wdiff rfc7870.original rfc7870.txt

Internet Engineering Task Force (IETF) Y. Fu
Internet-Draft
Request for Comments: 7870 CNNIC
Intended status:
Category: Standards Track S. Jiang
Expires: July 6, 2016
ISSN: 2070-1721 Huawei Technologies Co., Ltd
J. Dong
Y. Chen
Tsinghua University
January 3,
June 2016

DS-Lite

Dual-Stack Lite (DS-Lite) Management Information Base (MIB) for AFTRs
draft-ietf-softwire-dslite-mib-15 Address
Family Transition Routers (AFTRs)

Abstract

This memo defines a portion of the Management Information Base (MIB)
for using use with network management protocols in the Internet community.
In particular, it defines managed objects for Address Family
Transition Routers (AFTRs) of Dual-Stack Lite (DS-Lite).

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 an Internet Standards Track document.

This document is a product of the Internet Engineering Task Force
(IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list It represents the consensus of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.

Internet-Drafts are draft documents valid the IETF community. It has
received public review and has been approved for a maximum publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.

Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained 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 July 6, 2016.
http://www.rfc-editor.org/info/rfc7870.

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
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.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 ....................................................2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 ...........................................2
3. The Internet-Standard Management Framework . . . . . . . . . 3 ......................3
4. Relationship to the IF-MIB . . . . . . . . . . . . . . . . . 3 ......................................3
5. Difference from the IP tunnel Tunnel MIB and NATV2-MIB . . . . . . . 3 .................3
6. Structure of the MIB Module . . . . . . . . . . . . . . . . . 4 .....................................4
6.1. The Object Group . . . . . . . . . . . . . . . . . . . . 5 ...........................................5
6.1.1. The dsliteTunnel Subtree . . . . . . . . . . . . . . 5 ............................5
6.1.2. The dsliteNAT Subtree . . . . . . . . . . . . . . . . 5 ...............................5
6.1.3. The dsliteInfo Subtree . . . . . . . . . . . . . . . 5 ..............................5
6.2. The Notification Group . . . . . . . . . . . . . . . . . 5 .....................................5
6.3. The Conformance Group . . . . . . . . . . . . . . . . . . 5 ......................................5
7. MIB modules required Modules Required for IMPORTS . . . . . . . . . . . . . . 5 ................................5
8. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 6 .....................................................6
9. Security Considerations . . . . . . . . . . . . . . . . . . . 22 ........................................22
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 ...........................................24
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 24
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 24
12.1. ....................................................24
11.1. Normative References . . . . . . . . . . . . . . . . . . 24
12.2. .....................................24
11.2. Informative References . . . . . . . . . . . . . . . . . 25 ...................................26
Acknowledgements ..................................................27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26 ................................................27

1. Introduction

Dual-Stack Lite [RFC6333] is a solution to offer that offers both IPv4 and
IPv6 connectivity to customers crossing an IPv6 only IPv6-only infrastructure.
One of its key components is an IPv4-over-IPv6 tunnel, which is used
to provide IPv4 connectivity across a service provider's IPv6
network. Another key component is a carrier-grade IPv4-IPv4 Network
Address Translation (NAT) to share service provider IPv4 addresses
among customers.

This document defines a portion of the Management Information Base
(MIB) for using use with network management protocols in the Internet
community. This MIB module may be used for configuration and
monitoring of Address Family Transition Routers (AFTRs) in a Dual-Stack Dual-
Stack Lite scenario.

2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119] when they appear in ALL CAPS. BCP
14, RFC 2119 [RFC2119]. When these words are not in ALL CAPS (such
as "should" or "Should"), they have their usual English meanings, meanings and
are not to be interpreted as [RFC2119] key words.

3. The Internet-Standard Management Framework

For a detailed overview of the documents that describe the current
Internet-Standard Management Framework, please refer to section 7 of
[RFC3410].

Managed objects are accessed via a virtual information store, termed
the Management Information Base or MIB. MIB objects are generally
accessed through the Simple Network Management Protocol (SNMP).
Objects in the MIB are defined using the mechanisms defined in the
Structure of Management Information (SMI). This memo specifies a MIB
module that is compliant to the SMIv2, which is described in STD 58,
RFC 2578 [RFC2578], [RFC2579] STD 58, RFC 2579 [RFC2579], and STD 58, RFC 2580
[RFC2580].

4. Relationship to the IF-MIB

The Interfaces MIB [RFC2863] defines generic managed objects for
managing interfaces. Each logical interface (physical or virtual)
has an ifEntry. Tunnels are handled by creating a logical interface
(ifEntry) for each tunnel. Each DS-Lite tunnel endpoint also acts as
a virtual interface, which interface that has a corresponding entry in the IP Tunnel
MIB and Interface MIB. Those corresponding entries are indexed by
ifIndex.

The ifOperStatus in ifTable is used to represent whether the DS-Lite
tunnel function has been triggered. The ifInUcastPkts defined in
ifTable will represent the number of IPv4 packets that have been
encapsulated into IPv6 packets sent to a B4. Basic Bridging BroadBand
(B4). The ifOutUcastPkts defined in ifTable contains the number of
IPv6 packets that can be decapsulated to IPv4 in the virtual
interface. Also, the IF-MIB defines ifMtu for the MTU of this tunnel
interface, so the DS-Lite MIB does not need to define the MTU for the
tunnel.

5. Difference from the IP tunnel Tunnel MIB and NATV2-MIB

The key technologies for DS-Lite are IP in IP IP-in-IP (IPv4-in-IPv6) tunnels
and NAT (IPv4 to IPv4 (IPv4-to-IPv4 translation).

