Internet DRAFT - draft-irtf-hiprg-proxies
draft-irtf-hiprg-proxies
Network Working Group D. Zhang
Internet-Draft X. Xu
Intended status: Informational Huawei Technologies Co.,Ltd
Expires: September 10, 2012 J. Yao
CNNIC
Z. Cao
China Mobile
March 9, 2012
Overview of HIP Proxy Scenarios and Solutions
draft-irtf-hiprg-proxies-05
Abstract
A Host Identity Protocol (HIP) proxy is a host that holds the keying
material, and participates in HIP-based communications, on behalf of
one or more hosts.
HIP proxies play an important role in the transition from the current
Internet architecture to the HIP architecture. A core objective of a
HIP proxy is to facilitate the communication between legacy (or Non-
HIP) hosts and HIP hosts while not modifying the host protocol
stacks. In this document, the legacy hosts served by proxies are
referred to as Legacy Hosts (LHs). Currently, various design
solutions of HIP proxies have been proposed. These solutions may be
applicable in different working circumstances. In this document,
these solutions are investigated in detail to compare their
effectiveness in different scenarios.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 10, 2012.
Copyright Notice
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Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. HIP Proxies . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Essential Functionality of HIP Proxies . . . . . . . . . . 5
3.2. A Taxonomy of HIP Proxies . . . . . . . . . . . . . . . . 6
3.3. DI Proxies . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4. N-DI Proxies . . . . . . . . . . . . . . . . . . . . . . . 9
3.5. Distributed Implementation of DI Proxies . . . . . . . . . 9
3.5.1. Distributed DI-HIT Proxies . . . . . . . . . . . . . . 10
3.5.2. Distributed DI-NAT Proxies . . . . . . . . . . . . . . 10
3.5.3. Distributed DI-transparent Proxies . . . . . . . . . . 10
3.6. DI Proxies Supporting Communication Initiated by HIP
hosts . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4. Issues with LBMs in Supporting LHs to Initiate
Communication . . . . . . . . . . . . . . . . . . . . . . . . 12
4.1. LBMs adopting Load Balancers . . . . . . . . . . . . . . . 12
4.1.1. Load Balancer Supporting DI Proxy Components . . . . . 13
4.1.2. Load Balancer Supporting N-DI Proxy Components . . . . 13
4.2. LBMs without Load Balancers . . . . . . . . . . . . . . . 14
4.2.1. Issues Caused by Intercepting DNS Lookups . . . . . . 14
4.2.2. Issues with LBMs in Capturing and Processing
Replies from HIP hosts . . . . . . . . . . . . . . . . 15
5. Issues with LBMs that also Support HIP Hosts to Initiate
Communication . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1. DNS Resource Records for LHs . . . . . . . . . . . . . . . 17
5.2. An Asymmetric Path Issue . . . . . . . . . . . . . . . . . 18
6. Issues with Dynamic Load Balancing . . . . . . . . . . . . . . 20
6.1. Operations of DI-HIT Proxies . . . . . . . . . . . . . . . 21
6.2. Operations of DI-NAT Proxies . . . . . . . . . . . . . . . 21
6.3. Operations of DI-Transparent Proxies . . . . . . . . . . . 21
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 22
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
9. Security Considerations . . . . . . . . . . . . . . . . . . . 22
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
11.1. Normative References . . . . . . . . . . . . . . . . . . . 23
11.2. Informative References . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
The Host Identity Protocol (HIP) and its architecture propose an
alternative to the dual use of IP addresses as "locators" (routing
labels) and "identifiers" (endpoint, or host, identifiers). It
introduces a new host identifier layer between the network layer and
the transport layer so as to comprehensively address the issues of
mobility, multi-homing and net-layer security. The Host Identities
(HIs) of HIP enabled hosts are cryptographically verifiable. When
two HIP hosts initiate their communication, they need to perform a
handshaking process to authenticate each other and distribute
symmetric keys for securing subsequent packet exchanges. A HIP host
and a legacy host cannot communicate with each other directly by
using HIP, since HIP is designed to communicate between HIP hosts.
As core components of HIP deployment solutions, HIP proxies have
attracted increasing attention from both industry and academia. A
HIP proxy is a middlebox located between a legacy host and a HIP
enabled host. With the assistance of a HIP proxy, a legacy host can
communicate with its desired HIP host without updating its protocol
stack.
Currently, multiple research efforts are engaged in both design and
performance assessment of HIP proxies. In this document, we attempt
to investigate several important alternatives and compare their
effectiveness in different scenarios. There has previously been a
detailed discussion of HIP proxies in [SAL05]. This document can be
regarded as a complement of that paper. Some new topics (e.g., the
asymmetric path issues occurred in the load-balancing mechanisms for
HIP proxies and the necessity of extending the HIP RR for HIP
proxies) are discussed in the document. Theoretically, legacy hosts
and the HIP hosts which the legacy hosts intend to communicate with
can be located anywhere in the network. However, in this document,
without mentioning otherwise, it is assumed that legacy hosts are
located within a private network and HIP hosts are located in the
public network, since this is the most important scenario that HIP
proxies are expected to support [SAL05].
The remainder of this document is organized as follows. Section 2
lists the key terminology used in this document. In section 3, the
essential functions of HIP proxies are indicated, and a
classification of HIP proxies is proposed to facilitate subsequent
analysis. In section 4, we analyze the issues that HIP proxies have
to face in constructing a Load Balancing Mechanism (LBM) which
facilitates communication initiated by LHs. Section 5 analyzes the
issues that HIP proxies in a LBM have to face if they also need to
support communication initiated by HIP hosts. In section 6, we
investigate the issues that HIP proxies have to deal with in
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supporting dynamic load balancing and redundancy. Section 7 provides
conclusions, and Section 8 notes that no requests of IANA are made.
Section 9 is the security considerations.
2. Terminology
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].
BEX: HIP Base Exchange, a two-party cryptographic protocol used to
establish communications context between HIP enabled hosts.
