CCNA - what's inbound , outbound n/working

Author

what's inbound , outbound n/working

dark_light

2002-09-25, 8:30 pm

HI guyz
what's inbound and outbound n/working and whats the range of inbound

kphua

2002-09-26, 12:51 am

Hi dark_light

Are you referring to NAT?

quote:
Originally posted by dark_light
HI guyz
what's inbound and outbound n/working and whats the range of inbound

vschristopher

2002-09-26, 1:31 am

r u referring to NAT or access lists ?????

need more information to answer ur query...

dark_light

2002-09-26, 6:20 pm

well both

edmonds_robert

2002-09-26, 9:01 pm

Well then, let's answer both, shall we?
In case you're not familiar with the term access list, it refers to part of a router's configuration that is used to control access to certain networks, hosts, interfaces, etc.

Inbound and outbound access-lists:
Inbound access lists are access lists that are applied as a packet enters a router's interface. They are processed before the packet goes to the routing process.
Outbound access lists refer to lists that control traffic heading out of the router, such as routing updates.

A typical access list might look something like this:

router(config)#access-list 100 permit ip 172.16.1.0 0.0.0.255 host 172.16.2.15
router(config)#access-list 100 deny any any
router(config-if)#ip access-group 100 in

In this example, the first line permits any host on the 172.16.1.0 subnet to access the host at 172.16.2.15. The second line denies all other traffic. The third line applies the access list to an interface.

Now, for NAT. Again, in case you are not familiar with the term: NAT (Network Address Translation) works to change the source address of a packet from that of the actual host that sent the packet to the host that is performing the NAT service (usually a firewall). When the host at the destination replies, it will reply to the NATed address of the firewall, which then in turn relays the packet back to the actual originating host.
This is done for several reasons. One example would be a network that is using rfc 1918 (private) IP addresses. These IP addresses are not routable by the Internet and therefore must be represented to the Internet by a computer that translates the internal addresses into routable, "legal" internet addresses.
Another reason NAT is used (and rfc 1918 addresses) is preservation of the IP version 4 address space that was originally allocated by the original designers of the TCP/IP protocol suite. With NAT, several hosts (even hundreds) on an internal network can be represented to the Internet using a single IP address, or a group of IP addresses. This lessens the amount of "legal" IP addresses that an organization must use to represent its network, thereby saving valuable IP addresses for allocation elsewhere.
Finally, NAT can be used when two networks that are using identical addressing schemes are merged (by corporate merger, for example) and routing must be accomplished. NetworkA and NetworkB will perform NAT between them in order to hide the structure from the networks they are routing for.
Anyway, inbound or outbound NAT depends on the application, as referenced above. Outbound NAT refers to what happens when a host is sending packets out of a network and its address is hidden by the computer performing NAT. Inbound NAT usually refers to representing an internal host to the Internet using a legal address. An example of this would be a web server that is protected by a firewall. Its actuall IP address on the internal network may be 10.10.10.10, but is represented on the Internet by the IP address 64.64.64.65. When the firewall receives a packet bound for 64.64.64.65, it performs a lookup in its NAT table, sees that the packet should be redirected to 10.10.10.10, and directs the packet out the appropriate interface.
Well, sorry to be so long winded, but you did ask.

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