routing
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This document provides a summary of known request routing techniques
that are used by the industry before December 2000. Request routing
...
... This document provides a summary of known request routing techniques
that are used by the industry before December 2000. Request routing
techniques are generally used to direct client requests to surrogates
...
... directing clients' requests to surrogates is also called
Request-Routing, Content Routing or Content Redirection.
...
... clients' requests to surrogates is also called
Request-Routing, Content Routing or Content Redirection.
Request-Routing ...
... Routing or Content Redirection.
Request-Routing techniques are commonly used in Content Networks
(also known as Content Delivery Networks ...
... network infrastructure that exists in layers 4 through 7.
Content Networks deal with the routing and forwarding of requests and
responses for content. Content Networks rely on layer ...
... transport.
Request-Routing techniques are generally used to direct client
requests for objects to a surrogate or a set of surrogates that could
best serve that content. Request-Routing ...
... Routing techniques are generally used to direct client
requests for objects to a surrogate or a set of surrogates that could
best serve that content. Request-Routing mechanisms could be used to
direct client requests to surrogates that are within a Content
...
... 8].
Request-Routing techniques are used as a vehicle to extend the reach
and scale of Content Delivery Networks. There exist multiple
...
... and scale of Content Delivery Networks. There exist multiple
Request-Routing mechanisms. At a high-level, these may be classified
under: DNS ...
... high-level, these may be classified
under: DNS Request-Routing, transport-layer Request-Routing, and
...
... Routing.
A request routing system uses a set of metrics in an attempt to
direct users to surrogate that can best serve the request. For
example, the choice of the surrogate could be based on network ...
... The memo is organized as follows: Section 2 provides a summary of
known DNS based Request-Routing techniques. Section 3 discusses
transport-layer Request-Routing ...
... Routing techniques. Section 3 discusses
transport-layer Request-Routing methods. In section 4 application
layer Request-Routing ...
... Routing methods. In section 4 application
layer Request-Routing mechanisms are explored. Section 5 provides
insight on combining the various methods that were discussed in the
...
... earlier sections in order to optimize the performance of the
Request-Routing System. Appendix A provides a summary of possible
metrics and measurements techniques that could be used by the
Request-Routing system ...
... Routing System. Appendix A provides a summary of possible
metrics and measurements techniques that could be used by the
Request-Routing system to choose a given surrogate.
...
... 12][13]. In DNS based Request-Routing
techniques, a specialized DNS server is inserted in the DNS ...
...
In this approach, the Request-Routing DNS server returns multiple
replies such as several A records ...
... in a single DNS resolution. The rationale of utilizing multiple
Request-Routing DNS servers in a single DNS resolution is to allow
...
... one to distribute more complex decisions from a single server to
multiple, more specialized, Request-Routing DNS servers. The most
common mechanisms used to insert multiple Request-Routing ...
... Routing DNS servers. The most
common mechanisms used to insert multiple Request-Routing DNS servers
in a single DNS ...
... authority of the next
level domain to another Request-Routing DNS server. The, technique
allows multiple DNS server ...
... name server authoritative for this domain might be a
Request-Routing NS server. In this case the Request-Routing DNS
server ...
... Request-Routing NS server. In this case the Request-Routing DNS
server can either return a set of A records or can redirect the
...
... One drawback of using NS records is that the number of
Request-Routing DNS servers are limited by the number of parts in the
DNS name ...
... resolving the new domain name. The main advantage of this approach
is that the number of Request-Routing DNS servers is independent of
the format of the domain name ...
...
Furthermore, to combine measurement and redirection, the
Request-Routing DNS server can advertise an anycast address as its IP
address ...
... physical DNS servers.
In this scenario, the Request-Routing DNS server that is the closest
to the client ...
... client site DNS server in terms of OSPF and BGP routing will
receive the packet containing the DNS resolution request. The server
...
... receive the packet containing the DNS resolution request. The server
can use this information to make a Request-Routing decision.
Drawbacks of this approach are listed below:
...
... client.
o Typically, routing protocols are not load sensitive. Hence, the
closest server may not be the one with the least network latency ...
