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Versions: (draft-bi-savi-dhcp) 00 01 02 03 04
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29 30 31 32 33 34 RFC 7513
SAVI J. Bi, J. Wu
Internet Draft CERNET
Intended status: Standard Tracks G. Yao
Expires: January 2011 Tsinghua Univ.
F. Baker
Cisco
July 29, 2010
SAVI Solution for DHCP
draft-ietf-savi-dhcp-05.txt
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Abstract
This document specifies the procedure for creating bindings between a
DHCPv4 [RFC2131]/DHCPv6 [RFC3315] assigned source IP address and a
binding anchor (refer to [SAVI-framework]) on SAVI (Source Address
Validation Improvements) device. The bindings can be used to filter
packets generated on the local link with forged source IP address.
Table of Contents
Copyright Notice ............................................... 2
Abstract ....................................................... 2
1. Introduction ................................................ 3
2. Conventions used in this document............................ 4
3. Mechanism Overview .......................................... 4
4. Terminology ................................................. 4
5. Conceptual Data Structures................................... 4
5.1. Control Plane Data Structure: Binding State Table (BST). 4
5.2. Data Plane Data Structure: Filtering Table (FT)......... 5
6. DHCP Scenario ............................................... 5
7. Binding Anchor Attributes.................................... 6
7.1. No Attribute ........................................... 6
7.2. SAVI-Validation Attribute............................... 6
7.3. SAVI-DHCP-Trust Attribute............................... 7
7.4. SAVI-SAVI Attribute..................................... 7
7.5. SAVI-BindRecovery Attribute............................. 7
7.6. SAVI-ExtSnooping Attribute.............................. 7
8. Binding Set Up .............................................. 7
8.1. Rationale .............................................. 8
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8.2. Binding States Description.............................. 8
8.3. Events ................................................. 8
8.3.1. Timer expiration event............................. 8
8.3.2. Control message arriving event..................... 8
8.4. Process of Control Packet Snooping...................... 9
8.4.1. From INIT to other states.......................... 9
8.4.1.1. Trigger Event................................. 9
8.4.1.2. Following Actions............................ 10
8.4.2. From START to other states........................ 11
8.4.2.1. Trigger Event................................ 11
8.4.2.2. Following Actions............................ 11
8.4.3. From BOUND to other states........................ 12
8.4.3.1. Trigger Event................................ 12
8.4.3.2. Following Actions............................ 12
8.5. State Machine of DHCP Snooping......................... 12
9. Supplemental Binding Process: Handling Link Topology Change. 13
9.1. Binding Recovery Process............................... 14
9.2. Extended Control Packet Snooping Process............... 15
10. Filtering Specification.................................... 16
10.1. Data Packet Filtering................................. 16
10.2. Control Packet Filtering.............................. 16
11. Handle Binding Anchor Off-link Event....................... 17
12. Binding Number Limitation.................................. 17
13. State Restoration ......................................... 17
14. Confirm Triggered Binding.................................. 18
15. Consideration on Link Layer Routing Complexity............. 18
16. Duplicate Bindings of Same Address......................... 19
17. Constants ................................................. 19
18. Security Considerations.................................... 19
19. IANA Considerations........................................ 19
20. References ................................................ 19
20.1. Normative References.................................. 19
20.2. Informative References................................ 19
21. Acknowledgments ........................................... 20
22. Change Log ................................................ 21
1. Introduction
This document describes the procedure for creating bindings between
DHCP assigned addresses and a binding anchor (refer to [savi-
framework]). Other related details about this procedure are also
specified in this document.
These bindings can be used to filter packets with forged IP address.
Section 12 suggests usage of these bindings for common practice.
[savi-framework] may specify different usages of binding, depending
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on the environment and configuration. The definition and examples of
binding anchor is specified in [savi-framework].
The binding process is inspired by the work of IP Source Guard [IP
Source Guard].
