresponding
attachment are completely trustable.
SAVI devices will not set up bindings for attachments with Trust
attribute; DHCP messages and data packets from such attachments with
this attribute will not be checked. If the DHCP Server-Client
messages from attachments with this attribute can trigger the state
transitions specified in Section 6 and Section 7, these messages will
be handled by the corresponding processes in Section 6 and Section 7.
This attribute is generally configured on the attachments from other
SAVI devices. For example, in Figure 1, the attachment from the SAVI
Device A to the SAVI Device B and the attachment from the SAVI Device
B to the SAVI Device A should be configured with this attribute.
Besides, it can be configured on attachments from Non-SAVI devices
only if the Non-SAVI devices will not introduce unchecked traffic
from DHCP clients. For example, the attachments from Non-SAVI device
Bi, et al. Expires November 7, 2013 [Page 9]
Internet-Draft SAVI DCHP May 2013
3 to SAVI device A, SAVI device B and SAVI device C can be configured
with this attribute, only if Non-SAVI device 3 does not have
attachment from DHCP clients.
4.2.2. DHCP-Trust Attribute
The "DHCP-Trust Attribute" indicates the DHCP Server-Client messages
from the corresponding attachment is trustable.
SAVI devices will forward DHCP Server-Client messages coming from the
attachments with this attribute. If the DHCP Server-Client messages
can trigger the state transitions, they will be handled by the
binding setup processes specified in Section 6 and Section 7.
This attribute is generally used on the direct attachments from the
trusted DHCP servers/relays. In Figure 1, the attachment from the
DHCP Relay to the SAVI Device B, and the attachment from the DHCP
Server B to the SAVI Device B should be configured with this
attribute. It is NOT RECOMMENDED to configure this attribute on the
indirect attachments from the non-neighboring DHCP servers/relays
unless the attachments do not introduce bogus DHCP Server-Client
messages. For example, in Figure 1, the attachment from the Non-SAVI
Device 1 to the SAVI Device C should not be configured with this
attribute. The related security problem is discussed in
Section 12.6.
4.2.3. DHCP-Snooping Attribute
The "DHCP-Snooping Attribute" indicates bindings will be set up based
on DHCP snooping.
DHCP Client-Server messages from attachments with this attribute will
trigger the setup of bindings. SAVI devices will set up bindings on
attachments with this attribute based on the DHCP snooping procedure
described in Section 6.
DHCP-Snooping attribute is configured on the attachments from DHCP
clients. This attribute can be also used on the attachments from
downstream Non-SAVI devices which are attached by DHCP clients. In
Figure 1, the attachment from the Client A to the SAVI Device A, the
attachment from the Client B to the SAVI Device B, and the attachment
from the Non-SAVI Device 2 to the SAVI Device A can be configured
with this attribute.
4.2.4. Data-Snooping Attribute
The "Data-Snooping Attribute" indicates data packets from the
corresponding attachment may trigger binding setup procedure.
Bi, et al. Expires November 7, 2013 [Page 10]
Internet-Draft SAVI DCHP May 2013
Data packets from attachments with this attribute may trigger the
setup of bindings. SAVI devices will set up bindings on attachments
with this attribute based on the data-triggered process described in
Section 7.
If DHCP-Snooping attribute is configured on an attachment, the
bindings on this attachment are set up based on DHCP message
snooping. However, in some scenarios, a DHCP address may be used by
a DHCP client without DHCP address assignment procedure performed on
its current attachment. For such attachments, the Data-Snooping
process, which is described in Section 7, is necessary. This
attribute is configured on such attachments. The usage of this
attribute is further discussed in Section 7.
4.2.5. Validating Attribute
The "Validating Attribute" indicates packets from the corresponding
attachment will be checked based on binding entries on the
attachment.
Packets coming from attachments with this attribute will be checked
based on binding entries on the attachment as specified in Section 8.
Validating attribute is configured on the attachments from which the
data packets should be checked. For example, the DHCP clients.
4.2.6. Table of Mutual Exclusions
Different types of attributes may indicate mutually exclusive actions
on packet. Mutually exclusive attributes MUST NOT be set on the same
attachment. The compatibility of different attributes is listed in
Figure 2. Note that although Trust and DHCP-Trust are compatible,
there is no need to configure DHCP-Trust on an attachment with Trust
attribute.
Bi, et al. Expires November 7, 2013 [Page 11]
Internet-Draft SAVI DCHP May 2013
+----------+----------+----------+----------+----------+----------+
| | | | DHCP- | Data- | |
| | Trust |DHCP-Trust| Snooping | Snooping |Validating|
+----------+----------+----------+----------+----------+----------+
| | | | mutually | mutually | mutually |
| Trust | - |compatible| exclusive| exclusive| exclusive|
+----------+----------+----------+----------+----------+----------+
| | | | | | |
|DHCP-Trust|compatible| - |compatible|compatible|compatible|
+----------+----------+----------+----------+----------+----------+
|DHCP- |mutually | | | | |
|Snooping |exclusive |compatible| - |compatible|compatible|
+----------+----------+----------+----------+----------+----------+
|Data- |mutually | | | | |
|Snooping |exclusive |compatible|compatible| - |compatible|
+----------+----------+----------+----------+----------+----------+
| |mutually | | | | |
|Validating|exclusive |compatible|compatible|compatible| - |
+----------+----------+----------+----------+----------+----------+
Figure 2: Table of Mutual Exclusions
4.3. Perimeter
SAVI-DHCP can provide perimetrical security as SAVI-FCFS (refer to
Section 2.5 in [savi-fcfs]). Through configuring attribute of each
attachment properly, a perimeter separating untrusted area and
trusted area can be formed:
(1) Configure Validating attribute on the attachments of all the
DHCP clients. Configure DHCP-Snooping attribute on these
attachments.
(2) Configure Validating attribute on the attachments of downstream
Non-SAVI devices which are attached by DHCP clients. Configure
DHCP-Snooping attribute on these attachments.
(3) Configure Trust attribute on the attachments of other SAVI
devices.
(4) If a Non-SAVI device, or a number of connected Non-SAVI devices,
have only attachments from SAVI devices or upstream devices, set
their attachments to SAVI devices with Trust attribute.
Bi, et al. Expires November 7, 2013 [Page 12]
Internet-Draft SAVI DCHP May 2013
(5) Configure DHCP-Trust attribute on the direct attachments of DHCP
relays/servers.
In this way, attachments with Validating attribute (and generally
together with attachments of upstream devices) can form a perimeter
separating DHCP clients and trusted devices. Data packet check is
only performed on the perimeter.
The perimeter is primarily designed for scalability. Each SAVI
device only needs to establish bindings for clients directly attached
or indirectly attached through Non-SAVI devices. Binding entries for
addresses in the network are distributed on SAVI devices. Then the
SAVI devices can protect the inside of the perimeter collaboratively,
and each SAVI device is not requred to set up bindings for all the
addresses assigned in the network.
Particularly, SAVI-DHCP perimeter only contains trusted DHCP servers/
relays inside. The SAVI devices only trust DHCP Server-Client
messages originated inside the perimeter. Because bogus DHCP servers
are out of the perimeter, the SAVI devices can be protected from
fabricated DHCP messages. Note that even if a DHCP server is valid,
it may be not contained in the perimeter. For example, in Figure 1,
DHCP server A is valid, but it is attached to a Non-SAVI device. The
Non-SAVI device may be attached by attackers which generate
fabricated DHCP messages. This binding based mechanism may not have
the ability to distinguish whether a message received from the
attachment of the Non-SAVI device 1 is from DHCP server A or the
attackers. If the DHCP server A is contained in the perimeter, the
Non-SAVI device 1 will also be contained in the perimter. However,
the Non-SAVI device 1 can introduce fabricated DHCP messages into the
perimeter. Thus, the DHCP server A cannot be contained in the
perimeter. In this case, the SAVI devices can set up bindings for
addresses assigned by DHCP server A through snooping the messages
relayed by trusted relay in the network. For example, the DHCP relay
may relay messages between DHCP server A and the clients in the
network, and the SAVI devices can snoop messages from the DHCP relay
which is inside the perimeter. The authentication mechanism enforced
between the DHCP relay and the DHCP server outside the perimeter can
compensate this binding based mechanism.
