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Network Working Group                                           A. RomaoRequest for Comments: 1713                                          FCCNFYI: 27                                                    November 1994Category: InformationalTools for DNS debuggingStatus of this Memo   This memo provides information for the Internet community.  This memo   does not specify an Internet standard of any kind.  Distribution of   this memo is unlimited.Abstract   Although widely used (and most of the times unnoticed), DNS (Domain   Name System) is too much overlooked, in the sense that people,   especially administrators, tend to ignore possible anomalies as long   as applications that need name-to-address mapping continue to work.   This document presents some tools available for domain administrators   to detect and correct those anomalies.1. Introduction   Today more than 3,800,000 computers are inter-connected in a global   Internet [1], comprising several millions of end-users, able to reach   any of those machines just by naming it.  This facility is possible   thanks to the world widest distributed database, the Domain Name   System, used to provide distributed applications various services,   the most notable one being translating names into IP addresses and   vice-versa.  This happens when you do an FTP or Telnet, when your   gopher client follows a link to some remote server, when you click on   a hypertext item and have to reach a server as defined by the URL,   when you talk to someuser@some.host, when your mail has to be routed   through a set to gateways before it reaches the final recipient, when   you post an article to Usenet and want it propagated all over the   world.  While these may be the most visible uses of DNS, a lot more   applications rely on this system to operate, e.g., network security,   monitoring and accounting tools, just to mention a few.   DNS owes much of its success to its distributed administration.  Each   component (called a zone, the same as a domain in most cases), is   seen as an independent entity, being responsible for what happens   inside its domain of authority, how and what information changes and   for letting the tree grow downwards, creating new components.Romao                                                           [Page 1]

RFC 1713                Tools for DNS debugging            November 1994   On the other hand, many inconsistencies arise from this distributed   nature: many administrators make mistakes in the way they configure   their domains and when they delegate authority to sub-domains; many   of them don't even know how to do these things properly, letting   problems last and propagate.  Also, many problems occur due to bad   implementations of both DNS clients and servers, especially very old   ones, either by not following the standards or by being error prone,   creating or allowing many of the above problems to happen.   All these anomalies make DNS less efficient than it could be, causing   trouble to network operations, thus affecting the overall Internet.   This document tries to show how important it is to have DNS properly   managed, including what is already in place to help administrators   taking better care of their domains.2. DNS debugging   To help finding problems in DNS configurations and/or implementations   there is a set of tools developed specifically for this purpose.   There is probably a lot of people in charge of domain administration   having no idea of these tools (and, worse, not aware of the anomalies   that may exist in their configurations).  What follows is a   description of some of these programs, their scope, motivations and   availability, and is hoped to serve as an introduction to the subject   of DNS debugging, as well as a guide to those who are looking for   something to help them finding out how healthy their domains and   servers are.   Some prior knowledge from the reader is assumed, both on DNS basics   and some other tools (e.g., dig and nslookup), which are not analyzed   in detail here; hopefully they are well-known enough from daily   usage.2.1. Host   Host is a program used to retrieve DNS information from name servers.   This information may be used simply to get simple things like   address-to-name mapping, or some more advanced purposes, e.g.,   performing sanity checks on the data.  It was created at Rutgers   University, but then Eric Wassenaar from Nikhef did a major rewrite   and still seems to be actively working on improving it.  The program   is available fromftp://ftp.nikhef.nl/pub/network/host_YYMMDD.tar.Z   (YYMMDD is the date of the latest release).   By default, host just maps host names to Internet addresses, querying   the default servers or some specific one.  It is possible, though, to   get any kind of data (resource records) by specifying different query   types and classes and asking for verbose or debugging output, fromRomao                                                           [Page 2]