In a stateless DHCP scenario [RFC3736], DHCP is used to configure
other parameters but rather IP address. The address of the client
SHOULD be bound based on other SAVI solutions, but rather this
solution designed for stateful DHCP.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Mechanism Overview
The mechanism specified in this document is designed to provide an
address level source IP address validation granularity, as a
supplement to BCP38 [BCP38]. This mechanism is deployed on the access
device (including access switch, wireless access point/controller,
etc), and performs mainly DHCP snooping to set up bindings between
DHCP assigned IP addresses and corresponding binding anchors. The
bindings can be used to validate the source address in the packets.
4. Terminology
Main terms used in this document are described in [savi-framework],
[RFC2131] and [RFC3315].
5. Conceptual Data Structures
This section describes the possible conceptual data structures used
in this mechanism.
Two main data structures are used to record bindings and their states
respectively. There is redundancy between the two structures, for the
consideration of separation of data plane and control plane.
5.1. Control Plane Data Structure: Binding State Table (BST)
This table contains the state of binding between source address and
binding anchor. Entries are keyed on the binding anchor and source IP
address. Each entry has a lifetime field recording the remaining
lifetime of the entry, a state field recording the state of the
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binding and a field recording other information. The lifetime field
is used to help remove expired bindings. The state field is used to
identify state. The other field is used to keep temporary information,
e.g., the transaction ID in DHCP request. Before a binding is
finished, the lease time of the address is also kept in this field
because it is improper to keep it in the lifetime field which keeps
the lifetime of the binding entry but not the address.
+---------+----------+-------+-----------+-------+
| Anchor | Address | State | Lifetime |Other |
+---------+----------+-------+-----------+-------+
| A | IP_1 | Bound | 65535 | |
+---------+----------+-------+-----------+-------+
| A | IP_2 | Bound | 10000 | |
+---------+----------+-------+-----------+-------+
| B | IP_3 |_Start | 1 | |
+---------+----------+-------+-----------+-------+
Figure 1 Instance of BST
5.2. Data Plane Data Structure: Filtering Table (FT)
This table contains the bindings between binding anchor and address,
keyed on binding anchor and address. This table doesn't contain any
state of the binding. This table is only used to filter packets. An
Access Control List can be regarded as a practical instance of this
table.
+---------+----------+
| Anchor |Address |
+---------+----------+
|A |IP_1 |
+---------+----------+
|A |IP_2 |
+---------+----------+
Figure 2 Instance of FT
6. DHCP Scenario
Figure 3 shows the main elements in a DHCP enabled network. At least
one DHCP server must be deployed in the network, and DHCP relay may
be used to relay message between client and server.
Other address assignment mechanisms may be also used in such network.
However, this solution is primarily designed for a pure DHCP scenario,
in which only DHCP servers can assign valid global address. In a
mixed address assignment scenario where multiple address assignment
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methods such as DHCPv6 and SLAAC, or DHCPv4 and manually
configured assign addresses that share the common prefix, the SAVI
device may need additional state in the state machine to detect and
avoid address conflict. The SAVI solution for mixed environment
is proposed in a separate document [draft-bi-savi-mixed].
+--------+
| DHCP |
| Server |
+--------+
|
|
|
+----'-----+
| SAVI |
| Device |
+-/------/-+
| |
+----\-+ +\-----+
|DHCP | |Client|
|Relay | | |
+------+ +------+
Figure 3 DHCP Scenario
7. Binding Anchor Attributes
This section specifies the binding anchor attributes involved in this
mechanism.
Binding anchor is defined in the [savi-framework]. Attribute of each
binding anchor is configurable. In default, binding anchor has no
attribute. A binding anchor MAY be configured to have one or more
compatible attributes. However, a binding anchor MAY have no
attribute.
7.1. No Attribute
By default, a binding anchor has no attribute. Server type DHCP
message from binding anchor with no attribute MUST be dropped.
However, other packets SHOULD NOT be dropped.