Notes: According to section Section 5.2 of [RFC6333], DS-Lite only defines
IPv4 in IPv6 tunnels at this moment, but other types of encapsulation
could be defined in the future. So this So, the DS-Lite MIB only supports IP
in IP
IP-in-IP encapsulation. If another RFC defines other tunnel types in
the future, this the DS-Lite MIB will be updated then.

The NATV2-MIB [RFC7659] is designed to carry translation from any
address family to any address family, therefore family; therefore, it supports IPv4 to IPv4-to-
IPv4 translation.

The IP Tunnel MIB [RFC4087] is designed for managing to manage tunnels of any type
over IPv4 and IPv6 networks, therefore networks; therefore, it has already supports
IP in IP IP-in-IP
tunnels. But in a DS-Lite scenario, the tunnel type is
point-to-multipoint IP in IP point-to-
multipoint IP-in-IP tunnels. The direct(2) defined in the IP Tunnel
MIB only supports point-to-point tunnel. So tunnels. So, it needs to define a
new tunnel type for DS-Lite.

However, the NATV2-MIB and IP Tunnel MIB together are not sufficient
to support DS-Lite. This document describes the specific features
for the DS-Lite MIB, as below.

In the DS-Lite scenario, the Address Family Transition Router (AFTR)
is not only the tunnel end tunnel-end concentrator, but also an IPv4-to-IPv4
NAT. So So, as defined in [RFC6333], when the IPv4 packets come back
from the Internet to the AFTR, it knows how to reconstruct the IPv6
encapsulation by doing a reverse lookup in the extended IPv4 NAT
binding table (section (Section 6.6 of [RFC6333]). The NAT binding table in
the AFTR is extended to include the IPv6 address of the tunnel
initiator. However, the NAT binding information defined in the
NATV2-MIB as natv2PortMapTable is indexed by the NAT instance,
protocol, and external realm and address. Because the
tunnelIfTable defined in the TUNNEL-MIB [RFC4087] is indexed by the
ifIndex, the DS-Lite-MIB DS-Lite MIB needs to define the tunnel objects to extend
the NAT binding entry by interface. Therefore, a combined MIB is
necessary.

An implementation of the IP Tunnel MIB is required for DS-Lite. As
the tunnel is not point-to-point in DS-Lite, it needs to define a new
tunnel type for DS-Lite. And the The tunnelIfEncapsMethod in the
tunnelIfEntry should be set to dsLite ("xx"), dsLite(17), and a corresponding entry
in the DS-Lite module will exist for every tunnelIfEntry with this
tunnelIfEncapsMethod. The tunnelIfRemoteInetAddress must be set to
"::".

6. Structure of the MIB Module

The DS-Lite MIB provides a way to monitor and manage the devices
(AFTRs) in a DS-Lite scenario through SNMP.

The DS-Lite MIB is configurable on a per-interface basis. It depends
on several parts of the IF-MIB [RFC2863], IP Tunnel MIB [RFC4087],
and NATV2-MIB [RFC7659].

6.1. The Object Group

This group defines objects that are needed for the DS-Lite MIB.

6.1.1. The dsliteTunnel Subtree

The dsliteTunnel subtree describes managed objects used for managing
tunnels in the DS-Lite scenario. Because the
tunnelInetConfigLocalAddress and the tunnelInetConfigRemoteAddress
defined in the IP Tunnel MIB are not readable, a few new objects are
defined in the DS-Lite MIB.

6.1.2. The dsliteNAT Subtree

The dsliteNAT subtree describes managed objects used for
configuration as well as and monitoring of an AFTR which that is capable of a NAT
function. Because the NATV2-MIB supports the NAT management function
in DS-Lite, we may reuse it in the DS-Lite MIB. The dsliteNAT
subtree also provides the mapping information between the tunnel
entry (dsliteTunnelEntry) and the NAT entry (dsliteNATBindEntry) by
adding the IPv6 address of the B4 to the natv2PortMapEntry in the
NATV2-MIB. The mapping behavior, filtering behavior, and pooling
behavior described in this subtree are all defined in [RFC4787].

6.1.3. The dsliteInfo Subtree

The dsliteInfo subtree provides statistical information for DS-Lite.

6.2. The Notification Group

This group defines some notification objects for a DS-Lite scenario.

6.3. The Conformance Group

The dsliteConformance subtree provides conformance information of MIB
objects.

7. MIB modules required Modules Required for IMPORTS

This MIB module IMPORTs objects from [RFC2578], [RFC2580], [RFC2863],
[RFC3411], [RFC4001] [RFC4001], and [RFC7659].

8. Definitions

DSLite-MIB DEFINITIONS ::= BEGIN

IMPORTS
MODULE-IDENTITY, OBJECT-TYPE, mib-2,
NOTIFICATION-TYPE, Integer32,
Counter64, Unsigned32
FROM SNMPv2-SMI

OBJECT-GROUP, MODULE-COMPLIANCE,
NOTIFICATION-GROUP
FROM SNMPv2-CONF

SnmpAdminString
FROM SNMP-FRAMEWORK-MIB

ifIndex
FROM IF-MIB

InetAddress, InetAddressType, InetAddressPrefixLength,
InetPortNumber
FROM INET-ADDRESS-MIB

ProtocolNumber, Natv2InstanceIndex, Natv2SubscriberIndex
FROM NATV2-MIB;

dsliteMIB MODULE-IDENTITY
LAST-UPDATED "201601030000Z" "201605110000Z" -- January 03, May 11, 2016
ORGANIZATION "IETF Softwire Working Group"
CONTACT-INFO
"Yu Fu
CNNIC
No.4 South 4th Street, Zhongguancun, Zhongguancun
Hai-Dian District
Beijing, P.R. China District, Beijing 100090
EMail:
China
Email: fuyu@cnnic.cn

Sheng Jiang
Huawei Technologies Co., Ltd
Huawei Building, 156 Beiqing Rd., Rd.
Hai-Dian District
Beijing, P.R. China District, Beijing 100095
EMail:
China
Email: jiangsheng@huawei.com
Jiang Dong
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.
China
Email: knight.dongjiang@gmail.com

Yuchi Chen
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.
China
Email: flashfoxmx@gmail.com "

DESCRIPTION
"The MIB module is defined for management of objects in the
DS-Lite scenario.

