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Maintaining BIND
Next: 8. Growing Your Domain
 

7.6 Keeping Everything Running Smoothly

A significant part of maintenance is being aware when something has gone wrong, before it becomes a real problem. If you catch a problem early, chances are it'll be that much easier to fix. As the old adage says, an ounce of prevention is worth a pound of cure.

This isn't quite troubleshooting - we'll devote an entire chapter to troubleshooting later - think of it as "pre-troubleshooting." Troubleshooting (the pound of cure) is what you have to do if you ignore maintenance, after your problem has developed complications, and you need to identify the problem by its symptoms.

The next two sections deal with preventative maintenance: looking periodically at the syslog file and at the BIND name server statistics to see whether any problems are developing. Consider this a name server's medical checkup.

7.6.1 Common Syslog Messages

There are a large number of syslog messages named can emit. In practice, you'll only see a few of them. We'll cover the most common syslog messages here, excluding reports of syntax errors in DNS database files.

Every time you start named , it sends out this message at priority LOG_NOTICE :

Jan 10 20:48:32 terminator named[3221]: starting.  named 8.1.2

This message logs the fact that named started at this time, and tells you the version of BIND you're running. This is, of course, nothing to be concerned about. It is a good place to look if you're not sure what version of BIND your operating system supports. (Older versions of BIND used "restarted" instead of "starting." )

Every time you send the name server a HUP signal, it sends out this message at priority LOG_NOTICE :

Jan 10 20:50:16 terminator named[3221]: reloading nameserver

The "reloading" message just tells you that named reloaded its database (as a result of a HUP signal) at this time. Again, this is nothing to be concerned about. This message will most likely be of interest when you are tracking down how long a bad resource record has been in your name server data or how long a whole zone has been missing because of a mistake during an update.

Another message you may see shortly after your name server starts is:

Jan 10 20:50:20 terminator named[3221]: cannot set resource limits on
                this system

This means that your name server thinks your operating system does not support the getrlimit() and setrlimit() system calls, which are used when you try to define coresize , datasize , stacksize or files on a BIND 8 name server. It doesn't matter whether you're actually using any of these substatements in your configuration file; BIND will print the message anyway. If you're not using these substatements, ignore the message. If you are, and you think your operating system does support getrlimit() and setrlimit() , you'll have to recompile BIND with HAVE_GETRUSAGE defined. This message in logged at priority LOG_INFO .

If you run your name server on a host with many network interfaces, especially virtual network interfaces, you may see this message soon after startup, or even after your name server has run well for a while:

Jan 10 20:50:31 terminator named[3221]: fcntl(dfd, F_DUPFD, 20): Too
                many open files




Jan 10 20:50:31 terminator named[3221]: fcntl(sfd, F_DUPFD, 20): Too
                many open files

This means that BIND has run out of file descriptors. BIND uses a fair number of file descriptors: two for each network interface it's listening on (one for UDP and one for TCP ), and one for opening zone data files. If that's more than the limit your operating system places on processes, BIND won't be able to get any more file descriptors and you'll see this message. The priority will depend on which part of BIND fails to get the file descriptor: the more critical the subsystem, the higher the priority.

The next step is to either get BIND to use fewer file descriptors, or to raise the limit the operating system places on the number of file descriptors BIND can use:

  • If you don't need BIND listening on all of your network interfaces (particularly the virtual ones), use the listen-on substatement to configure BIND to listen only on those interfaces it needs to. See Chapter 10 for details on the syntax of listen-on .

  • If your operating system supports getrlimit() and setrlimit() (see above), configure your name server to use a larger number of files with the files substatement. See Chapter 10 for details on using the files substatement.

  • If your operating system places too restrictive a limit on open files, raise that limit before you start named with the ulimit command.

Every time a BIND 8 name server loads a zone, it sends out a message at priority LOG_INFO :

Jan 10 21:49:50 terminator named[3221]: master zone "movie.edu" (IN)
                loaded(serial 1996011000)



( BIND 4.9 name servers call it a "primary zone" instead of a "master zone." ) This tells you when the name server loaded the zone, the class (in this case, IN ) of the zone, and the serial number in the zone's SOA record.

