Your local DNS can be configured to function as a caching and forwarding nameserver. What this accomplishes is that instead of queurying the external nameservers each time host and domain information is needed, they will be queuried once, and the information will be cached locally for subsequent queuries.
named keeps it's cache in memory, not on disk. Over time, the cache will grow to contain more and more DNS information specific to your internet access patterns. This speeds up connections by avoiding external lookups once the information is stored locally.
18.1 Configuring DNS Caching in RedHat 5.1 and earlier
NOTE: The following applies to RedHat version 5.1 and below. The newer version of bind uses a different configuration file and syntax.
If you are running RedHat 5.1, most of the setup is done for you if you install caching-nameserver-5.1-1.noarch.rpm. Otherwise, here's how, based on the DNS-HOWTO and the DNS and Bind book by Paul Albitz and Cricket Liu.
Make a backup of /etc/named.boot/ first...
Edit named.boot to contain something like:
; a caching only nameserver config
;
; named.ca: periodically update from ftp.rs.internic.net /domain/named.root
; LAST DOWNLOAD: 10-17-98
; -----------------------------------------------------------------------
; SIGHUP Causes server to read named.boot and reload the database
; kill -HUP `cat /var/run/named.pid`
; -----------------------------------------------------------------------
directory /var/named
cache . named.ca
primary 0.0.127.in-addr.arpa named.local
; ISP name servers from /etc/resolv.conf
;forwarders 24.128.60.8 24.128.60.7 24.128.1.81
forwarders 24.128.60.8 24.128.60.7 24.128.1.81
; forward-only: only query the listed forwarders
options forward-only
Edit /etc/sysconfig/network-scripts/ifdhcpc-done/.
Add the following two sections:
#---------------------------------------------------------------------
# Update /etc/named.boot forwarders to be the original
# nameservers from /etc/resolv.conf.
forwarders=""
fgrep nameserver /etc/dhcpc/resolv.conf | sed -e "s/nameserver//" |
while read naddr
do
forwarders=$forwarders" "$naddr
done
sed -e "s/^forwarders.*$/forwarders $forwarders/" /etc/named.boot > /var/tmp/named.boot
cp /var/tmp/named.boot /etc/named.boot
rm /var/tmp/named.boot
#---------------------------------------------------------------------
# Update /etc/resolv.conf for local caching nameserver.
# Replace the ISP nameservers with an entry for localhost.
domain=`fgrep domain /etc/dhcpc/resolv.conf | sed -e "s/domain//"`
echo "domain $domain" > /var/tmp/resolv.conf
echo "nameserver 127.0.0.1" >> /var/tmp/resolv.conf
cp /etc/dhcpc/resolv.conf /etc/dhcpc/resolv.conf.bak
cp /var/tmp/resolv.conf /etc/dhcpc/resolv.conf
rm /var/tmp/resolv.conf
# This applies to RedHat 5.+ only.
# Earlier releases used a symbolic link.
cp /etc/dhcpc/resolv.conf /etc
18.2 Configuring DNS Caching in RedHat 5.2 and later
NOTE: The following only applies to RedHat version 5.2 or above. The newer version of bind uses a different configuration file and syntax.
Make a backup of /etc/named.conf/ first...
Edit named.conf to contain something like:
options {
directory "/var/named";
forward only;
forwarders {
24.128.60.8;
24.128.60.7;
24.128.1.81;
};
/*
* If there is a firewall between you and nameservers you want
* to talk to, you might need to uncomment the query-source
* directive below. Previous versions of BIND always asked
* questions using port 53, but BIND 8.1 uses an unprivileged
* port by default.
*/
query-source address * port 53;
/*
* This makes named only listen for queuries from your LAN
* and localhost.
*/
listen-on {
your_internal_lan_ip_address_range
127/8;
};
};
// -----------------------------------------------------------------------
// SIGHUP Causes server to read named.boot and reload the database
// kill -HUP `cat /var/run/named.pid`
// -----------------------------------------------------------------------
zone "." {
type hint;
file "named.ca";
};
zone "0.0.127.in-addr.arpa" {
type master;
file "named.local";
};
Edit /etc/sysconfig/network-scripts/ifdhcpc-done/.
