DHCP from ISP not working with NAT

[ricky levesque]

Hello All,

I have an issue with an ISR router i'm setting up on my home lab.

my ISP provides IP addresses on a vlan interface.

when my router is configured with this Dot1Q interface, it gets an IP from the ISP DHCP server.

when i configure NAT on the outside interface, (ip nat outside) i can no longer receive an IP from the DHCP server for that interface.

here are my configs:

outside interface:

interface GigabitEthernet0/0/0.35
description ISP_vlan_35
encapsulation dot1Q 35
ip address dhcp
ip nat outside

NAT configs:

ip nat inside source list 100 interface GigabitEthernet0/0/0.35 overload

ACL config:

access-list 100 permit ip any any

default route:

ip route 0.0.0.0 0.0.0.0 GigabitEthernet0/0/0.35 dhcp

if i get an IP address and configure NAT afterwards, i can get on the internet from internal devices... until the DHCP lease expires.

any ideas on why i'm not getting an IP when i configure NAT-Outside?

thanks in advances for your help and attemtion to my question

[johnd2310]

Hi,

What router and ios version are you running?

Thanks

John

[ricky levesque]

router is an ISR 1111

curently running: IOS version 16.06.04

also tried: 16.07.01

[Deepak Kumar · Accepted solution]

Hi,

If I am getting your point correctly. As I am getting that this issue with NATTing. It is not happing if you will connect ISP after configuring the NAT. 

Please share some output:

sho ip nat statistics

Show IP nat translation

Show ip route

show ip access-list

But same time, you can try to edit ACL 100 with a specific LAN subnet.

Regards,

Deepak Kumar

[ricky levesque]

Thank you Deepak kumar

changing the ACL to the specific subnet has fixed the issue.

i'll have to find out why the ACL was stopping the DHCP traffic.

thanks for your help.

[Michael Gerencser]

This really helped me too! I actually had "ip access-group 100 out" on the WAN side and this caused big problems. I was loosing hours of troubleshooting NAT..and then I just removed it...the more specified ACL did it for me too...WOW...what a relief...esp. running an ISR 1111x-8P at home..too good of a device to have considered defective or whatever have you...