5. Binding State Table (BST)
Binding State Table is used to contain the bindings between the IP
addresses assigned to the attachments and the corresponding binding
anchors of the attachments. Each entry of the table, i.e., binding
entry, has 5 fields:
Bi, et al. Expires November 7, 2013 [Page 13]
Internet-Draft SAVI DCHP May 2013
o Binding Anchor(Anchor): the binding anchor, i.e., a link-layer
property of the attachment.
o IP Address(Address): the IP address assigned to the attachment by
DHCP.
o State: the state of the binding. Possible values of this field
are listed in Section 6.2 and Section 7.3.
o Lifetime: the remaining seconds of the binding. The Lifetime
field counts down automatically.
o TID: the Transaction ID (TID) (refer to [rfc2131] [rfc3315]) of
the corresponding DHCP transaction. TID field is used to
associate DHCP Server-Client messages with corresponding binding
entries.
An instance of this table is shown in Figure 3.
+---------+----------+----------+-----------+-------+
| Anchor | Address | State | Lifetime |TID |
+---------+----------+----------+-----------+-------+
| A | IP_1 | BOUND | 65535 |TID_1 |
+---------+----------+----------+-----------+-------+
| A | IP_2 | BOUND | 10000 |TID_2 |
+---------+----------+----------+-----------+-------+
| B | IP_3 |INIT_BIND | 1 |TID_3 |
+---------+----------+----------+-----------+-------+
Figure 3: Instance of BST
6. DHCP Snooping Process
This section specifies the process of setting up bindings based on
DHCP snooping, named DHCP Snooping Process. This process is
illustrated making use of a state machine.
6.1. Rationale
The rationale of the DHCP Snooping Process is that if a DHCP client
is legitimate to use a DHCP address, the DHCP address assignment
procedure which assigns the IP address to the client must have been
performed on the attachment of the client. This basis stands when
Bi, et al. Expires November 7, 2013 [Page 14]
Internet-Draft SAVI DCHP May 2013
the SAVI device is always on the path(s) from the DHCP client to the
DHCP server(s)/relay(s). Without considering the movement of DHCP
clients, the SAVI device should be the cut node which separates the
DHCP clients and the remaining network containing the DHCP server(s)/
relay(s). For most of the layer-2 networks whose topologies are
simple, it is possible to deploy this SAVI function at proper devices
to meet this requirement.
However, a deployment of this SAVI function may not meet the
requirement. Besides, the movement of DHCP clients may make bindings
are not set up on their new attachments. These exceptions and the
solutions are discussed in Section 7.
6.2. Binding States Description
Following binding states present in this process and the
corresponding state machine:
NO_BIND: The state before a binding has been set up.
INIT_BIND: A potential binding has been set up.
BOUND: The binding has been set up.
6.3. Events
This section describes events in this process and the corresponding
state machine.
6.3.1. Timer Expiration Event
EVE_ENTRY_EXPIRE: The lifetime of a binding entry expires.
6.3.2. Control Message Arriving Events
EVE_DHCP_REQUEST: A DHCPv4 Request or a DHCPv6 Request message is
received.
EVE_DHCP_CONFIRM: A DHCPv6 Confirm message is received.
EVE_DHCP_REBOOT: A DHCPv4 Reboot message is received.
EVE_DHCP_REBIND: A DHCPv4 Rebind or a DHCPv6 Rebind message is
received.
EVE_DHCP_RENEW: A DHCPv4 Renew or a DHCPv6 Renew message is received.
EVE_DHCP_OPTION_RC: A DHCPv6 Solicitation message with Rapid Commit
Bi, et al. Expires November 7, 2013 [Page 15]
Internet-Draft SAVI DCHP May 2013
option is received.
EVE_DHCP_REPLY_REQUEST: A DHCPv4 ACK or a DHCPv6 Reply message is
received, and there is an entry in the BST whose TID field is the
same as the message. The DHCPv6 Reply message must be in response to
a DHCPv6 Request message, and the assignment is successful. (Note: A
DHCPv6 Reply may be a response to DHCPv6 Request, DHCPv6 Confirm,
DHCPv6 Renew, DHCPv6 Rebind, DHCPv6 Decline, DHCPv6 Release and
DHCPv6 Information-request. Through checking the Status Code option,
IA options and other related options in the Reply message, it is
possible to determine the purpose of the DHCPv6 Reply. An
implementation should refer to [rfc3315] to identify such messages.
The processing of the following six events should check the purpose
of the DHCP Reply similarly.)
EVE_DHCP_REPLY_REQUEST_NULL: A DHCPv4 ACK or a DHCPv6 Reply message
is received, and there is no entry in the BST whose TID field is the
same as the message. The DHCPv6 Reply message must be in response to
a DHCPv6 Request message, and the assignment is successful.
EVE_DHCP_REPLY_REBIND: A DHCPv4 ACK or a DHCPv6 Reply message is
received, and there is an entry in the BST whose TID field is the
same as the message. The DHCPv6 Reply message must be in response to
a DHCPv6 Rebind message.
EVE_DHCP_REPLY_REBIND_NULL: A DHCPv4 ACK or a DHCPv6 Reply message is
received, and there is no entry in the BST whose TID field is the
same as the message. The DHCPv6 Reply message must be in response to
a DHCPv6 Rebind message.
EVE_DHCP_REPLY_CONFIRM: A DHCPv4 ACK or a DHCPv6 Reply message is
received, and there is an entry in the BST whose TID field is the
same as the message. The DHCPv6 Reply message must be in response to
a DHCPv6 Confirm message.
EVE_DHCP_REPLY_RENEW: A DHCPv4 ACK or a DHCPv6 Reply message is
received, and there is an entry in the BST whose TID field is the
same as the message. The DHCPv6 Reply message must be in response to
a DHCPv6 Renew message.
EVE_DHCP_REPLY_RENEW_NULL: A DHCPv4 ACK or a DHCPv6 Reply message is
received, and there is no entry in the BST whose TID field is the
same as the message. The DHCPv6 Reply message must be in response to
a DHCPv6 Renew message.
EVE_DHCP_DECLINE: A DHCPv4 Decline or a DHCPv6 Decline message is
received.
Bi, et al. Expires November 7, 2013 [Page 16]
Internet-Draft SAVI DCHP May 2013
EVE_DHCP_RELEASE: A DHCPv4 Release or a DHCPv6 Release message is
received.
EVE_DCHP_LEASEQUERY: A successful DHCPv6 LEASEQUERY_REPLY (refer to
section 4.3.3 of [rfc5007]) is received.
Moreover, only if a DHCP message can pass the following checks, the
corresponding event is regarded as a valid event:
o Attribute check: the DHCP Server-Client messages and
LEASEQUERY_REPLY should be from attachments with DHCP-Trust
attribute; the DHCP Client-Server messages should be from
attachments with DHCP-Snooping attribute.
o Destination check: the DHCP Server-Client messages should be
destined to attachments with DHCP-Snooping attribute.
o Binding anchor check: the DHCP Client-Server messages which may
trigger modification or removal of an existing binding entry must
have matched binding anchor with the corresponding entry.
o TID check: the DHCP Server-Client/Client-Server messages must
have matched TID with the corresponding entry.
o Binding limitation check: the DHCP messages must not cause new
binding setup on an attachment whose binding entry limitation has
been reached. (refer to Section 12.8).
o Address check: the address of the DHCP messages should pass the
check specified in Section 8.2.