Add the following two sections:
#---------------------------------------------------------------------
# The following 2 sections support a caching-only nameserver.
# /etc/named.conf, /etc/dhcpc/resolv.conf and /etc/resolv.conf are modified.
# Update /etc/named.conf forwarders to be the original
# nameservers from /etc/resolv.conf.
# NOTE: this is for RedHat versions 5.2 and NEWER
let cnt=1
fgrep nameserver /etc/dhcpc/resolv.conf | sed -e "s/nameserver //" |
while read naddr
do
case $cnt in
1 ) forwarder1=$naddr ;;
2 ) forwarder2=$naddr ;;
3 ) forwarder3=$naddr ;;
esac
let cnt=$cnt+1
done
awk '/forwarders {/ { active = 1; print } \
/};/ { \
if ( active == 1 ) { \
active = 0; \
print "\t\t" f1 ";"; \
print "\t\t" f2 ";"; \
print "\t\t" f3 ";"; \
} \
} \
\
{ \
if ( active == 0 ) \
print; \
} ' \
f1=$forwarder1 f2=$forwarder2 f3=$forwarder3 /etc/named.conf > /tmp/named.conf
cp /var/tmp/named.conf /etc/named.conf
rm /var/tmp/named.conf
#---------------------------------------------------------------------
# Update /etc/resolv.conf for local caching nameserver.
# Replace the ISP nameservers with an entry for localhost.
# Save the original
cp /etc/dhcpc/resolv.conf /etc/dhcpc/resolv.conf.bak
domain=`fgrep domain /etc/dhcpc/resolv.conf | sed -e "s/domain //"`
echo "domain $domain" > /var/tmp/resolv.conf
echo "nameserver 127.0.0.1" >> /var/tmp/resolv.conf
cp /var/tmp/resolv.conf /etc/dhcpc/resolv.conf
rm /var/tmp/resolv.conf
18.3 Configuring DNS Caching in All Versions
Download a copy of the root name servers file from ftp.rs.internic.net:domain/named.root/ and place it in /var/named/named.ca/.
Note that this file is provided in the RedHat 5.1 caching-nameserver package.
Create the file: /var/named/named.local/
Note that this file is provided in the RedHat 5.1 caching-nameserver package.
Add the following:
@ IN SOA localhost. root.localhost. (
1 ; Serial
28800 ; Refresh after 8 hours
3600 ; Retry 1 hour
604800 ; Expire after 1 week
86400 ) ; Minimum TTL of 1 day
IN NS localhost.
1 IN PTR localhost.
Make a backup of /etc/dhcpc/resolv.conf/ (and /etc/resolv.conf/ if it's not a symbolic link). Change it to contain:
domain Your_Domain
nameserver 127.0.0.1
Edit /etc/host.conf/ and make sure it contains:
order hosts, bind
Edit /etc/rc.d/rc.firewall/ and enable the caching only rules. Re-run the script.
Restart the nameserver by:
kill -HUP `cat /var/run/named.pid`
Check /var/log/messages/ for errors.
Test nslookup. You should see:
Default Server: localhost
Address: 127.0.0.1
>
Try a known address a few times. The first time you should just see the hostname and address list. The second time, you should also see a line that this is a "Non-authoritative answer".
The "Non-authoritative answer" means the information was provided by your local name server rather than your ISP's.
18.4 Configuring an Internal DHCP Server for the LAN
In the rc.firewall script, add the following lines.
In the section where variables are declared:
THIS_MACHINE="192.168.1.1/32" # used for local DHCP service
Substitute the IP address of the Linux firewall machine
Add the following sections:
# -------------------------------------------------------------- # Accept DHCP requests from Windows machines
ipfwadm -I -a accept -W $LOCAL_INTERFACE \ -S 0.0.0.0/32 \ -D 255.255.255.255/32
# -------------------------------------------------------------- # DHCP server to local net is valid
ipfwadm -O -a accept -W $LOCAL_INTERFACE \ -S $THIS_MACHINE \ -D 0.0.0.0/0
Add the following lines to /etc/rc.d/rc.local:
# Start DHCP daemon /sbin/route add -host 255.255.255.255 dev eth0 /usr/sbin/dhcpd eth0
Your local Ethernet interface is eth1, so make the appropriate changes. If you get an error with the route command, you may have to add a host to your /etc/hosts file:
255.255.255.255 all-ones.localdomain all-ones
There's a different route command to be entered if this is the case -- I'm sorry, I don't remember where on the web I found that information. The first case worked for me.
Edit or create /etc/dhcpd.conf to contain the following information:
aoption domain-name "your_domain"; option subnet-mask 255.255.255.0; option broadcast-address 192.168.1.255; option routers 192.168.1.1; option domain-name-servers 192.168.1.1;
subnet 192.168.1.0 netmask 255.255.255.0 { range 192.168.1.10 192.168.1.19; default-lease-time 3600; max-lease-time 7200; }
This assumes you're using the same Class C network I am using. This file provides the IP range 192.168.1.10 through 192.168.1.19 inclusive to any machine connected on the local net which requests an IP address.
Adjust the lease times (in seconds) to your preferences. My experience is that a Windows machine will request an extension of the lease after it's half expired. This adds two lines to /var/log/messages for every renewal.
Run the commands you added to /etc/rc.d/rc.local manually to start the DHCP server.