Cisco 1921 ISR Routing

[Senbonzakura]

Quick question,

When it comes to routing with a Cisco ISR 1921, how would I create the routing table for this certain setup?

So lets say I have a modem running DHCP handing out 10.0.0.1 /24 and it's hooked into g0/0 then I have 192.168.0.1 /24 hooked into g0/1. How do I route traffic from 192.168.0.1 to and from 10.0.0.1 and have functioning internet? Any help would be appreciated.

Or does the modem have to be statically configured for this to work?

[balaji.bandi]

If the Router having both the interface on Router, inter vlan routing automatically take place. if the devices have gateway is 10.0.0.1 and same with 192.168.0.1 network.

if you like both the subnet required internet you need to add an access list for both and add ACL to NAT configuration as the example below :

access-list 1 permit 192.168.1.0 0.0.0.255

access-list 1 permit 10.0.0.0 0.0.0.255

ip nat inside source list 1 interface FastEthernet0/0 overload   ( change the interface going towards internet)

Still have an issue, please post a complete show run from the router to suggest better

[balaji.bandi]

So lets say I have a modem running DHCP handing out 10.0.0.1 /24 and it's hooked into g0/0 then I have 192.168.0.1 /24 hooked into g0/1. How do I route traffic from 192.168.0.1 to and from 10.0.0.1 and have functioning internet? Any help would be appreciated.

I may have read the wrong original post, i was in the impression both the are Lan side IP address, if 10.x.x.x is coming rom modem you do not need NAT for that  IP address, So i have corrected as below - make sure on the DHCP you use any Public DNS IP google (8.8.8.8 or provider DNS IP to resolve DNS Lookup for the range of IP address 192.168.1.0 DHCP settings)

access-list 1 permit 192.168.1.0 0.0.0.255

ip nat inside source list 1 interface GigabitEthernet0/0 overload   ( change the interface going towards internet)

[Georg Pauwen]

Hello,

if you connect the modem to the router, the router will get an 10.0.0.0/24 address, but clients connected to the router won't. You need to use double NAT (on the router and the modem). The config of your 1921 ISR would look something like below:

ISR1921

ip dhcp excluded-address 192.168.0.1
!
ip dhcp pool LAN
network 192.168.0.0 255.255.255.0
default-router 192.168.0.1
dns-server 8.8.8.8 8.8.4.4
!
interface GigabitEthernet0/0
description Uplink to ISP Modem
ip address dhcp
ip nat outside
!
interface Gigabitethernet0/1
description Link to 192.168.0.1/24 LAN
ip address 192.168.0.1 255.255.255.0
ip nat inside
!
ip nat inside source list 1 interface GigabitEthernet0/0 overload
!
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/0 dhcp
!
access-list 1 permit 192.168.0.0 0.0.0.255

[Senbonzakura]

Thank you both, that helped out a lot. So ill be attaching two other ISRs to mess around with OSPF. I plan to get internet functioning out of R2 and R3. Now when using OSPF correct me if I'm wrong but you don't need to do like a ip route x.x.x.x x.x.x.x command correct? But if I wasn't to use OSPF and wanted to route let's say 192.168.0.1 is R2s G0/0 which is going to the client and G0/1 is 10.0.0.1 going to R1 from R2. Then R1s pointing towards R2 is 10.0.0.2, what would the command be to route traffic from R2 to R1 and R1 to R2? Also, can you do this without nat and if so what are the ways with it and without it.

You guys are awesome, thanks for taking the time to help. I greatly appreciate it.

[Georg Pauwen]

Hello,

it is a bit hard to follow what you are planning. If you want to attach two more routers, make sure they are connected on common subnets, and advertise the connecting and any local networks on R2 and R3 in OSPF, so R1 has visibility of all networks. On R1, make sure the local networks on R2 and R2 are added to the NAT access list.

[Senbonzakura]

Okay, so I'd pretty much just create an access list for the other networks
coming off of R2 and R3 onto R1 only then? After I've connected them up
properly. Or does the access list have to be created on R2 and R1?

[Georg Pauwen · Accepted solution]

Hello,

you got it. Just the access list on R1 needs to be amended.

ip nat inside source list 1 interface GigabitEthernet0/0 overload
!
ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/0 dhcp
!
access-list 1 permit 192.168.0.0 0.0.0.255

--> access-list 1 permit 192.168.10.0 0.0.0.255

--> access-list 1 permit 192.168.20.0 0.0.0.255