How to check the IP:PORT firewall uses? Post: 303004043

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Top Forums Shell Programming and Scripting How to check the IP:PORT firewall uses? Post 303004043 by bakunin on Monday 25th of September 2017 05:11:04 PM

09-25-2017

Registered User

Quote:

Originally Posted by mohtashims

2. Also, from @Chubler_XL's statement I understand that there is no way to remotely monitor the firewall like we monitor SMTP [port 25] or SSH [port 22].

Correct.

A firewall is not a service, but a software controlling the network operation of a system:

Let us start with a router: a router basically is a system with two network interfaces which stand in different IP-networks and a machinery in between which relays traffice between these two networks from one interface to the other, based on some rules (the "routing table"). Routing takes place on layer 3 of the network and hence the router "operates at layer 3".

A firewall is a similar machinery but operates on (more correctly: on top of) layer 4: again two network interfaces homed in different IP-networks, but the machinery (usually some software - the firewall process) in between operates on layer 4 and relays layer-4-packets (TCP, UDP, and similar protocols) between these two interfaces.

Per default all packets are "not relayed" (blocked) this way. By configuring rules some of these packets are allowed nonetheless and therefore indeed relayed.

There are two fundamental ways such firewalls operate: packet-filtering and stateful inspection.

In packet filtering the rules state which port of a certain IP on one side may communicate with which port on which IP on the other side. No effort is made to monitor the communication other than allowing some IP/port/destination/origin-combinations and blocking everything else.

Stateful inspection is different: packets are interpreted and their content is checked. Packets (or, rather, whole connections) are allowed/disallowed based on these checks. This needs a lot more computing and is a lot more intrusive than packet filtering and therefore real-world firewalls are usually a combination of both packet filters and some stateful inspection.

I hope this helps.

bakunin

bakunin

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LEARN ABOUT BSD

xnsrouted

XNSROUTED(8)						      System Manager's Manual						      XNSROUTED(8)

NAME

       XNSrouted - NS Routing Information Protocol daemon

SYNOPSIS

       /sbin/XNSrouted [ -s ] [ -q ] [ -t ] [ logfile ]

DESCRIPTION

       XNSrouted  is invoked at boot time to manage the Xerox NS routing tables.  The NS routing daemon uses the Xerox NS Routing Information Pro-
       tocol in maintaining up to date kernel routing table entries.

       In normal operation XNSrouted listens for routing information packets.  If the host is connected to multiple NS networks,  it  periodically
       supplies copies of its routing tables to any directly connected hosts and networks.

       When  XNSrouted is started, it uses the SIOCGIFCONF ioctl to find those directly connected interfaces configured into the system and marked
       ``up'' (the software loopback interface is ignored).  If multiple interfaces are present, it is	assumed  the  host  will  forward  packets
       between	networks.  XNSrouted then transmits a request packet on each interface (using a broadcast packet if the interface supports it) and
       enters a loop, listening for request and response packets from other hosts.

       When a request packet is received, XNSrouted formulates a reply based on the information maintained in its internal tables.   The  response
       packet generated contains a list of known routes, each marked with a ``hop count'' metric (a count of 16, or greater, is considered ``infi-
       nite'').  The metric associated with each route returned provides a metric relative to the sender.

       Response packets received by XNSrouted are used to update the routing tables if one of the following conditions is satisfied:(1)    No routing table entry exists for the destination network or host, and the metric indicates the destination is  ``reachable''  (i.e.
	      the hop count is not infinite).

       (2)    The  source host of the packet is the same as the router in the existing routing table entry.  That is, updated information is being
	      received from the very internetwork router through which packets for the destination are being routed.(3)    The existing entry in the routing table has not been updated for some time (defined to be 90 seconds) and the route is at  least	as
	      cost effective as the current route.(4)    The  new	route  describes a shorter route to the destination than the one currently stored in the routing tables; the metric of the
	      new route is compared against the one stored in the table to decide this.

       When an update is applied, XNSrouted records the change in its internal tables and generates a response packet to  all  directly  connected
       hosts  and  networks.   Routed waits a short period of time (no more than 30 seconds) before modifying the kernel's routing tables to allow
       possible unstable situations to settle.

       In addition to processing incoming packets, XNSrouted also periodically checks the routing table entries.  If an entry has not been updated
       for 3 minutes, the entry's metric is set to infinity and marked for deletion.  Deletions are delayed an additional 60 seconds to insure the
       invalidation is propagated to other routers.

       Hosts acting as internetwork routers gratuitously supply their routing tables every 30 seconds to all directly  connected  hosts  and  net-
       works.

       Supplying  the  -s  option  forces  XNSrouted  to supply routing information whether it is acting as an internetwork router or not.  The -q
       option is the opposite of the -s option.  If the -t option is specified, all packets sent or received are printed on the  standard  output.
       In  addition,  XNSrouted  will not divorce itself from the controlling terminal so that interrupts from the keyboard will kill the process.
       Any other argument supplied is interpreted as the name of file in which XNSrouted's actions should be logged.  This log	contains  informa-
       tion about any changes to the routing tables and a history of recent messages sent and received which are related to the changed route.

SEE ALSO

       ``Internet Transport Protocols'', XSIS 028112, Xerox System Integration Standard.
       idp(4P)

4.3 Berkeley Distribution					 November 1, 1996						      XNSROUTED(8)