On receiving a DHCP message without triggering a valid event, the
state will not transit and actions will not be performed.
6.4. State Machine of DHCP Packet Snooping
This section specifies the transits of each state and the
corresponding actions.
6.4.1. From NO_BIND to Other States
6.4.1.1. Trigger Event
EVE_DHCP_REQUEST, EVE_DHCP_OPTION_RC, EVE_DHCP_CONFIRM,
EVE_DHCP_REBOOT, EVE_DHCP_REBIND, EVE_DHCP_RENEW,
EVE_DHCP_REPLY_NULL.
Bi, et al. Expires November 7, 2013 [Page 17]
Internet-Draft SAVI DCHP May 2013
6.4.1.2. Following Actions
If the triggering event is EVE_DHCP_REQUEST/EVE_DHCP_OPTION_RC/
EVE_DHCP_REBOOT:
The SAVI device MUST forward the message.
The SAVI device will generate an entry in the Binding State Table
(BST). The Binding anchor field is set to the binding anchor of the
attachment from which the message is received. The State field is
set to INIT_BIND. The Lifetime field is set to be
MAX_DHCP_RESPONSE_TIME. The TID field is set to the TID of the
message. If the message is DHCPv4 Request or DHCPv4 Reboot, the
Address field can be set to the address to request, i.e., the
'requested IP address'. An example of the entry is illustrated in
Figure 4.
+---------+-------+---------+-----------------------+-------+
| Anchor |Address| State | Lifetime |TID |
+---------+-------+---------+-----------------------+-------+
| A | |INIT_BIND|MAX_DHCP_RESPONSE_TIME | TID |
+---------+-------+---------+-----------------------+-------+
Figure 4: Binding entry in BST on Request/Rapid Commit/Reboot
triggered initialization
If the triggering event is EVE_DHCP_CONFIRM/EVE_DHCP_REBIND/
EVE_DHCP_RENEW:
If the message is DHCPv4 Rebind/Renew, the message MUST be forwarded.
In DHCPv6, a DHCP client may try to confirm or rebind or renew
multiple addresses in a message. In such case, the SAVI device MUST
check whether setting up corresponding bindings will make the binding
number limitation exceeded. If the limitation will be exceeded, the
message MUST be discarded and the following actions will not be
performed; or else the message MUST be forwarded.
The SAVI device will generate corresponding entries in the Binding
State Table (BST). The Binding anchor field is set to the binding
anchor of the attachment from which the message is received. The
State field is set to INIT_BIND. The Lifetime field is set to be
MAX_DHCP_RESPONSE_TIME. The TID field is set to the TID of the
message. The Address field is set to the address to confirm/
rebind(i.e., 'ciaddr' in DHCPv4 Rebind, IPv6 address in IA Address
Bi, et al. Expires November 7, 2013 [Page 18]
Internet-Draft SAVI DCHP May 2013
options of DHCPv6 Confirm/Rebind). An example of the entries is
illustrated in Figure 5.
+---------+--------+---------+-----------------------+-------+
| Anchor | Address| State | Lifetime |TID |
+---------+--------+---------+-----------------------+-------+
| A | Addr1 |INIT_BIND|MAX_DHCP_RESPONSE_TIME | TID |
+---------+--------+---------+-----------------------+-------+
| A | Addr2 |INIT_BIND|MAX_DHCP_RESPONSE_TIME | TID |
+---------+--------+---------+-----------------------+-------+
Figure 5: Binding entry in BST on Confirm/Rebind/Renew triggered
initialization
If the triggering event is EVE_DHCP_REPLY_REQUEST_NULL/
EVE_DHCP_REPLY_REBIND_NULL/EVE_DHCP_REPLY_RENEW_NULL:
If the message is DHCPv4 ACK, the message MUST be forwarded. For
DHCPv6, a DHCPv6 Reply message may assign multiple addresses to an
attachment. In such case, the SAVI device MUST check whether setting
up corresponding bindings will make the binding number limitation
exceeded. If the limitation will be exceeded, the message MUST be
discarded and the following actions will not be performed; or else
the message MUST be forwarded.
If the message is DHCPv4 ACK, the SAVI device MUST generate a
corresponding entry in the BST.
If the message is DHCPv6 Reply, the SAVI device MUST generate as many
new entries in the BST as the number of assign addresses(IPv6
addresses in all the IA Address options of the message). The Binding
anchor field is set to the binding anchor of the destined attachment.
The State field is set to be BOUND. The Lifetime field is set to the
sum of the lease time in Reply message and MAX_DHCP_RESPONSE_TIME.
The Address field is set to the assigned address (i.e., 'yiaddr' in
DHCPv4 ACK, IPv6 address in IA Address options of DHCPv6 Reply).
An example of the entries is illustrated in Figure 6.
This process is designed to handle the situation that the client
moves after sending a Request/Rebind/Renew message. Vulnerability in
this process is discussed in Section 12.1.
Bi, et al. Expires November 7, 2013 [Page 19]
Internet-Draft SAVI DCHP May 2013
+---------+----------+-------+------------------------+-------+
| Anchor | Address | State | Lifetime |TID |
+---------+----------+-------+------------------------+-------+
| A | Addr1 | BOUND | Lease time 1 |TID |
| | | | +MAX_DHCP_RESPONSE_TIME| |
+---------+----------+-------+------------------------+-------+
| A | Addr2 | BOUND | Lease time 2 |TID |
| | | | +MAX_DHCP_RESPONSE_TIME| |
+---------+----------+-------+------------------------+-------+
Figure 6: Binding entry in BST on Reply triggered initialization
6.4.2. From INIT_BIND to Other States
6.4.2.1. Trigger Event
EVE_DHCP_REPLY_REQUEST, EVE_DHCP_REPLY_REBIND,
EVE_DHCP_REPLY_CONFIRM, EVE_ENTRY_EXPIRE.
6.4.2.2. Following Actions
If the trigger event is EVE_DHCP_REPLY_REQUEST/EVE_DHCP_REPLY_REBIND/
EVE_DHCP_REPLY_RENEW:
If the message is DHCPv4 ACK, the message MUST be forwarded. In
DHCPv6, a DHCPv6 Reply message may assign multiple addresses to an
attachment. In such case, the SAVI device MUST check whether setting
up corresponding bindings will make the binding number limitation
exceeded. If the limitation will be exceeded, the message MUST be
discarded and the following actions will not be performed; or else
the message MUST be forwarded.
The Address field of the corresponding entry in the BST is set to the
address in the message(i.e., 'yiaddr' in DHCPv4 ACK, IPv6 address in
IA Address options of DHCPv6 Reply). The Lifetime field is set to
the sum of the lease time in Reply message and
MAX_DHCP_RESPONSE_TIME. The State field is changed to BOUND. For
DHCPv6, if more than one IA Address options is found in the message,
corresponding new entries MUST be generated.
An example of the entries is illustrated in Figure 7.
Bi, et al. Expires November 7, 2013 [Page 20]
Internet-Draft SAVI DCHP May 2013
+---------+----------+-------+------------------------+-------+
| Anchor | Address | State | Lifetime |TID |
+---------+----------+-------+------------------------+-------+
| A | Addr1 | BOUND |Lease time+ |TID |
| | | |MAX_DHCP_RESPONSE_TIME | |
+---------+----------+-------+------------------------+-------+
| A | Addr2 | BOUND |Lease time+ |TID |
| | | |MAX_DHCP_RESPONSE_TIME | |
+---------+----------+-------+------------------------+-------+
Figure 7: From INIT_BIND to BOUND on DHCP Reply in response to
Request/Rebind/Renew
If the trigger event is EVE_DHCP_REPLY_CONFIRM:
The DHCP Reply message is in response to a Confirm message. If the
Status Code option of the message is not Success (refer to Section
24.4 of [rfc3315]), the message will be forwarded, but no following
actions will be performed. If the Status Code option of the message
is Success, the state of the corresponding entry is changed to BOUND.
