Internet DRAFT - draft-xu-savax-data
draft-xu-savax-data
Network Working Group K. Xu
Internet-Draft J. Wu
Intended status: Standards Track X. Wang
Expires: 25 May 2024 Tsinghua University
Y. Guo
Zhongguancun Laboratory
22 November 2023
Data Plane of Inter-Domain Source Address Validation Architecture
draft-xu-savax-data-05
Abstract
Because the Internet forwards packets according to the IP destination
address, packet forwarding typically takes place without inspection
of the source address and malicious attacks have been launched using
spoofed source addresses. The inter-domain source address validation
architecture is an effort to enhance the Internet by using state
machines to generate consistent tags. When communicating between two
end hosts at different ADs of the IPv6 network, tags will be added to
the packets to identify the authenticity of the IPv6 source address.
This memo focuses on the data plane of the SAVA-X mechanism.
Status of This Memo
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This Internet-Draft will expire on 25 May 2024.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
2.1. Terminology and Abbreviation . . . . . . . . . . . . . . 3
3. State Machine Mechanism . . . . . . . . . . . . . . . . . . . 4
4. Tag . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Tag Generation Algorithm . . . . . . . . . . . . . . . . 5
4.1.1. Pseudo-Random Number Algorithm . . . . . . . . . . . 5
4.1.2. Hash Chain Algorithm . . . . . . . . . . . . . . . . 6
4.2. Tag Update . . . . . . . . . . . . . . . . . . . . . . . 7
5. Packet Processing at AER . . . . . . . . . . . . . . . . . . 8
5.1. Port Classification . . . . . . . . . . . . . . . . . . . 9
5.2. Source Address Validation . . . . . . . . . . . . . . . . 9
5.3. Packet Classification . . . . . . . . . . . . . . . . . . 9
5.4. Tag Addition . . . . . . . . . . . . . . . . . . . . . . 10
5.5. Tag Verification . . . . . . . . . . . . . . . . . . . . 10
5.6. Tag Replacement . . . . . . . . . . . . . . . . . . . . . 11
6. Packet Signature . . . . . . . . . . . . . . . . . . . . . . 12
7. MTU Consideration . . . . . . . . . . . . . . . . . . . . . . 13
8. Security Consideration . . . . . . . . . . . . . . . . . . . 14
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
10. Normative References . . . . . . . . . . . . . . . . . . . . 15
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16
1. Introduction
The Inter-Domain Source Address Validation (SAVA-X) mechanism
establishes a trust alliance among Address Domains (AD), maintains a
one-to-one state machine among ADs, generates a consistent tag, and
deploys the tag to the ADs' border router (AER). The AER of the
source AD adds a tag to identify the identity of the AD to the packet
originating from one AD and sinking in another AD. The AER of the
destination AD verifies the source address by validating the
correctness of the tag to determine whether it is a packet with a
forged source address.
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In the process of packet forwarding, if the source address and the
destination address of this packet both belong to the trust alliance,
but the tag is not added or incorrectly added, the AER of the
destination AD determines that the source address is forged and
directly discards this packet. The destination AD forwards the
packet directly for packets whose source address is an address
outside the trust alliance.
This document mainly studies the relevant specifications of the data
plane of the inter-domain source address validation architecture
mechanism between ADs, which will protect IPv6 networks from being
forged source address. See [RFC8200] for more details about IPv6.
It stipulates the state machine, tag generation and update, tag
processing in AER, and packet signature Its promotion and application
can realize the standardization of the data plane in the SAVA-X to
facilitate the related equipment developed by different manufacturers
and organizations to cooperate to accomplish the inter-domain source
address validation jointly.