RFC 1713                Tools for DNS debugging            November 1994   any name server.  You can also control several parameters like   recursion, retry times, timeouts, use of virtual circuits vs.   datagrams, etc., when talking to name servers.  This way you can   simulate a resolver behavior, in order to find any problems   associated with resolver operations (which is to say, any application   using the resolver library).  As a query program it may be as   powerful as others like nslookup or dig.   As a debugger, host analyzes some set of the DNS space (e.g., an   entire zone) and produces reports with the results of its operation.   To do this, host first performs a zone transfer, which may be   recursive, getting information from a zone and all its sub-zones.   This data is then analyzed as requested by the arguments given on the   command line.  Note that zone transfers are done by contacting   authoritative name servers for that zone, so it must be possible to   make this kind of request from such servers: some of them refuse zone   transfers (except from secondaries) to avoid congestion.   With host you may look for anomalies like those concerning authority   (e.g., lame delegations, described below) or some more exotic cases   like extrazone hosts (a host of the form host.some.dom.ain, where   some.dom.ain is not a delegated zone of dom.ain).  These errors are   produced upon explicit request on the command line, but you may get a   variety of other error messages as a result of host's operations,   something like secondary effects.  These may be mere warnings (which   may be suppressed) or serious errors - in fact, warning messages are   not that simple, most of them are due to misconfigured zones, so it   might not be a good idea to just ignore them.   Error messages have to do with serious anomalies, either with the   packets exchanged with the queried servers (size errors, invalid   ancounts, nscounts and the like), or others related to the DNS   information itself (also called "status messages" in the program's   documentation): inconsistencies between SOA records as shown by   different servers for a domain, unexpected address-to-name mappings,   name servers not responding, not reachable, not running or not   existing at all, and so on.   Host performs all its querying on-line, i.e., it only works with data   received from name servers, which means you have to query a name   server more than once if you want to get different kinds of reports   on some particular piece of data.  You can always arrange arguments   in such a way that you get all information you want by running it   once, but if you forget something or for any reason have to run it   again, this means extra zone transfers, extra load on name servers,   extra DNS traffic.Romao                                                           [Page 3]

RFC 1713                Tools for DNS debugging            November 1994   Host is an excellent tool, if used carefully.  Like most other   querying programs it may generate lots of traffic, just by issuing a   simple command.  Apart from that, its resolver simulation and debug   capabilities make it useful to find many common and some not so   common DNS configuration errors, as well as generate useful reports   and statistics about the DNS tree.  As an example, RIPE (Reseaux IP   Europeens) NCC uses it to generate a monthly european hostcount,   giving an overview of the Internet usage evolution in Europe.  Along   with these counts, error reports are generated, one per country, and   the whole information is made available in the RIPE archive.2.2. Dnswalk   Dnswalk is a DNS debugger written in Perl by David Barr, from   Pennsylvania State University.  You'll find the latest version atftp://ftp.pop.psu.edu/pub/src/dnswalk.  With the software comes a   small document where the author points some useful advice so it may   be worth reading it.   The program checks domain configurations stored locally, with data   arranged hierarchically in directories, resembling the DNS tree   organization of domains.  To set up this information dnswalk may   first perform zone transfers from authoritative name servers. You can   have a recursive transfer of a domain and its sub-domains, though you   should be careful when doing this, as it may generate a great amount   of traffic.  If the data is already present, dnswalk may skip these   transfers, provided that it is up to date.   Dnswalk looks for inconsistencies in resource records, such as MX and   aliases pointing to aliases or to unknown hosts, incoherent PTR, A   and CNAME records, invalid characters in names, missing trailing   dots, unnecessary glue information, and so on.  It also does some   checking on authority information, namely lame delegations and   domains with only one name server.  It is easy to use, you only have   to specify the domain to analyze and some optional parameters and the   program does the rest.  Only one domain (and its sub-domains, if   that's the case) can be checked at a time, though.   While in the process of checking data, dnswalk uses dig and resolver   routines (gethostbyXXXX from the Perl library) a lot, to get such   data as authority information from the servers of the analyzed   domains, names from IP addresses so as to verify the existence of PTR   records, aliases and so on.  So, besides the zone transfers you may   count on some more extra traffic (maybe not negligible if you are   debugging a relatively large amount of data and care about query   retries and timeouts), just by running the program.Romao                                                           [Page 4]