Because [rfc3315] does not require lease time of addresses to be
contained in the Reply message, the SAVI device MUST send a
LEASEQUERY [rfc5007] message querying by IP address to
All_DHCP_Relay_Agents_and_Servers multicast address [rfc3315] or a
configured server address. The Lifetime of corresponding entries is
set to MAX_LEASEQUERY_DELAY.
An example of the entries is illustrated in Figure 8.
The related security problem about DHCPv6 LEASEQUERY is discussed in
Section 12.7.
+---------+----------+-------+------------------------+-------+
| Anchor | Address | State | Lifetime |TID |
+---------+----------+-------+------------------------+-------+
| A | Addr1 | BOUND | MAX_LEASEQUERY_DELAY |TID |
+---------+----------+-------+------------------------+-------+
| A | Addr2 | BOUND | MAX_LEASEQUERY_DELAY |TID |
+---------+----------+-------+------------------------+-------+
Figure 8: From INIT_BIND to BOUND on DHCP Reply in response to
Bi, et al. Expires November 7, 2013 [Page 21]
Internet-Draft SAVI DCHP May 2013
Confirm
If the trigger event is EVE_ENTRY_EXPIRE:
The entry MUST be deleted from BST.
Note: If no DHCP Server-Client messages which assign addresses or
confirm addresses are received, corresponding entries will expire
automatically. Thus, other DHCP Server-Client messages (e.g., DHCPv4
NAK) are not specially processed.
6.4.3. From BOUND to Other States
6.4.3.1. Trigger Event
EVE_ENTRY_EXPIRE, EVE_DHCP_RELEASE, EVE_DHCP_DECLINE,
EVE_DHCP_REPLY_REQUEST, EVE_DHCP_REPLY_RENEW, EVE_DHCP_REPLY_REBIND,
EVE_DCHP_LEASEQUERY.
6.4.3.2. Following Actions
If the trigger event is EVE_ENTRY_EXPIRE:
Remove the corresponding entry in BST.
If the trigger event is EVE_DHCP_RELEASE/EVE_DHCP_DECLINE:
Remove the corresponding entry in BST. The Release or Decline
message MUST be forwarded.
If the trigger event is EVE_DHCP_REPLY_REQUEST/EVE_DHCP_REPLY_RENEW/
EVE_DHCP_REPLY_REBIND:
Set the Lifetime field of the corresponding entries to be the sum of
the new lease time and MAX_DHCP_RESPONSE_TIME.
If the trigger event is EVE_DCHP_LEASEQUERY:
Set the Lifetime field to the sum of the lease time in the
LEASEQUERY_REPLY message and MAX_DHCP_RESPONSE_TIME.
6.5. Table of State Machine
The main state transits are listed as follows.
Bi, et al. Expires November 7, 2013 [Page 22]
Internet-Draft SAVI DCHP May 2013
State Event Action Next State
NO_BIND RQ/RC/CF/RE Generate entry INIT_BIND
NO_BIND RPL_NULL Generate entry with lease BOUND
INIT_BIND RPL_RE Record lease time BOUND
INIT_BIND RPL_CF Send Leasequery BOUND
INIT_BIND Timeout Remove entry NO_BIND
BOUND RLS/DCL Remove entry NO_BIND
BOUND Timeout Remove entry NO_BIND
BOUND RPL_RE Set new lifetime BOUND
BOUND LQR Record lease time BOUND
Figure 9: Table of Transit
RQ: EVE_DHCP_REQUEST
CF: EVE_DHCP_CONFIRM
RC: EVE_DHCP_OPTION_RC
RE: EVE_DHCP_REBIND/EVE_DHCP_RENEW/EVE_DHCP_REBOOT
RPL_NULL: EVE_DHCP_REPLY_REQUEST_NULL/EVE_DHCP_REPLY_REBIND_NULL/
EVE_DHCP_REPLY_RENEW_NULL
RPL_RE: EVE_DHCP_REPLY_REQUEST/EVE_DHCP_REPLY_REBIND/
EVE_DHCP_REPLY_RENEW
RPL_CF: EVE_DHCP_REPLY_CONFIRM
DCL: EVE_DHCP_DECLINE
RLS: EVE_DHCP_RELEASE
LQR: EVE_DCHP_LEASEQUERY
Timeout: EVE_ENTRY_EXPIRE
Bi, et al. Expires November 7, 2013 [Page 23]
Internet-Draft SAVI DCHP May 2013
+-------------+
| |
/---------| NO_BIND |<----------\
| ------>| |---------\ |
| | +-------------+ | |EVE_DHCP_RELEASE
EVE_DHCP_REQUEST | | EVE_DHCP_RENEW_NULL| |EVE_DHCP_DECLINE
EVE_DHCP_CONFIRM | |TIMEOUT EVE_DHCP_REPLY_NULL| |TIMEOUT
EVE_DHCP_OPTION_RC| | EVE_DHCP_REBIND_NULL| |
EVE_DHCP_REBIND | | | |
EVE_DHCP_RENEW | | EVE_DHCP_REPLY_RENEW | |
EVE_DHCP_REBOOT | | EVE_DHCP_REPLY_REBIND | |
v | EVE_DHCP_REPLY_REQUEST v |
+-------------+ EVE_DHCP_REPLY_CONFIRM +------------+
| | | |
| INIT_BIND ------------------------>| BOUND |<-\
| | | | |
+-------------+ +------------+ |
| |
\--------/
EVE_DHCP_REPLY_RENEW
EVE_LEASEQUERY_REPLY
EVE_DHCP_REPLY_REBIND
EVE_DHCP_REPLY_REQUEST
Figure 10: Diagram of Transit
7. Data Snooping Process
7.1. Scenario
The rationale of the DHCP Snooping Process specified in Section 6 is
that if a DHCP client is legitimate to use a DHCP address, the
corresponding DHCP address assignment procedure must have been
finished on the attachment of the DHCP client. This basis stands
when the SAVI device is always on the path(s) from the DHCP client to
the DHCP server(s)/relay(s). However, there are two exceptions:
o Multiple paths: there are more than one feasible layer-2 paths
from the client to the DHCP server/relay, and the SAVI device is
not on all of them. The client may get the address through one
of the paths not passing by the SAVI device, but packets from the
client can travel through the other paths passing by the SAVI
device. Because the SAVI device does not snoop the DHCP
assignment procedure, the DHCP snooping procedure will not set up
the corresponding binding.
Bi, et al. Expires November 7, 2013 [Page 24]
Internet-Draft SAVI DCHP May 2013
o Dynamic path: there is only one feasible layer-2 path from the
client to the DHCP server/relay, but the path is dynamic due to
topology change or layer-2 path change. This situation also
covers the local-link movement of clients without address
confirm/re-configuration process. In such cases, the DHCP
snooping process will not set up the corresponding binding.
Data Snooping Process is designed to avoid permanently blocking
legitimate traffic in case of these two exceptions. This process is
performed on attachments with Data-Snooping attribute. Data packets
without matched binding entry may trigger this process to set up
bindings.
Snooping data traffic will introduce considerable burden on the
processor and ASIC-to-Processor bandwidth of SAVI devices.
Considering the overhead of this process, the implementation of this
process is a conditional SHOULD. This function SHOULD be implemented
unless the implementation is known to be used in the scenarios
without the above exceptions. For example, if the implementation is
to be used in networks with tree topology and without host local-link
movement, there is no need to implement this process in such
scenarios.
This process is not supposed to set up a binding whenever a data
packet without matched binding entry is received. Instead, unmatched
data packets trigger this process with a probability and generally a
number of unmatched packets will be discarded before the binding is
set up.
