Network working group Dacheng Zhang
Internet Draft Xiaohu Xu
Intended status: Experimental Huawei Technologies Co.,Ltd
Created: March 8, 2010 Jiankang Yao
Expires: September 2010 CNNIC
Investigation in HIP Proxies
draft-zhang-hip-investigation-proxy-01
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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.
Conventions used in this document
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].
Table of Contents
1. Introduction.................................................3
2. Terminologies................................................4
3. HIP Proxies..................................................4
3.1. Essential Operations of HIP Proxies.....................4
3.2. A Taxonomy of HIP Proxies...............................5
3.3. DI Proxies..............................................5
3.4. N-DI Proxies............................................7
4. Issues with LBMs in Supporting ML Hosts to Initiate Communication
...............................................................8
4.1. An Issues Caused by Intercepting DNS Lookups............9
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4.2. Issues with LBMs in Capturing and Processing Replies from
HIP hosts...................................................10
5. Issues with LBMs which also Support HIP Hosts to Initiate
Communication..................................................11
5.1. DNS Resource Records for ML Hosts......................12
5.2. An Asymmetric Path Issue...............................13
6. Issues with LBMs in supporting dynamic load balance and
redundancy.....................................................15
6.1. Application of DI1 proxies in supporting dynamic load
balance and redundancy......................................16
6.2. Application of DI2 proxies in supporting dynamic load
balance and redundancy......................................16
6.3. Application of DI3 proxies in supporting dynamic load
balance and redundancy......................................17
7. Security Consideration......................................17
8. Conclusions.................................................17
9. IANA Considerations.........................................18
10. Acknowledgments............................................18
11. References.................................................18
Authors' Addresses.............................................19
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 the 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. 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 LBM which facilitates communications
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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. Section 6 discusses an
asymmetric path issue in details. In section 6, we analyze 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
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 found, the proxy then
uses the HA to encrypt the packet and forwards it to the HIP host.
However, if there is no such a 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) with the HIP host to generate a new HIP
association. The newly generated HIP association 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.
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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 intend to contact by 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 RR, it will try to contact
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 to the resolver to inquire about the
information it needs (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 essential 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
can be 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. There are several kind of proxies can be
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deployed in this way, which will be 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 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 answers of DNS lookups do not contain
any NS RRs, they can be easily distinguished from those 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 HITs as
destination addresses. In addition, [PAT07] proposes a solution in
which a HIP proxy maintains 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 remote host 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, the proxies adopting the solutions depicted above 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 common 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
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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
and re-homing. For DI1 or DI2 proxies, these issues can be largely
mitigated. When DI1 or DI2 proxies are deployed, the IP addresses of
HIP hosts are covered from ML hosts; and in the communications
between HIP proxies and HIP hosts HITs are used to identify
communicating partners.
Moreover, it is difficult for DI3 proxies to advertise routing
information to attract the packets they needs to process.
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, which may bring benefit in various cases.
For instance, 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. Therefore, the proxy 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 deployment can reduce the overhead on the proxy
imposed by intercepting DNS lookups.
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 prior by intercepting DNS
lookups transported between legacy hosts 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. Therefore, if the
destination address of a received packet is maintained in the list,
the proxy can ensure the packet is for a HIP hosts [SAL05].
Obviously, this solution is infeasible in the scenarios where it is
difficult to identify the HIP hosts that ML hosts intend to contact
in advance. This issue can be addressed by storing 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
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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 for 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
facilitating HIT-based routing in the public network (e.g., HIP
Bone).
Compared with DI proxies, N-DI proxies can be deployed in more
flexible way. For instance, in order to facilitate the legacy hosts
in the private networks without HIP proxies to communicate with HIP
hosts, 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
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.
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
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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 multiple
sections (e.g., according to their IP addresses), and the ML hosts
in different section is taken in charge of by different HIP proxies.
The second solution is to divide the HIP hosts in the Internet into
multiple sections (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
section. 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 desirable in many cases. Therefore, in
existing LBM solutions, the second type of solution is widely
adopted. In the remainder of this document, we mainly consider the
second one.
4.1. An 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. 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
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section of IP addresses (or a default route) 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 which intercepts
data packets will lack essential knowledge to correctly process them.
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 the
above problem.
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
information it gained to the proxy which is 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 such a DI2-proxy-based LBM, each DI2 proxy needs to
advertise two routes, one of the IP addresses in the pool and the
other 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 resolver). Therefore, the subsequent data packets will be stuck to
the same proxy.
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 host 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 located on the path of the
packets transferred between HIP hosts and the ML hosts it serves in
order to capture the reply packets from the HIP host. 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. To benefit the discussion, assume there are two
HIP proxies located at the border of a private network. If the
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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 intercepted by 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 issue 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 IPsec
packet transmitted or received, because this 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. Therefore, in the following discussions, we assume
that a HIP proxy use 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
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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 using
opportunistic model which 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 associate legacy host or the address of its HIP proxy.
In the preceding approach, 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 approach, 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 only need to process the packets for ML hosts rather
than intercept all the packets transported across the network border.
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 sent 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 is difficult to identify the
ML host which the packet should be forwarded to.
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, the proxy field can bring
additional benefits in security. For instance, it is normally
assumed that the base-exchange protocol is able to establish a
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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, 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.
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+----------------------+ +--------------------------+
| | | |
| +---+-------+ | (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 receivers 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 the ICMP packets, 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
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
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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.
If DI2 proxies are adopted in the LBM depicted in Figure 1, the
asymmetric path issue can be eliminated. 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
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
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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 more 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
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.
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Moreover, the synchronization of mappings from IP addresses to HITs
is 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. Security Consideration
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].
8. 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
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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.
9. IANA Considerations
No such considerations.
10. Acknowledgments
11. References
[PAT07] P. Salmela, J. Wall 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] P. Salmela, "Host Identity Protocol proxy in a 3G system,"
Master's thesis. Helsinki University of Technology 2005.
[TSC05] H. Tschofenig, A. Gurtov, J. Ylitalo, A. Nagarajan and
M. Shanmugam, "Traversing Middleboxes with the Host Identity
Protocol," Proc. ACISP, 2005.
[RFC5338] T. Henderson, P. Nikander and M. Komu, "Using the Host
Identity Protocol with Legacy Applications," RFC 5338, Sep. 2008.
[RFC5205] P. Nikander and J. Laganier, "Host Identity Protocol (HIP)
Domain Name System (DNS) Extension," RFC 5205, April 2008.
[RFC4035] R. Arends, R. Austein , M. Larson, D. Massey and S. Rose,
"Protocol Modifications for the DNS Security Extensions," RFC 4035,
March 2005.
[Nir 2009] Y. Nir, "IPsec High Availability Problem Statement,"
Internet Draft, 2009.
[Narayanan 07] V. Narayanan, "IPsec Gateway Failover and Redundancy
- Problem Statement and Goals," Internet Draft, 2007.
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Authors' Addresses
Dacheng Zhang
Huawei Technologies Co.,Ltd
KuiKe Building, No.9 Xinxi Rd.,
Hai-Dian District
Beijing, 100085
P.R. China
Email: zhangdacheng@huawei.com
Xiaohu Xu
Huawei Technologies Co.,Ltd
KuiKe Building, No.9 Xinxi Rd.,
Hai-Dian District
Beijing, 100085
P.R. China
Email: xuxh@huawei.com
Jiankang Yao
CNNIC
No.4 South 4th Street, Zhongguancun
Bejing,
P.R. China
Phone: +86 10 58813007
Email: yaojk@cnnic.cn
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