7.2. SAVI-Validation Attribute
SAVI-Validation attribute is used on binding anchor on which the
source addresses are to be validated. The filtering process on
binding anchor with such attribute is described in section 13.
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7.3. SAVI-DHCP-Trust Attribute
SAVI-DHCP-Trust Attribute is used on binding anchor on the path to a
trustable DHCP server/relay.
DHCP server/relay message coming from binding anchor with this
attribute will be forwarded.
7.4. SAVI-SAVI Attribute
This attribute is used on binding anchor from which the traffic is
not to be checked. All traffic from binding anchor with this
attribute will be forwarded without check. Note that DHCP server
message and router message will also be trusted.
Through configuring this attribute on binding anchor that joins two
or more SAVI devices, SAVI-Validation and SAVI-SAVI attributes
implement the security perimeter concept in [savi-framework]. Since
no binding entry is needed on such binding anchor, the binding entry
resource requirement can be reduced greatly.
This attribute can also be set on other binding anchors if the
administrator decides not to validate the traffic from the binding
anchor.
This attribute is mutually exclusive with SAVI-Validation.
7.5. SAVI-BindRecovery Attribute
This attribute is used on binding anchor that requires binding
recovery described in section 10.1.
This attribute is mutually exclusive with SAVI-SAVI.
7.6. SAVI-ExtSnooping Attribute
This attribute is used on binding anchor that requires extended
control packet snooping described in section 10.2.
This attribute is mutually exclusive with SAVI-SAVI.
8. Binding Set Up
This section specifies the procedure of setting up bindings based on
control packet snooping. The binding procedure specified here is
exclusively designed for binding anchor with SAVI-Validation
attribute.
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8.1. Rationale
The rationale of this mechanism is that if a node attached to a
binding anchor intends to use a valid DHCP address, the DHCP
procedure which assigns the address to the node goes first on the
same binding anchor. This basis stands when the link layer routing is
stable. However, unstable link layer routing may result in that data
packet is received from a different binding anchor with the DHCP
messages. Infrequent link layer path change can be handled (but not
perfectly) by the mechanism described in section 10. Section 20
discusses the situation that link layer routing is naturedly unstable.
To handle this situation is above the scope of this document.
8.2. Binding States Description
This section describes the binding states of this mechanism.
INIT The state before a binding has been set up.
START A DHCP request (or a DHCPv6 Confirm, or a DHCPv6
Solicitation with Rapid Commit option) has been received from host,
and it may trigger a new binding.
BOUND The address is authorized to the client.
8.3. Events
8.3.1. Timer expiration event
EVE_ENTRY_EXPIRE: The lifetime of an entry expires
8.3.2. Control message arriving event
EVE_DHCP_REQUEST: A DHCP Request message is received from a binding
anchor with SAVI-Validation attribute, and the binding entry limit on
the binding anchor has not been reached.
EVE_DHCP_CONFIRM: A DHCPv6 Confirm message is received from a binding
anchor with SAVI-Validation attribute, and the binding entry limit on
the binding anchor has not been reached.
EVE_DHCP_OPTION_RC: A DHCPv6 Solicitation message with Rapid Commit
option is received from a binding anchor with SAVI-Validation
attribute, and the binding entry limit on the binding anchor has not
been reached.
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EVE_DHCP_REPLY: A DHCPv4 Acknowledgement or DHCPv6 Reply message is
received from a binding anchor with SAVI-DHCP-Trust attribute, and
the message should be forwarded to a binding anchor with SAVI-
Validation attribute, which has an entry in the state of START. The
TID field in the entry matches the TID in the message.
EVE_DHCP_REPLY_NULL: A DHCPv4 Acknowledgement or DHCPv6 Reply message
is received from a binding anchor with SAVI-DHCP-Trust attribute, and
the message should be forwarded to a binding anchor with SAVI-
Validation attribute, which has no entry in the state of START or
matches the TID field.
EVE_DHCP_DECLINE: A DHCP Decline message is received from a binding
anchor with SAVI-Validation attribute. The message declines an
address bound with the binding anchor in state of LIVE or DETECTION
or BOUND.