7.2. Rationale
This process makes use of duplication detection and DHCP Leasequery
to set up bindings. If an address is not used by another client in
the network, and the address has been assigned in the network, the
address can be bound with the binding anchor of the attachment from
which the unmatched packet is received.
The security issues about this process is discussed is Section 12.2.
7.3. Additional Binding States Description
In addition to Section 6.2, new states used in this process are
listed here:
DETECTION: The address in the entry is under local duplication
detection.
RECOVERY: The SAVI device is querying the assignment and lease time
Bi, et al. Expires November 7, 2013 [Page 25]
Internet-Draft SAVI DCHP May 2013
of the address in the entry through DHCP Leasequery.
7.4. Events
Additional events in this process are described here. Also, if an
event will trigger to set up a new binding entry, the binding entry
limit on the binding anchor MUST NOT have not been reached.
EVE_DATA_UNMATCH: A data packet without matched binding is received.
EVE_DATA_CONFLICT: ARP Response/Neighbor Advertisement(NA) message
against an address in DETECTION state is received.
EVE_DATA_LEASEQUERY:
IPv4: A DHCPLEASEACTIVE message with IP Address Lease Time option
is received.
IPv6: A successful LEASEQUERY-REPLY is received.
The triggering packet should pass the following checks to trigger a
valid event:
o Attribute check: the data packet should be from attachments with
Data-Snooping attribute; the DHCPLEASEACTIVE/LEASEQUERY_REPLY
messages should be from attachments with DHCP-Snooping attribute.
o Binding limitation check: the DHCP messages must not cause new
binding setup on an attachment whose binding entry limitation has
been reached. (refer to Section 12.8).
o Address check: the address of the DHCP/ARP/NA messages should
pass the check specified in Section 8.2.
o Interval check: the interval between two successive
EVE_DATA_UNMATCH events triggered by an attachment MUST be no
smaller than DATA_SNOOPING_INTERVAL.
o TID check: the DHCPLEASEACTIVE/LEASEQUERY-REPLY messages must
have matched TID with the corresponding entry.
7.5. State Machine of Binding Recovery Process
Through using additional states, the state machine of this process
doesn't conflict the regular process described in Section 6. Thus,
it can be implemented separately without changing the state machine
in Section 6.
Bi, et al. Expires November 7, 2013 [Page 26]
Internet-Draft SAVI DCHP May 2013
7.5.1. From NO_BIND to Other States
7.5.1.1. Trigger Event
EVE_DATA_UNMATCH.
7.5.1.2. Following Actions
Determine whether to process this event with a probability. The
probability can be configured or calculated based on the state of the
SAVI device. This probability should be low enough to mitigate the
damage from DoS attack against this process.
Create a new entry in the BST. Set the Binding Anchor field to the
corresponding binding anchor of the attachment. Set the Address
field to be source address of the packet. Set the State field to
DETECTION. Set the Lifetime of the created entry to 2*DAD_TIMEOUT.
Check if the address has a local conflict (it violates an address
being used by another node):
(1) IPv4 address: send an Address Resolution Protocol (ARP) Request
[rfc826]or a ARP probe [rfc5227] on the address; if there is no
response message after DAD_TIMEOUT, send another ARP Request or
ARP probe;
(2) IPv6 address: perform Duplicate Address Detection (DAD)
[rfc4862] on the address; if there is no response message after
DAD_TIMEOUT, perform another DAD procedure.
Because the delivery of detection message is unreliable, the
detection message is of a certain possibility of not reaching the
targeting node. If the targeting node doesn't get the detection
message, the address may be bound with a wrong binding anchor in the
further stages. This fault may introduce attack against this
mechanism. Thus, the detection is performed again if there is no
response after the first detection.
The messages MUST NOT be sent to the attachment from which the
triggering packet is received.
The packet which triggers this event SHOULD be discarded.
An example of the entry is illustrated in Figure 11.
Bi, et al. Expires November 7, 2013 [Page 27]
Internet-Draft SAVI DCHP May 2013
+---------+-------+---------+-----------------------+-------+
| Anchor |Address| State | Lifetime |TID |
+---------+-------+---------+-----------------------+-------+
| A | Addr1 |DETECTION|2*DAD_TIMEOUT | |
+---------+-------+---------+-----------------------+-------+
Figure 11: Binding entry in BST on data triggered initialization
7.5.2. From DETECTION to Other States
7.5.2.1. Trigger Event
EVE_ENTRY_EXPIRE, EVE_DATA_CONFLICT.
7.5.2.2. Following Actions
If the trigger event is EVE_ENTRY_EXPIRE:
(1) IPv4 address: Send a DHCPLEASEQUERY [rfc4388] message querying
by IP address to all DHCPv4 servers with IP Address Lease Time
option (option 51). The server addresses can be found through
DHCPv4 Discovery or from configuration. Change the state of the
corresponding entry to RECOVERY. Change the lifetime of the
entry to be MAX_LEASEQUERY_DELAY.
(2) IPv6 address: Send a LEASEQUERY [rfc5007] message querying by IP
address to All_DHCP_Relay_Agents_and_Servers multicast address
or a configured server address.
Change the state of the corresponding entry to RECOVERY. Change the
lifetime of the entry to be MAX_LEASEQUERY_DELAY. The TID field is
set to the TID used in the Leasequery message.
An example of the entry is illustrated in Figure 12.
+---------+-------+---------+-----------------------+-------+
| Anchor |Address| State | Lifetime |TID |
+---------+-------+---------+-----------------------+-------+
| A | Addr1 |RECOVERY |MAX_LEASEQUERY_DELAY |TID |
+---------+-------+---------+-----------------------+-------+
Figure 12: Binding entry in BST on Lease Query
Bi, et al. Expires November 7, 2013 [Page 28]
Internet-Draft SAVI DCHP May 2013
If the trigger event is EVE_DATA_CONFLICT:
Remove the entry.
7.5.3. From RECOVERY to Other States
7.5.3.1. Trigger Event
EVE_ENTRY_EXPIRE, EVE_DATA_LEASEQUERY.
7.5.3.2. Following Actions
If the trigger event is EVE_DATA_LEASEQUERY:
(1) IPv4 address: Check if the 'chaddr' field (hardware address) of
the DHCPLEASEACTIVE message matches the hardware address of the
triggering message. If the two addresses do not match, the
following actions will not be performed. Change the state of
the corresponding binding to BOUND. Set life time to the sum of
the value encoded in IP Address Lease Time option of the
DHCPLEASEACTIVE message and MAX_DHCP_RESPONSE_TIME. Erase the
TID field.
(2) IPv6 address: Change the state of the corresponding binding to
BOUND. Set the lifetime to the sum of the valid lifetime
extracted from OPTION_CLIENT_DATA option in the LEASEQUERY-REPLY
message and MAX_DHCP_RESPONSE_TIME. Erase the TID field.
If multiple addresses are specified in the LEASEQUERY-REPLY message,
new entries MUST also be created correspondingly on the same binding
anchor.
If the trigger event is EVE_ENTRY_EXPIRE:
Remove the entry.
7.5.4. After BOUND
Note that the TID field contains no value after the binding state
changes to BOUND. The TID field is recovered from snooping DHCP
Renew/Rebind messages. Because TID is used to associate binding
entries with messages from DHCP servers, it must be recovered; or
else a number of state transits of this mechanism will be not
executed normally.
Bi, et al. Expires November 7, 2013 [Page 29]
Internet-Draft SAVI DCHP May 2013
7.5.4.1. Trigger Event
EVE_DHCP_RENEW/EVE_DHCP_REBIND.
7.5.4.2. Following Action
Set the TID field of the corresponding entry to the TID in the
triggering message.
7.6. Table of State Machine
The main state transits are listed as follows.
