nethserver-dnsmasq

DNS

The system will resolve host and domain names using DNS queries to external DNS servers. The configuration is saved inside the dns key from nethserver-base package.

Properties:

  • NameServers: comma separated IP list of external DNS
  • role: can be set to none or resolver. If role is set to none the server will always use external DNS. For resolver role see DNS server.

Example:

dns=configuration
   NameServers=8.8.8.8,208.67.222.222
   role=none

Hosts

The system can handle local DNS records. When the server performs a DNS lookup, first it will search inside local DNS records. If no local record is found, an external DNS query will be done.

Note

Local DNS record will always override records from external DNS servers.

DNS records are called hosts and are saved inside the hosts database. Each entry is saved inside the /etc/hosts file.

There are three types of records:

  • local: hosts inside the internal network
  • remote: hosts outside the internal network
  • self: alias for the server itself

Records of type local and remote can have following properties:

  • IpAddress: address of the host
  • Description: optional description
  • MacAddress: mac address of the host. Used only for DHCP reservation. See IP reservation.

For hosts inside local network, the record key doesn’t have the domain part. Example:

host1=local
    Description=Internal network host #1
    IpAddress=192.168.1.23

For hosts outside local network, the record key must have the domain part. Example:

external.otherdomain.tld=remote
    Description=Other domain host
    IpAddress=8.9.10.11

Records of type self can have following properties:

  • Description: optional description

Example:

vhost1.domain.tld=self
    Description=Virtual Host #1

DNS server

The system uses dnsmasq as DNS and DHCP server and it directly resolves all hosts inside its domain. All other names will be queried to external DNS servers.

The server will forward reverse lookups to upstream DNS servers, only if upstream DNS servers are inside a private network (eg. network address is 192.168.x.x).

The option bind-interfaces is always enabled, as consequence (from dnsmasq man):

This option has been patched to always use SO_BINDTODEVICE socket option when binding to interfaces. As consequence, dnsmasq WILL NOT ANSWER to any DNS Queries that come to the socket with the correct destination IP address, but originally on different interface. This behavior differs from the original dnsmasq upstream version and is used for security reasons.

Properties:

  • CacheSize: entry to be cached by server, default is 4000
  • dhcp-boot: directly pass parameters to dhcp-boot option
  • except-interface: comma-separated list of interfaces. Do not listen to listed interfaces, useful to avoid conflicts with libvirt
  • tftp-status: can be enabled or disabled. If enabled, enable the TFTP server for BOOTP (port 67)
  • access: default is private, do NOT set to public

Database example:

dnsmasq=service
  AllowHosts=
  CacheSize=4000
  DenyHosts=
  TCPPort=53
  UDPPorts=53,67
  access=private
  dhcp-boot=pxelinux.0,myserver.mydomain.com,192.168.1.1
  except-interface=virbr0,tunspot
  status=enabled
  tftp-status=enabled

DHCP

The system can act as DHCP server for the local network. Machines which are configured by DHCP have their names automatically included in the DNS server.

The DHCP can be enabled only on green and blue interfaces (see Roles and zones). Configuration is saved inside the dhcp database.

Each record of range type is associated to an ethernet interface and can have following properties:

  • status: can be enabled or disabled
  • DhcpRangeStart: first IP address of DHCP range
  • DhcpRangeEnd: last IP address of DHCP range
  • DhcpLeaseTime: seconds of lease time. Default is 86400
  • DhcpGatewayIp: (optional) set a custom gateway ip. If not set, the gateway is the ip address of associated interface (record key)

The key of the record is the name of the associated interface. Example:

eth0=range
  DhcpGatewayIp=
  DhcpLeaseTime=86400
  DhcpRangeEnd=192.168.1.100
  DhcpRangeStart=192.168.5.200
  status=enabled

Hosts inside the blue network can always access the local DNS server.

The gateway for clients will be:

  • if set, the value of property DhcpGatewayIp
  • otherwise if the server has a red interface, the gateway is the IP address of the interface where the DHCP is enabled (eg. IP of the blue interface for clients in the guest’s network)
  • otherwise if the server has only a green interface, the gateway of the green interface will be used

IP reservation

It’s possible to reserve IPs for specific devices associating the MAC address of the device with the reserved IP. The reservation is saved inside the hosts database.

Example:

host1=local
    Description=Internal network host #1
    IpAddress=192.168.1.23
    MacAddress=08:00:27:48:BF:F3

TFTP server

TFTP module contains configuration fragments that enables dnsmasq built-in TFTP server.

TFTP server han no authentication or encription support.

When installed tftp is disabled by default and need to be enabled with:

config setprop tftp status enabled
signal-event nethserver-tftp-save

The package also add directory /var/lib/tftpboot that is the root of tftp server.

Enabling TFTP adds 5 new configuration options to /etc/dnsmasq.conf. Here variables explanation according with dnsmasq documentation

  • enable-tftp: enable tftp server
  • tftp-secure: allow only files owned by the user dnsmasq is running as will be send over the net
  • dhcp-boot= ...: Set the boot filename for netboot/PXE. You will only need this is you want to boot machines over the network and you will need a TFTP server; driven by db prop
  • tftp-root=/var/lib/tftpboot: Set the root directory for files available via FTP.
  • dhcp-option=66, LOCAL_IP: set local ip as default tftp server for machines that receive dhcp from this server

Properties

  • status: can be enabled or disabled. If enabled, TFTP server is configured and port 69 UDP is opened.
  • UDPPort: UDP port used. Only 69 is allowed.
  • access: define if access is public, private or none.
  • dhcp-boot: Set the boot filename for PXE. Ths is needed for booting machines over the network. Empty by default.
  • type: only service is allowed.

Test TFTP

Testing is very simple:

Install package and enable TFTP server:

yum install nethserver-tftp
config setprop tftp status enabled
signal-event nethserver-tftp-save

Create a file to share, owned by nobody user:

echo "test"  > /var/lib/tftpboot/foobar
chown nobody:nobody /var/lib/tftpboot/foobar

From another machine, install tftp and get file (on Fedora):

yum install tftp

Always from the other machine, allow incoming UDP connection from our TFTP server. Loading TFTP conntrack module should be enough:

modprobe nf_conntrack_tftp

Connect to TFTP server:

tftp TFTP_SERVER_HOST

…and get the file:

tftp> get foobar

Configure a PXE server

Those instructions set up a PXE server for CentOS Install and configure syslinux and nethserver-tftp:

yum install syslinux
cp /usr/share/syslinux/{pxelinux.0,menu.c32,memdisk,mboot.c32,chain.c32} /var/lib/tftpboot/
config setprop tftp dhcp-boot pxelinux.0
signal-event nethserver-tftp-save
mkdir /var/lib/tftpboot/pxelinux.cfg

Create the file /var/lib/tftpboot/pxelinux.cfg/default with the following content:

default menu.c32
prompt 0
timeout 300

MENU TITLE PXE Menu

LABEL CentOS
kernel CentOS/vmlinuz
append initrd=CentOS/initrd.img

Create a CentOS directory:

Create a CentOS directory:

mkdir -p /var/lib/tftpboot/CentOS

Copy inside the directory vmlinuz and initrd.img files. These files can be found inside the ISO or browsing the yum os mirror.

Change files owner to nobody:

chown -R nobody /var/lib/tftpboot/*