2. Conventions and Definitions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.1. Terminology and Abbreviation
+==============+====================================================+
| Abbreviation | Description |
+==============+====================================================+
| ACS | AD Control Server. The server maintains |
| | the state machine with other ACS and |
| | distributes information to AER. |
+--------------+----------------------------------------------------+
| AD | Address Domain. The unit of a trust |
| | alliance. It is an address set |
| | consisting of all IPv6 addresses |
| | corresponding to an IPv6 address prefix. |
+--------------+----------------------------------------------------+
| ADID | The identity of an AD. |
+--------------+----------------------------------------------------+
| ADID_Rec | The record of a number of an AD. |
+--------------+----------------------------------------------------+
| AER | AD border router, which is placed at the |
| | boundary of an AD of STA. |
+--------------+----------------------------------------------------+
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| API_Rec | The record of the prefix of an AD or |
| | STA. |
+--------------+----------------------------------------------------+
| ARI_Rec | The record with relevant information of |
| | an AD or STA. |
+--------------+----------------------------------------------------+
| SM | State Machine, which is maintained by a |
| | pair of ACS to generate tags. |
+--------------+----------------------------------------------------+
| TA | Trust Alliance. The IPv6 network that |
| | uses the SAVA-X mechanism. |
+--------------+----------------------------------------------------+
| Tag | The authentic identification of the |
| | source address of a packet. |
+--------------+----------------------------------------------------+
Table 1
3. State Machine Mechanism
In SAVA-X, the state machine mechanism is used to generate, update,
and manage the tags.
+------+ +-------+ +---------+
| S_n | triger | A-Box | transition | S_(n+1) |
| |------------->| |------------------->| |
+------+ +-------+ +---------+
| generation
|
v
+-------+
| Tag_n |
+-------+
Figure 1: State machine mechanism.
State: S_n and S_(n+1) represent the current state and next state of
the SM respectively.
Tag: Tag_n is generated in the progress of state transiting from S_n
to S_(n+1).
Algorithm Box: A-Box is Alogorithm Box. It is used to transmit the
State and generate the tag. It takes the current State as the
input and the following State and current tag as the output. The
algorithm box consists of two parts: one is the transition
function transit(), S_(n+1) = transit(S_n); the second is the
function generate() to generate tags. Tag_n = generate(S_n). The
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algorithm box (A-Box) is the core of the state machine. It
determines the data structure of state and tag, the specific mode
of state machine implementation, as well as its security and
complexity.
Trigger: It is used to trigger the transition of State.
Transition: It reprents the progress of state transiting from S_n to
S_(n+1).
Generation: It represents the progress of calculating the current
tag from the current State.
4. Tag
4.1. Tag Generation Algorithm
There are two ways to generate tags: pseudo-random number algorithm
and hash chain algorithm.
4.1.1. Pseudo-Random Number Algorithm
In the pseudo-random number generation algorithm, an initial number
or string is usually used as the "seed", which corresponds to the
initial state of the state machine. Using seeds, a pseudo-random
number sequence is generated as a tag sequence through some
algorithm. Next, we would take KISS (keep it simple stub), a pseudo-
random number generation algorithm, as an example to introduce how to
apply it to the state machine mechanism. For the algorithm details
of KISS, you could refer to the following reference pseudo code:
/* Seed variables */
uint x = 123456789,y = 362436000,z = 521288629,c = 7654321;
uint KISS(){
const unsigned long a = 698769069UL;
unsigned long t;
x = 69069*x+12345;
y ^= (y<<13); y ^= (y>>17); y ^= (y<<5);
t = a*z+c; c = (t>>32);
z=cast(uint)t;
return x+y+z;
}
Figure 2: KISS99: Pseudo-random number generatation
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In this algorithm, State S can be expressed as (x, y, z, c). The
algorithm box is KISS(). After each calculation, the state undergoes
a transition from S_n to S_(n+1), that is, the four variables x, y,
z, and c are all changed. At the same time, a pseudo-rng number (x +
y + z) is generated.
As the state machine shown above, the initial state is S_0 =
(123456789, 362436000, 521288629, 7654321). In fact, the initial
state can be arbitrarily selected by the algorithm shown below:
void init_KISS() {
x = devrand();
while (!(y = devrand())); /* y must not be zero */
z = devrand();
/* Don't really need to seed c as well
but if you really want to... */
c = devrand() % 698769069; /* Should be less than 698769069 */
}
Figure 3: KISS99: Initial state selection
The basic design goal of the pseudo-random number generation
algorithm is mainly a long cycle and pretty distribution, however,
without or little consideration of safety factors. The backstepping
security and prediction ability of the KISS algorithm have not been
proved.
