Network Working Group D. Zhang
Internet-Draft X. Xu
Intended status: Informational Huawei Technologies Co.,Ltd
Expires: April 26, 2011 J. Yao
CNNIC
October 23, 2010
Investigation in HIP Proxies
draft-irtf-hiprg-proxies-01
Abstract
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 communications between legacy (or Non-
HIP) hosts and HIP hosts while not modifying their protocol stacks.
In this document, the legacy hosts served by proxies are referred to
as the Made-up Legacy (ML) hosts. Currently, various designing
solutions of HIP proxies have been proposed. These solutions may be
applicable in different working circumstances. In this document, we
attempt to investigate these solutions in detail and compare their
performances in different scenarios.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 26, 2011.
Copyright Notice
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Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 4
3. HIP Proxies . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Essential Operations of HIP Proxies . . . . . . . . . . . 5
3.2. A Taxonomy of HIP Proxies . . . . . . . . . . . . . . . . 5
3.3. DI Proxies . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. N-DI Proxies . . . . . . . . . . . . . . . . . . . . . . . 8
3.5. DNS Resolvers Supporting HIP Proxies . . . . . . . . . . . 9
4. Issues with LBMs in Supporting ML Hosts to Initiate
Communication . . . . . . . . . . . . . . . . . . . . . . . . 10
4.1. An Issues Caused by Intercepting DNS Lookups . . . . . . . 10
4.2. Issues with LBMs in Capturing and Processing Replies
from HIP hosts . . . . . . . . . . . . . . . . . . . . . . 12
5. Issues with LBMs which also Support HIP Hosts to Initiate
Communication . . . . . . . . . . . . . . . . . . . . . . . . 13
5.1. DNS Resource Records for ML Hosts . . . . . . . . . . . . 13
5.2. An Asymmetric Path Issue . . . . . . . . . . . . . . . . . 14
6. Issues with LBMs in supporting dynamic load balance and
redundancy . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.1. Application of DI1 proxies in supporting dynamic load
balance and redundancy . . . . . . . . . . . . . . . . . . 17
6.2. Application of DI2 proxies in supporting dynamic load
balance and redundancy . . . . . . . . . . . . . . . . . . 17
6.3. Application of DI3 proxies in supporting dynamic load
balance and redundancy . . . . . . . . . . . . . . . . . . 18
7. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 18
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
9. Security Considerations . . . . . . . . . . . . . . . . . . . 19
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 19
11.1. Normative References . . . . . . . . . . . . . . . . . . . 19
11.2. Informative References . . . . . . . . . . . . . . . . . . 19
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
As core components of HIP extensional solutions, HIP proxies have
attracted increasing attention from both the industry and the
academia. Currently, multiple research work is engaged in the design
and the performance assessment of HIP proxies. In this document, we
attempt to investigate several important designing solutions and
compare their effectiveness in different scenarios. Actually, there
has 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 necessary of extending
the HIP RR for HIP proxies) are discussed in the draft.
Theoretically, ML hosts and the HIP hosts they intend to communicate
with can be located anywhere in the network. However, in this
document, without mentioned otherwise, legacy hosts are located
within a private network and HIP hosts are located in the public
network, as 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 terminologies used in this document. In section 3, we
indicate the essential functions of HIP proxies and provide a
classification. In section 4， we analyze the issues that HIP
proxies have to face in constructing a Load Balancing Mechanism (LBM)
which facilitates communications initiated by ML hosts. Section 5
analyzes the issues that HIP proxies in a LBM have to face if they
also need to support communications initiated by HIP hosts. In
section 6, we investigate the issues that HIP proxies have to deal
with in supporting dynamic load balancing and redundancy. Section 7
provides a brief discussion about the influence brought by DNSsec to
the deployment of HIP proxies. Section 8 is the conclusion of the
entire document.
2. Terminologies
BEX: HIP Base Exchange
DI Proxy: DNS Inspecting Proxy
HA: HIP association
LBM: Load Balancing Mechanism
N-DI proxy: Non-DNS Inspecting Proxy
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3. HIP Proxies
3.1. Essential Operations of HIP Proxies
A primary function of HIP proxies is to exchange messages with HIP
hosts on the performance of legacy hosts, using standard HIP
protocols. In order to achieve this, a HIP proxy needs to intercept
the packets transported between legacy 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 host which the packet is destined for. Assume a proxy captures a
packet sent out by a ML host. If the packet is destined to a HIP
host, the proxy first checks whether there is an appropriate HIP
association (HA) in its local database which can be used to process
the packet. If such a HA is located, the proxy then find the proper
key maintained in the HA and use it to encrypt the payload in the
packet. The packet is then forwarded to the HIP host. However, if
there is no such an HA or it has expired, the proxy needs to use the
HI and HIT assigned to the ML host 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. After capturing packet
from a HIP host, the proxy also needs to use the keying material in
the associated HA to decrypt the packet, transfer it into an ordinary
IP packet, and forwards the IP packet to the legacy host.