Redistribution and use in source and binary forms, with or
without modification, is part permitted pursuant to, and subject
to the license terms contained in, the Simplified BSD License
set forth in Section 4.c of RFC yyyy; see the RFC itself
for full legal notices. " IETF Trust's Legal Provisions
Relating to IETF Documents
(http://trustee.ietf.org/license-info)."
REVISION "201601030000Z" "201605110000Z"
DESCRIPTION
"Initial version. Published as RFC xxxx."
--RFC Ed.: RFC-edtitor pls fill in xxxx 7870."
::= { mib-2 xxx 240 }
--RFC Ed.: assigned by IANA, see section 10 for details

--Top level

--Top-level components of this MIB module

dsliteMIBObjects OBJECT IDENTIFIER
::= { dsliteMIB 1 }
dsliteTunnel OBJECT IDENTIFIER
::= { dsliteMIBObjects 1 }

dsliteNAT OBJECT IDENTIFIER
::= { dsliteMIBObjects 2 }

dsliteInfo OBJECT IDENTIFIER
::= { dsliteMIBObjects 3 }

--Notifications section
dsliteNotifications OBJECT IDENTIFIER
::= { dsliteMIB 0 }

--dsliteTunnel

--dsliteTunnelTable

dsliteTunnelTable OBJECT-TYPE
SYNTAX SEQUENCE OF DsliteTunnelEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The (conceptual) table containing information on
configured tunnels. This table can be used to map
a B4 address to the associated AFTR address. It can
also be used for row creation."
REFERENCE
"B4, AFTR: RFC6333." RFC 6333."
::= { dsliteTunnel 1 }

dsliteTunnelEntry OBJECT-TYPE
SYNTAX DsliteTunnelEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Each entry in this table contains the information on a
particular configured tunnel."
INDEX { dsliteTunnelAddressType,
dsliteTunnelStartAddress,
dsliteTunnelEndAddress,
ifIndex }
::= { dsliteTunnelTable 1 }

DsliteTunnelEntry ::=
SEQUENCE {
dsliteTunnelAddressType InetAddressType,
dsliteTunnelStartAddress InetAddress,
dsliteTunnelEndAddress InetAddress,
dsliteTunnelStartAddPreLen InetAddressPrefixLength
}

dsliteTunnelAddressType OBJECT-TYPE
SYNTAX InetAddressType
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"This object MUST be set to the value of ipv6(2).

It describes the address type of the IPv4-in-IPv6
tunnel initiator and endpoint."
REFERENCE
"ipv6(2): RFC4001." RFC 4001."
::= { dsliteTunnelEntry 1 }

dsliteTunnelStartAddress OBJECT-TYPE
SYNTAX InetAddress (SIZE (0..16))
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The IPv6 address of the initiator of the tunnel tunnel.
The address type is given by dsliteTunnelAddressType."
::= { dsliteTunnelEntry 2 }

dsliteTunnelEndAddress OBJECT-TYPE
SYNTAX InetAddress (SIZE (0..16))
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The IPv6 address of the endpoint of the tunnel tunnel.
The address type is given by dsliteTunnelAddressType."
::= { dsliteTunnelEntry 3 }

dsliteTunnelStartAddPreLen OBJECT-TYPE
SYNTAX InetAddressPrefixLength
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The IPv6 prefix length of the IP address for the
initiator of the tunnel(dsliteTunnelStartAddress)."
::= { dsliteTunnelEntry 4 }

--dsliteNATBindTable(according to the NAPT scheme)

dsliteNATBindTable OBJECT-TYPE
SYNTAX SEQUENCE OF DsliteNATBindEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"This table contains information about currently
active NAT binds in the NAT of the AFTR. This table
adds the IPv6 address of a B4 to the natv2PortMapTable
defined in NATV2-MIB (RFC7659)." (RFC 7659)."
REFERENCE
"NATV2-MIB: section Section 4 of RFC7659." RFC 7659."
::= { dsliteNAT 1 }
dsliteNATBindEntry OBJECT-TYPE
SYNTAX DsliteNATBindEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The entry in this table holds the mapping relationship
between tunnel information and NAT bind information.
Each entry in this table not only need needs to match a
corresponding entry in the natv2PortMapTable natv2PortMapTable, but
also a corresponding entry in the dsliteTunnelTable.
So
So, the INDEX of the entry needs to match a corresponding
value in the natv2PortMapTable INDEX and a correspongding corresponding
value in the dsliteTunnelTable INDEX. These entries are
lost upon agent restart."
REFERENCE
"natv2PortMapTable: section Section 4 of RFC7659." RFC 7659."
INDEX { dsliteNATBindMappingInstanceIndex,
dsliteNATBindMappingProto,
dsliteNATBindMappingExtRealm,
dsliteNATBindMappingExtAddressType,
dsliteNATBindMappingExtAddress,
dsliteNATBindMappingExtPort,
ifIndex,
dsliteTunnelStartAddress }
::= { dsliteNATBindTable 1 }