State Event Action Next State
NO_BIND EVE_DATA_UNMATCH Duplication detection DETECTION
DETECTION Timeout Send Leasequery RECOVERY
DETECTION EVE_DATA_CONFLICT Remove entry NO_BIND
RECOVERY EVE_DATA_LEASEQUERY Set lease time BOUND
RECOVERY Timeout Remove entry NO_BIND
BOUND RENEW/REBIND Record TID BOUND
Figure 13: Table of Transit
RENEW: EVE_DHCP_RENEW
REBIND: EVE_DHCP_REBIND
Timeout: EVE_ENTRY_EXPIRE
Bi, et al. Expires November 7, 2013 [Page 30]
Internet-Draft SAVI DCHP May 2013
+-------------+
| |
/---------| NO_BIND |<----------\
| ------>| | |
| | +-------------+ |
EVE_DATA_UNMATCH | |EVE_DATA_CONFLICT |
| | |TIMEOUT
| | |
| | |
| | |
| | |
v | |
+-------------+ TIMEOUT +------------+
| | | |
| DETECTION ------------------------>| RECOVERY |
| | | |
+-------------+ +------------+
EVE_DATA_LEASEQUERY|
/----------\ |
EVE_DHCP_RENEW| | |
EVE_DHCP_REBIND| +-----v-------+ |
| | | |
\----| BOUND |<----------/
| |
+-------------+
Figure 14: Diagram of Transit
8. Filtering Specification
This section specifies how to use bindings to filter out spoofing
packets.
Filtering policies are different for data packet and control packet.
DHCP and NDP (Neighbor Discovery Protocol) [rfc4861] messages that
may cause state transit are classified into control packet. Neighbor
Advertisement (NA) and ARP Response are also included in control
packet because the Target Address of NA and ARP Response should be
checked to prevent spoofing. All other packets are considered to be
data packets.
8.1. Data Packet Filtering
Data packets from attachment with attribute Validating MUST be
checked.
Bi, et al. Expires November 7, 2013 [Page 31]
Internet-Draft SAVI DCHP May 2013
Packet whose source IP address is a link-local address SHOULD be
forwarded.
If the source IP address of a packet is not a link-local address, but
there is not a matched entry in BST with state BOUND, this packet
MUST be discarded. However, the packet may trigger Data Snooping
Process if Data-Snooping attribute is set on the attachment.
The SAVI device MAY record any violation.
8.2. Control Packet Filtering
For attachments with Validating attribute:
Discard DHCPv4 Request message whose source IP address is neither all
zeros nor a bound address in BST.
Discard DHCPv6 Request message whose source IP address is neither a
link-local address nor bound with the corresponding binding anchor in
BST.
Discard NDP messages whose source IP address is neither a link-local
address nor bound with the corresponding binding anchor. In
addition, discard NA message whose target address is neither a link-
local address nor bound with the corresponding binding anchor.
Discard ARP messages whose protocol is IP and sender protocol address
is neither all zeros address nor bound with the corresponding binding
anchor. In addition, discard ARP Reply messages whose target address
is not bound with the corresponding binding anchor.
For attachments with other attributes:
Discard DHCP server/relay type message not from attachments with the
DHCP-Trust attribute or Trust attribute.
The SAVI device MAY record any violation.
For attachments with no attribute:
No action will be performed on traffic from such attachments.
9. State Restoration
If a SAVI device reboots, the information kept in volatile memory
will be lost. This section specifies the restoration of attribute
configuration and BST.
Bi, et al. Expires November 7, 2013 [Page 32]
Internet-Draft SAVI DCHP May 2013
9.1. Attribute Configuration Restoration
The lost of attribute configuration will not break the network: no
action will be performed on traffic from attachments with no
attribute. However, the lost of attribute configuration makes this
SAVI function unable to work.
To avoid the loss of binding anchor attribute configuration, the
configuration MUST be able to be stored in non-volatile storage.
After the reboot of SAVI device, if the configuration of binding
anchor attribute can be found in non-volatile storage, the
configuration MUST be used.
9.2. Binding State Restoration
The loss of binding state will cause the SAVI devices discard
legitimate traffic. Purely using the Data Snooping Process to
recover a large number of bindings is of heavy overhead and
considerable delay. Thus, to recover bindings from non-volatile
storage, as specified below, is RECOMMENDED.
Binding entries MAY be saved into non-volatile storage whenever a new
binding entry changes to BOUND state. If a binding with BOUND state
is removed, the saved entry MUST be removed correspondingly.
Immediately after reboot, the SAVI device SHOULD restore binding
states from the non-volatile storage. The system time of save
process MUST be stored. After rebooting, the SAVI device MUST check
whether each entry has been obsolete through comparing the saved
lifetime and the difference between the current system time and saved
system time.
10. Constants
MAX_DHCP_RESPONSE_TIME 120s
DATA_SNOOPING_INTERVAL 60s and configurable
MAX_LEASEQUERY_DELAY 10s
OFFLINK_DELAY 30s
DAD_TIMEOUT 0.5s
Bi, et al. Expires November 7, 2013 [Page 33]
Internet-Draft SAVI DCHP May 2013
11. MLD Consideration
To perform the duplicate detection in Data Snooping Process
Section 7, the SAVI device MUST join the Solicited Node Multicast
group of the source address of triggering IPv6 data packet whenever
performing duplicate detection.
12. Security Considerations
12.1. Security Problem about Binding Setup Triggered by
EVE_DHCP_REPLY_NULL
Whenever the triggering event is EVE_DHCP_REPLY_NULL(EVE_DHCP_REPLY_R
EQUEST_NULL/EVE_DHCP_REPLY_REBIND_NULL/EVE_DHCP_REPLY_RENEW_NULL),
the SAVI device will try to bind the assigned address with the
attachment whose link layer address is the destination link layer
address of the message. However, the assigned address could be bound
with a wrong attachment if an attacker can pollute the mapping from
the link layer address to attachment in the SAVI device.
For example, the SAVI device is a switch and switch port is used as
binding anchor. When the SAVI device receives a DHCP Reply with
assigned address IP_A and destination link layer address MAC_A, it
will check its MAC-to-port table to find the right port. But the
MAC-to-port table might be polluted. For example, the requester with
MAC_A is attached to Port_A, but an attacker attached to Port_B
announces it has MAC_A. If there is no security mechanism used to
protect MAC addresses, the SAVI device can bind MAC_A with Port_B.
Then the SAVI device will find MAC_A is at Port_B from the polluted
MAC-to-port table and it will bind IP_A with Port_B.
Protection from this attack can be ensured by making sure that one of
the following conditions is satisfied:
(1) DHCP Option 82 is used to keep binding anchor in DHCP Request
and Reply. DHCP Option 82 can be used to keep the circuit
information of the client and returned by the DHCP server.
Thus, the binding anchor can be determined from the circuit
information in the Option. It can be used whenever an
implementation doesn't want to create an entry on receiving DHCP
Request message.
(2) MAC address is hard to spoof (e.g., 802.11i, 802.1ae/af).
Bi, et al. Expires November 7, 2013 [Page 34]
Internet-Draft SAVI DCHP May 2013
(3) The mapping table from MAC to binding anchor is secure. For
example, whenever switch port is used as binding anchor, some
security mechanism is used to ensure the mapping from MAC to
switch port is secure.
Specially, if the binding anchor is just link layer address, there is
no such security problem due to there is no need to map link layer
address to binding anchor.
It is RECOMMENDED to implement/enable one of the mechanisms in the
SAVI device.
12.2. Security Problems about the Data Snooping Process
There are two security problems about the Data Snooping Process
Section 7:
(1) The Data Snooping Process is costly, but an attacker can trigger
it simply through sending a number of data packets. To avoid
Denial of Services attack against the SAVI device itself, the
Data Snooping Process MUST be rate limited. A constant
DATA_SNOOPING_INTERVAL is used to control the frequency. Two
Data Snooping Processes on one attachment MUST have a minimum
interval time DATA_SNOOPING_INTERVAL. This constant SHOULD be
configured prudently to avoid Denial of Service attacks.