About every hour, a BIND 8 name server will send a message at priority LOG_INFO that snapshots the current statistics:

Feb 18 14:09:02 terminator named[3565]: USAGE 824681342 824600158
                CPU=13.01u/3.26s CHILDCPU=9.99u/12.71s
Feb 18 14:09:02 terminator named[3565]: NSTATS 824681342 824600158
                A=4 PTR=2
Feb 18 14:09:02 terminator named[3565]: XSTATS 824681342 824600158
                RQ=6 RR=2 RIQ=0 RNXD=0 RFwdQ=0 RFwdR=0 RDupQ=0 RDupR=0
                RFail=0 RFErr=0 RErr=0 RTCP=0 RAXFR=0 RLame=0 Ropts=0
                SSysQ=2 SAns=6 SFwdQ=0 SFwdR=0 SDupQ=5 SFail=0 SFErr=0
                SErr=0 RNotNsQ=6 SNaAns=2 SNXD=1

(This feature was also present in BIND 4.9 through 4.9.3, then turned off in the 4.9.4 server.) The first two numbers for each message are time. If you subtract the second number from the first number, you'll find out how many seconds your server has been running. (You'd think the name server could do that for you.) The CPU entry tells you how much time your server has spent in user mode (13.01 seconds) and system mode (3.26 seconds). Then it tells you the same statistic for child processes. The NSTATS message lists the query types your server has received and the counts for each. The XSTATS message lists additional statistics. The statistics under NSTATS and XSTATS are explained in more detail later in this chapter.

If BIND version 4.9.4 or later finds a name that doesn't conform to RFC 952, it logs a syslog error:

Jul 24 20:56:26 terminator named[1496]: owner name "ID_4.movie.edu IN"
                                      (primary) is invalid - rejecting

This message is logged at level LOG_NOTICE . See Chapter 4 for the host naming rules.

Another syslog message, sent at priority LOG_INFO , is a warning message about the zone data:

Jan 10 20:48:38 terminator named[3221]: terminator2 has CNAME
                and other data (invalid)

This message means that there's a problem with your zone data. For example, you may have entries like these:

terminator2  IN  CNAME t2
terminator2  IN  MX    10 t2
t2           IN  A     192.249.249.10
t2           IN  MX    10 t2

The MX record for terminator2 is incorrect, and would cause the message given above. terminator2 is an alias for t2 , which is the canonical name. As described earlier, when DNS looks up a name and finds a CNAME , it replaces the original name with the canonical name, and then tries looking up the canonical name. Thus, when the server looks up the MX data for terminator2 , it finds a CNAME record and then looks up the MX record for t2 . Since the server follows the CNAME record for terminator2 , it will never use the MX record for terminator2 ; in fact, this record is illegal. In other words, all resource records for a host have to use the canonical name ; it's an error to use an alias in place of the canonical name.

The following message indicates that a slave was unable to reach any master server when it tried to do a zone transfer:

Jan 10 20:52:42 wormhole named[2813]: zoneref: Masters for
                secondary zone "movie.edu" unreachable

This message is sent at priority LOG_NOTICE , and is only sent the first time the zone transfer fails. When the zone transfer finally succeeds, a 4.9 or later server will tell you that the zone transferred by issuing another syslog message. Older servers don't tell you when the zone transferred. When this message first appears, you don't need to take any immediate action. The name server will continue to attempt to transfer the zone, according to the retry period in the SOA record. After a few days (or half the expire time), you might check that the server was able to transfer the zone. On servers that don't issue the syslog message when the zone transfers, you can verify that the zone transferred by checking the timestamp on the backup file. When a zone transfer succeeds, a new backup file is created. When a zone is found to be up to date, the backup file is touched (а la the UNIX touch command). In both cases, the timestamp on the backup file is updated, so go to the slave and give the command ls -l /usr/local/named/db.* . This will tell you when the slave last synchronized each zone with the master server. We'll cover how to troubleshoot slaves failing to transfer zones in Chapter 13 .

If you are watching the syslog messages on your 4.9 or later master server, you'll see a LOG_INFO syslog message when the slave does pick up the new zone data or when a tool, like nslookup , transfers a zone:

Mar  7 07:30:04 terminator named[3977]: approved AXFR from
                           [192.249.249.1].2253 for "movie.edu"

If you are using the version 4 xfrnets configuration file statement or version 8 allow-transfer option statement (explained in Chapter 10 ) to limit which servers can load zones, you may see this message saying unapproved instead of approved .