3.2. A Taxonomy of HIP Proxies
In practice, there are various design solutions for HIP proxies.
These solutions are based on different presumptions and supposed to
execute in different circumstances. To benefit the analysis, we
classify HIP proxies into DNS lookups Intercepting Proxies (DI
proxies) and Non-DNS lookups 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 legacy
hosts and HIP hosts, while N-DI proxies do not have to.
To avoid confusion, in the remainder of this document we use the
terms "lookup" and "answer" 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 legacy host communicates with a remote host, it
needs to query DNS servers to obtain the IP address of its
destination. On this premise, a DI proxy can effectively identify
the hosts which legacy hosts may contact in near future by
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intercepting DNS lookups. In practice, it is common to deploy one
more multiple local DNS servers (resolvers) for a private network.
Therefore, the hosts in the network can send their queries to the
resolver instead of communicating with authoritative DNS servers
directly. If the resolver does not cache the inquired RRs, it will
try to obtain them from authoritative DNS servers. The resolver may
have to contact multiple authoritative DNS servers to get the IP
address of the authoritative DNS server which actually contains
desired DNS RRs. If the resolver is located out of the private
network, a HIP proxy located at the border of the network can
intercept an initial DNS query from a legacy host and then use the
FQDN obtained from the query to initiate a new DNS lookup with 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, IPs addresses) in the local
database, 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 can be located on the path
between ML hosts and the resolver, it can work exactly as same as
what is illustrated above. 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, it has to spend more
efforts to intercept and modify 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.
In this case, to be more efficient, the proxy can only inspect the
responses from DNS services 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 sever 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 DNS answers for resolvers or
ML hosts in order to benefit their following up operations. For
instance, [RFC5338] indicates that a HIP proxy can returns HITs
rather than IP addresses in DNS answers to ML hosts. Consequently,
the data packets from ML hosts to HIP hosts will use the HITs of the
HIP hosts as destination addresses. [PAT07] also proposes a proxy
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solution which requires a HIP proxy to maintain an IP address pool.
When sending a DNS answer to a ML host, the proxy selects an IP
address from its pool and inserts it in 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 selected IP
address as the destination address. In the remainder of this
document, these two types of proxies are referred to as DI1 proxies
and DI2 proxies respectively, and the 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 DI3 proxies.
Different modifications on DNS answers introduce different influences
on the performances of DI proxies and impose different restrictions
on their locations.
Compared with DI1 and DI2 proxies, DI3 proxies show their limitations
in many aspects. For instance, it is a practical solution for a ML
host to publish the IP address of its proxy in its DNS AAAA RR so
that the packets for the host will be directly forwarded to the
proxy. Therefore, when a ML host served by a DI3 proxy attempts to
communicate with two remote ML hosts 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, DI3 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 DI1 or DI2 proxies, these issues can be largely
mitigated as the IP addresses of HIP hosts will never be used by DI1
or DI2 proxies to identity hosts.
Moreover, it is difficult for DI3 proxies to advertise routing
information to attract the packets they needs to process (i.e., the
packets transported between ML hosts and remote HIP hosts).
Consequently, they can be only deployed at the borders of private
networks. DI1 (or DI2) proxies, however, can attract the packets for
HIP hosts to themselves by advertising associated routes, because the
packets destined to HIP hosts use HITs (or the IP addresses selected
from pools) as their destination addresses. Hence, they can locate
inside the networks. Therefore, in a private network whose resolver
are located inside, a DI1 or a DI2 proxy can be deployed on the path
between the resolver and legacy hosts, and it needs only to
intercept, modify and forward the queries from legacy host to the
resolver. Compared with deploying HIP proxies at the border of the
network, this deploying solution can reduce the overhead on the proxy
imposed by intercepting DNS lookups.
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3.4. N-DI Proxies
Unlike DI proxies, an N-DI proxy does not attempt to find out the HIP
hosts a legacy host may contact in advance by intercepting DNS
lookups transported between legacy hosts (or resolvers) and DNS
servers. Instead, it identifies whether the receiver of a packet is
HIP enabled when it capture the packet. Typically, an N-DI proxy
achieves this by inspecting the destination address of the packet.
