One document matched: draft-zhou-softwire-b4-nat-00.txt
Network Working Group X. Deng
Internet-Draft France Telecom
Intended status: Standards Track C. Zhou
Expires: September 30, 2011 Huawei Technologies
M. Boucadair
France Telecom
G. Bajko
Nokia
T. Tsou
Huawei Technologies
March 29, 2011
DS-Lite AFTR NAT Bypass: Co-located B4 and NAT Model
draft-zhou-softwire-b4-nat-00
Abstract
This document describes the behavior of the B4 when co-located with a
NAT while the NAT in the AFTR is disabled. The proposed solution is
expected to offload the burden on the AFTR, by delegating the NAT to
B4.
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].
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 September 30, 2011.
Copyright Notice
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Copyright (c) 2011 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. B4 Behavior . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Provisioning . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Plain IPv4 Address . . . . . . . . . . . . . . . . . . . . 3
2.3. Restricted IPv4 Address . . . . . . . . . . . . . . . . . . 3
2.3.1. Outgoing Packets Processing . . . . . . . . . . . . . . 4
2.3.2. Incoming Packets Processing . . . . . . . . . . . . . . 4
2.4. Stateless Encapsulation . . . . . . . . . . . . . . . . . . 4
2.5. Fragmentation and Reassembly . . . . . . . . . . . . . . . 4
2.6. DNS . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . . 4
3.1. Port Randomization . . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6
5. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Normative References . . . . . . . . . . . . . . . . . . . 6
5.2. informative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
As currently defined in [I-D.ietf-softwire-dual-stack-lite], B4
element SHOULD NOT operate a NAT function because the NAT function
will be performed by the AFTR in the service provider's network. To
reduce the processing requirement of NAT device at the network side,
address and port translation can be made at the customer side, e.g.,
CPE. For convenience, we call this solution as NAT-Bypass.
To mitigate the port randomization issue identified in
[I-D.ietf-intarea-shared-addressing-issues], a solution is elaborated
in Section 3.1.
This document provides descriptions on the B4 behavior when
supporting NAT-Bypass.
2. B4 Behavior
2.1. Provisioning
The provisioning of the B4 element is similar to what is defined in
[I-D.ietf-softwire-dual-stack-lite].
2.2. Plain IPv4 Address
A B4 MAY be assigned with a plain IPv4 address.
When a plain, IPv4 address is assigned, the NAT operations are
enforced as per current legacy CPEs. The NAT in the AFTR is disabled
for that user.
IPv4 datagrams are encapsulated in IPv6 as specified in
[I-D.ietf-softwire-dual-stack-lite].
2.3. Restricted IPv4 Address
In the NAT-Bypass solution, the port set is provisioned to B4 through
PCP option defined in [I-D.tsou-pcp-natcoord] or specific DHCP
options [I-D.bajko-pripaddrassign].
The PCP Server or IPv4 DHCP server may be co-located with the AFTR.
The B4 is responsible for performing NAT and/ALG functions, as well
as supporting NAT Traversal mechanisms (e.g., UPnP or NAT-PMP).
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2.3.1. Outgoing Packets Processing
Upon receiving an IPv4 packet, the B4 performs NAT using the public
IPv4 address and port set assigned to it. Then B4 encapsulates the
resulting IPv4 packet into an IPv6 packet, and delivers it through
IPv6 connectivity to AFTR which will then decapsulate the
encapsulated packet and forward it through IPv4. The destination
IPv6 address used for encapsulation should be the AFTR's address.
2.3.2. Incoming Packets Processing
Upon receipt of IPv4-in-IPv6 packet from AFTR, B4 will decapsulate
the packet and translate the public IPv4 address to the private IPv4
address. Finally, it delivers the packet to the host using the
translated IPv4 address. The source IPv6 address used for
encapsulation at AFTR is the AFTR's address, and the destination
address is set to the external address of B4.
2.4. Stateless Encapsulation
B4 may implement the stateless encapsulation specified in Section 4.4
of [I-D.ymbk-aplusp].
2.5. Fragmentation and Reassembly
No change to Section 5.3 of [I-D.ietf-softwire-dual-stack-lite].
2.6. DNS
The DNS behavior is the same as described in
[I-D.ietf-softwire-dual-stack-lite].
3. Security Considerations
3.1. Port Randomization
A successful attack against the TCP or UDP requires the attacker to
have knowledge of a valid five-tuple (protocol, source IP address,
source port, destination IP address, destination port). As the
destination IP, the protocol and the destination port together
identifies a specific service on a specific target that the attacker
will be spoofing, they are usually known by an attacker. Take BGP
TCP RESET attack for example, an attacker assumes the destination
port of 179 for BGP. When it comes to Domain Name System (DNS) cache
poisoning attack, a hacker assumes the destination port of 53 (the
port number IANA has assigned for DNS). There is a chance source IP
is also known by an attacker. Therefore, for an attacker, the
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difficult part of guessing five-tuple is source IP and the TCP/UDP
source port which is different per TCP/UDP session. Random source
ports could increase the numerical guessing space, thereby increasing
the difficulty of an attack.