EVE_DHCP_RELEASE: A DHCP Release message is received from a binding
anchor with SAVI-Validation attribute. The message releases an
address bound with the binding anchor in state of LIVE or DETECTION
or BOUND.
EVE_DHCP_REPLY_RENEW: A DHCPv4 Acknowledgement or DHCPv6 Reply
message is received, which suggests a new lease time of address in
state of BOUND.
8.4. Process of Control Packet Snooping
8.4.1. From INIT to other states
8.4.1.1. Trigger Event
EVE_DHCP_REQUEST, EVE_DHCP_CONFIRM, EVE_DHCP_OPTION_RC,
EVE_DHCP_REPLY_NULL.
Note that vulnerability may be caused by DHCP Reply triggered
initialization. The binding of assigned address and binding anchor
may be threatened if the binding mechanism between binding anchor and
link layer address is not secure. If one of the following conditions
is satisfied, the security can be ensured.
1. Option 82 is used to keep binding anchor in DHCP Request and Reply,
or
2. Unspoofable MAC is used as binding anchor(802.11i,802.1ae/af), or
3. The mapping table from MAC to binding anchor is secure.
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It is SUGGESTED not to initialize a binding based on DHCP Reply,
until the associated mechanism is also implemented.
8.4.1.2. Following Actions
If the triggering event is EVE_DHCP_REQUEST/EVE_DHCP_OPTION_RC:
The SAVI device MUST forward the message.
The SAVI device MUST generate an entry for the binding anchor in
the Binding State Table (BST) and set the state field to START. The
lifetime of this entry MUST set to be MAX_DHCP_RESPONSE_TIME. The
Transaction ID (Refer to Section 2 in [RFC2131] and Section 4.2 in
[RFC3315]) field of the request packet MUST be recorded in the
entry, except that the mapping from link layer address to binding
anchor is secure as specified in section 9.2.1.1.
+---------+----------+-------+-----------------------+-------+
| Anchor | Address | State | Lifetime |Other |
+---------+----------+-------+-----------------------+-------+
| A | | START |MAX_DHCP_RESPONSE_TIME | TID |
+---------+----------+-------+-----------------------+-------+
Figure 4 Binding entry in BST on client triggered initialization
The TID is kept as a mediator of assigned address and the binding
anchor of requesting node, to assure that the assigned address can
be bound with binding anchor secure.
If the triggering event is EVE_DHCP_CONFIRM:
Other than the actions above, the address to be confirmed MUST be
recorded in the entry.
+---------+----------+-------+-----------------------+-------+
| Anchor | Address | State | Lifetime |Other |
+---------+----------+-------+-----------------------+-------+
| A | Addr | START |MAX_DHCP_RESPONSE_TIME | TID |
+---------+----------+-------+-----------------------+-------+
Figure 5 Binding entry in BST on Confirm triggered initialization
If the triggering event is EVE_DHCP_REPLY_NULL:
The SAVI device MUST deliver the message to the destination.
The SAVI device MUST generate a new entry in BST and FT. The
binding anchor in entry is looked up based on the destination link
layer address, from mapping table from link layer address to
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binding anchor (e.g., the MAC-Port mapping table in case that port
is used as binding anchor). The state of the corresponding entry is
set to be BOUND. The lifetime of the entry MUST be set to be the
lease time.
+---------+----------+-------+------------------------+-------+
| Anchor | Address | State | Lifetime |Other |
+---------+----------+-------+------------------------+-------+
| A | Addr | BOUND | Lease time | |
+---------+----------+-------+------------------------+-------+
Figure 6 Binding entry in BST on Reply triggered initialization
+---------+----------+
| Anchor |Address |
+---------+----------+
|A |Addr |
+---------+----------+
Figure 7 Binding entry in FT on Reply triggered initialization
8.4.2. From START to other states
8.4.2.1. Trigger Event
EVE_DHCP_REPLY, EVE_ENTRY_EXPIRE.