DsliteNATBindEntry ::=
SEQUENCE {
dsliteNATBindMappingInstanceIndex Natv2InstanceIndex,
dsliteNATBindMappingProto ProtocolNumber,
dsliteNATBindMappingExtRealm SnmpAdminString,
dsliteNATBindMappingExtAddressType InetAddressType,
dsliteNATBindMappingExtAddress InetAddress,
dsliteNATBindMappingExtPort InetPortNumber,
dsliteNATBindMappingIntRealm SnmpAdminString,
dsliteNATBindMappingIntAddressType InetAddressType,
dsliteNATBindMappingIntAddress InetAddress,
dsliteNATBindMappingIntPort InetPortNumber,
dsliteNATBindMappingPool Unsigned32,
dsliteNATBindMappingMapBehavior INTEGER,
dsliteNATBindMappingFilterBehavior INTEGER,
dsliteNATBindMappingAddressPooling INTEGER
}

dsliteNATBindMappingInstanceIndex OBJECT-TYPE
SYNTAX Natv2InstanceIndex
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Index of the NAT instance that created this port
map entry."
::= { dsliteNATBindEntry 1 }

dsliteNATBindMappingProto OBJECT-TYPE
SYNTAX ProtocolNumber
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"This object specifies the mapping's transport protocol
number."
::= { dsliteNATBindEntry 2 }

dsliteNATBindMappingExtRealm OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..32))
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The realm to which dsliteNATBindMappingExtAddress
belongs."
::= { dsliteNATBindEntry 3 }

dsliteNATBindMappingExtAddressType OBJECT-TYPE
SYNTAX InetAddressType
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Address type for the mapping's external address.
This object MUST be set to the value of iPv4(1).
The values of ipv6(2), ipv4z(3) ipv4z(3), and ipv6z(4) are
not allowed."
REFERENCE
"ipv4(1), ipv6(2), iPv4z(3) iPv4z(3), and ipv6z(4): RFC4001." RFC 4001."
::= { dsliteNATBindEntry 4 }

dsliteNATBindMappingExtAddress OBJECT-TYPE
SYNTAX InetAddress (SIZE (0..4))
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The mapping's external address. This is the source
address for translated outgoing packets. The address
type is given by dsliteNATBindMappingExtAddressType."
::= { dsliteNATBindEntry 5 }

dsliteNATBindMappingExtPort OBJECT-TYPE
SYNTAX InetPortNumber
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The mapping's assigned external port number.
This is the source port for translated outgoing
packets. This MUST be a non-zero value."
::= { dsliteNATBindEntry 6 }

dsliteNATBindMappingIntRealm OBJECT-TYPE
SYNTAX SnmpAdminString (SIZE(0..32))
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The realm to which natMappingIntAddress belongs. This
realm defines the IPv6 address space from which the
tunnel source address is taken. The realm of the
encapsulated IPv4 address is restricted in scope to
the tunnel, so there is no point in identifying it
separately."
::= { dsliteNATBindEntry 7 }

dsliteNATBindMappingIntAddressType OBJECT-TYPE
SYNTAX InetAddressType
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Address type of the mapping's internal address.
This object MUST be set to the value of iPv4z(3).
The values of ipv4(1), ipv6(2) ipv6(2), and ipv6z(4) are
not allowed."
REFERENCE
"ipv4(1), ipv6(2), iPv4z(3) iPv4z(3), and ipv6z(4): RFC4001." RFC 4001."
::= { dsliteNATBindEntry 8 }

dsliteNATBindMappingIntAddress OBJECT-TYPE
SYNTAX InetAddress
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The mapping's internal address. It is the IPv6 tunnel
source address. The address type is given by
dsliteNATBindMappingIntAddressType."
::= { dsliteNATBindEntry 9 }

dsliteNATBindMappingIntPort OBJECT-TYPE
SYNTAX InetPortNumber
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"The mapping's internal port number. This MUST be a
non-zero value."
::= { dsliteNATBindEntry 10 }

dsliteNATBindMappingPool OBJECT-TYPE
SYNTAX Unsigned32 (0|1..4294967295)
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Index of the pool that contains this mapping's external
address and port. If zero, no pool is associated with
this mapping."
::= { dsliteNATBindEntry 11 }

dsliteNATBindMappingMapBehavior OBJECT-TYPE
SYNTAX INTEGER{
endpointIndependent (0),
addressDependent(1),
addressAndPortDependent (2)
}
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Mapping behavior as described in [RFC4787] section 4.1. Section 4.1 of RFC 4787.

endpointIndependent(0), the behavior REQUIRED by
RFC4787, REQ-1,
RFC 4787, REQ-1 maps the source address and port to
the same external address and port for all destination
address and port combinations reached through the same
external realm and using the given protocol.

addressDependent(1) maps to the same external address
and port for all destination ports at the same
destination address reached through the same external
realm and using the given protocol.

addressAndPortDependent(2) maps to a separate external
address and port combination for each different
destination address and port combination reached
through the same external realm.

For the DS-Lite scenario, it must be
addressAndPortDependent(2)."
REFERENCE
"Mapping behavior: section Section 4.1 of RFC4787. RFC 4787.
DS-Lite: RFC 6333."
::= { dsliteNATBindEntry 12 }
dsliteNATBindMappingFilterBehavior OBJECT-TYPE
SYNTAX INTEGER{
endpointIndependent (0),
addressDependent(1),
addressAndPortDependent (2)
}
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Filtering behavior as described in [RFC4787] section 5. Section 5 of RFC 4787.

endpointIndependent(0) accepts for translation packets
from all combinations of remote address and port
destined to the mapped external address and port via
the given external realm and using the given protocol.

addressDependent(1) accepts for translation packets from
all remote ports from the same remote source address
destined to the mapped external address and port via the
given external realm and using the given protocol.

addressAndPortDependent(2) accepts for translation only
those packets with the same remote source address, port,
and protocol incoming from the same external realm as
identified when the applicable port map entry was
created.

RFC 4787, REQ-8 recommends either endpointIndependent(0)
or addressDependent(1) filtering behavior behavior, depending on
whether application friendliness or security takes
priority.

