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by Edgar C Francis
The firewall is a barrier between LAN and WAN networks (trusted
and untrusted networks), we configure the firewall in the forwarding path of the
network so each packet have to be checked by our firewall.
There are two kinds of firewalls one is software firewalls
just like preinstalled with Microsoft Windows. The second one is the hardware firewall
which we are going to see.
From the above diagram, we have LAN with two host PC and a cisco switch. On the other hand, you
can see a router that is connected to the ISP for an internet connection. We place
our firewall in between to protect our LAN network.
Stateless and
stateful filtering.
You can use a router
as a firewall but it's not a good choice because most the router does not spend
much time on filtering, the router checks the access list for the port number source
and destination IP address if it matches in the entry of access-list router is
going to permit or deny the packet and router do not keep track of the
packet this is called stateless filtering but the firewall uses stateful
filtering, the firewall keeps track of all incoming and outgoing connections.
ASA (Adaptive
Security Appliance) is a cisco security device that combines the classic firewall with VPN, IPS (Intrusion Prevention System), and antivirus
capabilities. ASA is capable of providing threat defense before most of the
attacks spread into our LAN network.
I think we have done
enough talking rest of the theory we will see in the next section.
The leak-map name keyword configures the stub
router to advertise selected EIGRP-learned routes which are not ordinarily
advertised. The name refers to a route map that matches one or more ACLs or
prefix lists and permits the matched subnets or addresses to be leaked.
The EIGRP Stub feature is very useful when we want to
prevent unnecessary EIGRP queries and want to filter a few routes that we
advertise but when we want to configure our EIGRP router as a stub and still we
want to make an exception to some routes (network) to advertise this is
possible with the help of Leak-map.
In summary route-
Whenever we configure our EIGRP summary route, all the networks
within the range of our summary are no longer advertised on interfacing the only
this is left is a summary route, but we want to advertise some networks separately
next to our summary route this can also be done with summary leak-map. Let's see
how to configure the leak map.
Topology: -
Goal:
Configure the topology as per the diagram.
Assigning the IP addresses to their interfaces.
Configure EIGRP 1234 on all the routers.
Configure EIGRP STUB connected on router 3.
Configure Leak-Map on router 3 with the exception that network 192.168.32.1 network only advertises to all the routers.