When the HIP hosts that ML hosts intend to contact are predicable and
the number of the HIP hosts is finite, an N-DI proxy can maintain a
list of mapping information between HITs and IP addresses[SAL05].
After intercepting a packet from a legacy host, the proxy can ensure
the packet is for a HIP host, if the destination address of the
packet is maintained in the list. Obviously, this solution is
infeasible in the circumstances where it is difficult to identify the
HIP hosts that ML hosts intend to contact in advance. On such
occasions, an N-DI proxy has to find out whether a packet from a ML
host is destined to a HIP host and or a legacy host. It is
infeasible for an N-DI proxy to consult resolution systems to find
out whether an IP address belongs to a HIP host or a legacy host.
Therefore, the N-DI proxy has to maintain to list of IP addresses.
One is for HIP hosts, and the other is for legacy hosts. When
intercepting a packet, the N-DI can compare the destination address
of the packet against the addresses in the lists to find out whether
the packet is destined to a HIP host. If no address is matched, the
proxy has to consult resolution systems and maintain the address in
the associated list according the answer from resolution systems.
Obviously, an N-DI proxy may have to maintain a large amount of state
information, which makes it less efficient and scaleable than DI-
proxies. Fortunately, this issue can be mitigated by inserting HITs
instead of IPv6 addresses in the AAAA RRs of HIP hosts in DNS
servers. When receiving an answer containing the AAAA RR of a HIP
host (e.g., host B), a legacy host (e.g., host A) will regard the HIT
in the answer as the IPv6 address of B. Afterwards, when A sends a
data packet to B, it use the HIT of B as the destination address.
Because HITs share a prefix which is different from those of ordinary
IP addresses, when an N-DI proxy (e.g., proxy P) catches the packet,
P can easily distinguish it from the packets for legacy hosts. In
addition, P can advertise a route of the prefix of HITs within the
private network so as to avoid dealing with the packets transported
between legacy hosts. After processing the packet, P may need to get
the associated IP address from resolution servers which provide ID to
locator mapping information (e.g., DHT servers), using the HIT found
in the packet header. Otherwise, P can try to send the packet to an
overlay which supports HIT-based routing in the public network (e.g.,
HIP Bone).
Compared with DI proxies, N-DI proxies can be deployed in a more
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flexible way. For instance, in order to facilitate the legacy hosts
in the private networks without HIP proxies to communicate with HIP
hosts, Internet services providers (ISPs) may deploy HIP proxies in
transit networks. If DI proxies are adopted, they need to locate in
the places where they can intercept all the packets transported
inside the transit network to find out DNS lookups because the IP
addresses of DNS servers are normally unknown in advance. The jobs
of processing packets are cumbersome. In addition, such locations
may be quite difficult to find out. In this case, N-DI proxies show
their advantages; an N-DI proxy can advertise a route of the HIT
prefix (or a sub-prefix of HIT) in the transit network and easily
attract the desired packets to it. Therefore, they can be deployed
in a more flexible way and have to process fewer packets. However,
there is a realistic problem which may prevent N-DI proxies from
being widely employed. It is predicable that, in the initial period
of widely deploying HIP hosts, various HIP proxy solutions will be
adopted by different organizations and the information of HIP hosts
in DNS servers will organized in an ad hoc way. At least in this
period, it is extremely difficult to guarantee that all the RRs of
HIP hosts are modified appropriately. This issue makes it difficult
for N-DI proxies to effectively distinguish packets for HIP hosts
from those for legacy packets. From this perspective, the capability
of DI proxies in modifying DNS answers is desirable.
3.5. DNS Resolvers Supporting HIP Proxies
As discussed above, DI proxies have to intercept and modify the DNS
communications between legacy hosts and DNS servers in order to
facilitate the communications between legacy hosts and HIP hosts.
This requires a DI proxy be deployed on the boundary of the private
network or on the path between legacy hosts and the DNS resolver.
Such inflexibility may be undesired under certain circumstances. In
this section, we analyze a design option of DI proxies which improve
the deployment flexibility of DI proxies by separating the DNS
related functionality ( i.e., intercepting and modifying the DNS
communications from DI proxies to DNS resolvers) from DI proxies and
implementing it in DNS resolvers.