LHs: Legacy Hosts which are represented as HIP hosts by HIP proxies.
DI Proxy: DNS lookup Inspecting Proxy, A HIP proxy which needs to
inspect or modify DNS lookups between the hosts it serves and their
DNS servers or resolvers so as to collect essential information for
subsequent service.
HA: HIP Association, an IP-layer communications context for two HIP
enabled host generated during a BEX execution.
LBM: Load Balancing Mechanism, a mechanism which is able to
distribute workload across multiple compments to avoid overload on a
single component and increase the availability of the whole system.
N-DI proxy: Non-DNS lookup Inspecting Proxy, A HIP proxy which does
not need to intercept DNS lookups between the hosts and DNS servers
in order to perform HIP proxying correctly.
3. HIP Proxies
3.1. Essential Functionality of HIP Proxies
A primary function of HIP proxies is to facilitate the communication
between legacy (or Non-HIP) hosts and HIP hosts while not modifying
the host protocol stacks. In order to achieve this, a HIP proxy
needs to intercept the packets transported between LHs and HIP hosts
before they arrive at their destinations. Upon capturing such a
packet, a HIP proxy needs to transfer it into the format which can be
recognized by the destination host.
Assume a proxy intercepts a packet sent out by a LH. If the packet
is destined to a HIP host, the proxy first tries to find out whether
there is an appropriate HIP association (HA) in its local database to
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process the packet. If the HA exists, the proxy then uses the key
maintained in the HA to encrypt the payload in the packet, transmits
the packet into the HIP compatible format, and transfers it to the
HIP host. However, if there is no proper HA found, the proxy needs
to use the HI and HIT assigned to the LH to carry out a HIP Base
Exchange (BEX) and generate a new HA with the HIP host. The newly
generated HA is then maintained in the local database.
Similarly, when processing a packet from a HIP host, the proxy needs
to find a proper HA and use the keying material in the HA to decrypt
the packet, and thus the packet is transferred into an ordinary IP
packet and forwarded to the legacy host.
3.2. A Taxonomy of HIP Proxies
In practice, there are various design alternatives for HIP proxies.
To benefit the analysis, in this document HIP proxies are classified
into DNS lookup Intercepting Proxies (DI proxies) and Non-DNS lookup
Intercepting Proxies (N-DI proxies). As indicated by the name, a DI
proxy needs to intercept DNS lookups in order to correctly process
the follow-up communication between LHs and HIP hosts, while N-DI
proxies do not have to.
Note that a DI proxy implementation may also be designed to cooperate
with a resolution server other than DNS. That is, the DI proxy is
able to intercept the lookup between a host that the proxy serves and
the resolution server to benefit the pacekt transforming job.
However, currently DNS is the only resolution mechanism analyzed and
extended to support HIP communication. Hence, DNS is only resolution
mechanism considered in this document.
To avoid confusion, in the remainder of this document, the terms
"lookup" and "answer" are used in specific ways. A lookup refers to
the entire process of translating a domain name for a legacy host.
The answer of a lookup is the response from a resolution server which
terminates the lookup.
3.3. DI Proxies
Usually, before a host communicates with a remote host, the legacy
host needs to consult a DNS server for the IP address of its
destination. On this premise, a DI proxy can effectively identify
the HIP hosts which legacy hosts MAY contact in near future by
intercepting DNS lookups.
In practice, it is common to deploy one or multiple DNS resolvers for
a private network. A host in the private network can thus send its
queries to a resolver instead of communicating with authoritative DNS
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servers directly. If the resolver has not cached the requested RRs,
it will try to collect them from authoritative DNS servers. In a
lookup process, a resolver MAY have to contact multiple authoritative
DNS servers before it eventually gets the desired DNS RRs.
On the occasions where a resolver is located outside a private
network, a HIP proxy located at the border of the network can
intercept the DNS queries from LHs and then use the FQDNs obtained
from the queries to initiate a new DNS lookup to the resolver to
inquire about the desired information (AAAA RRs, HIP RRs, and etc.).
If the host that the legacy host intends to communicate with is HIP
enabled, the DNS resolver will hand out a HIP RR associated with an
AAAA RR to the proxy. After maintaining the needed information
(e.g., HITs, HIs, and IPs addresses of the HIP hosts) in the local
database for future usage, the proxy returns an answer with an AAAA
RR to the legacy host.
When the resolver is located inside the private network, conditions
are a little more complex. If a proxy is deployed on the path
between LHs and the resolver, it can operate the same as what is
illustrated in the above paragraph. The proxies which can be
deployed in this way are introduced in the remainder of this sub-
section. However, if a proxy is located at the border of the network
(i.e., between the resolver and authoritative DNS servers), the proxy
has to intercept the DNS lookups between the resolver and
authoritative DNS servers. Because the resolver MAY have to contact
multiple authoritative DNS servers to get a desired answer, for the
purpose of efficiency, the proxy can only inspect the responses from
DNS servers and find out DNS answers. Because the answer of a DNS
lookup does not contain any NS RR, it can be easily distinguished
from the intermediate responses. After identifying a DNS answer, a
DI proxy can locate the DNS server maintaining the desired RRs from
the packet header and identify the FQDN of the inquired host from the
packet payload. Then, the proxy initiates an independent lookup to
the DNS server to check whether the host is HIP enabled. If it is,
the proxy maintains the information of the host for future usage and
returns an answer with an AAAA RR to the resolver.
Besides intercepting DNS lookups, some kinds of DI proxies also
modify the contents of the AAAA RRs in the DNS answers for LHs to
enhance the efficiency or deploying flexibility. For instance,
[RFC5338] indicates that a HIP proxy can return HITs rather than IP
addresses in DNS answers to LHs. Consequently, when sending data
packets, LHs will use the those HITs as the destination addresses.