For the DS-Lite scenario, it must be
addressAndPortDependent(2)."
REFERENCE
"Filtering behavior: section Section 5 of RFC4787. RFC 4787.
DS-Lite: RFC6333." RFC 6333."
::= { dsliteNATBindEntry 13 }

dsliteNATBindMappingAddressPooling OBJECT-TYPE
SYNTAX INTEGER{
arbitrary (0),
paired (1)
}
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"Type of address pooling behavior that was used to create
this mapping.

arbitrary(0) pooling behavior means that the NAT instance
may create the new port mapping using any address in the
pool that has a free port for the protocol concerned.

paired(1) pooling behavior, the behavior RECOMMENDED by RFC
4787, REQ-2, REQ-2 means that once a given internal address has
been mapped to a particular address in a particular pool,
further mappings of the same internal address to that pool
will reuse the previously assigned pool member address."
REFERENCE
"Pooling behavior: section Section 4.1 of RFC4787." RFC 4787."
::= { dsliteNATBindEntry 14 }

--dsliteInfo

dsliteAFTRAlarmScalar OBJECT IDENTIFIER ::= { dsliteInfo 1 }

dsliteAFTRAlarmB4AddrType OBJECT-TYPE
SYNTAX InetAddressType
MAX-ACCESS accessible-for-notify
STATUS current
DESCRIPTION
"This object indicates the address type of
the B4 B4, which will send an alarm."
::= { dsliteAFTRAlarmScalar 1 }

dsliteAFTRAlarmB4Addr OBJECT-TYPE
SYNTAX InetAddress
MAX-ACCESS accessible-for-notify
STATUS current
DESCRIPTION
"This object indicates the IP address of
B4
B4, which will send an alarm. The address type is
given by dsliteAFTRAlarmB4AddrType."
::= { dsliteAFTRAlarmScalar 2 }

dsliteAFTRAlarmProtocolType OBJECT-TYPE
SYNTAX INTEGER{
tcp (0),
udp (1),
icmp (2),
total (3)
}
MAX-ACCESS accessible-for-notify
STATUS current
DESCRIPTION
"This object indicates the transport protocol type
of alarm.

tcp (0) means that the transport protocoal protocol type of
alarm is tcp.

udp (1) means that the transport protocoal protocol type of
alarm is udp.

icmp (2) means that the transport protocoal protocol type of
alarm is icmp.

total (3) means that the transport protocoal protocol type of
alarm is total."
::= { dsliteAFTRAlarmScalar 3 }

dsliteAFTRAlarmSpecificIPAddrType OBJECT-TYPE
SYNTAX InetAddressType
MAX-ACCESS accessible-for-notify
STATUS current
DESCRIPTION
"This object indicates the address type of the IP address
whose port usage has reached the threshold."
::= { dsliteAFTRAlarmScalar 4 }

dsliteAFTRAlarmSpecificIP OBJECT-TYPE
SYNTAX InetAddress
MAX-ACCESS accessible-for-notify
STATUS current
DESCRIPTION
"This object indicates the IP address whose port usage
has reached the threshold. The address type is given by
dsliteAFTRAlarmSpecificIPAddrType."
::= { dsliteAFTRAlarmScalar 5 }

dsliteAFTRAlarmConnectNumber OBJECT-TYPE
SYNTAX Integer32 (60..90)
MAX-ACCESS read-write
STATUS current
DESCRIPTION
"This object indicates the notification threshold
of the DS-Lite tunnels which that is active in
the AFTR device."
REFERENCE
"AFTR: section Section 6 of RFC6333." RFC 6333."
DEFVAL
{ 60 }
::= { dsliteAFTRAlarmScalar 6 }

dsliteAFTRAlarmSessionNumber OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS read-write
STATUS current
DESCRIPTION
"This object indicates the notification threshold of
the IPv4 session for the user."
REFERENCE
"AFTR: section Section 6 of RFC6333 RFC 6333
B4: section Section 5 of RFC6333." RFC 6333."
DEFVAL
{ -1 }
::= { dsliteAFTRAlarmScalar 7 }

dsliteAFTRAlarmPortNumber OBJECT-TYPE
SYNTAX Integer32
MAX-ACCESS read-write
STATUS current
DESCRIPTION
"This object indicates the notification threshold of the NAT
ports which that have been used by the user."
DEFVAL
{ -1 }
::= { dsliteAFTRAlarmScalar 8 }

dsliteStatisticsTable OBJECT-TYPE
SYNTAX SEQUENCE OF DsliteStatisticsEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"This table provides statistical information
about DS-Lite."
::= { dsliteInfo 2 }

dsliteStatisticsEntry OBJECT-TYPE
SYNTAX DsliteStatisticsEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Ench
"Each entry in this table provides statistical information
about DS-Lite."
INDEX { dsliteStatisticsSubscriberIndex }
::= { dsliteStatisticsTable 1 }

DsliteStatisticsEntry ::=
SEQUENCE {
dsliteStatisticsSubscriberIndex Natv2SubscriberIndex,
dsliteStatisticsDiscards Counter64,
dsliteStatisticsSends Counter64,
dsliteStatisticsReceives Counter64,
dsliteStatisticsIpv4Session Counter64,
dsliteStatisticsIpv6Session Counter64
}

dsliteStatisticsSubscriberIndex OBJECT-TYPE
SYNTAX Natv2SubscriberIndex
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"Index of the subscriber or host. A unique value,
greater than zero, for each subscriber in the
managed system."
::= { dsliteStatisticsEntry 1 }

dsliteStatisticsDiscards OBJECT-TYPE
SYNTAX Counter64
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"This object indicates the number of packets
discarded from this subscriber."
::= { dsliteStatisticsEntry 2 }