(2) The Data Snooping Process may set up wrong bindings if the
clients do not reply to the detection probes. An attack will
pass the duplicate detection if the client assigned the target
address does not reply to the detection probes. The DHCP
Leasequery procedure performed by the SAVI device just tells
whether the address is assigned in the network or not. However,
the SAVI device cannot determine whether the address is just
assigned to the triggering attachment from the DHCP Leasequery
Reply.
12.3. Issues about Leaving Clients
After a binding is set up, the corresponding client may leave its
attachment point. It may leave temporarily due to link flapping, or
permanently due to it moves to a new attachment point or just leaves
the network. Considering the client may be back shortly, the binding
should be kept, or else the legtimate traffic from the client will be
blocked. However, if the client leaves permanently, it may be
insecure to keep the binding. In case that the binding anchor is a
property of the attachment point rather than the client, e.g., the
switch port, an attacker which is attached to the attachment point of
the leaving client can send spoofing packets with the addresses
Bi, et al. Expires November 7, 2013 [Page 35]
Internet-Draft SAVI DCHP May 2013
assigned to the client. Even if the binding anchor is a property of
the client, it is a waste of binding resource to keep bindings for
left clients.
The following mechanism is designed to handle the leaving of client:
(1) Whenever a client of Validating attribute leaves, a timer of
OFFLINK_DELAY is set with the corresponding binding entries.
(2) If receiving DAD Neighbor Solicitation/Gratuitous ARP request
targeting at the address during OFFLINK_DELAY, the entries MAY
be removed.
(3) If the binding anchor turns on-link during OFFLINK_DELAY, turn
off the timer.
In this way, the bindings of a leaving client is kept for
OFFLINK_DELAY. In case of link flapping, the client will not be
blocked. If the client leaves permanently, the bindings will be
removes after OFFLINK_DELAY.
12.4. Duplicate Bindings of the Same Address
The same address may be bound with multiple binding anchors, only if
the binding setup processes are finished on each binding anchor
successfully. This mechanism is designed in consideration that a
client may move on the local link, and a client may have multiple
attachments to a SAVI device.
There are two security issues about such a design:
Firstly, due to allowing one address bound with multiple binding
anchors, the traceability of address is weakened. An address can be
traced to multiple attachments.
Secondly, in the local link movement scenario, the former binding may
not be removed and it can be made use of by an attacker sharing the
same binding anchor. For example, when switch port is used as
binding anchor and the port is shared by an attacker and a client
with a hub, the attacker can make use of the address assigned to the
client after the client leaves.
12.5. Compatibility with DNA (Detecting Network Attachment)
DNA [rfc4436] [rfc6059] is designed to decrease the handover latency
after re-attachment to the same network. DNA mainly relies on
performing reachability test through sending unicast Neighbor
Solicitation/Router Solicitation/ARP Request message to determine
Bi, et al. Expires November 7, 2013 [Page 36]
Internet-Draft SAVI DCHP May 2013
whether a previously configured address is still valid. Though DNA
provides optimization for clients, there is not sufficient
information for this mechanism to migrate the previous binding or
establish a new binding. If a binding is set up only through
snooping the reachability test message, the binding can be invalid.
For example, an attacker can perform reachability test with address
bound to another client. If binding is migrated to the attacker, the
attacker can successful obtain the binding from the victim. Because
this mechanism wouldn't set up a binding based on snooping the DNA
procedure, it cannot achieve perfect compatibility with DNA.
However, it only means the re-configuration of the interface is
slowed but not prevented. Details are discussed as follows.
In Simple DNAv6 [rfc6059], the probe is sent with the source address
set to a link-local address, and such messages will not be discarded
by the policy specified in section Section 8.2. If a client is re-
attached to a previous network, the detection will be completed, and
the address will be regarded as valid by the client. However, the
candidate address is not contained in the probe. Thus, the binding
cannot be recovered through snooping the probe. As the client will
perform DHCP procedure at the same time, the binding will be
recovered from the DHCP Snooping Process. The DHCP Request messages
will not be filtered out by this solution as they have link-local
source addresses. Before the DHCP procedure is completed, packets
will be filtered out by the SAVI device. In another word, if this
SAVI function is enabled, Simple DNAv6 will not help reduce the
handover latency. If Data-Snooping attribute is configured on the
new attachment of the client, the data triggered procedure may reduce
the latency.
In DNAv4 [rfc4436], the ARP probe will be discarded because unbound
address is used as sender protocol address. As a result, the client
will regard the address under detection is valid. However, the data
traffic will be filtered. The DHCP Request message sent by the
client will not be discarded, because the source IP address field
should be all zero as required by [rfc2131]. Thus, if the address is
still valid, the binding will be recovered from the DHCP Snooping
Process.
12.6. Bogus DHCP Server Threat
DHCP-Trust attribute is designed to prevent attacks from bogus DHCP
servers. However, the security is not strict because messages from
the valid DHCP server and the bogus DHCP server may arrive at the
SAVI device through the same attachment point. As a result, the SAVI
device cannot distinguish valid messages from bogus messages.
Because the bindings are set up primarily based on DHCP message from
DHCP server, bogus DHCP servers can assign invalid addresses to
Bi, et al. Expires November 7, 2013 [Page 37]
Internet-Draft SAVI DCHP May 2013
clients and bindings for these addresses will be set up by the SAVI
device.
Thus, each valid DHCP server/relay MUST NOT share a binding anchor
with a untrusted device. In case that a binding anchor is shared by
a DHCP server/relay and an untrusted device, DHCP-Trust MUST NOT be
configured on the corresponding attachment. For example, in
Figure 1, if the SAVI device is a switch and the switch port is used
as binding anchor, the attachment from Non-SAVI Device 1 to SAVI
Device C cannot be configured with DHCP-Trust because the port is
shared by DHCP server A and other clients which are untrusted.
12.7. Authentication in DHCPv6 Leasequery
As required in section 5 of RFC5007, DHCPv6 Leasequery 'Should' use
IPsec-based authentication specified in the section 21.1 of RFC3315.
However, with the deployment of this mechanism, there may be no need
to enforce IPSec to perform DHCP Leasequery.
Through containing the DHCP servers in the protection perimeter, the
DHCP servers can be protected from spoofing based attacks. Then
through checking the source IP address of Leasequery messages, the
DHCP server can identify if the messages are from SAVI devices or
not. For the SAVI devices, because the perimeter filters out bogus
DHCP messages, they can trust the DHCP Leasequery responses. Thus,
there is no need to enforce IPSec to validate the DHCP Leasequery
messages in this mechanism.
12.8. Binding Number Limitation
A binding entry will cost a certain high-speed memory resource. In
general, a SAVI device can only afford a quite limited number of
binding entries. In order to prevent an attacker from overloading
the resource of the SAVI device, binding entry limit is set on each
attachment. The binding entry limit is the upper bound of binding
number for each attachment with Validating attribute. No new binding
should be set up after the limit has been reached. Besides, if a
DHCP Reply assigns more addresses than the remaining binding entry
quota of each client, the message will be discarded and no binding
will be set up.
12.9. Residual Threats
As described in [savi-framework], this solution cannot strictly
prevent spoofing. There are two scenarios in which spoofing can
still happen:
Bi, et al. Expires November 7, 2013 [Page 38]
Internet-Draft SAVI DCHP May 2013
(1) The binding anchor is spoofable. If the binding anchor is
spoofable, e.g., plain MAC address, an attacker can use forged
binding anchor to send packet which will not be regarded as
spoofing by SAVI device. Indeed, using binding anchor that can
be easily spoofed is more serious than allowing IP spoofing
traffic. For example, an attacker can use the binding anchor of
another client to get a large number of addresses, and the SAVI
device will refuse to set up new binding for the client whenever
the binding number limitation has been reached. Thus, it is
RECOMMENDED to use strong enough binding anchor, e.g., switch
port, secure association in 802.11ae/af and 802.11i.