A resolver extended to support a DI1 proxy returns HITs in DNS
answers to ML hosts. Therefore, the associated DI1 proxy can
advertise routing information inside the private network to attract
the packets using HITs as destination addresses. Additionally, the
resolver needs to transfer other information (e.g, IP addresses of
the HIP hosts and RVSes) of the HIP hosts to the DI1 proxy so that
the proxy can perform BEXes with the HIP hosts on behavior of ML
hosts.
A resolver extended to support a DI2 proxy needs to not only return
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the IP addresses in the address pool of the DI2 proxy but also
transfer the mapping information of the IP addresses and the HIs to
the DI2 proxy. Moreover, the resolver may have to maintain the
mapping information so as to avoid associated multiple HIs with a
single IP address. A resolver extended to support a DI3 proxy needs
not to modify DNS answers, but it needs to transport the IP addresses
of HIP hosts and their HIs to the DI2 proxy. Therefore, this
solution cannot make the development of DI3 proxies more flexible.
4. Issues with LBMs in Supporting ML Hosts 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 it the
bottleneck of the whole mechanism. A typical solution to mitigate
this issue is to organize multiple proxies to construct a LBM. By
sharing overheads amongst multiple HIP proxies, a LBM can be more
scalable and capable to tolerate the failures of a sub-set of HIP
proxies. However, a LBM is not just a collection of multiple HIP
proxies. Lots of issues need to be carefully considered.
Generally, there are two solutions to share communication between ML
hosts and HIP hosts among different HIP proxies. The first solution
is to divided the ML hosts in the private network into different
groups (e.g., according to their IP addresses), and the ML hosts in
different sections are taken in charge of 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 ML hosts in the private network but
only take in charge of the packets to and from the HIP hosts in a
group. Abstractly, the two solutions are identical. However, the
first solution actually attempts to divide a private network 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 is
more preferred. In the remainder of this document, we mainly
consider the second one.
4.1. An Issues Caused by Intercepting DNS Lookups
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+--------------------+ +------------------+
| | | |
| +---+-------+ | |
| +-----------+ |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. In this mechanism, n proxies are
deployed at the border of a private network. If such proxies are DI1
proxies, in order to share the overheads of processing data packets,
each proxy needs to advertise a route of the HIT section it takes in
charge of. In addition, each proxy also needs to advise 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 DI3
proxies, then each 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 DI3 proxy
intercepting the lookups for the HIP host will not be the one
intercepting subsequent data packets. Therefore, DI3-proxy-based
LBMs also suffer from a same problem with DI1-proxy-based LBMs.
A candidate solution to the problem is to propagate the mapping
information obtained from DNS lookups amongst HIP proxies.
Therefore, after intercepting a DNS conversation, a proxy can forward
the gained 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 addition
overheads to DI-proxies in communicating with resolution servers.
If the proxies in Figure 1 are DI2 proxies, the problem can be
eliminated. In a DI2-proxy-based LBM, each DI2 proxy needs to
advertise two routes, one of the IP addresses in the pool and one of
a section of IP addresses for intercepting DNS lookups. After
intercepting a DNS lookup, a DI2 proxy will return an IP address
within the pool in the answer to the requester (a ML host or a
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resolver), which can ensure the subsequent data packets will be
transported to the same proxy.
The DNS resolvers supporting DI proxies can simply address the issue
by forwarding the mapping information obtained from DNS lookups to
appropriate HIP proxies.
4.2. Issues with LBMs in Capturing and Processing Replies from HIP
hosts
Theoretically, when representing a ML host to communicate with a HIP
host in the public network, a HIP porxy can use either an IP address
it possesses or the IP address of the ML host as the source address
of the packets forwarded to the HIP host. However, in practice, the
succeeding option may cause several issues. For instance, in the
succeeding option, a Hip proxy must be placed on the path of the
packets transferred between HIP hosts and the ML hosts it serves in
order to capture the reply packets from HIP hosts. In addition, the
succeeding solution may cause problems in the load balancing
scenarios where multiple HIP proxies provide services for a same
group of ML hosts. Assume there are two HIP proxies located at the
border of a private network. If the proxies adopt the succeeding
solution, they need to advertise the routes of the ML hosts 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 stuck to a same HIP proxy, and thus after a proxy intercepts
a packet it may lack the proper HIP association to process it.
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-in-time fashion.
However, during communication, some context information such as the
sequence numbers of IPsec packets can change very fast. It is
infeasible to synchronize the IPsec message counters for every
transmitted or received IPsec packet, since such operations will
occupy large amounts of bandwidth and seriously affect the
performances of HIP proxies. [Nir 2009] indicates that this issue
can be partially mitigated by synchronizing IPsec message counters
only at regular intervals, for instance, every 10,000 packets.