RFC 1713                Tools for DNS debugging            November 19942.3. Lamers   A lame delegation is a serious error in DNS configurations, yet a   (too) common one.  It happens when a name server is listed in the NS   records for some domain and in fact it is not a server for that   domain.  Queries are thus sent to the wrong servers, who don't know   nothing (at least not as expected) about the queried domain.   Furthermore, sometimes these hosts (if they exist!) don't even run   name servers.  As a result, queries are timed out and resent, only to   fail, thus creating (more) unnecessary traffic.   It's easy to create a lame delegation: the most common case happens   when an administrator changes the NS list for his domain, dropping   one or more servers from that list, without informing his parent   domain administration, who delegated him authority over the domain.   From now on the parent name server announces one or more servers for   the domain, which will receive queries for something they don't know   about.  (On the other hand, servers may be added to the list without   the parent's servers knowing, thus hiding valuable information from   them - this is not a lame delegation, but shouldn't happen either.)   Other examples are the inclusion of a name in an NS list without   telling the administrator of that host, or when a server suddenly   stops providing name service for a domain.   To detect and warn DNS administrators all over the world about this   kind of problem, Bryan Beecher from University of Michigan wrote   lamers, a program to analyze named (the well-known BIND name server)   logging information [2].  To produce useful logs, named was applied a   patch to detect and log lame delegations (this patch was originally   written by Don Lewis from Silicon Systems and is now part of the   latest release of BIND thanks to Bryan Beecher, so it is expected to   be widely available in the near future).  Lamers is a small shell   script that simply scans these logs and reports the lame delegations   found.  This reporting is done by sending mail to the hostmasters of   the affected domains, as stated in the SOA record for each of them.   If this is not possible, the message is sent to the affected name   servers' postmasters instead.  Manual processing is needed in case of   bounces, caused by careless setup of those records or invalid   postmaster addresses.  A report of the errors found by the U-M   servers is also posted twice a month on the USENET newsgroup   comp.protocols.tcp-ip.domains.   If you ever receive such a report, you should study it carefully in   order to find and correct problems in your domain, or see if your   servers are being affected by the spreading of erroneous information.   Better yet, lamers could be run on your servers to detect more lame   delegations (U-M can't see them all!).  Also, if you receive mail   reporting a lame delegation affecting your domain or some of yourRomao                                                           [Page 5]

RFC 1713                Tools for DNS debugging            November 1994   hosts, please don't just ignore it or flame the senders.  They're   really trying to help!   You can get lamers fromftp://terminator.cc.umich.edu/dns/lame-delegations.2.4. DOC   Authority information is one of the most significant parts of the DNS   data, as the whole mechanism depends on it to correctly traverse the   domain tree.  Incorrect authority information leads to problems such   as lame delegations or even, in extreme cases, the inaccessibility of   a domain.  Take the case where the information given about all its   name servers is incorrect: being unable to contact the real servers   you may end up being unable to reach anything inside that domain.   This may be exaggerated, but if you're on the DNS business long   enough you've probably have seen some enlightened examples of this   scenario.   To look for this kind of problems Paul Mockapetris and Steve Hotz,   from the Information Sciences Institute, wrote a C-shell script   called DOC (Domain Obscenity Control), an automated domain testing   tool that uses dig to query the appropriate name servers about   authority for a domain and analyzes the responses.   DOC limits its analysis to authority data since the authors   anticipated that people would complain about such things as invasion   of privacy.  Also, at the time it was written most domains were so   messy that they thought there wouldn't be much point in checking   anything deeper until the basic problems weren't fixed.   Only one domain is analyzed each time: the program checks if all the   servers for the parent domain agree about the delegation information   for the domain.  DOC then picks a list of name servers for the domain   (obtained from one of the parent's servers) and starts checking on   their information, querying each of them: looks for the SOA record,   checks if the response is authoritative, compares the various records   retrieved, gets each one's list of NS, compares the lists (both among   these servers and the parent's), and for those servers inside the   domain the program looks for PTR records for them.   Due to several factors, DOC seems to have frozen since its first   public release, back in 1990.  Within the distribution there is an   RFC draft about automated domain testing, which was never published.   Nevertheless, it may provide useful reading.  The software can be   fetched fromftp://ftp.uu.net/networking/ip/dns/doc.2.0.tar.Z.Romao                                                           [Page 6]

