Network Working Group V. Aggarwal
Request for Comments: 1291 JvNCnet Computer Network
December 1991
Mid-Level Networks
Potential Technical Services
Status of this Memo
This RFC provides information for the Internet community. It does not
specify an Internet standard. Distribution of this memo is unlimited.
Abstract
This document proposes a set of technical services that each Internet
mid-level network can offer within the mid-level network itself and
and to its peer networks. The term "mid-level" is used as a generic
term to represent all regional and similar networks, which, due to
continuous evolutions and transitions, can no longer be termed
"regional" [MAN]. It discusses the pros and cons of offering these
services, as well as areas in which mid-level networks can work
together.
A large portion of the ideas stem from discussions at the IETF
Operational Statistics (OPstat), User Connectivity Problems (UCP) and
Network Joint Management (NJM) working groups.
Table of Contents
1. Introduction.................................................. 2
2. The Generic Model............................................. 2
3. Technical Services............................................ 3
3.1 Domain Name Service......................................... 3
3.2 Public Domain Software...................................... 4
3.3 Network Time................................................ 5
3.4 Network News................................................ 5
3.5 Mailing Lists............................................... 6
4. Experimental Testbeds......................................... 6
5. Network Information Services.................................. 7
6. Network Operations............................................ 7
7. References.................................................... 8
8. Security Considerations....................................... 9
9. Author's Address.............................................. 9
Appendix A Mailing Lists......................................... 10
Appendix B DNS Architecture Strategy............................. 10
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1. Introduction
Over the past few years, the Internet has grown to be a very large
entity and its dependability is critical to its users. Furthermore,
due to the size and nature of the network, the trend has been to
decentralize as many network functions (such as domain name-service,
whois, etc.) as possible. Efforts are being made in resource
discovery [SHHH90] so that the work of researchers is not lost in the
volumes of data that is available on the Internet.
A side result of this growth has been the logical structure imposed
in the Internet of networks classified by function. Tangible examples
in the present state are the NSFnet national backbone, the mid-
level/regional networks and campus networks. Each of these can be
viewed as hierarchies within an organization, each serving a slightly
different function than the other (campus LANs providing access to
local resources, mid-level networks providing access to remote
resources, etc.). The functions of each hierarchy then become the
"services" offered to the organizational layer below it, who in turn
depend on these services.
This document proposes a set of basic technical services that could
be offered by a mid-level network. These services would not only
increase the robustness of the mid-level network itself, but would
also serve to structure the distribution of resources and services
within the Internet. It also proposes a uniform naming convention for
locating the hosts offering these services.
2. The Generic Model
The Internet model that is used as the basis for this document is a
graph of mid-level networks connected to one another, each in turn
connecting the campus/organization networks and with the end users
attached to the campus networks. The model assumes that the mid-level
networks constitute the highest level of functional division within
the Internet hierarchy described above (this could change in the
unforeseen future). With this model in perspective, this document
addresses the objectives of minimizing unnecessary traffic within the
Internet as well as making the entire structure as robust as
possible.
The proposed structure is a derived extension of organizational LANs
where certain services are offered within the organizational LAN
itself, such as nameservice, mail, shared files, single or
hierarchical points of contact for problems, etc.
The following are the services that are discussed as possible
functions of a mid-level network:
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o Technical services
o Experimental sites for testing and dissemination of new
software and technology to end sites on the network
In addition, the following services are mentioned briefly which are
discussed in detail elsewhere [SSM91, ML91]:
o Network Operation services and the interaction between
different mid-level networks in this area
o Network Information services
3. Technical Services
The Internet has grown to be an essential entity because of the
services that it offers to its end users. The list of services is
long and growing, but some services are more widely used and deployed
than others. This section attempts to list and discuss those
technical services that could help a mid-level network provide robust
and improved services to its end sites.
3.1 Domain Name Service
According to the NSFnet traffic statistics collected for May 1991,
about 7% of the packets on the NSFnet backbone were domain nameserver
(DNS) packets. This is a significant amount of traffic, and since
most of the other network applications depend on this service, a
robust DNS service is critical to any Internet site.
Proper location of secondary nameservers so that they are located on
different physical networks can increase the reliability of this
service to a large extent [MOC87a, MOC87b]. However, the nature of
the service requires that the nameservers for the next highest level
be available in order to resolve names outline-mode side of one's
domain. Thus, for "foo.princeton.edu" to resolve "a.mid.net", the
root nameservers which point to mid.net's nameservers have to be
reachable.