8.4.2.2. Following Actions
If the trigger event is EVE_DHCP_REPLY:
The SAVI device MUST deliver the message to the destination.
The state of the corresponding entry is changed to be BOUND.
If the Address field is null, the lease time in Reply message MUST
be recorded in the entry.
If the Address field is not null, the Reply is in response to a
Confirm message. If the Reply message is of Status Code Success,
perform the procedure in section 19 to fetch the lease time.
Otherwise, delete the entry.
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+---------+----------+-------+------------------------+-------+
| Anchor | Address | State | Lifetime |Other |
+---------+----------+-------+------------------------+-------+
| A | Addr | BOUND | Lease time | |
+---------+----------+-------+------------------------+-------+
Figure 8 From START to BOUND
A corresponding entry MUST also be generated in FT.
If the trigger event is EVE_ENTRY_EXPIRE:
The entry MUST be deleted from BST.
8.4.3. From BOUND to other states
8.4.3.1. Trigger Event
EVE_ENTRY_EXPIRE, EVE_DHCP_RELEASE, EVE_DHCP_DECLINE,
EVE_DHCP_REPLY_RENEW.
8.4.3.2. Following Actions
If the trigger event is EVE_ENTRY_EXPIRE:
Remove the corresponding entry in BST and FT.
If the trigger event is EVE_DHCP_RELEASE or EVE_DHCP_DECLINE:
Remove the corresponding entry in BST and FT. The Release or
Decline message MUST be forwarded.
If the trigger event is EVE_DHCP_REPLY_RENEW:
Set the lifetime of the address to be the new lease time.
8.5. State Machine of DHCP Snooping
The main state transits are listed as follows.
State Event Action Next State
INIT REQ/CFM/RC Generate entry START
*INIT RPL Generate entry with lease BOUND
START RPL Record lease time BOUND
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START Timeout Remove entry INIT
BOUND RELEASE/DECLINE Remove entry INIT
BOUND Timeout Remove entry INIT
BOUND RPL_RENEW Set new lifetime BOUND
*: optional but NOT SUGGESTED.
REQ: EVE_DHCP_REQUEST
CFM: EVE_DHCP_CONFIRM
RC: EVE_DHCP_OPTION_RC
RPL: EVE_DHCP REPLY
DECLINE: DHCP DECLINE
RELEASE: DHCP RELEASE
RPL_RENEW: EVE_DHCP_RPL_RENEW
Timeout: EVE_ENTRY_EXPIRE
9. Supplemental Binding Process: Handling Link Topology Change
Supplemental binding process is designed to cover conditions that
packet is sent by node without previous DHCP procedure sensed by the
SAVI device. A typical situation is that the link topology change
after the binding has been set up, and then the node will send packet
to a different port with the bound port. Another scenario is that a
node moves on the local link without re-configuration process, which
can be regarded as a special case of link topology change. In DHCP
scenario, till this document is finished, link topology change is the
only two events that must be handled through this supplemental
binding process.
Supplemental binding process is designed to avoid permanent
legitimate traffic blocking. It is not supposed to set up a binding
whenever a data packet with unbound source address is received.
Generally, longer time and more packets are needed to trigger
supplemental binding processes.
For implementations that will face the above problem:
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1. Binding Recovery Process is a conditional SHOULD. This function
SHOULD be implemented if the vendor has such ability, unless the
implementation is known to be directly attached to host. If the
mechanism is not implemented and managed nodes are not directly
attached, permanent blocking will happen until the node is re-
configured.
2. Extended Control Packet Snooping Process is a MUST.
Other techniques may be prudently chosen as alternative if found to
have equivalent or even better function to avoid permanently blocking
after discussion, implementation and deployment.
9.1. Binding Recovery Process
Refer to [draft-baker-savi-one-implementation-approach] for a
detailed implementation suggestion. The process specified here can
only be enabled in condition that implementation can meet the
specified hardware requirements described in [draft-baker-savi-one-
implementation-approach].