dsliteStatisticsSends OBJECT-TYPE
SYNTAX Counter64
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"This object indicates the number of packets which that is
sent to this subscriber."
::= { dsliteStatisticsEntry 3 }

dsliteStatisticsReceives OBJECT-TYPE
SYNTAX Counter64
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"This object indicates the number of packets which that is
received from this subscriber."
::= { dsliteStatisticsEntry 4 }

dsliteStatisticsIpv4Session OBJECT-TYPE
SYNTAX Counter64
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"This object indicates the number of the
current IPv4 Sessions."
REFERENCE
"Session: the paragraph Paragraph 2 in Section 11 of RFC6333 section 11. RFC 6333.
(The AFTR should have the capability to log the
tunnel-id, protocol, ports/IP addresses, and
the creation time of the NAT binding to uniquely
identify the user sessions)."
::= { dsliteStatisticsEntry 5 }

dsliteStatisticsIpv6Session OBJECT-TYPE
SYNTAX Counter64
MAX-ACCESS read-only
STATUS current
DESCRIPTION
"This object indicates the number of the
current IPv6 Session. session. Because the AFTR is
also a dual-stack device, it will also
forward normal IPv6 packets for the
inbound and outbound direction."
REFERENCE
"Session: the paragraph Paragraph 2 in Section 11 of RFC6333 section 11. RFC 6333.
(The AFTR should have the capability to log the
tunnel-id, protocol, ports/IP addresses, and
the creation time of the NAT binding to uniquely
identify the user sessions)."
::= { dsliteStatisticsEntry 6 }

---dslite Notifications

dsliteTunnelNumAlarm NOTIFICATION-TYPE
OBJECTS { dsliteAFTRAlarmProtocolType,
dsliteAFTRAlarmB4AddrType,
dsliteAFTRAlarmB4Addr }
STATUS current
DESCRIPTION
"This trap is triggered when the number of
current dslite DS-Lite tunnels exceeds the value of
the dsliteAFTRAlarmConnectNumber."
::= { dsliteNotifications 1 }

dsliteAFTRUserSessionNumAlarm NOTIFICATION-TYPE
OBJECTS { dsliteAFTRAlarmProtocolType,
dsliteAFTRAlarmB4AddrType,
dsliteAFTRAlarmB4Addr }
STATUS current
DESCRIPTION
"This trap is triggered when user sessions
reach the threshold. The threshold
is specified by the dsliteAFTRAlarmSessionNumber."
REFERENCE
"Session: the paragraph Paragraph 2 in Section 11 of RFC6333 section 11. RFC 6333.
(The AFTR should have the capability to log the
tunnel-id, protocol, ports/IP addresses, and
the creation time of the NAT binding to uniquely
identify the user sessions)."
::= { dsliteNotifications 2 }

dsliteAFTRPortUsageOfSpecificIpAlarm NOTIFICATION-TYPE
OBJECTS { dsliteAFTRAlarmSpecificIPAddrType,
dsliteAFTRAlarmSpecificIP }
STATUS current
DESCRIPTION
"This trap is triggered when the used NAT
ports of map address reach the threshold.
The threshold is specified by the
dsliteAFTRAlarmPortNumber."
::= { dsliteNotifications 3 }

--Module Conformance statement

dsliteConformance OBJECT IDENTIFIER
::= { dsliteMIB 2 }

dsliteCompliances OBJECT IDENTIFIER ::= { dsliteConformance 1 }

dsliteGroups OBJECT IDENTIFIER ::= { dsliteConformance 2 }

-- compliance statements

dsliteCompliance MODULE-COMPLIANCE
STATUS current
DESCRIPTION
"Describes the minimal requirements for conformance
to the DSLite-MIB." DS-Lite MIB."
MODULE -- this module
MANDATORY-GROUPS { dsliteNATBindGroup,
dsliteTunnelGroup,
dsliteStatisticsGroup,
dsliteNotificationsGroup,
dsliteAFTRAlarmScalarGroup }
::= { dsliteCompliances 1 }

dsliteNATBindGroup OBJECT-GROUP
OBJECTS {
dsliteNATBindMappingIntRealm,
dsliteNATBindMappingIntAddressType,
dsliteNATBindMappingIntAddress,
dsliteNATBindMappingIntPort,
dsliteNATBindMappingPool,
dsliteNATBindMappingMapBehavior,
dsliteNATBindMappingFilterBehavior,
dsliteNATBindMappingAddressPooling }
STATUS current
DESCRIPTION
"A collection of objects to support basic
management of NAT binds in the NAT of the AFTR."
::= { dsliteGroups 1 }

dsliteTunnelGroup OBJECT-GROUP
OBJECTS { dsliteTunnelStartAddPreLen }
STATUS current
DESCRIPTION
"A collection of objects to support management
of ds-lite DS-Lite tunnels."
::= { dsliteGroups 2 }

dsliteStatisticsGroup OBJECT-GROUP
OBJECTS { dsliteStatisticsDiscards,
dsliteStatisticsSends,
dsliteStatisticsReceives,
dsliteStatisticsIpv4Session,
dsliteStatisticsIpv6Session }
STATUS current
DESCRIPTION
" A collection of objects to support management
of statistical information for AFTR devices."
::= { dsliteGroups 3 }

dsliteNotificationsGroup NOTIFICATION-GROUP
NOTIFICATIONS { dsliteTunnelNumAlarm,
dsliteAFTRUserSessionNumAlarm,
dsliteAFTRPortUsageOfSpecificIpAlarm }
STATUS current
DESCRIPTION
"A collection of objects to support management
of trap information for AFTR devices."
::= { dsliteGroups 4 }

dsliteAFTRAlarmScalarGroup OBJECT-GROUP
OBJECTS { dsliteAFTRAlarmB4AddrType,
dsliteAFTRAlarmB4Addr,
dsliteAFTRAlarmProtocolType,
dsliteAFTRAlarmSpecificIPAddrType,
dsliteAFTRAlarmSpecificIP,
dsliteAFTRAlarmConnectNumber,
dsliteAFTRAlarmSessionNumber,
dsliteAFTRAlarmPortNumber}
STATUS current
DESCRIPTION
"A collection of objects to surpport support management of
the information about the AFTR alarming Scalar." scalar."
::= { dsliteGroups 5 }