This syslog message is seen only if you capture LOG_INFO syslog messages:

Jan 10 20:52:42 wormhole named[2813]: Malformed response


                from 192.1.1.1

Most often, this message means that some bug in a name server caused it to send an erroneous response packet. The error probably occurred on the remote name server (192.1.1.1) rather than the local server ( wormhole ). Diagnosing this kind of error involves capturing the response packet in a network trace and decoding it. Decoding DNS packets manually is beyond the scope of this book, so we won't go into much detail. You see this type of error when the response packet says it has several answers in the answer section (like four address resource records), and yet the answer section only contains a single answer. The only course of action is to notify the hostmaster (or root) of the offending host via email (assuming you can get the name of the host by looking up the address). You would also see this message if the underlying network altered (damaged) the UDP response packets in some way. Checksumming of UDP packets is optional, so this error might not be caught at a lower level.

named logs this message when you try to sneak into your zone file data that belongs in another zone:

Jun 13 08:02:03 terminator named[2657]: db.movie:28: data "foo.bar.edu"


                           outside zone "movie.edu" (ignored)

For instance, if we tried to use this zone data:

robocop       IN A  192.249.249.2
terminator    IN A  192.249.249.3

; Add this entry to the name server's cache
foo.bar.edu.  IN A  10.0.7.13

we'd be adding data for the bar.edu zone into our movie.edu zone file. A 4.8.3 vintage name server would blindly add foo.bar.edu to its cache. It wouldn't check that all the data in the db.movie file was in the movie.edu zone. You can't fool a name server newer than 4.9, though. This syslog message is logged at priority LOG_INFO .

Earlier in the book we said that you can't use a CNAME in the data portion of a resource record. BIND versions 4.9 and later will catch this misuse:

Jun 13 08:21:04 terminator named[2699]: "movie.edu IN NS" points to a
                                        CNAME (dh.movie.edu)

Here is an example of the guilty resource records:

@                      NS       terminator.movie.edu.
                       NS       dh.movie.edu.
terminator.movie.edu.  IN A     192.249.249.3
diehard.movie.edu.     IN A     192.249.249.4
dh                     IN CNAME diehard

The second NS record should have listed diehard.movie.edu instead of dh.movie.edu . This syslog message won't show up immediately when you start your name server.

NOTE: You'll only see the syslog message when the offending data is looked up. This syslog message is logged by a 4.9.3 or BIND 8 server at priority LOG_INFO , and by a 4.9.4 to 4.9.7 server at priority LOG_DEBUG .

This message indicates that your name server may be guarding itself against one type of network attack:

Jun 11 11:40:54 terminator named[131]: Response from unexpected source
                                       ([204.138.114.3].53)

Your name server sent a query to a remote name server, and a response came, but it wasn't from any of the addresses your name server had listed for the remote name server. The potential security breach is this: an intruder causes your name server to query a remote name server, and at the same time the intruder sends responses (pretending the responses are from the remote name server) that the intruder hopes your name server will add to its cache. Perhaps he sends along a false PTR record, pointing the IP address of one of his hosts to the domain name of a host you trust. Once the false PTR record is in your cache, the intruder uses one of the BSD "r" commands (e.g., rlogin ) to gain access to your system.

Less paranoid admins will realize that this situation can also happen if the parent name server only knows about one of the IP addresses of a multihomed name server host. The parent tells your name server the one IP address it knows about, and when your server queries the remote name server, the remote name server responds from the other IP address. This shouldn't happen if BIND is running on the remote name server host, because BIND makes every attempt to use the same IP address in the response as the query was sent to. This syslog message is logged at priority LOG_INFO .

Here's an interesting syslog message:

Jun 10 07:57:28 terminator named[131]: No root nameservers for
                class 226

The only classes defined to date are: class 1, Internet ( IN ); class 3, Chaos ( CH ); and class 4, Hesiod ( HS ). Where does class 226 come from? That's exactly the point your name server is making with this syslog message. Something is wrong in the world because there is no class 226. What can you do about it? Nothing, really. This message doesn't give you enough information - you don't know who the query is from or what the query was for. Then again, if the class field is corrupted, the query name may be garbage too. The actual cause of the problem could be a broken remote name server or resolver, or it could be a corrupted UDP datagram. This syslog message is logged at priority LOG_INFO .