If a binding anchor is set to have SAVI-BindRecovery attribute, a
FIFO queue or register MUST be used to save recently filtered packets.
The SAVI device will fetch packet from the queue/register to check
the source address can be used by corresponding client on the local
link with limited rate:
1. If the address has a local conflict, meaning the DAD on the
address fails, the packet MUST be discarded. If the address is not
being used, go to the next step.
2.
IPv4 address:
Send a DHCPLEASEQUERY [RFC4388] message querying by IP address to all
DHCPv4 servers for IPv4 address or a configured server address. The
server addresses may be discovered through DHCPv4 Discovery. If no
DHCPLEASEACTIVE message is received, discard the packet; otherwise
generate a new binding entry for the address.
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. If no successful LEASEQUERY-REPLY is received,
discard the packet; otherwise generate a new binding entry for the
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address. The SAVI device may repeat this process if a LEASEQUERY-
REPLY with OPTION_CLIENT_LINK is received, in order to set up binding
entries for all the address of the client.
This process MUST be rate limited to avoid Denial of Services attack
against the SAVI device itself. A constant BIND_RECOVERY_INTERVAL is
used to control the frequency. Two data based processes on one
binding anchor must have a minimum interval time
BIND_RECOVERY_INTERVAL. This constant SHOULD be configured prudently
to avoid Denial of Services.
This process is not strict secure. The node with SAVI-BindRecovery
binding anchor has the ability to use the address of an inactive node,
which doesn't reply to the DAD probe.
In case that the SAVI device is a pure layer-2 device, DHCP Confirm
MAY be used to replace the DHCP LEASEQUERY. The security degree may
degrade for the address may not be assigned by DHCP server.
This process may fail if any DHCP server doesn't support LEASEQUERY.
9.2. Extended Control Packet Snooping Process
In this snooping process, other than DHCP initialization messages,
other types of control packets processed by processor of SAVI device,
if the source address is not bound, may trigger the device to perform
binding process.
The control messages that MUST be processed include: (1) address
resolution Neighbor Solicitation; (2) Neighbor Advertisement; (3)
neighbor unreachability detection; (4) Multicast Listener Discovery;
(5) Address Resolution Protocol; (6) DHCP Renew/Rebind. Other ICMP
messages that may be processed by intermediate device may also
trigger the binding process.
The SAVI device MUST first perform DAD to check if the address has a
local conflict, and then send DHCP LEASEQUERY or Confirm to recover
binding based on DHCP server message.
A minimum time interval EXT_SNOOPING_INTERVAL MUST be set to limit
the rate of such triggering process.
Note that this process may not be able to avoid permanent block, in
case that only data packets are sent by node. Generally, this
mechanism is still practical, because data packet sending without
control plane communication is rare and suspicious in reality. Normal
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traffic will contain control plane communication packets to help
traffic setup and fault diagnosis.
10. Filtering Specification
This section specifies how to use bindings to filter packets.
Filtering policies are different for data packet and control packet.
DHCP and ND messages that may cause state transit are classified into
control packet. Neighbor Advertisement 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.
10.1. Data Packet Filtering
Data packets with a binding anchor which has attribute SAVI-
Validation MUST be checked.
If the source of a packet associated with its binding anchor is in
the FT, this packet SHOULD be forwarded; or else the packet SHOULD be
discarded, or alternatively the SAVI SHOULD record this violation.
10.2. Control Packet Filtering
For binding anchors with SAVI-Validation attribute:
Discard/record DHCPv4 Discovery with non-all-zeros source IP address.
Discard/record DHCPv4 Request whose source IP address is neither all
zeros nor a bound address in FT.
Discard/record DHCPv6 Request whose source is not bound with the
corresponding binding anchor in FT. Discard/record DHCPv6 Confirm/
Solicit whose source is not a link local address bound with the
corresponding binding anchor in FT. The link layer address may be
bound based on SAVI-SLAAC solution or other solutions.