An issue similar with 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 middle boxes obtain
the SPIs used in a HIP base exchange and cannot be directly used to
address the issue mentioned above.
Note that all these issues can be simply addressed by adopting the
preceding option because it can guarantee the packets transported
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between a ML host and a HIP host are intercepted by a same proxy.
Therefore, in the following discussions, without mentioned otherwise
we assume that a HIP proxy uses one of its IP addresses as the source
IP address of a packet which it sends to a HIP host.
5. Issues with LBMs which also Support HIP Hosts to Initiate
Communication
Apart from the basic functions (i.e., supporting ML hosts to
communicate 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 conditions where HIP hosts proactively initiate
communication with legacy hosts.
In order to support the communication initiated by HIP hosts, the HIP
proxies of a private network should have the knowledge essential to
represent the ML hosts to perform HIP BEXs. Such knowledge consists
of the IP addresses of the legacy hosts, their pre-assigned HITs, the
corresponding HI key pairs, and any other necessary information. In
addition, such information of the ML hosts 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 ML host in the opportunistic
model which, however, should only be adopted in secure environments.
5.1. DNS Resource Records for ML Hosts
In practice, the AAAA RR of a ML host can consist of either the IP
address of the ML host or the address of its HIP proxy. In the
preceding case, the packets destined to a legacy host are transported
to the host directly, and thus HIP proxies must be located on the
path of such packets to intercept them. In the succeeding case, the
packets for a legacy host are firstly transported to the associated
HIP proxy. Therefore the proxy can be deployed anywhere desired. In
addition, the succeeding approach is more efficient than the
preceding one in private networks where legacy hosts and HIP hosts
are deployed in an intermixed way, since the HIP proxy will not have
to process the packets transported between HIP hosts. However, the
succeeding approach may cause problems in the process of packets sent
by legacy hosts in the public network. Normally, a HIP proxy needs
to serve a number of ML hosts. When using the succeeding approach,
the packets destined to these ML hosts 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 ML host which the
packet should be forwarded to.
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A simple approach which combines the advantages of the above two
solutions but avoids their disadvantages is to extend the RDATA field
in HIP RRs [RFC5205] with a new proxy field, which contains the IP
address of a HIP proxy. In the extended HIP RR of a ML host, 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 ML host 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.
Although it is also possible to use the RVS field in a HIP RR to
transport the information of a HIP proxy, a special proxy field can
bring additional benefits in security. For instance, it is normally
assumed that the base-exchange 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 made up 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 specific way.
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 DI1 proxies and their IP addresses are maintained
in the DNS RRs of the ML hosts. 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 forwards it to the legacy host. In the forwarded packets,
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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 DI1 proxies, DI3 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 sharing HIP
associations and IPsec association amongst HIP proxies can be used to
address this issue. However, this issue will introduce addition
communication overhead on HIP proxies. Here, we discuss several
other alternative solutions.
The simplest solution is to allow a HIP proxy to discard the I1
packets it receives if they are not original from HIP hosts which the
proxy takes in charge of. 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 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 ML host, 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 even exacerbated.
A solution which is able to avoid the delay issue is to endow DNS
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servers with the capability of returning the IP address of an
appropriate HIP proxy in an answer according to the HIT (if the proxy
is a DI1 proxy or a N-DI proxy) or the IP address (if the proxy is a
DI3 proxy) of a requester. That is, the HIP proxy described in a DNS
answer should take in charge of the namespace section which the
requester belongs to. In order to achieve this, DNS servers need to
1) maintain the information about the sections of the namespaces that
HIP proxies take in charge of, 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 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.
It is also possible to register HIP proxies to a RVS server.
Therefore, upon receiving an I1 packet, the RVS server can forward it
to a proper proxy to process.
The asymmetric path issue can be eliminated by adopting DI2 proxies.
A DI2 proxy located at the border of a private network maintains a
pool of IP addresses which are routable in the private network.
After receiving a packet from a HIP host, the DI2 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 responding
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 LBMs in supporting dynamic load balance and redundancy
The load balancing solutions discussed above are simple and static.
They cannot modify routes of packets according to the loads on
different HIP proxies. In practice, there are requirements for LBMs
to support dynamic load balance and redundancy. That is, when a
proxy (called a prim proxy) in a LBM is not able to work properly or
the overheads imposed on it surpass a threshold, the proxy can
delegate all of (or a part of) its job to other proxies (called
backup proxies). In this section, we analyze the performance of
different types of HIP proxies in supporting dynamic load balance and
redundancy.