This message might happen if you are backing up some other zone:

Jun  7 20:14:26 wormhole named[29618]: Zone "253.253.192.in-addr.arpa"
                (class 1) SOA serial# (3345) rcvd from [192.249.249.10]
                is < ours (563319491)

Ah, the pesky admin for 253.253.192.in-addr.arpa changed the serial number format and neglected to tell you about it. Some thanks you get for running a slave for this zone, huh? Drop the admin a note to see if this change was intentional or just a typo. If the change was intentional, or you don't want to contact the admin, then you have to deal with it locally - kill your slave, remove the backup copy of this zone, and restart your server. This procedure removes all knowledge your slave had of the old SOA serial number, at which point it is quite happy with the new serial number. This syslog message is logged at priority LOG_NOTICE .

By the way, if that pesky admin was running a BIND 8 name server, then he must have missed (or ignored) a message his server logged, telling him that he'd rolled the zone's serial number back:

Jun 7 19:35:14 terminator named[3221]: WARNING: new serial number < old
              (zp->z_serial < serial)

This message is logged at LOG_NOTICE .

You might want to remind him of the wisdom of checking syslog after making any changes to the name server.

This message will undoubtedly become familiar to you:

Aug 21 00:59:06 jade named[12620]: Lame server on 'foo.movie.edu'
         (in 'MOVIE.EDU'?): [10.0.7.125].53 'NS.HOLLYWOOD.LA.CA.US':
         learnt (A=10.47.3.62,NS=10.47.3.62)

"Aye, Captain, she's sucking mud!" There's some mud out there in the Internet waters in the form of bad delegations. A parent name server is delegating a subdomain to a child name server, and the child name server is not authoritative for the subdomain. In this case, the edu name server is delegating movie.edu to 10.0.7.125, and the name server on this host is not authoritative for movie.edu . Unless you know the admin for movie.edu , there's probably nothing for you to do about this. The syslog message is logged by a 4.9.3 server at priority LOG_WARNING , by a 4.9.4 to 4.9.7 server at priority LOG_DEBUG , and by a BIND 8 server at LOG_INFO .

If your version 4.9 or later name server's configuration file has:

options query-log







or your version 8 configuration file has:

logging { category queries { default_syslog; }; };

you will get a LOG_INFO syslog message for every query your name server receives:

Feb 20 21:43:25 terminator named[3830]:
            XX /192.253.253.2/carrie.movie.edu/A
Feb 20 21:43:32 terminator named[3830]:
            XX /192.253.253.2/4.253.253.192.in-addr.arpa/PTR

These messages include the IP address of the host that made the query and the query. Make sure you have lots of disk space if you log all the queries to a busy name server. (On a running server, you can toggle query logging on and off with the WINCH signal.)

Starting with version 8.1.2, you might see this set of syslog messages:

May 19 11:06:08 named[21160]: bind(dfd=20, [10.0.0.1].53):
                Address already in use
May 19 11:06:08 named[21160]: deleting interface [10.0.0.1].53
May 19 11:06:08 named[21160]: bind(dfd=20, [127.0.0.1].53):
                Address already in use
May 19 11:06:08 named[21160]: deleting interface [127.0.0.1].53
May 19 11:06:08 named[21160]: not listening on any interfaces
May 19 11:06:08 named[21160]: Forwarding source address
                is [0.0.0.0].1835
May 19 11:06:08 named[21161]: Ready to answer queries.

What has happened is that you had a name server running and you started up a second name server without killing the first one. Unlike what you might expect, the second name server continues to run; it just isn't listening on any interfaces.

7.6.2 Understanding the BIND Statistics

Periodically, you should look over the statistics on some of your name servers, if only to see how busy they are. We will show you an example of the name server statistics and discuss what each line means. Name servers handle many queries and responses during normal operation, so first, we need to show you what a typical exchange might look like.

Reading the explanations for the statistics is hard without a mental picture of what goes on during a lookup. To help you understand the name server's statistics, Figure 7.2 shows what might go on when an application tries to look up a name. The application, ftp , queries a local name server. The local name server had previously looked up data from this domain and knows where the remote name servers are. It queries each of the remote name servers - one of them twice - trying to find the answer. In the meantime, the application times out and sends yet another query, asking for the same information.

Keep in mind that even though a name server has sent a query to a remote name server, the remote name server may not receive the query right away. The query might be delayed or lost by the underlying network, or perhaps the remote name server host might be busy with another application.