END

9. Security Considerations

There are three a number of management objects defined in this MIB module
with a MAX-ACCESS clause of read-write. read-write and/or read-create. Such
objects may be considered sensitive or vulnerable in some network
environments. The support for SET operations in a non-secure
environment without proper protection opens devices to attack. These
are the tables and objects and their sensitivity/vulnerability:

dsliteAFTRAlarmConnectNumber

dsliteAFTRAlarmSessionNumber

dsliteAFTRAlarmPortNumber

Notification thresholds: An attacker setting an arbitrarily low
threshold can cause many useless notifications to be generated.
Setting an arbitrarily high threshold can effectively disable
notifications, which could be used to hide another attack.

dsliteAFTRAlarmConnectNumber

dsliteAFTRAlarmSessionNumber

dsliteAFTRAlarmPortNumber

Some of the readable objects in this MIB module (i.e., objects with a
MAX-ACCESS other than not-accessible) may be considered sensitive or
vulnerable in some network environments. It is thus important to
control even GET and/or NOTIFY access to these objects and possibly
to even encrypt the values of these objects when sending them over
the network via SNMP. These are the tables and objects and their
sensitivity/vulnerability:

entries in dsliteTunnelTable

entries in dsliteNATBindTable
Objects that reveal host identities: Various objects can reveal the
identity of private hosts that are engaged in a session with external
end nodes. A curious outsider could monitor these to assess the
number of private hosts being supported by the AFTR device. Further,
a disgruntled former employee of an enterprise could use the
information to break into specific private hosts by intercepting the
existing sessions or originating new sessions into the host. If
nothing else, unauthorized monitoring of these objects will violate
individual subscribers' privacy.

entries in dsliteTunnelTable

entries in dsliteNATBindTable

Unauthorized read access to the dsliteTunnelTable would reveal
information about the tunnel topology.

SNMP versions prior to SNMPv3 did not include adequate security.
Even if the network itself is secure (for example by using IPSec), IPsec),
there is no control as to who on the secure network is allowed to
access and GET/SET (read/change/create/delete) the objects in this
MIB module.

Implementations SHOULD provide the security features described by the
SNMPv3 framework (see [RFC3410]), and implementations claiming
compliance to the SNMPv3 standard MUST include full support for
authentication and privacy via the User-based Security Model (USM)
[RFC3414] with the AES cipher algorithm [RFC3826]. Implementations
MAY also provide support for the Transport Security Model (TSM)
[RFC5591] in combination with a secure transport such as SSH
[RFC5592] or TLS/DTLS [RFC6353].

Further, deployment of SNMP versions prior to SNMPv3 is NOT
RECOMMENDED. Instead, it is RECOMMENDED to deploy SNMPv3 and to
enable cryptographic security. It is then a customer/operator
responsibility to ensure that the SNMP entity giving access to an
instance of this MIB module is properly configured to give access to
the objects only to those principals (users) that have legitimate
rights to indeed GET or SET (change/create/delete) them.

10. IANA Considerations

The MIB module in this document uses

IANA has allocated the following IANA-assigned OBJECT IDENTIFIER value and recorded
it in the SMI Numbers registry, and the
following IANA-assigned tunnelType value recorded registry in the
IANAtunnelType-MIB registry: subregistry called "SMI Network
Management MGMT Codes Internet-standard MIB" under the mib-2 branch
(1.3.6.1.2.1):

Descriptor OBJECT IDENTIFIER value
---------- -----------------------
DSLite-MIB { mib-2 XXX 240 }

IANA has recorded the following IANAtunnelType Textual Convention
within the IANAifType-MIB:

IANAtunnelType ::= TEXTUAL-CONVENTION
SYNTAX INTEGER {

dsLite ("XX")
dsLite(17) -- dslite DS-Lite tunnel
}

11. Acknowledgements

The authors would like to thanks the valuable comments made by Suresh
Krishnan, Ian Farrer, Yiu Lee, Qi Sun, Yong Cui, David Harrington,
Dave Thaler, Tassos Chatzithomaoglou, Tom Taylor, Hui Deng, Carlos
Pignataro, Matt Miller, Terry Manderson and other members of The
SOFTWIRE WG.

This document was produced using the xml2rfc tool [RFC2629].

12. References

12.1.

11.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.

[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578,
DOI 10.17487/RFC2578, April 1999,
<http://www.rfc-editor.org/info/rfc2578>.

[RFC2580]

[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Conformance Statements "Textual Conventions for SMIv2",
STD 58, RFC 2580, 2579, DOI 10.17487/RFC2580, 10.17487/RFC2579, April 1999,
<http://www.rfc-editor.org/info/rfc2580>.

[RFC2863] McCloghrie,
<http://www.rfc-editor.org/info/rfc2579>.

[RFC2580] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Conformance Statements for SMIv2",
STD 58, RFC 2580, DOI 10.17487/RFC2580, April 1999,
<http://www.rfc-editor.org/info/rfc2580>.

[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,
<http://www.rfc-editor.org/info/rfc2863>.

[RFC3411] Harrington, D., Presuhn, R., and B. Wijnen, "An
Architecture for Describing Simple Network Management
Protocol (SNMP) Management Frameworks", STD 62, RFC 3411,
DOI 10.17487/RFC3411, December 2002,
<http://www.rfc-editor.org/info/rfc3411>.