RFC 1713                Tools for DNS debugging            November 19942.5. DDT   DDT (Domain Debug Tools) is a package of programs to scan DNS   information for error detection, developed originally by Jorge Frazao   from PUUG - Portuguese UNIX Users Group and later rewritten by the   author, at the time at the Faculty of Sciences of University of   Lisbon.  Each program is specialized in a given set of anomalies: you   have a checker for authority information, another for glue data, mail   exchangers, reverse-mappings and miscellaneous errors found in all   kinds of resource records.  As a whole, they do a rather extensive   checking on DNS configurations.   These tools work on cached DNS data, i.e., data stored locally after   performing zone transfers (presently done by a slightly modified   version of BIND's named-xfer, called ddt-xfer, which allows recursive   transfers) from the appropriate servers, rather than querying name   servers on-line each time they run.  This option was taken for   several reasons [3]: (1) efficiency, since it reads data from disk,   avoiding network transit delays, (2) reduced network traffic, data   has to be fetched only once and then run the programs over it as many   times as you wish and (3) accessibility - in countries with limited   Internet access, as was the case in Portugal by the time DDT was in   its first stages, this may be the only practical way to use the   tools.   Point (2) above deserves some special considerations: first, it is   not entirely true that there aren't additional queries while   processing the information, one of the tools, the authority checker,   queries (via dig) each domain's purported name servers in order to   test the consistency of the authority information they provide about   the domain.  Second, it may be argued that when the actual tests are   done the information used may be out of date.  While this is true,   you should note that this is the DNS nature, if you obtain some piece   of information you can't be sure that one second later it is still   valid.  Furthermore, if your source was not the primary for the   domain then you can't even be sure of the validity in the exact   moment you got it in the first place.  But experience shows that if   you see an error, it is likely to be there in the next version of the   domain information (and if it isn't, nothing was lost by having   detected it in the past).  On the other side, of course there's   little point in checking one month old data...   The list of errors looked for includes lame delegations, version   number mismatches between servers (this may be a transient problem),   non-existing servers, domains with only one server, unnecessary glue   information, MX records pointing to hosts not in the analyzed domain   (may not be an error, it's just to point possibly strange or   expensive mail-routing policies), MX records pointing to aliases, ARomao                                                           [Page 7]

RFC 1713                Tools for DNS debugging            November 1994   records without the respective PTR and vice-versa, missing trailing   dots, hostnames with no data (A or CNAME records), aliases pointing   to aliases, and some more.  Given the specialized nature of each   tool, it is possible to look for a well defined set of errors,   instead of having the data analyzed in all possible ways.   Except for ddt-xfer, all the programs are written in Perl.  A new   release may come into existence in a near future, after a thorough   review of the methods used, the set of errors checked for and some   bug fixing (in particular, a Perl version of ddt-xfer is expected).   In the mean time, the latest version is available fromftp://ns.dns.pt/pub/dns/ddt-2.0.1.tar.gz.2.6. The Checker Project   The problem of the huge amount of DNS traffic over the Internet is   getting researchers close attention for quite some time, mainly   because most of it is unnecessary.  Observations have shown that DNS   consumes something like twenty times more bandwidth than it should   [4].  Some causes for this undoubtedly catastrophic scenario lie on   deficient resolver and name server implementations spread all over   the world, from personal to super-computers, running all sorts of   operating systems.   While the panacea is yet to be found (claims are made that the latest   official version of BIND is a great step forward [5]), work has been   done in order to identify sources of anomalies, as a first approach   in the search for a solution.  The Checker Project is one such   effort, developed at the University of Southern California [6].  It   consists of a set of C code patched into BIND's named, for monitoring   server activity, building a database with the history of that   operation (queries and responses).  It is then possible to generate   reports from the database summarizing activity and identifying   behavioral patterns from client requests, looking for anomalies.  The   named code alteration is small and simple unless you want do have PEC   checking enabled (see below).  You may find sources and documentation   atftp://catarina.usc.edu/pub/checker.   Checker only does this kind of collection and reporting, it does not   try to enforce any rules on the administrators of the defective sites   by any means whatsoever.  Authors hope that the simple exhibition of   the evidences is a reason strong enough for those administrators to   have their problems fixed.   An interesting feature is PEC (proactive error checking): the server   pretends to be unresponsive for some queries by randomly choosing   some name and start refusing replies for queries on that name during   a pre-determined period.  Those queries are recorded, though, to tryRomao                                                           [Page 8]