Figure 7.2: Example query/response exchange

Figure 7.2

Notice that a BIND name server is able to detect duplicate queries only while it is still trying to answer the original query. The local name server detects the duplicate query from the application because the local name server is still working on it. But, remote name server 1 does not detect the duplicate query from the local name server because it answered the previous query. After the local name server receives the first response from remote name server 1, all other responses are discarded as duplicates. This dialog required the following exchanges:

Exchange

Number

Application to local name server

2 queries

Local name server to application

1 response

Local name server to remote name server 1

2 queries

Remote name server 1 to local name server

2 responses

Local name server to remote name server 2

1 query

Remote name server 2 to local name server

1 response

Local name server to remote name server 3

1 query

Remote name server 3 to local name server

0 responses

These exchanges would make the following contributions to the local name server's statistics:

Statistic

Cause

2 queries received

From the application on the local host

1 duplicate query

From the application on the local host

1 answer sent

To the application on the local host

3 responses received

From remote name servers

2 duplicate responses

From remote name servers

2 A queries

Queries for address information

In our example, the local name server received queries only from an application, yet it sent queries to remote name servers. Normally, the local name server would also receive queries from remote name servers (that is, in addition to asking remote servers for information it needs to know, the local server would also be asked by remote servers for information they need to know), but we didn't show any remote queries, for the sake of simplicity.

Now that you've seen a typical exchange between applications and name servers, and the statistics it generated, let's go over a more extensive example of the statistics. To get the statistics from your name server, send the version 4 name server an ABRT signal (on many systems, called IOT ):

% 

kill -ABRT `cat /etc/named.pid`

Or send a version 8 name server an ILL signal instead of ABRT :

% 

kill -ILL `cat /etc/named.pid`

(The process ID is stored in /var/run/named.pid on an SVR 4 filesystem.) Wait a few seconds and look at the file /usr/tmp/named.stats (or /var/tmp/named.stats ). A version 8 name server leaves the file named.stats in its current directory ( /usr/local/named in most of our examples). If the statistics are not dumped to this file, your server may not have been compiled with STATS defined and, thus, may not be collecting statistics. Following are the statistics from one of Paul Vixie's name servers. These statistics came from a 4.9.3 name server. An 8.1.2 name server has all of the same items as below except RN otNsQ and the items are arranged in a different order. If your name server is newer than 8.1.2, the statistics may not look at all like those shown here - the BIND statistics may be replaced with the DNS server and resolver MIB extensions defined in RFC 1611 and RFC 1612.

+++ Statistics Dump +++ (800708260) Wed May 17 03:57:40 1995
746683    time since boot (secs)
392768    time since reset (secs)
14        Unknown query types
268459    A queries
3044      NS queries
5680      CNAME queries
11364     SOA queries
1008934   PTR queries
44        HINFO queries
680367    MX queries
2369      TXT queries
40        NSAP queries
27        AXFR queries
8336      ANY queries
++ Name Server Statistics ++
(Legend)
      RQ    RR    RIQ   RNXD    RFwdQ
      RFwdR RDupQ RDupR RFail   RFErr
      RErr  RTCP  RAXFR RLame   ROpts
      SSysQ SAns  SFwdQ SFwdR   SDupQ
      SFail SFErr SErr  RNotNsQ SNaAns
      SNXD
(Global)
   1992938 112600 0 19144 63462 60527 194 347 3420 0  5 2235 27 35289 0
   14886 1927930 63462 60527 107169  10025 119 0 1785426 805592  35863
[15.255.72.20]
   485 0 0 0 0  0 0 0 0 0  0 0 0 0 0  0 485 0 0 0  0 0 0 0 485  0
[15.255.152.2]
   441 137 0 1 2 108 0 0 0 0  0 0 0 0 0  13 439 85 7 84  0 0 0 0 431  0
[15.255.152.4]
   770 89 0 1 4  69 0 0 0 0  0 0 0 0 0  14 766 68 5 7  0 0 0 0 755  0
...  <
lots of entries deleted
>

Let's look at these statistics one line at a time:

746683    time since boot (secs)

This is how long the local name server has been running. To convert to days, divide by 86400 (60x60x24, the number of seconds in a day). This server has been running for about 8.5 days.

392768    time since reset (secs)

This is how long the local name server has run since the last HUP signal - i.e., the last time it loaded its database. You'll probably see this number differ from the time since boot only if the server is a primary master name server for some zone. Name servers that are slaves for a zone automatically pick up new data with zone transfers and are not usually sent HUP signals. Since this server has been reset, it is probably a primary master name server for some zone.