4.1.2. Hash Chain Algorithm
For the design of a hash chain-based tag generating algorithm, one
can see S/Key in [RFC1760]. In the S/Key system, there is an
encryption end and an authentication end. The encryption end
generates an initial state W, and then uses some hash algorithm H()
to iterate on W to obtain a string sequence: H_0(W), H_1(W), ...,
H_N(W), where H_n(W) represents the iterative operation of H() on W n
times, H_0(W) = W. The state sequence {S} is defined as the reverse
order of the hash chain, that is, S_n = H_(N-n)(W). For example, the
initial state S_0 = H_N(W) and the final state S_N = H_0(W) = W, so
the transfer function transit() is repsented as the invere H().
Different from the KISS pseudo-random number generation algorithm
mentioned in the previous section, in the hash chain, the tag is the
state itself, that is, the output and input of generate() are
consistent, and Tag_n = S_n. In the following discussion, S_n is
temporarily used instead of Tag_n for the convenience of expression.
The encryption end sends the initial state S_0 to the verification
end, and maintains S_1 ~ S_n, which is also the tag sequence used.
The encryption end sends S_(n+1) to the verification end every time.
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The verification end uses the S_n maintained by itself to verify the
tag correctness of the encryption end by calculating S_(n+1) =
transit(S_n). As explained above, transit() is the inversion of H().
In practice, a secure hash algorithm is usually used as H(), such as
SHA-256. For these hash algorithms, it is easy to calculate H(), but
it is difficult to calculate the inversion of H(). Therefore, the
actual operation is as follows: after receiving S_(n+1), the
verification end calculates whether H(S_(n+1)) is equal to S_n. If
it is equal, the verification is successful, otherwise, it fails.
Hash chain algorithm has high security. It can prevent backstepping
and prediction well. Not only the attacker cannot backstep or
predict, but also the verification end cannot do that. The
disadvantage of the hash chain algorithm is that before using tags,
the encryption end needs to calculate all tag sequences, and then
send the last of the sequence to the verification end as the initial
state. At the same time, the encryption end needs to save a complete
tag sequence, although it can be deleted after each tag is used up.
The cost of storage of the hash chain algorithm can not be ignored
4.2. Tag Update
After the state machine is enabled, the source AD uses the initial
state S_0 to transfer to the state S_1 through the algorithm box, and
generates the tag Tag_1. In the subsequent state transition
interval, the AER of the source AD uses the same tag, Tag_1, to add
to the message sent from this AD to the destination AD. The source
AD does not transfer from the state S_1 to the state S_2 until the
transition interval passes, and starts to use tag Tag_2. In this
cycle, the state sequence S_1 ~ S_N and tag sequence Tag_1 ~ TAG_N
are experienced, in which Tag_1 ~ Tag_N are used as tags in turn and
added to the message by the source AER. Similarly, the destination
AER uses the same state machine to calculate the tag sequence, so as
to verify the tag in the message. If the source AD and the
destination AD can ensure the synchronization of the state machine,
it would guarantee the synchronization of the tags. So the tags can
be verified correctly.
Each state machine has an activation time and an Expiration Time.
After the expiration time comes, the current state machine is
deactivated. If a new state machine is available, the new state
machine will be used and perform the same label verification process.
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5. Packet Processing at AER
SAVA-X does not require the intermediate router to recognize and
process the SAVA-X option, which we will describe at Section 9, as
long as the intermediate router correctly implements the extension
header and option processing method described in IPv6 protocol
[RFC8200]. The intermediate router could correctly forward the
packet regardless of its specific content even if it does not
recognize the SAVA-X option well.
The border router, AER, needs to handle the tag correctly. The AER
of the source AD judges whether the IPv6 destination address belongs
to the trust alliance. If no, the packet will be forwarded directly.
If yes, the AER continues to judge the hierarchical relationship
between the source AD and the member ADs to which the packet's
destination IP address belongs. If the source AD and the destination
AD are under the same sub-trust alliance, the AER would add the tag
between the two ADs, otherwise add the AD_V tag.
Note that the packet will not be processed at other AERs in the sub-
trust alliance.
