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DHCP from ISP not working with NAT

ricky levesque
Level 1
Level 1

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

1 Accepted Solution

Accepted Solutions

Deepak Kumar
VIP Alumni
VIP Alumni

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

Regards,
Deepak Kumar,
Don't forget to vote and accept the solution if this comment will help you!

View solution in original post

5 Replies 5

johnd2310
Level 8
Level 8

Hi,

 

What router and ios version are you running?

 

Thanks

John

**Please rate posts you find helpful**

router is an ISR 1111

 

curently running: IOS version 16.06.04

also tried: 16.07.01

 

 

Deepak Kumar
VIP Alumni
VIP Alumni

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

Regards,
Deepak Kumar,
Don't forget to vote and accept the solution if this comment will help you!

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.

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...

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