RFC 1713                Tools for DNS debugging            November 1994   to reason about the retry and timeout schemes used by name servers   and resolvers.  It is expected that properly implemented clients will   choose another name server to query, while defective ones will keep   on trying with the same server.  This feature seems to be still under   testing as it is not completely clear yet how to interpret the   results.  A PEC-only error checker is available from USC that is much   simpler than the full error checker.  It examines another name server   client every 30 minutes to see if this client causes excessive load.   Presently Checker has been running on a secondary for the US domain   for more than a year with little trouble.  Authors feel confident it   should run on any BSD platform (at least SunOS) without problems, and   is planned to be included as part of the BIND name server.   Checker is part of a research project lead by Peter Danzig from USC,   aimed to implement probabilistic error checking mechanisms like PEC   on distributed systems [7].  DNS is one such system and it was chosen   as the platform for testing the validity of these techniques over the   NSFnet.  It is hoped to achieve enough knowledge to provide means to   improve performance and reliability of distributed systems.   Anomalies like undetected server failures, query loops, bad   retransmission backoff algorithms, misconfigurations and resubmission   of requests after negative replies are some of the targets for these   checkers to detect.2.7. Others   All the tools described above are the result of systematic work on   the issue of DNS debugging, some of them included in research   projects.  For the sake of completeness several other programs are   mentioned here.  These, though just as serious, seem to have been   developed in a somewhat ad-hoc fashion, without an implicit intention   of being used outside the environments where they were born.  This   impression is, of course, arguable, nevertheless there was no   necessity of dedicating an entire section to any of them.  This   doesn't mean they are not valuable contributions, in some cases they   may be just what you are looking for, without having to install a   complete package to do some testings on your domain.   The reference taken was the contrib directory in the latest BIND   distribution (where some of the above programs can also be found).   There you will find tools for creating your DNS configuration files   and NIS maps from /etc/hosts and vice-versa or generate PTR from A   records (these things may be important as a means of avoiding common   typing errors and inconsistencies between those tables), syntax   checkers for zone files, programs for querying and monitoring name   servers, all the small programs presented in [8], and more.  It is   worth spending some time looking at them, maybe you'll find thatRomao                                                           [Page 9]

RFC 1713                Tools for DNS debugging            November 1994   program you were planning to write yourself.  The latest public   version of BIND can be found atftp://gatekeeper.dec.com/pub/misc/vixie/4.9.2-940221.tar.gz.  As of   this writing BIND-4.9.3 is in its final beta stages and a public   release is expected soon, also at gatekeeper.dec.com.   You may also want to consider using a version control system like   SCCS or RCS to maintain your configuration files consistent through   updates, or use tools like M4 macros to generate those files.  As   stated above, it's important to avoid human-generated errors,   creating problems that are difficult to track down, since they're   often hidden behind some mistyped name.  Errors like this may end up   in many queries for a non-existing name, just to mention the less   serious kind.  See [9] for a description of the most common errors   made while configuring domains.3. Why look after DNS?   Several pieces of software were presented to help people administer   and debug their name services.  They exhibit many differences in   their way of doing things, scope and requirements and it may be   difficult just to choose one of them to work with.  For one thing,   people's expectations from these tools vary according to their kind   of involvement with DNS.  If you are responsible for a big domain,   e.g., a top-level one or a big institution with many hosts and sub-   domains, you probably want to see how well is the tree below your   node organized, since the consequences of errors tend to propagate   upwards, thus affecting your own domain and servers.  For that you   need some program that recursively descends the domain tree and   analyzes each domain per se and the interdependencies between them   all.  You will have to consider how deep you want your analysis to   be, the effects it will have on the network infrastructure, i.e.,   will it generate traffic only inside a campus network, no matter how   big it is, or will it be spread over, say, a whole country (of   course, your kind of connectivity plays an important role here).   You may simply want to perform some sanity checks on your own domain,   without any further concerns.  Or you may want to participate in some   kind of global effort to monitor name server traffic, either for   research purposes or just to point out the "trouble-queries" that   flow around.   Whatever your interest may be, you can almost surely find a tool to   suit it.  Eliminating problems like those described in this document   is a major contribution for the efficiency of an important piece of   the Internet mechanism.  Just to have an idea of this importance,   think of all the applications that depend on it, not just to get   addresses out of names.  Many systems rely on DNS to store, retrieveRomao                                                          [Page 10]