At the AER of the boundary of the sub-trust alliance, the packet is
classified according to the IPv6 destination address. If the
destination address is not within the trust alliance, it will be
forwarded directly. If the destination address belongs to this sub-
trust alliance, it will be classified according to the source IP
address. If the source address also belongs to this sub-trust
alliance, it will be forwarded directly. If the source address does
not belong to this sub-trust alliance, the AER needs to verify the
sub-trust alliance tag and replace it with the AD_V tag in this sub-
trust alliance for following forwarding. If the destination IP
address of the packet belongs to another sub-trust alliance, it SHALL
be classified according to the source address. If the source address
belongs to this sub-trust alliance, verify the AD_V tag. If
consistent, replace with a sub-trust alliance tag. If the source
address is not in this sub-trust alliance, it will be forwarded
directly. Otherwise, the packet will be discarded.
The AER of the destination AD classifies the packet according to the
source address of the packet to be forwarded to determine whether it
originates from a member AD. If yes, enter the label check.
Otherwise, it will be forwarded directly. Tag verification process:
if the tag carried by the packet is consistent with the tag used by
the source AD, remove the tag and forward the packet. Otherwise, the
packet will be discarded.
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5.1. Port Classification
In order to classify packets correctly to complete tag addition,
inspection, and packet forwarding, it is necessary to classify the
ports (interfaces) of AER. Any connected port of AER must belong to
and only belong to the following types of ports:
* Ingress Port: Connect to the port of the non-SAVA-X router in this
AD. Generally connected to IGP router in the domain.
* Egress Port: Connect to other AD ports.
* Trust Port: Connect to the port of the SAVA-X router in this AD.
5.2. Source Address Validation
In SAVA-X, AER must check the source address of the packet. Only the
packet passing the check will be subject to the Section 5.3 step, and
the packet using the fake source IP address will be discarded. The
source address is checked using the ingress filtering method. AER
only checks the source address according to the following three
rules:
* The packet entering an AER from the Ingress Port SHALL only carry
the source address prefix belonging to this AD.
* The packet entering an AER from the Egress Port SHALL NOT carry
the source address prefix belonging to this AD.
* Packets entering an AER from Trust Port are not checked.
The prefix of IP address owned by one AD SHALL be configured by the
administrator or obtained from the control plane and deployed to AER
by ACS of this AD.
5.3. Packet Classification
It SHALL be classified after the packet entering an AER passes the
source address validation. There are three types of packets: packets
that SHOULD be tagged, packets that SHOULD check tags and other
messages. The judgment rules of the three packets are as follows:
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* Packets entering AER from Ingress Port. If the source address
belongs to this AD and the IPv6 destination address belongs to
another AD in the same sub-trust alliance, the tag must be added.
If the source IP address belongs to another AD in the same sub-
trust alliance and the IPv6 destination address belongs to another
sub-trust alliance, the tag must be verified and replaced with the
sub-trust alliance tag. Other packets are forwarded directly.
* Packets entering AER from the Egress Port. The tag must be
checked if the source address belongs to another AD in the same
sub-trust alliance and the IPv6 destination address belongs to
this AD. If the source address belongs to another sub-trust
alliance and the IPv6 destination address belongs to another AD in
the same sub-trust alliance, the tag must be checked and replaced.
And other packets can be forwarded directly.
* Packets entering AER from Trust Port. These packets SHOULD be
forwarded directly.
The relationship between IP address and ADs SHALL be obtained from
the control plane and deployed to the AER by the ACS of the AD. When
the SAVA-X option of the packet received from the progress port
carries the active AD number, you can skip the "mapping from address
to AD number" process and directly use the AD number carried in the
message.
5.4. Tag Addition
AER SHOULD add a destination option header and add the SAVA-X option
into the packet according to the requirements of IETF [RFC8200].
According to [RFC8200], the destination option header SHOULD be
filled so that its length is an integer multiple of 8 bytes,
including the Next Hader and Hdr Ext Len fields of the destination
option header, the Next Header and Payload Length fields of the IPv6
packet header, and the upper protocol header (such as TCP, UDP,
etc.). If it is necessary, AER SHOULD recalculate the Checksum
field.
5.5. Tag Verification
AER will process the first option with Option Type equal to the
binary code of 00111011 in the destination header. It is detailed
described at Section 9.
1. If the packet does not contain a destination option header or
SAVA-X option. the packet SHOULD be discarded.
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2. If the packet contains the SAVA-X option but the parameters or
tag are incorrect, the packet SHOULD be discarded.