In order to provide backup services, a backup proxy needs to
advertise the same routes as those advertised by the prim proxy in
both the private and the public networks. To avoid affecting the
normal operations of the prim proxy, the routes advertised by the
backup proxy have a much higher cost than that of the routes
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advertised by the prim proxy. When the abnormal conditions mentioned
above occurs, the prim proxy can withdraw the routes it previously
advertised so that the packets supposed to be processed by the prim
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
achieve its primary job as the prim routes of the proxy. In
practice, the proxies in a LBM can provide backup services for one
another. Therefore, a proxy in such a LBM may needs to advertise
both prim and backup routes.
The synchronization of state information between prim and backup
proxies is also very important. Without proper HIP associations, a
backup proxy cannot correctly take place of the prim proxy to process
the packets. The state synchronization problem has been discussed
above. If there is no state synchronization, a backup proxy may
select to send signaling packets to HIP hosts to initiate new HIP
BEXs.
In the remainder of this section, we attempt to analyze the
performance of different types of HIP proxies in supporting dynamic
load balance and redundancy respectively.
6.1. Application of DI1 proxies in supporting dynamic load balance and
redundancy
As mentioned in section 3.1, a DI1 proxy needs to at least advertise
two prim routes in the private network, one for a section of HITs,
which is used to intercept data packets, and the other for a section
of IP addresses, which is used to intercept 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 DI1 proxy may only want to delegate a part of its
job to others so as to reduce the overloads it undertakes. To
achieve this objective, the proxy can advertise multiple specific
prim routes. When the overload on the proxy is high, it can only
withdraw a subset of those advertised routes. For instance, a DI1
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. Application of DI2 proxies in supporting dynamic load balance and
redundancy
A DI2 proxy needs to at least advertise two prim routes in the
private network, a route for its IP address pool, used to intercept
data packets, and the other for an IP address section, is used to
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intercept DNS lookups. When the proxy cannot work properly, it can
withdraw both routes to enable a backup proxy to take over its job.
In this case, the delegated backup proxy needs to maintain an IP
address pool identical to the one maintained by the prim proxy.
Moreover, apart from synchronizing HIP associations, the
synchronization of mappings from IP addresses to HITs is also
required. Otherwise, the backup proxy cannot translate the received
packet correctly.
If a DI2 proxy only intends to maintain existing communications
between ML hosts and HIP hosts while not facilitating any more, it
can withdraw the lookup intercepting route. As mentioned previously,
DI2 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
communications.
6.3. Application of DI3 proxies in supporting dynamic load balance and
redundancy
Unlike DI1 and DI2 proxies, the routes advertised by a DI3 proxy are
used for intercepting both DNS lookups and data packets. Therefore,
before a DI3 proxy withdraws a route, it needs to synchronize the
states of the on-going communications 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, DI2 proxies show its advantages in
multiple scenarios. In addition, we argue that the state
synchronization among HIP proxies is very important to achieve
academic load balancing and redundancy. There is a topic which is
important but not covered in this document is the compatibility among
different HIP proxies. The different types of HIP proxies are
designed based on different presumptions. The presumptions of
different type of HIP proxies maybe conflict with each other. Then
how to make a trade-off and enable different types of proxies work
cooperatively is an important issue that the designers of HIP
extensible solutions have to consider.
8. IANA Considerations
This document makes no request of IANA.
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9. Security Considerations
Security is an important benefit introduced by HIP. In the basic HIP
architecture, security requirement on DNS communications is not
compelled. But in practice, DNSSEC [RFC4305] is recommended in order
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, DI1 and DI2 proxies need to modify the
contents of NDS answers, and thus they should be only deployed on the
path between legacy hosts and their resolvers. Therefore, a DI1
proxy (or a DI2 proxy) should not be deployed in the middle of
DNSsec-enabled resolvers and authoritative DNS servers.
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 [Nir 2009]
and [Narayanan 07].
10. Acknowledgements
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
[Narayanan 07]
Narayanan, V., "IPsec Gateway Failover and Redundancy -
Problem Statement and Goals", 2007.
[Nir 2009]
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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.
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:
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Jiankang Yao
CNNIC
4, South 4th Street, Zhongguancun
Beijing, 100190
P.R. China
Phone:
Fax:
Email: shenshuo@cnnic.cn
URI:
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