To make the service more reliable, the mid-level network could have
at least one nameserver that is able to resolve nameserver queries
for all domains directly connected to it. Thus, in the event that the
entire mid-level network becomes isolated from the rest of the
Internet, applications can still resolve queries for sites directly
connected to the mid-level network. Without this functionality, there
is no way of resolving a name if the root (or higher level)
nameservers become unreachable, even if the query is for a site that
is directly connected and reachable.
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Strategies for implementing this architecture are discussed in
appendix B.
To locate such a "meta-domain" server within a mid-level network, it
is proposed that a nameserver entry for "meta-dns" exist within the
mid-level network's domain.
3.2 Public Domain Software
File transfer traffic constituted 23% of the NSFnet backbone traffic
for May 1991. Public shareware is a very valuable resource within the
Internet and a considerable amount of effort is being put into
developing applications to track all available resources in the
public archives [SHHH90].
It would be difficult, if not impossible to create an up-to-date
repository for every public domain package available on the Internet,
simply because of the volume of software and the rate at which new
software is being developed every day. Some hosts have gained
popularity as good public archives (such as uunet.uu.net, sumex-
aim.stanford.edu, wuarchive.wustl.edu) and new developers tend to
distribute the software to these sites as distribution points. The
economics of maintaining centralized archives is another deterrent to
centralization (the UUnet archives at uunet.uu.net take up roughly
1GB of disk storage).
Recently however, a number of methods for resource discovery have
been developed and are available on the Internet ("ftp-list" file
compiled by John Granose - odin@pilot.njin.net, Archie at
archie.cs.mcgill.ca and Prospero [NEU]).
It is desirable that the mid-level networks be able to provide up-
to-date pointers to the distribution hosts for available public
software archives. Coordinating the distribution of a static list is
difficult (though not impossible) and the use of automated resource
discovery mechanisms such as Archie and Prospero is recommended.
Under ideal conditions, any software that is popular and significant
(e.g., X11, TeX, RFC's) could be archived and distributed within the
mid-level network, but measuring "popularity" and "significance" are
debatable and left for further evaluation. Furthermore, a nameserver
entry for host "swdist" within the domain can provide information on
the various available alternatives for software distribution and
discovery (static file location, pointers to Archie servers, etc.) --
this nameserver entry can be an alias for a CNAME or a TXT entry.
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3.3 Network Time
An important feature of any computer network providing distributed
services is the capability to synchronize the local clocks on the
various systems in the network. Ideally, the clocks of all the
reference sources would be synchronized to national standards by wire
or radio. The importance and immense popularity of this service makes
Network Time a very useful potential service that can be provided by
a mid-level network. No specific protocol for maintaining time is
proposed, and any available protocol that maintains time with
reasonable accuracy could be used.
Network Time Protocol (NTP) traffic constituted 1% of the NSFnet
traffic during May 1991. The traffic might seem insignificant, but
there have been instances where a particular stratum-1 timeserver
(e.g., one of the stratum-1 servers at University of Delaware) has
reached a point of overload with too many different sites trying to
peer with it.
It is proposed that at least one stratum-1 and two stratum-2 servers
be located within a mid-level network (the selection of three servers
is based on the NTP standards documentation [MIL89]). Note that the
servers can be located at any of the directly connected sites in the
network as long as they are publicly accessible. All sites connected
to the mid-level network can then coordinate their system times with
the servers within the mid-level network itself. Besides increasing
the reliability of the timekeeping network, this approach would also
limit the load on each timeserver.
For locating the network time servers within a domain, nameserver
entries for "timekeeper-x" (where x= 1,2,3..) can be made within the
domain. The servers are numbered in order of preference and accuracy.
Thus, "timekeeper-1.foo.net" would be the primary timekeeper and
"timekeeper-2.foo.net" would be additional (possibly secondary)
timekeepers within domain "foo.net". If such hosts are not available
within a domain, a TXT entry pointing to other recommended time-
servers could be provided instead.
3.4 Network News
Network News (or Usenet News) constituted 14% of the NSFnet traffic
in May 1991. Netnews is an expensive service, both in terms of disk
and CPU power, as well as network bandwidth consumed.
