Bind DNS zone file explained

$ORIGIN example.com.     ; designates the start of this zone file in the name space
$TTL 1h                  ; default expiration time of all resource records without their own TTL value
example.com.  IN  SOA  ns.example.com. username.example.com. (
              2007120710 ; serial number of this zone file
              1d         ; slave refresh (1 day)
              2h         ; slave retry time in case of a problem (2 hours)
              4w         ; slave expiration time (4 weeks)
              1h         ; minimum caching time in case of failed lookups (1 hour)
              )
example.com.  NS    ns                    ; ns.example.com is a nameserver for example.com
example.com.  NS    ns.somewhere.example.     ; ns.somewhere.example is a backup nameserver for example.com
example.com.  MX    10 mail.example.com.  ; mail.example.com is the mailserver for example.com
@             MX    20 mail2.example.com. ; equivalent to above line, "@" represents zone origin
@             MX    50 mail3              ; equivalent to above line, but using a relative host name
example.com.  A     10.0.0.1              ; IPv4 address for example.com
              AAAA  2001:db8:10::1        ; IPv6 address for example.com
ns            A     10.0.0.2              ; IPv4 address for ns.example.com
              AAAA  2001:db8:10::2        ; IPv6 address for ns.example.com
www           CNAME example.com.          ; www.example.com is an alias for example.com
wwwtest       CNAME www                   ; wwwtest.example.com is another alias for www.example.com
mail          A     10.0.0.3              ; IPv4 address for mail.example.com,
                                          ;  any MX record host must be an address record
                                          ; as explained in RFC 2181 (section 10.3)
mail2         A     10.0.0.4              ; IPv4 address for mail2.example.com
mail3         A     10.0.0.5              ; IPv4 address for mail3.example.com

Linux bonding modes

Mode 0: Balance Round-Robin (balance-rr)
Round-robin policy: Transmit packets in sequential order from the first available slave through the
last. This mode provides load balancing and fault tolerance.

Mode 1: Active-Backup
Active-backup policy: Only one slave in the bond is active. A different slave becomes active if, and only if, the active slave fails. The bond’s MAC address is externally visible on only one port (network adapter) to avoid confusing the switch.In bonding version 2.6.2 or later, when a failover occurs in active-backup mode, bonding will issue one or more gratuitous ARPs on the newly active slave. One gratuitous ARP is issued for the bonding master interface and each VLAN interfaces configured above
it, provided that the interface has at least one IP address configured. Gratuitous ARPs issued for VLAN interfaces are tagged with the appropriate VLAN id.This mode provides fault tolerance. The primary option, documented below, affects the behavior of this mode.

Check for open ports on linux

lsof -i -P -n

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Bind DNS zone file explained

Linux bonding modes

Check for open ports on linux

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