As a result, it is recommended that NAT devices implement random
source port selection algorithms in [RFC6056]. However, contiguous
port set allocation might be hurdle to port randomization. A simple
non-contiguous port set allocation algorithm is therefore proposed to
achieve a better port randomization NAT.
On every external IPv4 address, according to port set size N, log2(N)
bits are randomly choosing by AFTR as subscribers identification bit
(s bit) among 1st and 16th bits. Take a sharing ration 1:32 for
example, Figure 1 shows an example of 5 random selected bits of s
bit.
|1st |2nd |3rd |4th |5th |6th |7th | 8th|
+----+----+----+----+----+----+----+----+
| 0 | s | 0 | 0 | s | 0 | s | 0 |
+----+----+----+----+----+----+----+----+
|9th |10th|11th|12th|13th|14th|15th|16th|
+----+----+----+----+----+----+----+----+
| s | 0 | s | 0 | 0 | 0 | 0 | 0 |
+----+----+----+----+----+----+----+----+
Figure 1: A s bit selection example (on a sharing ration 1:32
address).
Subscriber ID pattern is formed by setting all the s bits to 1 and
other trivial bits to 0. Figure 2 illustrates an example of
subscriber ID pattern on a sharing ration 1:32 address. Note that
the subscriber ID pattern will be different, guaranteed by the random
s bit selection, on every restricted IP address no matter whether the
sharing ratio varies.
|1st |2nd |3rd |4th |5th |6th |7th | 8th|
+----+----+----+----+----+----+----+----+
| 0 | 1 | 0 | 0 | 1 | 0 | 1 | 0 |
+----+----+----+----+----+----+----+----+
|9th |10th|11th|12th|13th|14th|15th|16th|
+----+----+----+----+----+----+----+----+
| 1 | 0 | 1 | 0 | 1 | 0 | 0 | 0 |
+----+----+----+----+----+----+----+----+
Figure 2: A subscriber ID pattern example (on a sharing ration 1:32
address).
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Subscribers ID value is then assigned by setting subscriber ID
pattern bits according to a subscriber identification and other
trivial bits setting to 1.
|1st |2nd |3rd |4th |5th |6th |7th | 8th|
+----+----+----+----+----+----+----+----+
| 0 | 1 | 0 | 0 | 1 | 0 | 1 | 0 |
+----+----+----+----+----+----+----+----+
|9th |10th|11th|12th|13th|14th|15th|16th|
+----+----+----+----+----+----+----+----+
| 1 | 0 | 1 | 0 | 1 | 0 | 0 | 0 |
+----+----+----+----+----+----+----+----+
Figure 3: A subscriber ID value example (0# subscriber on this
restricted address).
Subscriber ID pattern and subscriber ID value together uniquely
defines a non-overlapping port set on a restricted IP address.
Pseudo-code shown in the Figure 4 describe how to use subscriber ID
pattern and subscriber ID value to implement a random ephemeral port
selection in a restricted port set.
do{
restricted_next_ephemeral = random()|| customer_ID_pattern
& customer_ID_value;
if(five-tuple is unique)
return restricted_next_ephemeral;
}
Figure 4: Random ephemeral port selection of restricted port set
algorithm.
4. IANA Considerations
None.
5. References
5.1. Normative References
[I-D.ietf-softwire-dual-stack-lite]
Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", draft-ietf-softwire-dual-stack-lite-07 (work
in progress), March 2011.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport-
Protocol Port Randomization", BCP 156, RFC 6056,
January 2011.
5.2. informative References
[I-D.bajko-pripaddrassign]
Bajko, G., Savolainen, T., Boucadair, M., and P. Levis,
"Port Restricted IP Address Assignment",
draft-bajko-pripaddrassign-03 (work in progress),
September 2010.
[I-D.ietf-intarea-shared-addressing-issues]
Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing",
draft-ietf-intarea-shared-addressing-issues-05 (work in
progress), March 2011.
[I-D.tsou-pcp-natcoord]
ZOU), T., Zhou, C., Sun, Q., Boucadair, M., and G. Bajko,
"Using PCP To Coordinate Between the CGN and Home Gateway
Via Port Allocation", draft-tsou-pcp-natcoord-01 (work in
progress), March 2011.
[I-D.ymbk-aplusp]
Bush, R., "The A+P Approach to the IPv4 Address Shortage",
draft-ymbk-aplusp-09 (work in progress), February 2011.
Authors' Addresses
Xiaohong Deng
France Telecom
Email: xiaohong.deng@orange-ftgroup.com
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Cathy Zhou
Huawei Technologies
Bantian, Longgang District
Shenzhen 518129
P.R. China
Phone:
Email: cathyzhou@huawei.com
Mohamed Boucadair
France Telecom
Rennes, 35000
France
Email: mohamed.boucadair@orange-ftgroup.com
Gabor Bajko
Nokia
Email: gabor.bajko@nokia.com
Tina TSOU
Huawei Technologies
P.R. China
Phone:
Email: tena@huawei.com
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