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how Linux Network Configuration

Posted on 2013-02-02
Medium Priority
Last Modified: 2013-02-09
Hello everyone,
I'm confused between iptables and route
-I have a fedora server that has 2 interfaces
External : p2p1

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Internal : p2p2

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The firewall is disable in the server
it pings from server device internal IP to client IP but doesn’t ping from server external IP to client IP
I did the iptables to allow the traffic in the forward chain
# iptables –t nat –A POSTROUTING –o p2p1 –MASQUERADE
#iptables –t nat –A PREROUTING –p tcp –d–dport 80 –j DNAT -–to
#iptable  -A FORWARD –p tcp –d–-dport  80 –j ACCEPT

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also changed to enable sysctl net.ipv4.ip_forward=1
after doing these the client can access the internet..
now why do we need route?
And I wish I could use route but I didn’t understand it. I did like that on server but I really don’t understand it and I delete it before doing iptables
route add -net netmask
    gw p2p2

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please I am really confused between these if someone can help me. I need my network has more security..
and also I have another a question how can I use my external ip address as DNS.
Thanks guys!
Question by:PCANW
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LVL 80

Accepted Solution

arnold earned 525 total points
ID: 38847666
iptables is a firewall.
route deals with a routing table.

What is this system supposed to do?
Are you trying to set it up as a router to allow traffic between the two segments to pass through the fedora box?
your route directive on the fedora is incorrect.
your routing table on the fedora box should be p2p2 p2p1

within your DHCP configuration you will push the the settings to one side.

You need to be clear what functionality you want to get from this fedora box.
LVL 35

Assisted Solution

by:Duncan Roe
Duncan Roe earned 525 total points
ID: 38847723
iptables is a firewall. Incorrect - it is also a router.
It is indeed confusing that there are routers and route tables, but they are quite separate.
route tables are for how a box routes internally generated IP datagrams: which network interface (NIC) to send them on, what is the address of the gateway (on the local LAN segment unless this box is the gateway)
Gateway and router mean essentially the same thing. iptables rules cause packets coming in from one NIC to be sent out on another. When traffic is toward the Internet, an iptables rule will modify the source address of the outgoing IP datagram to be that of the interface on which it is being sent. This is Network Adress Translation (NAT). When a response datagram is received, the destination address of that datagram is modified to be that of the originating system and the datagram sent out via the NIC on the local LAN. This is Connection Tracking (conntrack)
I've only scratched the surface of what iptables can do. Just remember that route is always internal to the system where it is issued and iptables enables Internet connection.

Author Comment

ID: 38848103
Thanks guys! I really appreciate that
what about DNS?
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Author Comment

ID: 38848111
oop, I made a mistake. i will correct the point between you guys I will call them to correct that on monday because you all helped me

Thanks again

Author Closing Comment

ID: 38871976
arnold, I think you mean the routing table on the fedora box should be p2p1 p2p2 ? Is that right?
LVL 80

Expert Comment

ID: 38872159

Author Comment

ID: 38872360

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