RFC 1713                Tools for DNS debugging            November 1994   and spread the information they need: Internet electronic mail was   already mentioned (see [10] for details) and work is in progress to   integrate X.400 operations with DNS [11]; others include "remote   printing" services [12], distributed file systems and network routing   purposes, among others.  These features may be accomplished by some   standard, well-known resource records [13], or by new, experimental   ones [14,15].  Even if some of them won't succeed, one may well   expect some more load on the DNS burden.   The ubiquitous DNS thus deserves a great deal of attention, perhaps   much more than it generally has.  One may say that it is a victim of   its own success: if a user triggers an excessive amount of queries   only to have one request satisfied, he won't worry about it (in fact,   he won't notice it), won't complain to his system administrator, and   things will just go on like this.  Of course, DNS was designed to   resist and provide its services despite all these anomalies.  But by   doing so it is frequently forgotten, as long as people can Telnet or   ftp.  As DNS will be given new responsibilities, as pointed in the   above paragraph, the problems described in this text will grow more   serious and new ones may appear (notably security ones [16], with a   lot of work being presently in progress addressing security in DNS),   if nothing is done to purge them.References   [1] Lottor, M., "Internet Domain Survey, October 1994",http://www.nw.com/zone/WWW/report.html, October 1994.   [2] Beecher, B., "Dealing With Lame Delegations", Univ. Michigan,       LISA VI, October 1992.   [3] Frazao, J. and J. L. Martins, "Ddt - Domain Debug Tools, A       Package to Debug the DNS Tree", Dept. Informatica Faculdade       Ciencias Univ. Lisboa, DI-FCUL-1992-04, January 1992.   [4] Danzig, P., "Probabilistic Error Checkers: Fixing DNS", Univ.       Southern California, Technical Report, February 1992.   [5] Kumar, A., J. Postel, C. Neuman, P. Danzig and S. Miller, "Common       DNS Implementation Errors and Suggested Fixes",RFC 1536,       USC/Information Sciences Institute, October 1993.   [6] Miller, S. and P. Danzig, "The Checker Project, Installation and       Operator's Manual", Univ. Southern California, TR CS94-560, 1994.   [7] Danzig, P., K. Obraczka and A. Kumar, "An Analisys of Wide-Area       Name Server Traffic", Univ. Southern California, TR 92-504, 1992.Romao                                                          [Page 11]

RFC 1713                Tools for DNS debugging            November 1994   [8] Albitz, P. and C. Liu, "DNS and BIND", O'Reilly and Associates       Inc., October 1992.   [9] Beertema, P., "Common DNS Data File Configuration Errors",RFC1537, CWI, October 1993.  [10] Partridge, C., "Mail Routing and the Domain System", STD 14,RFC974, CSNET CIC BBN Laboratories Inc., January 1986.  [11] Allocchio, C., A. Bonito, B. Cole, S. Giordano and R. Hagens,       "Using the Internet DNS to DistributeRFC1327 Mail Address       Mapping Tables",RFC 1664, GARR, Cisco Systems Inc., Centro       Svizzero Calcolo Scientifico, ANS, August 1994.  [12] Malamud, C. and M. Rose, "Principles of Operation for the TPC.INT       Subdomain: General Principles and Policy",RFC 1530, Internet       Multicasting Service, Dover Beach Consulting Inc., October 1993.  [13] Rosenbaum, R., "Using the Domain Name System to Store Arbitrary       String Attributes",RFC 1464, Digital Equipment Corporation, May       1993.  [14] Everhart, C., L. Mamakos, R. Ullmann and P. Mockapetris (Ed.),       "New DNS RR Definitions",RFC 1183, Transarc, Univ. Maryland,       Prime Computer, Information Sciences Institute, October 1990.  [15] Manning, B., and R. Colella, "DNS NSAP Resource Records",RFC1706, USC/Information Sciences Institute, NIST, October 1994.  [16] Gavron, E., "A Security Problem and Proposed Correction With       Widely Deployed DNS Software",RFC 1535, ACES Research Inc.,       October 1993Romao                                                          [Page 12]

RFC 1713                Tools for DNS debugging            November 1994Security Considerations   Security issues are not discussed in this memo (although security is   briefly mentioned at the end ofsection 3).Author's Address   Artur Romao   DI - Faculdade de Ciencias e Tecnologia   Universidade Nova de Lisboa   Quinta da Torre   P-2825 Monte de Caparica   Portugal   Phone: +351 1 294 28 44   Fax:   +351 1 295 77 86   EMail: artur@fct.unl.ptRomao                                                          [Page 13]