The HIP proxy can then advertise a route of the HIT prefix to attract
the packet for HIP hosts. [PAT07] also proposes a solution in which
a HIP proxy maintains an IP address pool. When sending a DNS answer
to a LH, the proxy selects an IP address from its pool and inserts it
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within the answer. The legacy host will regard this IP address as
the IP address of the peer it intends to communicate with. In the
subsequent communication, when the host sends a packet for the remote
HIP host, it will use the IP address assigned by the proxy as the
destination address. Therefore, the HIP proxy can intercept the
packets for the HIP hosts by advertising the routes of the IP
addresses in its pool. In the remainder of this document, these two
types of proxies are referred to as DI-HIT proxies and DI-NAT proxies
respectively, and the DI proxies which do not modify the contents of
DNS answers (i.e., return the IP addresses of HIP hosts in answers)
are referred to as DI-transparent proxies.
Compared with DI-HIT and DI-NAT proxies, DI-transparent proxies show
their limitations in multiple ways. For instance, in practice it is
reasonable for a LH to publish the IP address of its proxy instead of
its own IP address within its DNS AAAA RR so that the packets for the
LH will be firstly forwarded to the proxy. Therefore, when a LH
served by a DI-transparent proxy attempts to communicate with two
remote LHs served by a same HIP proxy, it is difficult for the host
to distinguish one remote host from the other as they both use the
same IP address. In addition, DI-transparent proxies cannot work
properly in the circumstance where HIP hosts renumber their IP
addresses during the communication due to, e.g., mobility or re-
homing. For DI-HIT or DI-NAT proxies, these issues can be largely
mitigated as the IP addresses of HIP hosts will never be used by DI-
HIT or DI-NAT proxies to identify hosts.
Moreover, it is difficult for DI-transparent proxies to advertise
routing information to attract the packets transported between LHs
and remote HIP hosts. Consequently, they need to be deployed at the
borders of private networks. DI-HIT (or DI-NAT) proxies, however,
can easily attract the packets for HIP hosts to themselves by
advertising routes to them because the packets destined to HIP hosts
use HITs (or the IP addresses selected from pools) as their
destination addresses. Hence, they can be flexibly deployed inside
the networks. Therefore, in private networks which resolvers are
located inside, DI-HIT or DI-NAT proxies can be deployed on the path
between the resolvers and LHs and reduce the overhead on the proxies
imposed by intercepting DNS lookups.
DNSSEC [RFC4035] is desigend to prevent attackers from tampering or
forging DNS lookups between resolvers and DNS server. This solution
may affect the deployment of HIP proxies. For instance, DI-HIT and
DI-NAT proxies need to modify the contents of DNS answers, and thus
they should be only deployed on the path between legacy hosts and
their resolvers if DNSSEC is deployed. Therefore, a DI-HIT proxy (or
a DI-NAT proxy) cannot be deployed in the middle of DNSSEC-enabled
resolvers and authoritative DNS servers.
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3.4. N-DI Proxies
Unlike DI proxies, an N-DI proxy does not need to intercept DNS
lookups transported between LHs (or resolvers) and DNS servers.
In [SAL05], it is indicated that an N-DI proxy can maintain a list of
the information of the HIP hosts if the HIP hosts that LHs intend to
contact are predictable. After intercepting a packet from a LH, the
proxy can ensure the packet is for a HIP host if the destination
address of the packet is maintained in the list.
In the circumstances where it is difficult to predict the HIP hosts
that LHs intend to contact in advance, an N-DI proxy needs to consult
DNS servers to find out whether the destination IP address of a
packet is associated with a HIP host or a legacy host. The
information obtained from the DNS servers can be maintained within
two lists. One list is for the information of HIP hosts; the other
is for the information of legacy hosts. When intercepting a packet,
the N-DI first compares the destination address of the packet against
the addresses in the lists to find out whether the destination of the
packet is HIP enabled. If the address is not maintained in the
lists, the proxy then has to consult resolution systems and maintains
the information of the host which the packet is aimed for in the
correspondent list, according to the answers from resolution systems.
3.5. Distributed Implementation of DI Proxies
As discussed above, DI proxies have to intercept the DNS lookup
packets between legacy hosts and DNS servers in order to correctly
transform the packets transported between LHs and HIP hosts. This
requires that a DI proxy be deployed on the boundary of the private
network or on the path where LHs and the DNS resolver transport their
lookup packets. In the circumstance where DNSSEC is deployed, a DI
proxy cannot even be deployed on the boundary of the private network
either, if the proxy needs to modify DNS lookup packets. Such
inflexibility MAY be undesirable under certain circumstances.
This section analyzes a distributed design option of DI proxies which
improves the deployment flexibility of DI proxies and addresses the
DNSSEC issue by deploying the DNS related functionality (i.e.,
intercepting and modifying the DNS communication) and the packet
transforming functionality on different components. The component
performing the DNS lookup interception is referred to as the DNS
lookup inspector while the component performing the packet
transformation is referred to as the proxy component. A DNS lookup
inspector is located in a place where it can intercept and modify DNS
lookups. In practice, a DNS resolver can also be extended to act as
an inspector.
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3.5.1. Distributed DI-HIT Proxies
The DNS lookup inspector of a distributed DI-HIT proxy returns HITs
in DNS answers to LHs. Therefore, the associated DI-HIT proxy can
advertise routing information inside the private network to attract
the packets using HITs as destination addresses. Additionally, the
inspector needs to forward other information (e.g., IP addresses of
the HIP hosts and RVSes) of the HIP hosts contained in DNS RRs to the
DI-HIT proxy component so that the proxy can perform HIP base
exchanges with the HIP hosts on behavior of LHs.
A DI-HIT proxy component can work with multiple DNS lookup
inspectors, and thus it is possible for a DI-HIT proxy component to
be deployed in public networks to support multiple private networks.
This property is useful when Internet services providers (ISPs)
intend to facilitate the legacy hosts in the private networks without
HIP proxies to communicate with HIP hosts.
A DNS lookup inspector can also be associated with mutiple DI-HIT
proxy components in order to distribute the traffic process overhead
on different proxy components. This deployment is discussed in
Section 4 in details.
