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I have this network, and I need to configure NAT in order to give Internet access to computers in VLANs 11 and 12. When I test connectivity from computers to two public IP addresses of ISP, routers 1.1.1.1 and 2.2.2.1 display the Request timed out. message. Packets go to the ISP1 router but never come back.

Here are my commands so far:

R1

R1(config)#interface serial 0/0/0
R1(config-if)#ip nat inside
R1(config-if)#exit
R1(config)#ip nat inside source static 1.1.1.2 1.1.1.1
R1(config)#ip route 0.0.0.0 0.0.0.0 1.1.1.1
R1(config)#

ISP1

ISP1(config)#interface serial 0/0/0
ISP1(config-if)#ip nat outside
ISP1(config-if)#exit

show ip nat translations

R1#show ip nat translations 
Pro  Inside global     Inside local       Outside local      Outside global
---  1.1.1.1           1.1.1.2            ---                ---

R1 show ip route

R1#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is 1.1.1.1 to network 0.0.0.0

     1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C       1.1.1.0/30 is directly connected, Serial0/0/0
L       1.1.1.2/32 is directly connected, Serial0/0/0
     2.0.0.0/30 is subnetted, 1 subnets
O       2.2.2.0/30 [110/66] via 10.1.11.2, 10:08:42, GigabitEthernet0/0
                   [110/66] via 10.1.12.2, 10:08:42, GigabitEthernet0/1
     10.0.0.0/8 is variably subnetted, 6 subnets, 2 masks
C       10.1.11.0/24 is directly connected, GigabitEthernet0/0
L       10.1.11.1/32 is directly connected, GigabitEthernet0/0
C       10.1.12.0/24 is directly connected, GigabitEthernet0/1
L       10.1.12.1/32 is directly connected, GigabitEthernet0/1
O       10.2.21.0/24 [110/2] via 10.1.11.2, 10:08:42, GigabitEthernet0/0
O       10.2.22.0/24 [110/2] via 10.1.12.2, 10:08:42, GigabitEthernet0/1
S*   0.0.0.0/0 [1/0] via 1.1.1.1

ISP1 show ip route

ISP1#show ip route
Codes: L - local, C - connected, S - static, R - RIP, M - mobile, B - BGP
       D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
       N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
       E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
       i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
       * - candidate default, U - per-user static route, o - ODR
       P - periodic downloaded static route

Gateway of last resort is not set

     1.0.0.0/8 is variably subnetted, 2 subnets, 2 masks
C       1.1.1.0/30 is directly connected, Serial0/0/0
L       1.1.1.1/32 is directly connected, Serial0/0/0
     2.0.0.0/30 is subnetted, 1 subnets
O       2.2.2.0/30 [110/130] via 1.1.1.2, 00:29:20, Serial0/0/0
     10.0.0.0/24 is subnetted, 4 subnets
O       10.1.11.0/24 [110/65] via 1.1.1.2, 00:29:20, Serial0/0/0
O       10.1.12.0/24 [110/65] via 1.1.1.2, 00:29:20, Serial0/0/0
O       10.2.21.0/24 [110/66] via 1.1.1.2, 00:29:20, Serial0/0/0
O       10.2.22.0/24 [110/66] via 1.1.1.2, 00:29:20, Serial0/0/0

I'm kinda noob into networking, so I don't know what any other information I should provide.

Network im working on

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  • Did any answer help you? If so, you should accept the answer so that the question doesn't keep popping up forever, looking for an answer. Alternatively, you could provide and accept your own answer.
    – Ron Maupin
    Aug 14 '17 at 14:15
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You seem to be confused about how NAT works. You want to translate your network addresses to something else. NAT is configured and only works on a single router. Your ISP router doesn't need, and shouldn't have, any NAT configuration.

NAT is configured on your local router. You will have both the inside and outside interfaces on R1. The 1.1.1.2 interface will be the outside interface, and the 10.1.11.1 and 10.1.12.1 interfaces will be the inside interfaces. You need to translate the 10.1.11.0/24 and 10.1.12.0/24 addresses.

You also need to be careful with two WAN routers. If you get asymmetric routing (traffic goes out one WAN router, but comes back on the other WAN router), your NAT will break because the two WAN routers do not share a NAT table.

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  • Thanks for your help but 1.1.1.1 needs to be public instead of 1.1.1.2. I've seen other examples and they're exactly like you're saying. This is where i get confused. How do i make 1.1.1.1 as public?
    – Lura
    Jun 14 '16 at 16:27
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    The problem is that 1.1.1.1 is not under your control, it belongs to the ISP. In this scenario, both 1.1.1.1 and 1.1.1.2 are public addresses. NAT is a process on a single router. You cannot NAT across routers. The NAT table only exists within the one router, and it is not shared with any other routers. The translation happens in the router as a packet travels from the inside interface to the outside interface, as long as the traffic matches the NAT rules you have defined. You cannot NAT outside the router. Each router handles NAT on its own.
    – Ron Maupin
    Jun 14 '16 at 16:32
  • just tried it the way i was supposed to. still it doesn't work [img]i.imgur.com/mMoNubc.png?1[/img]
    – Lura
    Jun 14 '16 at 17:05
  • You are only translating traffic from the single router address (10.1.11.1), not from any other address. If you source traffic from that address it should be translated. Your PCs will have other addresses, so traffic from them will not be translated. I don't think you really understand NAT, and this document should help.
    – Ron Maupin
    Jun 14 '16 at 17:09
  • jesus! just tried ip nat inside source static _source_ _destination_ with both getting the host ip and the whole network 10.1.11.0 as sources still no results. what am i doing wrong?
    – Lura
    Jun 14 '16 at 17:29

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