14        Unknown query types

This name server received 14 queries for data of a type the name server didn't recognize. Either someone is experimenting with new types, or there is a defective implementation somewhere.

268459    A queries



There have been 268459 address lookups. Address queries are normally the most common type of query.

3044      NS queries



There have been 3044 name server queries. Internally, name servers generate NS queries when they are trying to look up servers for the root domain. Externally, applications like dig or nslookup can also be used to look up NS records.

5680      CNAME queries

Some versions of sendmail make CNAME queries in order to canonicalize a mail address (replace an alias with the canonical name). Other versions of sendmail use ANY queries instead (we'll get to those shortly). Otherwise, the CNAME lookups are most likely from dig or nslookup .

11364     SOA queries

SOA queries are made by slave name servers to check if their zone data are current. If the data are not current, an AXFR query follows to cause the zone transfer. Since this set of statistics does show AXFR queries, we can conclude that slave name servers load zone data from this server.

1008934   PTR queries

The pointer queries map addresses to names. Many kinds of software look up IP addresses: inetd , rlogind , rshd , network management software, and network tracing software.

44        HINFO queries

The host-information queries are most likely from someone interactively looking up HINFO records.

680367    MX queries

Mail exchanger queries are made by mailers like sendmail as part of the normal electronic mail delivery process.

2369      TXT queries

Some application must be making text queries for this number to be this large. It might be a tool like Harvest , which is an information search and retrieval technology developed at the University of Colorado.

40        NSAP queries

This is a relatively new data type used to map domain names to OSI Network Service Access Point addresses.

27        AXFR queries

An AXFR query is made by a slave name server to cause a zone transfer.

8336      ANY queries

ANY queries request data of any type for a name. This query type is used most often by sendmail . Since sendmail looks up CNAME , MX , and address records for a mail destination, it will make a query for ANY data type so that all the resource records are cached right away at the local name server.

The rest of the statistics are kept on a per-host basis. If you look over the list of hosts your name server has exchanged packets with, you'll find out just how garrulous your name server is - you'll see hundreds or even thousands of hosts in the list. While the size of the list is impressive, the statistics themselves are only somewhat interesting. We will explain all of the statistics, even the ones with zero counts, although you'll probably only find a handful of the statistics useful. To make the statistics easier to read, you'll need a tool to expand the statistics because the output format is rather compact. We wrote a tool, called bstat , to do just this. Here's what its output looks like:

hpcvsop.cv.hp.com
        485 queries received
        485 responses sent to this name server
        485 queries answered from our cache
relay.hp.com
        441 queries received
        137 responses received
          1 negative response received
          2 queries for data not in our cache or authoritative data
        108 responses from this name server passed to the querier
         13 system queries sent to this name server
        439 responses sent to this name server
         85 queries sent to this name server
          7 responses from other name servers sent to this name server
         84 duplicate queries sent to this name server
        431 queries answered from our cache
hp.com
        770 queries received
         89 responses received
          1 negative response received
          4 queries for data not in our cache or authoritative data
         69 responses from this name server passed to the querier
         14 system queries sent to this name server
        766 responses sent to this name server
         68 queries sent to this name server
          5 responses from other name servers sent to this name server
          7 duplicate queries sent to this name server
        755 queries answered from our cache

In the raw statistics (not the bstat output), each host IP address is followed by a table of counts. The column heading for this table is the cryptic legend at the beginning. The legend is broken into several lines, but the host statistics are all on a single line. In the following section, we'll explain briefly what each column means as we look at the statistics for one of the hosts this server conversed with - 15.255.152.2 ( relay.hp.com ). For the sake of our explanation, we'll first show you the column heading from the legend (e.g., RQ ) followed by the count for this column for relay .



RQ 441

RQ is the count of queries received from relay . These queries were made because relay needed information about a domain served by this name server.



RR 137

RR is the count of responses received from relay . These are responses to queries made from this name server. Don't try to correlate this number to RQ , because they are not related. RQ counts questions asked by relay ; RR counts answers relay gave to this name server (because this name server asked relay for information).



RIQ 0

RIQ is the count of inverse queries received from relay . Inverse queries were originally intended to map addresses to names, but that function is now handled by PTR records. Older versions of nslookup use an inverse query on startup, so you may see a nonzero RIQ count.



RNXD 1

RNXD is the count of "no such domain" answers received from relay .