3.5.2. Distributed DI-NAT Proxies
A DNS lookup inspector of a distributed DI-NAT proxy needs to not
only return the IP addresses in the address pool of the DI-NAT proxy
component but also transfer the mapping information of the IP
addresses and the correspondent HIP hosts to the DI-NAT proxy
component. Moreover, the resolver needs to maintain the mapping
information so as to avoid assigning an IP address for multiple HIP
hosts concurrently.
Similar with Distributed DI-HIT Proxies, a DI-NAT proxy component can
also be deployed in a public network. In this case, the addresses in
the address pool MUST be routable in the public network. Moreover, a
DNS lookup inspector can also be associated with mutiple DI-NAT proxy
components in order to distribute the traffic process overhead on
different proxy components. This deployment is discussed in Section
4 in details.
3.5.3. Distributed DI-transparent Proxies
A DNS lookup inspector of a distributed DI-transparent proxy does not
need to modify DNS answers, but it needs to forward the IP addresses
and HIs of queried HIP hosts to the DI-NAT proxy component. In this
case, a DI-transparent proxy component MUST be deployed on the
boundary of the private network in order to guarantee that it can
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intercept packets exchagne the local LHs and the remote HIP hosts.
3.6. DI Proxies Supporting Communication Initiated by HIP hosts
In the scenarios where HIP hosts initiate communication, the HIP-
enabled host first launches the DNS query to retrieve the remote
host's HI/HIT or RVS address. Without knowing if the remote host
supports HIP-based exchange, the HIP host is expecting to receiving
the remote host HIP based Identities.
+----------+ +---------+ +-------------+
| HIP Host | | Proxy | | non-HIP host|
+----------+ +---------+ +-------------+
| 1.DNS Query QTYPE=HIP | |
|---------------------------->| |
| 2.DNS Response HIT&HI | |
|<----------------------------| |
| 3.DNS Query QTYPE=A | |
|---------------------------->| |
| 4.DNS Response IP-A | |
|<----------------------------| |
| 5-8. | |
| BASE EXCHANGE(I1,R1,I2,R2) | |
|<--------------------------->| |
| | |
|9.HIP PACKET FORMAT | 10. LEGACY IP PACKET |
|---------------------------->|-------------------------->|
| | |
|11.HIP PACKET FORMAT | 12. LEGACY IP PACKET |
|<----------------------------|<--------------------------|
| | |
| | |
Figure 1: Translation Proxy
As shown in Figure 1 the proxy intercepts the DNS query and
iteratively forward the query to the global DNS to find an answer.
If the responder is HIP enabled, it will have its HI or HIT
registered in the DNS and the proxy will get an answer. However, if
the responder is not HIP aware, and only has type A or AAAA records
in the DNS system, the query for QTYPE=HIP will fail. On detecting
that the responder is not HIP aware, the DNS proxy will use a
temporary HI/HIT (T-ID) generated locally and reply this temporary
HI/HIT to the initiator. The proxy will associate the T-ID with the
IP address of the responder. After the HIP RR query reponse, the
Type-A query response is followed, via which the initiator get the
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the IP address of the proxy node.
The HIP base exchange will proceed between the initiator and the
proxy (step.5-8). Then, the HIP association is established between
the initiator and the proxy, i.e., between the host's HI and the
temporary HI assigned to the responder by the proxy. If the
initiator starts data communication towards the responder, the proxy
on the data path will be responsible for the translation between HIP
packets and IP packets. First, the proxy will de-capsulate the
packet and decrypt the packet to get the original IP packet inside.
By inspecting the HIP header after the IP header, the proxy is aware
of the destination's HIT/LSI. If the HIT and LSI are mapped to one
of the responder's IP addresses, the proxy will translate the packet
with the destination address as the responder's IP address, and
source address as the proxy IP address. The destination port is kept
unchanged, but the source port can be dynamically assigned.
4. Issues with LBMs in Supporting LHs to Initiate Communication
If there is only a single HIP proxy deployed for a private network,
the proxy may become the cause of a single-point-of-failure. In
addition, when the number of the users increases, the overhead
imposed on the proxy may overwhelm its capability, which makes the
proxy a bottleneck of the whole mechanism. A typical solution to
mitigate this issue is to organize multiple proxies to construct a
LBM. By sharing overhead of processing packets amongst multiple HIP
proxies, a LBM can be more scalable and fault tolerant.
4.1. LBMs adopting Load Balancers
Load balancers have been widely utilized in the design of LBMs. When
adopted in a HIP proxy LBM, a load balancer needs to pool all proxy
resources and be located in a position where it can intercept DNS
lookups or modify DNS lookups if necessary. In addition, the load
balancer needs to distribute the information it learned from the DNS
lookups to the appropriate proxies it manages. In some cases, the
load balancer MAY also need to take the responsibility of forwarding
the data packets to proper proxies.
Logically, a LBM adopting Load balancer can be regarded as a
variation of a distributed HIP Proxy. A load balancer is an extended
DNS lookup inspector that is able to distribute load to different DI
proxy components according to pre-specified policies. The policies
adopted by different load balancers can be varied. A load balancer
may require that all the packets from a LH be processed by the same
HIP proxy while other balancers may expect all the packets for a HIP
host to be processed by the same HIP proxy.
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4.1.1. Load Balancer Supporting DI Proxy Components
In a LBM where a load balancer manages multiple DI-HIT proxy
components, the load balancer MUST be able to intercept DNS lookup
packets and forward the information about the HIP hosts being queried
to the proxy components according to certain policies. Additionally,
the load balancer needs to modify DNS lookup packets and return HITs
in DNS answers to LHs (or resolvers). In order to intercept the
packets sent from LHs to HIP hosts, the load balancer MAY need to
advertise a route of the HIT prefix. After intercepting a data
packet from a LH, the balancer needs to forward the packet to the
proxy component which can correctly process it.