Discard/record other types of DHCP messages whose source is not an
address bound with the corresponding binding anchor.
Discard/record IPv6 NS and IPv4 gratuitous ARP whose source is not an
address bound with the corresponding binding anchor.
Discard/record NA and ARP Replies messages whose target address and
source address are not bound with the corresponding binding anchor.
For other binding anchors:
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Discard DHCP Reply/Ack messages not from binding anchor with the
SAVI-DHCP-Trust attribute or SAVI-SAVI attribute.
11. Handle Binding Anchor Off-link Event
Port DOWN event MUST be handled if switch port is used as binding
anchor. In more general case, if a binding anchor turns off-link,
this event MUST be handled.
Whenever a binding anchor with attribute SAVI-Validation turns down,
the bindings with the binding anchor MUST be kept for a short time.
To handle movement, if receiving DAD NS/Gra ARP request targeting at
the address during the period, the entry MAY be removed.
If the binding anchor turns on-link during the period, recover
bindings. It may result in some security problem, e.g., a malicious
node immediately associates with the binding anchor got off by a
previous node, and then it can use the address assigned to the
previous node. However, this situation is very rare in reality.
Authors decide not to handle this situation.
12. Binding Number Limitation
It is suggested to configure some mechanism in order to prevent a
single node from exhausting the binding table entries on the SAVI
device. Either of the following mechanism is sufficient to prevent
such attack.
1. Set the upper bound of binding number for each binding anchor with
SAVI-Validation.
2. Reserve a number of binding entries for each binding anchor with
SAVI-Validation attribute and all binding anchors share a pool of
the other binding entries.
3. Limit DHCP Request rate per binding anchor, using the bound entry
number of each binding anchor as reverse indicator.
13. State Restoration
If a SAVI device reboots accidentally or designedly, the states kept
in volatile memory will get lost. This may cause hosts indirectly
attached to the SAVI device to be broken away from the network,
because they can't recover bindings on the SAVI device of themselves.
Thus, binding entries MUST be saved into non-volatile storage
whenever a new binding entry changes to BOUND state or a binding with
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state BOUND is removed in condition that this function is supported
by hardware. Immediately after reboot, the SAVI device MUST restore
binding states from the non-volatile storage. The lifetime and the
system time of save process MUST be stored. Then the device MUST
check whether the saved entries are obsolete when rebooting.
The possible alternatives proposed but not suitable for general cases
are:
If the SAVI device is also the DHCP relay, an alternative mechanism
is fetching the bindings through bulk DHCP LEASEQUERY [RFC5460].
If the network enables 802.1ag, the bindings can be recovered with
the help of the first hop routers through snooping unicast Neighbor
Solicitations sent by routers based on the Neighbor Table.
14. Confirm Triggered Binding
If a binding entry is triggered by a CONFIRM message from the client,
no lease time will be contained in the REPLY from DHCP server. The
SAVI device MUST send LEASEQUERY message to get the lease time of the
address to complete the binding entry. If no successful LEASEQUERY-
REPLY is received, the binding entry SHOULD be removed. In this
scenario, the address is not regarded as assigned by DHCP, and it MAY
be bound through other SAVI solution.
If the confirmed address has local conflict, the Client-ID field of
Confirm and LEASEQUERY-REPLY MUST be compared. If they are not match,
the new binding entry MUST be deleted.
15. Consideration on Link Layer Routing Complexity
An implicit assumption of this solution is that data packet must
arrive at the same binding anchor of the control packet. If this
assumption is not valid, this control packet based solution may fail
or at least discard legitimate packet. Unfortunately, if the link
layer routing between host and SAVI device is inconsistent from time
to time, this assumption doesn't stand. Time consistency of link
layer routing is not assured by link layer routing protocol. TRILL, a
recent link layer routing protocol, is flexible and multiple link
layer paths are allowed.
To make the basic assumption stand, the best way is enforcing that
there should be only one topology path from downstream host to the
SAVI device.
