Ubuntu Manpage: dnswalk - A DNS database debugger

NAME

       dnswalk - A DNS database debugger

SYNOPSIS

       dnswalk [ -adilrfFm ] domain.

DESCRIPTION

       dnswalk  is  a DNS debugger.  It performs zone transfers of specified domains, and checks the database in
       numerous ways for internal consistency, as well as for correctness according to accepted  practices  with
       the Domain Name System.

       The  domain  name  specified  on the command line MUST end with a '.'.  You can specify a forward domain,
       such as dnswalk podunk.edu.  or a reverse domain, such as dnswalk 3.2.1.in-addr.arpa.

OPTIONS

-r Recursively descend sub-domains of the specified domain. Use with care.
-a Turn on warning of duplicate A records. (see below)
-d Print debugging and 'status' information to stderr. (Use only if redirecting stdout) See
DIAGNOSTICS section.
-m Perform checks only if the zone has been modified since the previous run.
-F perform "fascist" checking. When checking an A record, compare the PTR name for each IP address
with the forward name and report mismatches. (see below) I recommend you try this option at
least once to see what sorts of errors pop up - you might be surprised!.
-i Suppress check for invalid characters in a domain name. (see below)
-l Perform "lame delegation" checking. For every NS record, check to see that the listed host is
indeed returning authoritative answers for this domain.
ERRORS
The following the list of error messages that dnswalk will return if it sees a potential problem
with the database. Duplicate messages will be suppressed automatically for each zone. Error
messages are prefixed by a keyword indicating the message type: "WARN" (possible data problem),
"FAIL" (failure to access data), or "BAD" (invalid data). dnswalk exits with a return code equal
to the number of "BAD" errors.
X PTR Y: unknown host
X is a PTR record to Y, but Y is not a valid host (no A record). These are often left over from
when someone deleted a host from the DNS and forgot to delete the PTR record.
X PTR Y: A record not found
X is a PTR record to Y, but the IP address associated with the PTR record is not listed as an
address for Y. There should be an A record for every valid IP address for a host. Many Internet
services will not talk to you if you have mismatched PTR records.
X PTR Y: CNAME (to Z)
X is a PTR record to Y, but Y is a CNAME to Z. PTR records MUST point to the canonical name of a
host, not an alias.
X CNAME Y: unknown host
X is aliased to Y, but Y is not a valid host (no A record).
X CNAME Y: CNAME (to Z)
X is aliased to Y, but Y is aliased to Z. CNAMEs should not be chained.
X MX Y: unknown host
X is an MX to Y, but Y is not a valid host (no A record).
X MX Y: CNAME (to Z)
X is an MX to Y, but Y is an alias for Z. MX records must point to the canonical name, not an
alias.
X A Y: no PTR record
X has an IP address Y, but there is no PTR record to map the IP address Y back to a hostname
(usually X). Many Internet servers (such as anonymous FTP servers) will not talk to addresses that
don't have PTR records.
warning: X has only one authoritative nameserver
Zones must have at least one authoritative nameserver, in case one is down or unreachable. Make
sure the parent and child domains list all authoritative nameservers for a zone.
Cannot check X: no available nameservers!
The X zone was delegated with NS records but all the nameservers for the zone are either
unavailable or say that they have no data for the zone (are lame). Verify that the X zone isn't
a typo, and if so make sure that all the listed nameservers are configured to answer with data for
the zone.
X: invalid character(s) in name
Allowable characters in a domain name are the ASCII letters a through Z the digits 0 through 9,
and the "-" character. A "." may be used only as a domain separator. (checking can be suppressed
with -i )
X: domain occurred twice, forgot trailing '.'?
A sanity check which looks for "dom.ain.dom.ain." in a name. This is often caused by forgetting
to put a trailing '.' on the end of a name.
(with -a switch)
X: possible duplicate A record (glue of Z?)
A duplicate A records is listed for X. NOTE: this is most often caused by the practice of always
putting A records for all secondaries after NS glue records. While this is not an error, it is
usually redundant and makes changing IP addresses later more difficult, since they occur more than
one time in the file (and in multiple files). You may get spurious errors, mostly because of a
quirk in BIND releases before 4.9.x that reports cached glue A records in a zone transfer even
though they don't exist in the original zone file.
(with -F switch)
X A Y: points to Z
X has Y for an IP address, but the PTR record associated with Y returns "Z" as the name associated
with that host. This is not necessarily an error (for example if you have an A record for your
domain name), but can be useful to check for A records which point to the wrong host, or PTR
records that point to the wrong host.
Cannot find address for nameserver X
This error is generated if the address for a delegated nameserver X cannot be resolved. This
could be a lame delegation (due to a typo in delegation), or a temporary DNS error.
(with -l switch)
X NS Y: lame NS delegation
Y is a listed nameserver for zone X, but Y is not returning authoritative data for zone X. This
is usually the result of a lack of communication on the part of the respective hostmasters. Lame
delegations are not fatal problems except in severe cases, they just tend to create significant
increases in DNS traffic. NS records for the parent and child domains should be consistent, and
each server listed in the NS record MUST be able to answer with authoritative data, either by
being a primary or secondary for the zone.
Cannot get SOA record for X from Y (lame?)
This error is generated if dnswalk cannot get the SOA record for zone X from the nameserver Y.
This could mean a lame delegation, or simply that the host is temporarily unreachable.

DIAGNOSTICS

       When invoked with the -d option, dnswalk will  print  status  information  to  stderr.   It  consists  of
       information  about  what  zone is being checked, and a single letter corresponding to the resource record
       checked, and any errors.
       a      A record
       c      CNAME record
       p      PTR record
       m      MX record
       s      SOA record
       !      An error occurred
       .      A previous error in the zone was repeated, but suppressed.

BUGS

       dnswalk will make the directory tree before it has a chance to find out that you gave it a  bogus  domain
       name.
       When  checking  lots  of hosts and lots of options, it is very slow.  Running dnswalk on a machine with a
       local nameserver helps considerably.
       Perl's gethostby{name,addr}() routine doesn't seem to consistently return an error whenever it is  unable
       to  resolve  an  address.   Argh.   This will mean lots of "no PTR record" and "host unknown" errors if a
       server is unavailable, or for some reason the lookup fails.  You may get strange error messages  if  your
       perl was compiled without support for herror().

AUTHOR

       David Barr <barr@cis.ohio-state.edu>

                                                                                                      DNSWALK(1)