... Since only DNS names are visible during the DNS Request-Routing, some
solutions encode the object type, object hash, or similar information
...
...
o In DNS based Request-Routing systems servers may be required to
return DNS entries with a short time-to-live ...
... addresses are not relayed within DNS requests.
This limits the ability of the Request-Routing system to determine
a client's proximity to the surrogate.
...
... o DNS servers can request and allow recursive resolution of DNS
names. For recursive resolution of requests, the Request-Routing
DNS server will not be exposed to the IP address ...
... client's
site DNS server. In this case, the Request-Routing DNS server
will be exposed to the address ...
...
DNS based request routing techniques can suffer from serious
limitations. For example, the use of such techniques can overburden
third party ...
... Transport-Layer Request-Routing ...
... the close inspection of client's requests. In this approach, the
Request-Routing system inspects the information available in the
first packet of the client's request to make surrogate selection
...
...
In general, transport-layer Request-Routing can be combined with DNS
based techniques. As stated earlier, DNS ...
... be used as a first step in deciding on an appropriate surrogate with
more accurate refinement made by the transport-layer Request-Routing
system.
...
... Application-Layer Request-Routing ...
...
Application-layer Request-Routing systems perform deeper examination
of client's packets beyond the transport layer ...
... header. Deeper
examination of client's packets provides fine-grained Request-Routing
control down to the level of individual objects. The process could
be performed in real time at the time of the object request. The
...
... knowledge of the requested objects enable application-layer
Request-Routing systems to provide better control over the selection
of the best surrogate.
...
... 6]. In many cases, this information
is sufficient to disambiguate the content and suitably direct the
request. In most cases, it may be sufficient to make Request-Routing
decision just by examining the prefix or suffix ...
... element examines the client's content requests and performs
Request-Routing decisions.
The In-Path element ...
... web site.
Cookie based Request-Routing provides content service differentiation
based on the client ...
... This technique enables a content provider to take direct control over
Request-Routing decisions without the need for specific witching
devices or directory services in the path between the client ...
... URL rewriting alone does not allow consideration of client
specifics for Request-Routing. However, it can be used in
combination with DNS Request-Routing ...
... Routing. However, it can be used in
combination with DNS Request-Routing to direct related DNS queries
into the domain name ...
... domain name space of the service provider. Dynamic
Request-Routing based on client specifics are then done using the DNS
...
...
Content modification as a Request-Routing mechanism suffers from many
limitation [23]. For example:
...
...
A basic problem of DNS Request-Routing is the resolution granularity
that allows resolution on a per-domain level only. A per-object
...
... redirection cannot easily be achieved. However, content modification
can be used together with DNS Request-Routing to overcome this
problem. With content modification, references to different objects
on the same origin server can be rewritten to point into different
...
... domain name spaces. Using DNS Request-Routing, requests for those
objects can now dynamically be directed to different surrogates.
...
...
The main objective of this document is to provide a summary of
current Request-Routing techniques. Such techniques are currently
implemented in the Internet. However, security ...
... firewalls. Therefore, it is recommended that
implementers be aware of routing protocol security [25].
...
... It is important to note the impact of TLS [2] on request routing in
CNs. Specifically, when TLS is used the full URL ...
...
Request-Routing systems can use a variety of metrics in order to
determine the best surrogate that can serve a client's request. In
...
...
Proximity measurements can be used by the Request-Routing system to
direct users to the "closest" surrogate. In this document proximity
means round-trip time ...
... means round-trip time. In a DNS Request-Routing system, the
measurements are made to the client's local DNS server ...
... Crawley, E., Nair, R., Rajagopalan, B. and H. Sandick, "A Framework for QoS-based Routing in the Internet", RFC 2386, August 1998. ...
... C. Yang et al., "An effective mechanism for supporting content- based routing in scalable Web server clusters", Proc. International Workshops on Parallel Processing 1999, September 1999. ...
... F. Wang et al., "Secure routing protocols: Theory and Practice", Technical report, North Carolina State University 1997, May 1997. ...