(2) The binding anchor is shared by more than one clients. If the
binding anchor is shared by more than one clients, the clients
can spoof the addresses of each other. For example, if switch
port is used as binding anchor a number of clients can attach to
the same switch port of a SAVI device through a hub. The SAVI
device cannot distinguish packets from different clients and
thus the spoofing between them will not be detected. A number
of the above security problems are caused by sharing binding
anchor. Besides, if binding anchor is shared, TID spoofing
based attack is possible. Thus, it is RECOMMENDED to use
exclusive binding anchor.
13. IANA Considerations
This memo asks the IANA for no new parameters.
Note to RFC Editor: This section will have served its purpose if it
correctly tells IANA that no new assignments or registries are
required, or if those assignments or registries are created during
the RFC publication process. From the authors' perspective, it may
therefore be removed upon publication as an RFC at the RFC Editor's
discretion.
14. Acknowledgment
Special thanks to Jean-Michel Combes, Christian Vogt, Joel M.
Halpern, Eric Levy-Abegnoli, Marcelo Bagnulo Braun, Jari Arkko, Elwyn
Davies, Barry Leiba and Alberto Garcia for careful review and
valuation comments on the mechanism and text.
Thanks to Mark Williams, Erik Nordmark, Mikael Abrahamsson, David
Harrington, Pekka Savola, Xing Li, Lixia Zhang, Bingyang Liu, Duanqi
Zhou, Robert Raszuk, Greg Daley, John Kaippallimalil and Tao Lin for
their valuable contributions.
Bi, et al. Expires November 7, 2013 [Page 39]
Internet-Draft SAVI DCHP May 2013
This document was generated using the xml2rfc tool.
15. References
15.1. Informative References
[BA2007] Baker, F., "Cisco IP Version 4 Source Guard", IETF
Internet draft (work in progress), November 2007.
[BCP38] Paul, P. and D. Senie, "Network Ingress Filtering:
Defeating Denial of Service Attacks which employ IP Source
Address Spoofing", RFC 2827, BCP 38, May 2000.
[rfc3736] Droms, R., "Stateless Dynamic Host Configuration Protocol
(DHCP) Service for IPv6", RFC 3736, April 2004.
15.2. Normative References
[rfc2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, BCP 14, Match 1997.
[rfc2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, March 1997.
[rfc3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[rfc4388] Woundy, R. and K. Kinnear, "Dynamic Host Configuration
Protocol (DHCP) Leasequery", RFC 4388, February 2006.
[rfc4436] Aboba, B., Carlson, J., and S. Cheshire, "Detecting
Network Attachment in IPv4 (DNAv4)", RFC 4436, March 2006.
[rfc4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[rfc4862] Thomson, S., Narten, T., and T. Jinmei, "IPv6 Stateless
Address Autoconfiguration", RFC 4862, September 2007.
[rfc5007] Brzozowski, J., Kinnear, K., Volz, B., and S. Zeng,
"DHCPv6 Leasequery", RFC 5007, September 2007.
[rfc5227] Cheshire, S., "IPv4 Address Conflict Detection", RFC 5227,
July 2008.
Bi, et al. Expires November 7, 2013 [Page 40]
Internet-Draft SAVI DCHP May 2013
[rfc6059] Krishnan, S. and G. Daley, "Simple Procedures for
Detecting Network Attachment in IPv6", RFC 6059,
November 2010.
[rfc826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", RFC 826,
November 1982.
[savi-fcfs]
Nordmark, E., Bagnulo, M., and E. Levy-Abegnoli, "FCFS-
SAVI: First-Come First-Serve Source-Address Validation for
Locally Assigned Addresses", RFC 6620, May 2012.
[savi-framework]
Wu, J., Bi, J., Bagnulo, M., Baker, F., and C. Vogt, Ed.,
"Source Address Validation Improvement Framework",
draft-ietf-savi-framework-06 (work in progress),
December 2011.
Appendix A. change log
Main changes from 02 to 03:
(1) Section 12, data trigger and counter trigger are combined to
binding recovery process. The expression "one of MUST" is
changed to "conditional MUST. Conditions related with the
implementation are specified. Related constants are changed in
section 26."
Main changes from 03 to 04:
(1) Section "Prefix configuration" is removed.
(2) Section "Supplemental binding process" is modified in
requirement level.
(3) Sub-section 9.1 "Rationale" is added.
(4) Section "Filtering during Detection" is removed.
(5) Section "Handling layer 2 path change" is changed to
"Consideration on Link layer routing complexity"
Bi, et al. Expires November 7, 2013 [Page 41]
Internet-Draft SAVI DCHP May 2013
(6) Section "Background and related protocols" is removed.
Main changes from 04 to 05:
(1) Trigger events are listed explicitly in section 8.
(2) Detection and Live states are deleted, together with
corresponding sections.
Main change from 05 to 06:
(1) Section 8.1: reference to section 20 is changed to section 15.
Main changes from 06 to 07:
(1) So many changes in this modification. We suggest to track
http://www.ietf.org/mailarchive/web/savi/current/msg01543.ht ml.
Changes are made according to the comments.
Main changes from 07 to 08,09:
(1) The modifications are made according to the comments from Jean-
Michel Combes.
Main changes from 09 to 11:
(1) DNA issues raised by Jari Arkko
Main changes from 11 to 12:
(1) The modifications are made according to the comments from Eric,
http://www.ietf.org/mail-archive/web/savi/current/msg01778.html.
Main changes from 12 to 13:
(1) Main modifications are made based on comments from Elwyn Davies.
http://www.ietf.org/mail-archive/web/gen-art/current/
msg07297.html.
(2) Other modifications are made based on comments from Barry Leiba.
Main changes from 13 to 14:
(1) A symbol error is corrected.
Main changes from 14 to 15:
Bi, et al. Expires November 7, 2013 [Page 42]
Internet-Draft SAVI DCHP May 2013
(1) In corresponding to "1. Does section 8 describe the mechanism
that a SAVI device must perform if it has been unable to snoop
the DHCP traffic between a host and a DHCP server? It appears
that way in the document, but it would be good to explicitly
state that early in the document when the discussion of
topologies is being carried out. This becomes important when
arbitrary topologies do not provide a means for the SAVI device
to eavesdrop on the DHCP traffic." We specified in s7.1 p1 that
arbitrary topologies may result in the regular process cannot
set up correct bindings. This is also specified in the
beginning of s8.
(2) In corresponding to "2. Section 12 refers to the "tentative
address multicast group". Do you really mean the Solicited Node
Multicast address that is generated from the configured IPv6
unicast address?" Yes. We have changed s12 to "the SAVI device
MUST join the Solicited Node Multicast group of the source
address of triggering IPv6 data packet whenever performing
duplicate detection."
(3) Other modifications are made according to the gen-art review.
Refer to http://netarchlab.tsinghua.edu.cn/~yaog/review.txt.
Main changes from 15 to 16:
(1) Main modifications are made according to the second-round gen-
art review.
(2) Improve the quality of writing.
Authors' Addresses
Jun Bi
Tsinghua University
Network Research Center, Tsinghua University
Beijing 100084
China
Email: junbi@tsinghua.edu.cn
Bi, et al. Expires November 7, 2013 [Page 43]
Internet-Draft SAVI DCHP May 2013
Jianping Wu
Tsinghua University
Computer Science, Tsinghua University
Beijing 100084
China
Email: jianping@cernet.edu.cn
Guang Yao
Tsinghua University
Network Research Center, Tsinghua University
Beijing 100084
China
Email: yaoguang@cernet.edu.cn
Fred Baker
Cisco Systems
Santa Barbara, CA 93117
United States
Email: fred@cisco.com
Bi, et al. Expires November 7, 2013 [Page 44]