In a LBM where a load balancer manages multiple DI-NAT proxy
components, the load balancer MUST be able to intercept and forward
the information about the HIP hosts being queried to the appropriate
proxy components. Additionally, the load balancer needs to modify
DNS answers and return IP addresses in the address pools of the
assigned DI-NAT proxies in DNS answers to LHs (or resolvers). DI-NAT
proxies can advertise the routes of the IP addresses in the pools so
that the load balancer does not have to intercept the packets between
LHs and HIP hosts.
In a LBM where a load balancer manages multiple DI-transparent proxy
components, the load balancer MUST be able to intercept and forward
the information about the HIP hosts being queried to the appropriate
proxy components. The load balancer does not modify DNS answers, but
it needs to be located in a place (e.g., the egress of the private
network) where it is able to intercept the packets sent from LHs to
HIP hosts and forward them to the assigned proxies.
4.1.2. Load Balancer Supporting N-DI Proxy Components
When the HIP proxies that a load balancer manages are N-DI proxies,
the load balancer does not intercept DNS lookups. Instead, the load
balancer MUST be located in a place (e.g., the egress of the private
network) where it is able to intercept the packets sent to HIP hosts.
When receiving a packet from a LH, the load balancer needs to decide
the appropriate proxies which the pacekts should be forward to (e.g.,
according to the prefix of the destination address of the packet).
In this solution, because the load balancer does not forward the
information about the HIP hosts being queried to the appropriate
proxies, the N-DI proxy components need to consult resolution systems
themselves.
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4.2. LBMs without Load Balancers
Generally, in a LBM without a load balancer, there are two methods to
distribute communication between LHs and HIP hosts among different
HIP proxies. The first solution is to divide the LHs in the private
network into different groups (e.g., according to their IP
addresses), with the LHs in different sections served by different
HIP proxies. The second solution is to divide the HIP hosts in the
Internet into multiple groups (e.g., according to their HITs or IP
addresses); every HIP proxy serves all the LHs in the private network
but only processes the packets to and from the HIP hosts in a group.
Abstractly, the two solutions are identical. However, the first
solution requires a private network to be divided into multiple sub-
networks, and each of them is served by a HIP proxy. This may
introduce additional modification to the topology of the private
network, which is not desired in many cases. Therefore, in the
design of existing LBM solutions, the second type of solution can be
more preferred. In the remainder of this document, the second one is
mainly discussed.
4.2.1. Issues Caused by Intercepting DNS Lookups
+--------------------+ +------------------+
| | | |
| +---+-------+ | |
| +-----------+ |HIP proxy 1+---+ +---------+ |
| |Legacy Host| +---+-------+ | |HIP Host | |
| +-----------+ | . | | (HH1) | |
| | . | +---------+ |
| +---+--------+ | |
| |HIP proxy n +--+ |
|Private Network +---+--------+ | Public Network |
| | | |
+--------------------+ +------------------+
Figure 1: An example of LBM
Figure 1 illustrates a simple LBM without a load balancer. In this
mechanism, n proxies are deployed at the border of a private network.
If such proxies are DI-HIT proxies, in order to share the overhead of
processing data packets, each proxy needs to advertise a route of the
HIT section it takes responsibility for. In addition, each proxy
also needs to advertise a route of a section of IP addresses (or a
default route for the entire IP address namespace) inside the private
network to intercept DNS lookups. A problem occurs when the DNS
lookups and the data packets sent by a legacy host are intercepted by
different proxies. In such a case, the proxy intercepting a data
packet will lack essential knowledge to correctly process it. If the
proxies adopted in Figure 1 are DI-transparent proxies, then each
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proxy only needs to advertise a route of a section of IP addresses
which is adopted to intercept both DNS lookups and data packets. On
this occasion, if a HIP host and the DNS server maintaining its RR
fall into two different IP sections, the DI-transparent proxy
intercepting the lookups for the HIP host will not be the one
intercepting subsequent data packets.
A candidate solution to the problem that DI-HIT-proxy-based LBMs and
DI-transparent-proxy-based LBMs face is to propagate the mapping
information obtained from DNS lookups amongst HIP proxies.
Therefore, after intercepting a DNS conversation, a proxy can forward
the learned information to the proxy expected to process the
subsequent data packets. Alternatively, a proxy can attempt to
collect required information from resolution systems after
intercepting a data packet. This approach, however, imposes
additional overhead for DI-proxies to consult resolution servers.
If the proxies in Figure 1 are DI-NAT proxies, the problem is
eliminated. In a DI-NAT-proxy-based LBM, each DI-NAT proxy needs to
advertise two routes: a route to one of the IP addresses in the pool
and a route to one of a section of IP addresses for intercepting DNS
lookups. After intercepting a DNS lookup, a DI-NAT proxy will return
an IP address within the pool in the answer to the requester (a LH or
a resolver), which can ensure that subsequent data packets will be
delivered to the same proxy.
If a DNS resolver supporting DI proxies can forward the mapping
information obtained from DNS lookups to appropriate HIP proxies, the
issue can be easily addressed. In this case, the DNS resolver
actually acts as a load balancer.
4.2.2. Issues with LBMs in Capturing and Processing Replies from HIP
hosts
Theoretically, when representing a LH to communicate with a HIP host
in the public network, a HIP proxy can use either an IP address it
possesses or the IP address of the LH as the source address of the
packets forwarded to the HIP host. However, in practice, the latter
option may cause an asymmetric traffic issue in the load balancing
scenarios where multiple HIP proxies provide services for the same
group of LHs. Assume there are two HIP proxies located at the border
of a private network. If the proxies adopt the latter solution, they
need to advertise the routes of the LHs in the public network
respectively. As a result, it is difficult to guarantee the packets
transported between a legacy host and a HIP host are bound to the
same HIP proxy, and thus after a proxy intercepts a packet it may
lack the proper HIP association to process it.
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A possible solution to address this problem is to share HIP state
information (e.g., HIP associations, sequence number of IPsec
packets) amongst the related HIP proxies in a real-time fashion.