3. If the packet contains the SAVA-X option, and the parameters and
tag are correct, AER must replace the tag or remove the tag when
needed before forwarding the message.
In the following scenarios, the tag needs to be removed. If there
are only the SAVA-X option, Pad1, and PadN options in the destination
option header of the message, AER SHOULD remove the whole destination
option header. If there are other options besides the SAVA-X option,
Pad1 and PadN option in the destination option header, AER SHOULD
remove the SAVA-X option and adjust the alignment of other options
according to the relevant protocols of IPv6. In order to remove the
SAVA-X option, the destination option header may also be filled, or
some Pad1 and PadN may be removed, to make its length multiple of 8
bytes. At the same time, the Next Header field and Payload Length
field deployed in the IPv6 message header, and the Checksum field of
the upper protocol header (such as TCP, UDP, etc.) SHALL be
rewritten as necessary.
5.6. Tag Replacement
The tag needs to be replaced when the packet passes through different
sub-trust alliances. Tag replacement needs to be done on the AER of
the boundary address domain of the sub-trust alliance. This feature
is not necessary to realize the AER of each non-boundary address
domain in the sub-trust alliance.
When the packet arrives at the AER of the sub-trust alliance
boundary, it is classified according to the destination address.
1. If the destination address does not belong to the trust alliance,
it will be forwarded directly.
2. If the destination address belongs to this sub-trust alliance, it
will be classified according to the source address of the packet.
* If the source address also belongs to this sub-trust alliance,
the packet will be forwarded directly.
* If the source address does not belong to this sub-trust
alliance, AER should verify the sub-trust alliance tag and
replace it with the AD_V tag in this sub-trust alliance for
forwarding.
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3. If the destination address of the packet belongs to another sub-
trust alliance, it shall be classified according to the source
address.
* If the source address belongs to this sub-trust alliance, AER
should verify the AD_V tag and replace the tag with the sub-
trust alliance tag when it is consistent.
* If the source address is not in this sub-trust alliance, it
will be forwarded directly.
4. Otherwise, the packet will be discarded.
Alliance tag will be used when the packet crosses the upper AD which
is at the higher level of source AD and destination AD. Alliance tag
is the tag maintained between the source AD corresponding to the AD
in the parent AD and the destination AD corresponding to the address
domain in the parent AD.
6. Packet Signature
It is difficult to accurately synchronize time among the trust
alliance members. So we propose a shared time slice, which means
that there are two tags affecting at the same time in a period of
time. But it may suffer from a replay attack. Therefore, a packet
signature mechanism is proposed to prevent replay attacks and conceal
the original tag.
The tag is time-dependent. The state machine triggers state
transition by time and generates a new tag. In a short period of
time, all data packets are labeled with the same tag. Moreover, due
to the subtle differences in time synchronization, both old and new
tags can be used for this short period of time, so attackers can
reuse tags for replay attacks by simply copying tags.
The packet signature mechanism joins the 8-bit part of the payload in
the packet and the tags generated by the state machine. Then it
calculates the hash value with the parameters above to achieve the
effect of packet-by-packet signature and resist the attacker's reuse
of tags. Its processing flow is shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet by Packet Signature |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Level | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 4: Format of the packet by packet signature
Packet by Packet Signature: The hash value of the original tag,
source address, destination address, first 8-bit of payload,
credible level, and credible prefix length.
Level: 8-bit of credible level.
Length: 8-bit of credible prefix length.
Reserved: 16-bit of reserved field. 0 will be padded.
Firstly, it takes the source address, destination address and the
first 8-bit of the data part of the data packet from the data packet,
joins them in the way of (src-ip, dst-ip, first 8-bit of payload),
and then joins the tag generated by the state machine at this time,
the credible level of the SAVA architecture adopted by this AD and
the length of the credible prefix to hash the concatenated string
with the hash algorithm to get a new message digest. Then it is
reduced to a 32-bit packet signature by clipping and folding
algorithm. The AER adds the 32-bit packet signature together with
the 2-bit credible level and the 7-bit credible prefix length to the
SAVA-X option, fills the option into 64-bit, and forwards it. At the
AER of the destination AD, the same splicing and the same hash
operation are performed to verify whether the generated string is
consistent with the signature of the data packet. If they are
consistent, they are forwarded. Otherwise, it is considered that the
source address is forged and the data packet is discarded.