The present structure of Network News consists of several hub sites
which are distributed over the Internet. End sites get news feeds
from other sites, and an article gets injected into the news stream
by sending it to the nearest "upstream" site, which then forwards it
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to its connected news sites, and so on. There is no preset norm for
finding a site willing to provide a news feed, and it usually ends up
being a site with whom the site administrator happens to be
acquainted. However, this could easily result in some sites not being
able to get an economical news feed from within the mid-level network
and actually having to derive the feed from a site located on another
mid-level network.
A mid-level network could alleviate such occurrences by being able to
provide a newsfeed to any or all of its directly connected end sites.
Though an expensive resource, some of the costs can be moderated by
acting as a transit news feeder so that the news needn't be stored
for a long time on disk. The software for providing the news feed is
not specific and depends entirely on the newsfeed provider.
3.5 Mailing Lists
Internet mailing lists are another popular source of information in
parallel to Network News. However, like public software, there is no
central repository of all the possible mailing lists available on the
Internet, and it would require considerable effort to compile one (at
the time of writing this document, a fairly comprehensive list is
available on the Internet and mentioned in appendix A.
At this time, there is no clear strategy for distributing or
maintaining mailing lists. However, it can be very expensive for a
site to distribute mail to all individual end users directly, and if
a clear strategy for maintaining a list of mailing-lists can be
devised, then mail exploders can be set up at the mid-level networks,
each of which forwards the mail to exploders at the end sites. This
mechanism would reduce the load on the originating systems, and
provides a clean path for tracking down mailer problems. Also, in
order to prevent bounced mail from propagating back to the originator
of the message, the mailing lists should be set up in a way so that
bounced mail goes to the the "owner" of the list and not to the
originator of the mail message.
A list of major mailing lists for the services discussed in this
document are listed in appendix A.
4. Experimental Testbeds
Due to the working relationships that they have with their end sites
and peer networks, the mid-level networks are very good media for
distribution of new ideas and technology. Examples of this function
are the White Pages pilot project [RS90] established by NYSERnet, the
NSAP routing schema for OSI transitioning [CGC91], etc.
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The mid-level networks could establish cooperative experimental
testbeds for testing and deployment of new technologies similar to
the ones mentioned above. Besides deployment and testing of new
technology, this could also serve to provide a "help" service to the
end-sites and to get them started with the new software.
The exact interaction between the mid-level networks in this area is
not very clear. It is complicated by competition for members between
the mid-level networks and needs to be discussed further.
5. Network Information Services
There are a variety of new and useful user services available on the
Internet that are difficult to document and provide a comprehensive
list of. Some attempt has been made at documenting such resources
[NNS] and a mid-level network can be the initial point of contact for
distribution of such information on a wide basis. The information can
be disseminated in a more controlled and complete manner using this
hierarchical approach if each mid-level network maintains up-to-date
information about its directly connected sites. Network Information
services (NIC) also make the network easier and more attractive to
end users. Examples of these services are:
o provide information resources
- security advisory messages
- list of library catalogs [GL91]
- geographical information servers
- password generators
o resolve end user problems (user support)
These services are NIC related and discussed in detail elsewhere
[SSM91]. For accessibility information, an entry for "nic" could
exist in the DNS for the domain (this could be a TXT entry listing
email or phone number information for users or other NIC's).
6. Network Operations
The Network Operation Center's (NOC's) at the mid-level networks need
to cooperate with each other to resolve network problems. In the
event of a network problem between two mid-level networks or if an
end-site has trouble getting to any host, the mid-level network NOCs
can serve to be the initial point of contact. The procedures for
interaction among NOCs and the formats for exchange of trouble-
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tickets between the NOCs are described elsewhere [JOH91, ML91].
It is important for cooperating NOCs to have contact information for
their directly connected campus/organizational sites and also about
their peer mid-level networks. A distributed mechanism for
maintaining contact information could be implemented by using a
nameserver TXT entry for "noc" or by maintaining "finger" information
for user "noc@domain" or "noc@noc.domain". A NOC "phonebook" listing
the contact information for the various NOCs can be used as a static
non-distributed mechanism (it is understood that the phonebook can
contain outdated information, but the distributed mechanisms can
provide correct and updated NOC information provided that the hosts
are reachable at the desired time). If it is undesirable to publish
the phone number or email address of the NOC for any reason, an entry
saying "unpublished" (or words to that effect) could exist in the
nameserver or "finger" entry instead.