However, during communication, some context information such as the
sequence numbers of ESP packets can change very fast. It is
infeasible to synchronize the ESP message counters for every
transmitted or received packet, since such operations will occupy
large amounts of bandwidth and seriously affect the performance of
HIP proxies. [Nir 2009] indicates that this issue can be partially
mitigated by synchronizing ESP message counters only at regular
intervals, for instance, every 10,000 packets.
An issue similar to the one mentioned above is discussed in [TSC05],
and an extended HIP base exchange is proposed. But the proposed
solution only tries to help HIP-aware middleboxes obtain the SPIs
generated in a HIP base exchange and cannot be directly used to
address this problem.
When adopting the preceding option, proxies need to advertise the
routes to their addresses in the public network respectively, so that
the packets transported between a LH and a HIP host are intercepted
by the same proxy. The issue discussed above can thus be addressed.
In the following discussions, without mentioning otherwise we assume
that a HIP proxy uses one of its IP addresses as the source IP
addresses of the packets which it sends to a HIP host.
5. Issues with LBMs that also Support HIP Hosts to Initiate
Communication
Apart from the basic functions (i.e., supporting LHs to initiate
communication with HIP hosts), in many typical scenarios, HIP proxies
MAY also need to facilitate the communication initiated by HIP hosts.
In this section, we attempt to analyze the issues that a HIP proxy
has to face in the case where HIP hosts proactively initiate
communication with LHs.
In order to support the communication initiated by HIP hosts, the HIP
proxies of a private network should have the knowledge essential to
represent its LHs to perform HIP base exchanges with remote HIP
hosts. Such knowledge consists of the IP addresses of the LHs in the
private network, their pre-assigned HITs, the corresponding HI key
pairs, and any other necessary information. In addition, such
information of the LHs should be advertised in resolution systems
(e.g., DNS and DHT) as HIP hosts. Otherwise, a HIP host has to
obtain the HIT of the LH in the opportunistic model which, however,
should only be adopted in secure environments.
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5.1. DNS Resource Records for LHs
In difference impelementations, the AAAA RR of a LH can consist of
either the IP address of the LH or the address of its HIP proxy. In
the preceding approach, the routing infrastructure will try to
forward the packets for the LH to the host directly. Therefore, in
this case, HIP proxies MUST be located on the path of such packets to
intercept them. In the latter approach, the packets for a legacy
host are first forwarded to the associated HIP proxy. Compared with
the preceding approach, the latter approach enables a proxy to be
deployed in a more flexible way. In addition, this approach can be
more efficient in the private networks where LHs and HIP hosts are
deployed in an intermixed way, since the HIP proxy will not have to
intercept the packets transported between HIP hosts. However, the
latter approach may cause problems when processing packets sent by
legacy hosts in the public network. Normally, a HIP proxy needs to
serve a number of LHs. When using the latter approach, the packets
destined to these LHs will have a same destination address (i.e., the
IP address of the proxy). Therefore, when receiving a packet from a
legacy host located in the public network, the proxy may find it
difficult to identify the LH to which the packet should be forwarded.
A simple approach which combines the advantages of the above two
solutions but avoids their disadvantages is to extend the HIP RR
[RFC5205] with a new proxy field, which contains the IP address of a
HIP proxy. In the extended HIP RR of a LH, the proxy field consists
of the IP address of its HIP proxy, while the proxy field in the RR
of an ordinary HIP host is left empty. Therefore, a HIP host
intending to communicate with the LH can obtain the IP address of the
proxy from DNS servers and set it as the destination address of the
packets. The packets are then routed to the proxy. When a non-HIP
host intends to communicate with the legacy host, it can obtain the
IP address of the legacy host from the AAAA RR as usual and set it as
the destination address of the packets; the packets are then
transported to legacy host directly.
It is also possible to use the RVS field in a HIP RR to transport the
information of a HIP proxy. However, in certain scenarios, a special
proxy field can bring additional security benefits. For instance, it
is normally assumed that the BEX protocol is able to establish a
security channel for the hosts on the both sides of communication to
securely exchange messages. However, this presumption MAY be no
longer valid in the presence of HIP proxies, as the messages between
legacy hosts and proxies can be transported in plain text. With the
Proxy field, it is easy to distinguish the legacy hosts represented
by HIP proxies from the ordinary HIP hosts. Therefore, a HIP host
can assess the risks of exchanging sensitive information with its
communicating peers in a more precise way.
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5.2. An Asymmetric Path Issue
In a load balancing scenario where multiple HIP proxies are deployed
at the border of a private network, the packets transported between a
legacy host and a HIP host MAY be routed via different HIP proxies.
Therefore, when a packet is intercepted by a HIP proxy, the proxy may
find that it lacks essential knowledge to appropriately process the
packet. Hence, an asymmetric path issue occurs.
In order to explain the asymmetric path issue in more detail, let us
revisit the LBM illustrated in Figure 1. In addition, assume that
the HIP proxies are DI-HIT proxies and their IP addresses are
maintained in the DNS RRs of the LHs. When a HIP host (e.g., HH1)
looks up a legacy host at a DNS server, the DNS server returns the IP
addresses of all the HIP proxies in an answer (see Figure 2). Upon
receiving the answer, HH1 needs to select an IP address and sends an
I1 packet to the associated HIP proxy. Assume the HIP proxy 1 is
selected. Then after a base exchange, HIP proxy1 and HH1 establish a
HIP association respectively. Upon receiving the first data packet
from HH1, the HIP proxy uses the HIP association to de-capsulate the
packet and forward it to the legacy host. In the forwarded packets,
the HIT of HH1 is adopted as the source IP address, and thus the HIT
of HHI is adopted as the destination address in the reply packets
sent by the legacy host. Assume that the HIT of HH1 is within the
section managed by HIP proxy n. According the routes advertised by
the proxy n, the packet is forwarded to the HIP proxy n which,
however, does not have the corresponding HIP association to deal with
the packet. Similarly with DI-HIT proxies, DI-transparent proxies
and N-DI proxies also suffer from the asymmetric path issue in the
load balancing scenarios, since they cannot guarantee the data
packets which are transported between a legacy host and a HIP host
stick to a single HIP proxy too.