RFwdQ 2

RFwdQ is the count of queries received ( RQ ) from relay that needed further processing before they could be answered. This count is much higher for hosts that configure their resolver (with resolv.conf ) to send all queries to your name server.

RFwdR 108

RFwdR is the count of responses received ( RR ) from relay that answered the original query and were passed back to the application that made the query.



RDupQ 0

RDupQ is the count of duplicate queries from relay . You'll only see duplicates when the resolver is configured (with resolv.conf ) to query this name server.

RDupR 0

RDupR is the count of duplicate responses from relay . A response is a duplicate when the name server can no longer find the original query in its list of pending queries that caused the response.



RFail 0

RFail is the count of SERVFAIL responses from relay . A SERVFAIL response indicates some sort of server failure. Server failure responses often occur because the remote server read a db file and found a syntax error. Any queries for data in that zone (the one from the erroneous db file) will result in a server failure answer from the remote name server. This is probably the most common bad response. Server failure responses also occur when the remote name server tries to allocate more memory and can't, or when the remote name server's zone data expire.



RFErr 0

RFErr is the count of FORMERR responses from relay . FORMERR means that the remote name server said the local name server's query had a format error.



RErr  0

RErr is the count of errors that weren't either SERVFAIL or FORMERR .



RTCP  0

RTCP is the count of queries received on TCP connections from relay . (Most queries use UDP .)



RAXFR 0

RAXFR is the count of zone transfers initiated. The 0 count indicates that relay is not a slave for any zones served by this name server.



RLame 0

RLame is the count of lame delegations received. If this count is not 0, it means that some zone is delegated to the name server at this IP address, and the name server is not authoritative for the zone.



ROpts 0

ROpts is the count of packets received with IP options.



SSysQ 13

SSysQ is the count of system queries sent to relay . System queries are queries initiated by the local name server. Most system queries will go to root name servers, because system queries are used to keep up-to-date on who the root name servers are. But system queries are also used to find out the address of a name server if the address record timed out before the name server record did. Since relay is not a root name server, these queries must have been sent for the latter reason.



SAns  439

SAns is the count of answers sent to relay . This name server answered 439 out of the 441 ( RQ ) queries relay sent to it. I wonder what happened to the 2 queries it didn't answer...



SFwdQ 85

SFwdQ is the count of queries that were sent (forwarded) to relay when the answer was not in this name server's zone data or cache.

SFwdR 7

SFwdR is the count of responses from some name server that were sent (forwarded) to relay .



SDupQ 84

SDupQ is the count of the duplicate queries sent to relay . It's not as bad as it looks, though. The duplicate count is incremented if the query was sent to any other name server first. So, relay might have answered all the queries it received the first time it received them, and the query still counted as a duplicate because it was sent to some other name server before relay .



SFail 0

SFail is the count of SERVFAIL responses sent to relay .



SFErr 0

SFErr is the count of FORMERR responses sent to relay .



SErr  0

SErr is the count of sendto() system calls that failed when the destination was relay .



RNotNsQ 0

RNotNsQ is the count of queries received that were not from port 53, the name server port. Prior to version 8, all name server queries would come from port 53. Any queries from ports other than 53 came from a resolver. Now, name servers will query from ports other than 53, which makes this statistic useless since you can no longer distinguish resolver queries from name server queries. Hence, version 8 dropped RNotNsQ from its statistics.



SNaAns 431

SNaAns is the count of nonauthoritative answers sent to relay . Out of the 439 answers (SAns) sent to relay , 431 were from cached data.



SNXD  0

SNXD is the count of "no such domain" answers sent to relay .

Is this name server "healthy" ? How do you know what "healthy" operation is? From this one snapshot, we really couldn't say if the name server is healthy. You have to watch the statistics generated by your server over a period of time to get a feel for what sorts of numbers are normal for your configuration. These numbers will vary markedly among servers, depending on the mix of applications generating lookups, the type of server (primary, slave, caching-only), and the level in the domain tree it is serving.

One thing to watch for in the statistics is how many queries per second your server receives. Take the number of queries received (from the "Global" statistics) and divide by the number of seconds the name server has been running. This server received 1992938 queries in 746683 seconds, or approximately 2.7 queries per second - a pretty busy server. If the number you come up with for your server seems out of line, look at which hosts are making all the queries and decide if it makes sense for them to be making all those queries. At some point you may decide that you need more servers to handle the load; we cover that situation in the next chapter.







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