Linux Training in Chandigarh (4)

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Linux Training in Chandigarh

• CBitss Technologies

TCP Wrappers in Linux
CBitss Technologies SCO-23, 24,25, Level 3,Near
Passport office, Sector 34 A, Chandigarh Contact
9988741983, 9914641983
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What is TCP Wrappers in Linux

• TCP Wrapper is a host-based networking ACL
  system, used to filter network access to Internet
  Protocol servers on (Unix-like) operating systems
  such as Linux or BSD. It allows host or
  subnetwork IP addresses, names and/or ident query
  replies, to be used as tokens on which to filter
  for access control purposes.

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Understanding hosts.allow and hosts.deny

• When a network request reaches your server, TCP
  wrappers uses hosts.allow and hosts.deny (in that
  order) to determine if the client should be
  allowed to use a given service.
• By default, these files are empty, all commented
  out, or do not exist. Thus, everything is allowed
  through the TCP wrappers layer and your system is
  left to rely on the firewall for full protection.
  Since this is not desired, due to the reason we
  stated in the introduction, make sure both files
  exist
• ls -l /etc/hosts.allow /etc/hosts.deny

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Understanding hosts.allow and hosts.deny

• ltservicesgt ltclientsgt ltoption1gt ltoption2gt
  ...
• services is a comma-separated list of services
  the current rule should be applied to.
• clients represent the list of comma-separated
  hostnames or IP addresses affected by the rule.
  The following wildcards are accepted
• ALL matches everything. Applies both to clients
  and services.
• LOCAL matches hosts without a period in their
  FQDN, such as localhost.
• KNOWN indicate a situation where the hostname,
  host address, or user are known.
• UNKNOWN is the opposite of KNOWN.
• PARANOID causes a connection to be dropped if
  reverse DNS lookups (first on IP address to
  determine hostname, then on host name to obtain
  the IP addresses) return a different address in
  each case.
• Finally, an optional list of colon-separated
  actions indicate what should happen when a given
  rule is triggered.

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CBitss Technologies SCO-23, 24,25, Level 3,Near
Passport office, Sector 34 A, Chandigarh Mobile
- 9914641983 www.cbitss.in/linux-training-in-chan
digarh/
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CBitss Technologies SCO-23, 24,25, Level 3,Near
Passport office, Sector 34 A, Chandigarh Contact
9988741983, 9914641983