+----------------------+ +--------------------------+
| | | |
| +---+-------+ | (3) |
| (4) -|HIP proxy 1+-+<- |
| / +---+-------+ | \ +--------+ (1)+------+|
|+-----------+< - | . | -|HIP Host|--> | DNS ||
||Legacy Host|- | . | | (HH1) |<-- |Server||
|+-----------+ \ +---+-------+ | +--------+(2) +------+|
| (5) - >|HIP proxy n+-+ |
| Private Network +---+-------+ | Public Network |
| | | |
+----------------------+ +--------------------------+
Figure 2. An example of the asymmetric path issue
As we mentioned in section 3.3.1, the approach of synchronizing HIP
associations and IPsec associations amongst HIP proxies can be used
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to address this issue. However, this issue will introduce additional
communication overhead on HIP proxies. Here, several alternative
solutions are introduced as follows.
The simplest solution is to allow a HIP proxy to discard the I1
packets it receives if they are not originally from HIP hosts which
the proxy covers. In addition, the proxy can inform the senders of
the incidents using ICMP packets. Therefore, after waiting for a
certain period or upon receiving a ICMP packet, a HIP host will try
to select another HIP proxy from the list in the DNS answer and send
an I1 packet to it. In the worst case, this process needs to be
recursive until all the HIP proxies in the list have been contacted.
Because a HIP host may have to send the multiple I1 packets in order
to communicate with a LH, this solution may yield a long delay. Note
that in some DNS based load balancing approaches, a DNS server only
returns one HIP proxy in an answer. On such occasions, HIP hosts
have to communicate with DNS servers repeatedly, and the negative
influence caused by the communication delay can be exacerbated.
A solution which is able to avoid the delay issue is to endow DNS
servers with the capability of returning the IP address of an
appropriate HIP proxy in an answer according to certain policies (
e.g., the HIT (if the proxy is a DI-HIT proxy or a N-DI proxy) or the
IP address (if the proxy is a DI-transparent proxy) of a requester).
That is, the HIP proxy described in a DNS answer should be able to
correctly transform the packets exchanged between the requester and
the LH that it intends to access. In this case, DNS servers actually
act as load balancers. In order to support this solution, DNS
servers need to be extended to 1) maintain the information about the
sections of the namespaces that HIP proxies take in charge of and 2)
locate the appropriate HIP proxy according to the HIT or the IP
address of a HIP requester. These requirements result in
modifications to current DNS servers in terms of the implementation
of the DNS server applications and the conversation protocols between
requesters and DNS servers. For instance, a HIP host may need to
transport its HIT in DNS requests in order to help DNS servers locate
an appropriate HIP proxy. A negative impact of this solution is to
introduce additional complexity and overhead to DNS servers.
Another solution is to extend RVS servers as load balancers. After
receiving an I1 packet from a HIP host, the load balancer then
selects a proper HIP proxy and forwards the packet to it. Using this
solution, a DNS server only needs to reply wiht a record upon
receiving a query from a HIP host, which reduce the traffic
transported between DNS servers and HIP hosts.
The asymmetric path issue can be eliminated when DI-NAT proxies are
adopted. A DI-NAT proxy located at the border of a private network
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maintains a pool of IP addresses which are routable in the private
network. After receiving a packet from a HIP host, the DI-NAT proxy
processes the packet and forwards it to the destination legacy host.
In addition, an IP address selected from the pool is adopted as the
source address of the packet. Therefore, when the legacy host sends
response packets to the HIP host, the packets will be transported to
the same HIP proxy. The asymmetric path issue is thus eliminated.
6. Issues with Dynamic Load Balancing
In practice, there are requirements for LBMs to support dynamic load
balancing. That is, when the overhead imposed on a proxy surpasses a
threshold, the proxy can delegate all of (or a part of) its job to
other proxies. A proxy providing backup service for another proxy is
called a backup proxy, and the proxy being served is called a primary
proxy. Note that two proxies can be backup proxies for each other on
different sessions. In this section, we analyze the operations of
different types of HIP proxies in supporting dynamic load balancing.
In some LBMs adopting load balancers, when a load balancer detects
that the overhead imposed on a proxy is high, it can flexibly
distribute the load to other proxies. However, in the LBMs where no
load balancer is deployed, a backup proxy MUST be able to detect the
abnormal condition of its primary proxy and take over the job. A
simple but effective solution to achieve this is to allow a backup
proxy to advertise the routes identical to those advertised by the
primary proxy in both the private and the public networks (but with
high costs). When the overhead is high, the primary proxy can
withdraw the routes it previously advertised so that the packets
supposed to be processed by the primary proxy will be forwarded to
the backup proxy. We refer to the routes advertised by a proxy for
backup purposes as the backup routes of the proxy. In contrast, we
refer to the routes advertised by a proxy to conduct its primary job
as the primary routes of the proxy. Normally, the backup routes have
much higher costs than those of the corresponding primary routes, in
order to avoid affecting the normal operations of the primary proxy.
Note that the proxies in a LBM can provide backup services for one
another. In such a case, a proxy may need to advertise both primary
and backup routes.
It may be also important to synchronize state information between
primary and backup proxies since without proper HIP associations a
backup proxy cannot correctly take place of the primary proxy to
process the packets. The state synchronization problem has been
discussed above and is not dicussed here in detail. However, if
there is no state synchronization, a backup proxy MAY select to send
signaling packets to HIP hosts to initiate new HIP BEXs.
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In the remainder of this section, we discuss the operations of
different types of HIP proxies in achieving dynamic load balancing
and redundancy without the assistance of load balancers.
6.1. Operations of DI-HIT Proxies
As mentioned in section 3.1, a DI-HIT proxy needs to at least
advertise two primary routes in the private network, a route of a
section of HITs for intercepting data packets, and a route of a
section of IP addresses for intercepting DNS lookups. When the proxy
cannot work properly, it can withdraw both routes to enable a backup
proxy to take over its job.