[RFC3414] Blumenthal, U. and B. Wijnen, "User-based Security Model
(USM) for version 3 of the Simple Network Management
Protocol (SNMPv3)", STD 62, RFC 3414,
DOI 10.17487/RFC3414, December 2002,
<http://www.rfc-editor.org/info/rfc3414>.

[RFC3826] Blumenthal, U., Maino, F., and K. McCloghrie, "The
Advanced Encryption Standard (AES) Cipher Algorithm in the
SNMP User-based Security Model", RFC 3826,
DOI 10.17487/RFC3826, June 2004,
<http://www.rfc-editor.org/info/rfc3826>.

[RFC4001] Daniele, M., Haberman, B., Routhier, S., and J.
Schoenwaelder, "Textual Conventions for Internet Network
Addresses", RFC 4001, DOI 10.17487/RFC4001, February 2005,
<http://www.rfc-editor.org/info/rfc4001>.

[RFC4087] Thaler, D., "IP Tunnel MIB", RFC 4087,
DOI 10.17487/RFC4087, June 2005,
<http://www.rfc-editor.org/info/rfc4087>.

[RFC4787] Audet, F., Ed. and C. Jennings, "Network Address
Translation (NAT) Behavioral Requirements for Unicast
UDP", BCP 127, RFC 4787, DOI 10.17487/RFC4787, January
2007, <http://www.rfc-editor.org/info/rfc4787>.

[RFC5591] Harrington, D. and W. Hardaker, "Transport Security Model
for the Simple Network Management Protocol (SNMP)",
STD 78, RFC 5591, DOI 10.17487/RFC5591, June 2009,
<http://www.rfc-editor.org/info/rfc5591>.

[RFC5592] Harrington, D., Salowey, J., and W. Hardaker, "Secure
Shell Transport Model for the Simple Network Management
Protocol (SNMP)", RFC 5592, DOI 10.17487/RFC5592, June
2009, <http://www.rfc-editor.org/info/rfc5592>.

[RFC6333] Durand, A., Droms, R., Woodyatt, J., and Y. Lee, "Dual-
Stack Lite Broadband Deployments Following IPv4
Exhaustion", RFC 6333, DOI 10.17487/RFC6333, August 2011,
<http://www.rfc-editor.org/info/rfc6333>.

[RFC6353] Hardaker, W., "Transport Layer Security (TLS) Transport
Model for the Simple Network Management Protocol (SNMP)",
STD 78, RFC 6353, DOI 10.17487/RFC6353, July 2011,
<http://www.rfc-editor.org/info/rfc6353>.

[RFC7659] Perreault, S., Tsou, T., Sivakumar, S., and T. Taylor,
"Definitions of Managed Objects for Network Address
Translators (NATs)", RFC 7659, DOI 10.17487/RFC7659,
October 2015, <http://www.rfc-editor.org/info/rfc7659>.

12.2.

11.2. Informative References

[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Textual Conventions for SMIv2",
STD 58, RFC 2579, DOI 10.17487/RFC2579, April 1999,
<http://www.rfc-editor.org/info/rfc2579>.

[RFC2629] Rose, M., "Writing I-Ds and RFCs using XML", RFC 2629,
DOI 10.17487/RFC2629, June 1999,
<http://www.rfc-editor.org/info/rfc2629>.

[RFC3410] Case, J., Mundy, R., Partain, D., and B. Stewart,
"Introduction and Applicability Statements for Internet-
Standard Management Framework", RFC 3410,
DOI 10.17487/RFC3410, December 2002,
<http://www.rfc-editor.org/info/rfc3410>.

[RFC3826] Blumenthal, U., Maino, F., and K. McCloghrie, "The
Advanced Encryption Standard (AES) Cipher Algorithm in

Acknowledgements

The authors would like to thank the
SNMP User-based Security Model", RFC 3826,
DOI 10.17487/RFC3826, June 2004,
<http://www.rfc-editor.org/info/rfc3826>.

[RFC5591] Harrington, D. and W. Hardaker, "Transport Security Model following for the Simple Network Management Protocol (SNMP)",
STD 78, RFC 5591, DOI 10.17487/RFC5591, June 2009,
<http://www.rfc-editor.org/info/rfc5591>.

[RFC5592] their valuable
comments: Suresh Krishnan, Ian Farrer, Yiu Lee, Qi Sun, Yong Cui,
David Harrington, D., Salowey, J., Dave Thaler, Tassos Chatzithomaoglou, Tom Taylor,
Hui Deng, Carlos Pignataro, Matt Miller, Terry Manderson, and W. Hardaker, "Secure
Shell Transport Model for the Simple Network Management
Protocol (SNMP)", RFC 5592, DOI 10.17487/RFC5592, June
2009, <http://www.rfc-editor.org/info/rfc5592>.

[RFC6353] Hardaker, W., "Transport Layer Security (TLS) Transport
Model for other
members of the Simple Network Management Protocol (SNMP)",
STD 78, RFC 6353, DOI 10.17487/RFC6353, July 2011,
<http://www.rfc-editor.org/info/rfc6353>. Softwire working group.

Authors' Addresses

Yu Fu
CNNIC
No.4 South 4th Street, Zhongguancun
Hai-Dian District, Beijing, Beijing 100190
P.R.
China

Email: fuyu@cnnic.cn

Sheng Jiang
Huawei Technologies Co., Ltd
Q14, Huawei Campus, No.156 Beiqing Road
Hai-Dian District, Beijing, Beijing 100095
P.R.
China

Email: jiangsheng@huawei.com

Jiang Dong
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.
China

Email: knight.dongjiang@gmail.com

Yuchi Chen
Tsinghua University
Department of Computer Science, Tsinghua University
Beijing 100084
P.R.
China

Email: flashfoxmx@gmail.com