From: Phil (theccie@gmail.com)
Date: Mon Dec 06 2004 - 17:10:53 GMT-3
http://www.cisco.com/warp/public/cc/pd/iosw/ioft/ionetn/prodlit/1195_pp.htm
Autoaliasing of Pool Addresses:
Many customers want to configure the NAT software to translate their
local addresses to global addresses allocated from unused addresses
from an attached subnet. This requires that the router answer ARP
requests for those addresses so that packets destined for the global
addresses are accepted by the router and translated. (Routing takes
care of this packet delivery when the global addresses are allocated
from a virtual network which isn't connected to anything.) When a NAT
pool used as an inside global or outside local pool consists of
addresses on an attached subnet, the software will generate an alias
for that address so that the router will answer ARPs for those
addresses.
This automatic aliasing also occurs for inside global or outside local
addresses in static entries. It can be disabled for static entries can
be disabled by using the "no-alias" keyword:.
ip nat inside source static <local-ip-address> <global-ip-address> no-alias
On Mon, 6 Dec 2004 11:06:58 -0500, ccie2be <ccie2be@nyc.rr.com> wrote:
> Hi guys,
>
> I'm not getting this example with the no-alias keyword. Can someone
> elaborate?
>
> Router#configure terminal
> Enter configuration commands, one per line. End with CNTL/Z.
>
> Router(config)#ip nat outside source static network 172.16.0.0 172.17.0.0
> /16 no-alias <-- ???
>
> Router(config)#ip route 172.16.0.0 255.255.0.0 Ethernet1/0
> Router(config)#ip route 172.17.0.0 255.255.0.0 Ethernet1/0
> Router(config)#interface FastEthernet 0/0
> Router(config-if)#ip address 10.1.1.1 255.255.255.0
> Router(config-if)#ip nat inside
> Router(config-if)#exit
> Router(config)#interface Ethernet1/0
> Router(config-if)#ip address 172.16.1.6 255.255.255.252
> Router(config-if)#ip nat outside
> Router(config-if)#end
>
> Note that we have included the no-alias keyword in this command. If we
> didn't include this keyword, the router would try to generate aliases for
> the translated addresses to allow it to answer ARP requests for them. This
> keyword is necessary because one of the router's own interfaces belongs to
> the translated range.
>
> This example is from the Cisco Cookbook, recipe 21.6
>
> What do they mean, "the router would try to generate aliases for the
> translated addresses"?
>
> BTW, overall, I think this book is pretty good. It has lots of examples
> which for the most part they explain very well.
>
> TIA, Tim
>
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