7. References
[BOG] Dunlap, K., and M. Karels, "Nameserver Operations Guide
for Bind Release 4.8", CSRG, Department of Electrical
Engineering and Computer Sciences, University of
California, Berkeley, California.
[CCI88] CCITT Blue Book, "X.500 Series Recommendations", ITU,
1989.
[CGC91] Collela, R., Gardner, E., and R. Callon, "Guidelines for
OSI NSAP Allocation in the Internet'', RFC 1237,
NIST, Mitre, DEC, July 1991.
[SSM91] Sitzler, D., Smith, P., and A. Marine, "Building a Network
Information Services Infrastructure", RFC in
preparation.
[GL91] George, A., and R. Larsen, "Internet Accessible Library
Catalogs & Databases", Aug 1991.
Available via anonymous FTP from ariel.unm.edu.
[JOH91] Johnson, D., "NOC TT Requirements", RFC in
preparation.
[MAN] Mandelbaum, R., and P. Mandelbaum, "The Strategic Future
of the Mid-Level Networks", University of Rochester,
NY, 1991.
[MOC87a] Mockapetris, P., "Domain Names - Implementation and
Specification", RFC 1035, USC Information Sciences
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RFC 1291 Potential Technical Services December 1991
Institute, November 1987.
[MOC87b] Mockapetris, P., "Domain Names - Concepts and
Facilities", RFC 1034, USC Information Sciences
Institute, November 1987.
[MIL89] Mills, D., "Network Time Protocol", RFC 1129, UDel,
October 1989.
[ML91] Mathis, M., and D. Long, "User Connectivity Problems
Working Group", RFC in preparation.
[NEU] Neuman, B., "The Virtual System Model: A Scalable
Approach to Organizing Large Systems", Department of
Computer Science, University of Washington, FR-35,
Seattle, WA, May 1990.
[NNS] NSF Network Service Center, "Internet Resource Guide",
Cambridge, MA.
Available via anonymous FTP from nnsc.nsf.net.
[RS90] Rose, M., and M. Schoffstall, "The NYSERnet White Pages
Pilot Project", NYSERnet, Inc., Mar 1990.
[SHHH90] Schwartz, M., Hardy, D., Heinzman, W., and G.
Hirschowitz, "Supporting Resource Discovery Among
Public Internet Archives", Department of Computer
Science, University of Colorado, Boulder, CO.,
September 1990.
8. Security Considerations
Security issues are not discussed in this memo.
9. Author's Address
Vikas Aggarwal
JvNCnet
6 von Neumann Hall
Princeton University
Princeton, NJ 08544
Phone: +1-609-258-2403
Email: vikas@jvnc.net
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Appendix A - Mailing Lists
The following is a list of popular mailing lists for the services
listed in this document. To subscribe to a particular mailing list,
send a request to "mailing-list-request" (do not send a request to
the entire mailing list).
o ietf@isi.edu: The general mailing list for the Internet
Engineering Task Force. This group is concerned with the evolution
and development of Internet related protocols and standards. Old
mail is archived at "venera.isi.edu" in directory ftp/irg/ietf.
o ntp@trantor.umd.edu: For discussions on the Network Time
Protocol (NTP).
o namedroppers@nic.ddn.mil: Mailing list for discussions on DNS
topics. Old mail is archived at "nic.ddn.mil".
At the time of writing this document, a list of mailing lists on the
Internet is available via anonymous FTP from host "ftp.nisc.sri.com"
in the file "netinfo/interest-groups".
Appendix B - DNS Architecture Strategy
This section discusses practical strategies for implementing a
nameserver architecture within a mid-level network, so that it can
resolve nameserver queries for all domains directly attached to it.
In order to resolve queries for all directly connected networks, a
host that is authoritative for all directly attached domains will
need to exist within the mid-level network. Nameservers at the end
sites would then treat this "group-of-domains" nameserver as a
forwarding server to resolve all non-local queries.
This can be done by adding a line to the named.boot file on the end
site nameservers such as:
forwarders 128.121.50.7 128.32.0.4
This method has the added advantage that the forwarding server builds
up a very rich cache of data [BOG] and acts like a metacache that all
hosts can benefit from. Note that the forwarding server is queried
only if the end-site server cannot service a query locally -- hence
the "meta-domain" server is not overloaded with queries for all
nameserver lookups.
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