About NAT

[wesley_wang]

The Network topology is as the attachment.Two Routers (2505) link together with serial line .R1 connects to the address 172.16.12.1 , which is the gateway for the lan computers to go on the Internet.The two router's configuration are as the two attachments.

On R1 , I can ping the gateway 172.16.12.1 , also the Internet Global address ,such as Google .But I cann't do this On R2 . On R1 can ping the address 172.16.12.31 , but not 172.16.12.1 .

SO What's the problem ? Can Anyone who knows this help me ? Thanks a lot .

[o.hassairi]

when you make ping from R1 to 172.16.12.1 the source ip @ will be: 192.168.12.1 (s0) so it will not be NATted in R2 that NATs only IP paquet with source 10.0.0.x.

of course your gateway :172.16.12.1 doesn't know how to reply to 192.168.12.0 network. so the ping wll fail.

[wesley_wang]

Then , What else should I do ?

Could anyone help ?

[royalblues]

You would need to allow the Serial IP subnet on the access-lits for NAT

access-list 1 permit 192.168.12.0 0.0.0.3

Also your gateway should have a reverse route for this subnet.

But if your requirement is just to ping from the R1 router, then you can do an extended ping

router# ping ip

Target IP address: 172.16.12.1

Repeat count [5]:

Datagram size [100]:

Timeout in seconds [2]:

Extended commands [n]: y

Source address or interface:10.0.0.1

[wesley_wang]

Thank you for your reply, royalblues !

But it seems I cann't ping source from the 10.0.0.1 interface .

And I also have a question that do i have to add a route to 192.168.12.0/30 since i have nated the 192.168.12.0/30 to 172.16.12.31 ?

[jackyoung]

Try to connect a PC to R1 E0 at ping to Internet then check the NAT at R2 to determine the NAT is working.

I don't think we need static route for 192.168.12.0/30, it is a connected interface in both routers.

Please provide show nat

[zerozerotito]

Please provide sh ip route and show nat!

And please first clear access-list counters to do it

router# clear access-lists counters

then try to ping again,

and look sh access-lists to ensure that ping packets are passing through accesslists...

Pls let me know how it goes...

Regards