Due to the problem of time synchronization, when both old and new
tags are valid, both old and new tags need to be verified. As long
as one of them passes the verification, the packet should be
forwarded. The original tag generated by the state machine will not
appear in the packet. The attackers do not know the tag generated by
the state machine at this time, so they can not forge the packet
signature in the same way, which ensures the security of the data
communication plane.
7. MTU Consideration
As the AER adds an option to the packet, the length of this packet is
increasing, causing the MTU problem. This problem could taken place
in source AER or the link between source AER and destination AER. If
it occurs on the source AER, the source AER returns the ICMP message
of "packet too big" to the source host and informs the host to reduce
the packet size. Otherwise, if it occurs on other links from the
source AER to the destination AER, which means the packet size
exceeds the MTU of other links from the source AER to the destination
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AER after adding the tag, the corresponding router will return the
ICMP message of "packet too big" to the source host. However, after
the source host adjusts its own MTU, the problem MAY still exist
because the root cause is AER causing packet size to exceed MTU, and
the host does not know it. This problem can be solved by the
following two methods. First, the MTU of the external link is set to
1280 at the source AER as this is the minimum value of MTU under
IPv6. Then the MTU of the source host end will be set to the minimum
value of MTU subtracting the maximum value of the SAVA-X option.
This method can solve the problem, but it greatly limits the packet
size and wastes the available MTU. The second is to monitor the ICMP
message of "packet too big" sent to the host in the domain at the
source AER. If such a message is monitored, the expected MTU value
in the message minus the maximum value of the SAVA-X option will be
forwarded. This method makes good use of MTU value to a certain
extent, but it causes a large monitoring cost.
8. Security Consideration
TBD.
9. IANA Considerations
SAVA-X is designed for IPv6-enabled networks. It takes a destination
option, SAVA-X option, and header to carry the Tag. We recommend
using 00111011, i.e. 59, for the SAVA-X option. Here we give our
SAVA-X option format in use.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Option Type | Opt Data Len |Tag Len|AI Type| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TAG ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Additional Information ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Format of SAVA-X option.
Option Type: 8-bit field. The destination option type of SAVA-X =
59.
Opt Data Len: 8-bit field. The bytes length of the SAVA-X option.
Its value is 2 + LenOfAI + (TagLen + 1), where LenOfAI is 2 when
AI Type is 1, or 4 when AI Type is 2, or 0 default.
Tag Len: 4-bit field. The bytes length of TAG equals to (Tag Len +
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1) * 8, e.g. if Tag Len = 7, it means SAVA-X uses 64 bits long
TAG. It guarantees the length of TAG would be an integral
multiple of 8 bits. The maximum length of TAG is 128 bits and the
minimum length of TAG is 32 bits.
AI Type: 4-bit field. The type of Additional Information. 0 for no
Additional Information, 1 for 16-bit long Additional Information,
and 2 for 32-bit long Additional Information. Others are not
assigned.
Reserved: These bits are not used now and must be zero.
TAG: Variable-length field The actual tag, and its length is
determined by the Tag Len field.
Additional Information: As defined in the AI Type field.
10. Normative References
[RFC1760] Haller, N., "The S/KEY One-Time Password System",
RFC 1760, DOI 10.17487/RFC1760, February 1995,
<https://www.rfc-editor.org/rfc/rfc1760>.
[RFC5210] Wu, J., Bi, J., Li, X., Ren, G., Xu, K., and M. Williams,
"A Source Address Validation Architecture (SAVA) Testbed
and Deployment Experience", RFC 5210,
DOI 10.17487/RFC5210, June 2008,
<https://www.rfc-editor.org/rfc/rfc5210>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/rfc/rfc8200>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
Acknowledgments
TODO acknowledge.
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Authors' Addresses
Ke Xu
Tsinghua University
China
Email: xuke@tsinghua.edu.cn
Jianping Wu
Tsinghua University
China
Email: jianping@cernet.edu.cn
Xiaoliang Wang
Tsinghua University
China
Email: wangxiaoliang0623@foxmail.com
Yangfei Guo
Zhongguancun Laboratory
China
Email: guoyangfei@zgclab.edu.cn
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