In some cases, a DI-HIT proxy may only want to delegate a part of its
job to others so as to reduce the load it undertakes. To achieve
this objective, the proxy can divide its routes into multiple more
detailed routes. When the load on the proxy is high, it can only
withdraw a subset of the routes. For instance, a DI-HIT proxy can
selectively only delegate a part of the responsibility in processing
DNS lookups to a backup proxy by withdrawing one of its lookup
intercepting routes.
6.2. Operations of DI-NAT Proxies
A DI-NAT proxy needs to at least advertise two primary routes in the
private network, a route for its IP address pool, used to intercept
data packets, and a route for an IP address section used to intercept
DNS lookups. When the proxy is overloaded, it can withdraw both
routes so that the associated backup proxy can take over the job. In
this case, the delegated backup proxy needs to maintain an IP address
pool identical to the one maintained by the primary proxy. Moreover,
apart from synchronizing HIP associations, the synchronization of
mappings from IP addresses to HITs is also required. Otherwise, the
backup proxy cannot process the received packet correctly.
If a DI-NAT proxy only intends to maintain existing communication
between LHs and HIP hosts while not facilitating any more, it can
withdraw the lookup intercepting route. As mentioned previously, DI-
NAT proxies have the capability to stick the DNS lookups and the
subsequent data packets to the same proxy. Therefore, the backup
proxy can intercept DNS lookups as well as process the subsequent
communication.
6.3. Operations of DI-Transparent Proxies
Unlike DI-HIT and DI-NAT proxies, the routes advertised by a DI-
transparent proxy are used for intercepting both DNS lookups and data
packets. Therefore, before a DI-transparent proxy withdraws a route,
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it needs to synchronize the states of the on-going communication
affected by the routing adjustment to its backup proxies.
7. Conclusions
This document mainly analyzes and compares the performance of
different kinds of HIP proxies in LBMs. Amongst the HIP proxies
discussed in the document, DI-NAT proxies show their advantages in
multiple scenarios. In addition, we argue that the state
synchronization among HIP proxies is very important to achieve load
balancing and redundancy. A topic which is important but not covered
in this document is the compatibility between different HIP proxies.
The different types of HIP proxies are designed based on different
presumptions. The presumptions of different type of HIP proxies may
be in conflict with each other. How to make a trade-off and enable
different types of proxies to work cooperatively is an important
issue that the designers of HIP extensible solutions should consider.
8. IANA Considerations
This document makes no request of IANA.
9. Security Considerations
One design objective of HIP is to provide peer-to-peer security
between communicating hosts. However, when a HIP host communicates
with a LH under the assistance of a HIP proxy, the security of the
communication between the HIP proxy and the LH may not be protected.
If the HIP proxy is transparent to the HIP host, the host will
believe that it is communicating with a ordinary HIP host and will
not realize that the peer-to-peer security between it and the LH is
not guaranteed. This may cause potential security risks, especially
when the HIP proxy is located in the public network. Therefore, some
solutions should be provided for a HIP host to detect whether it is
actually communicating with HIP proxy.
When sharing HIP state information amongst HIP proxies, the integrity
and confidentiality of the state information should be protected.
The discussion about the similar issues can be found in [Nir2009]and
[Narayanan07].
If a HIP proxy is deployed at the border of a private network or
within the boundary of a private network, the security issues with
the communication between the proxy and LHs are not serious.
However, if a proxy is deployed in the public network, both the
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communication between LHs and the proxy and the communication between
the proxy and DNS servers should be secured.
10. Acknowledgements
Thanks to Tom Henderson for his kindly proof-reading and comments.
11. References
11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4035] Arends, R., Austein, R., Larson, M., Massey, D., and S.
Rose, "Protocol Modifications for the DNS Security
Extensions", RFC 4035, March 2005.
[RFC5205] Nikander, P. and J. Laganier, "Host Identity Protocol
(HIP) Domain Name System (DNS) Extensions", RFC 5205,
April 2008.
[RFC5338] Henderson, T., Nikander, P., and M. Komu, "Using the Host
Identity Protocol with Legacy Applications", RFC 5338,
September 2008.
11.2. Informative References
[Narayanan07]
Narayanan, V., "IPsec Gateway Failover and Redundancy -
Problem Statement and Goals", 2007.
[Nir2009] Nir, Y., "IPsec High Availability Problem Statement",
2009.
[PAT07] Salmela, P., Wall, J., and P. Jokela, "Addressing Method
and Method and Apparatus for Establishing Host Identity
Protocol (Hip) Connections Between Legacy and Hip Nodes,
US. 20070274312", 2007.
[SAL05] Salmela, P., "Host Identity Protocol proxy in a 3G
system", 2005.
[TSC05] Tschofenig, H., Gurtov, A., Ylitalo, J., Nagarajan, A.,
and M. Shanmugam, "Traversing Middleboxes with the Host
Identity Protocol", 2005.
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Authors' Addresses
Dacheng Zhang
Huawei Technologies Co.,Ltd
HuaWei Building, No.3 Xinxi Rd., Shang-Di Information Industry Base, Hai-Dian District
Beijing, 100085
P. R. China
Phone:
Fax:
Email: zhangdacheng@huawei.com
URI:
Xiaohu Xu
Huawei Technologies Co.,Ltd
HuaWei Building, No.3 Xinxi Rd., Shang-Di Information Industry Base, Hai-Dian District
Beijing, 100085
P. R. China
Phone:
Fax:
Email: xuxh@huawei.com
URI:
Jiankang Yao
CNNIC
4, South 4th Street, Zhongguancun
Beijing, 100190
P.R. China
Phone:
Fax:
Email: yaojk@cnnic.cn
URI:
Zhen Cao
China Mobile
32 Xuanwumenxi Ave,Xuanwu District
Beijing 100053
P.R. China
Email: zehn.cao@gmail.com, caozhen@chinamobile.com
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