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If the assumption doesn't stand, a better solution is requiring
inter-operation between SAVI protocol and the link layer routing
protocol to make SAVI protocol sensitive to the link layer routing
change. This solution is above the scope of this document.
16. Duplicate Bindings of Same Address
Note that the same address may be bound with multiple binding anchors,
only if the binding processes are finished on each binding anchor
successfully respectively.
This mechanism is designed in consideration that a node may move on
the local ink, and a node may have multiple binding anchors.
Note that the local link movement scenario is not handled perfectly.
The former binding may not be removed, unless the node is directly
attached to the SAVI device. The nodes sharing the same former
binding anchor of the moving node have the ability to use its address.
17. Constants
MAX_DHCP_RESPONSE_TIME 120s
BIND_RECOVERY_INTERVAL Device capacity depended and configurable
18. Security Considerations
There is no security consideration currently.
19. IANA Considerations
There is no IANA consideration currently.
20. References
20.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
20.2. Informative References
[RFC2131] R. Droms, "Dynamic Host Configuration Protocol", RFC2131,
March 1997.
[RFC3307] B. Haberman, "Allocation Guidelines for IPv6 Multicast
Addresses", RFC3307, August 2002.
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[RFC3315] R. Droms, Ed. "Dynamic Host Configuration Protocol for IPv6
(DHCPv6)", RFC3315, July 2003.
[RFC4388] R. Woundy and K. Kinnear, "Dynamic Host Configuration
Protocol (DHCP) Leasequery", RFC4388, February 2006.
[RFC4861] T. Narten, E. Nordmark, W. Simpson, and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC4861, September 2007.
[RFC4862] Thomson, S., Narten, T. and Jinmei, T., "IPv6 Stateless
Autoconfiguration", RFC4862, September, 2007.
[RFC5007] J. Brzozowski, K. Kinnear, B. Volz, S. Zeng, "DHCPv6
Leasequery", RFC5007, September 2007.
[RFC5227] S. Cheshire, "IPv4 Address Conflict Detection", RFC5227,
July 2008.
[IP Source Guard] Cisco, "Network Security Technologies and
Solutions", chapter 7, Cisco Press, May 20, 2008.
[draft-baker-savi-one-implementation-approach] F. Baker, "An
implementation approach to Source Address Validation",
draft-baker-savi-one-implementation-approach-00.
[draft-bi-savi-mixed] Jun Bi, "Mixed scenario analysis and best
effort solution", draft-bi-savi-mixed-00.
21. Acknowledgments
Special thanks to Christian Vogt and Joel M. Halpern for this careful
review and valuation comments.
Thanks to Marcelo Bagnulo Braun, Eric Levy-Abegnoli, Mark Williams,
Erik Nordmark, Mikael Abrahamsson, Alberto Garcia, Jari Arkko, David
Harrington, Pekka Savola, Xing Li, Lixia Zhang, Robert Raszuk, Greg
Daley, John Kaippallimalil and Tao Lin for their valuable contributions.
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Authors' Addresses
Jun Bi
CERNET
Beijing, China
Email: junbi@cernet.edu.cn
Jianping Wu
CERNET
Beijing, China
Email: jianping@cernet.edu.cn
Guang Yao
Network Research Center, Tsinghua University
Beijing 100084, China
Email: yaog@netarchlab.tsinghua.edu.cn
Fred Baker
Cisco Systems
Email: fred@cisco.com
22. Change Log
From 02 to 03: 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:
- Section "Prefix configuration" is removed.
- Section "Supplemental binding process" is modified in
requirement level.
- Sub-section 9.1 "Rationale" is added.
- Section "Filtering during Detection" is removed.
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- Section "Handling layer 2 path change" is changed to
"Consideration on Link layer routing complexity"
- Section "Background and related protocols" is removed.
Main changes from 04 to 05:
- Trigger events are listed explicitly in section 8.
- Dection and Live states are deleted, together with
corresponding sections.
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