overlapping subnets in virtual router and NAT

Reply
Highlighted
L3 Networker

overlapping subnets in virtual router and NAT

Hi

 

I have two virtual routers say customer-1 and customer-2 having subnets 10.10.10.0/24 (overlapping subnet). Now internet connection line is on eth1/1 which is in default virtual router. Both customer-1 and customer-2 needs to access the internet but I am wondering how source NAT will work in this case?

Also for reverse traffic for 10.10.10.0/24 subnet in default route will work?

 

Thanks


Accepted Solutions
Highlighted
L7 Applicator

I would setup NAT from one to a non-overlapping subnet on egress from the VR into the ISP VR.

 

This will give everything a unique address from the ISP VR perspective and return the traffic to the correct sources.

 

Steve Puluka BSEET - IP Architect - DQE Communications (Metro Ethernet/ISP)
ACE PanOS 6; ACE PanOS 7; ASE 3.0; PSE 7.0 Foundations & Associate in Platform; Cyber Security; Data Center

View solution in original post


All Replies
Highlighted
L7 Applicator

overlapping subnets on different VR will not interfere unless you need them to converge, at which time you will get a conflict

 

a solution to this situation could be to implement separate VSYS (rather than just separating VR) and enabling the 'shared gateway' feature which automatically provides for this sort of situation

 

Alternatively you can look into using PBF with symmetric return which will keep track of the original source when forwarding packets, and returns the packets to the proper origin

Tom Piens - PANgurus.com
Like my answer? check out my book! amazon.com/dp/1789956374
Highlighted
L3 Networker

Thanks for the reply.

 

For shared gateway solution, if traffic is initiated from 10.10.10.10 from VR1 (which is in VSYS1) and at the same time 10.10.10.10 from VR2 (which is in VSYS2) to internet through shared gateway (where source NAT is happening) then how I can define the reverse route for 10.10.10.0/24 in shared gateway?

 

 

Highlighted
L7 Applicator

I'm starting to think you will still need PBF, so simply implementing pbf will be your best shot without complicating things

Tom Piens - PANgurus.com
Like my answer? check out my book! amazon.com/dp/1789956374
Highlighted
L3 Networker

Thanks for reply @reaper for destination NAT in shared gateway, say public IP 100.100.100.100 into 10.10.10.10 then again problem is after getting NAT, in which VSYS traffic will go?

 

Some vendor like Juniper implement this using routing instance (virtual router) aware NAT that associate the public IP to virtual router, mean after destination NAT in which routing instance routelookup wil happen for policy lookup and forwarding. 

 

https://forums.juniper.net/t5/SRX-Services-Gateway/Overlapping-address-ranges-virtual-routers-and-NA...

 

Is there any feature in Palo Alto to support this? As it is very important for multi-tenant (customers) enviornemnt where customer can share same private subnets. 

Highlighted
L3 Networker

@reaper your comments please

Tags (1)
Highlighted
L7 Applicator

in your scenario the ideal solution would be to have eacht VR connected to the ISP independently, this will prevent collisions with your duplicate IP subnets

Tom Piens - PANgurus.com
Like my answer? check out my book! amazon.com/dp/1789956374
Highlighted
L7 Applicator

I would setup NAT from one to a non-overlapping subnet on egress from the VR into the ISP VR.

 

This will give everything a unique address from the ISP VR perspective and return the traffic to the correct sources.

 

Steve Puluka BSEET - IP Architect - DQE Communications (Metro Ethernet/ISP)
ACE PanOS 6; ACE PanOS 7; ASE 3.0; PSE 7.0 Foundations & Associate in Platform; Cyber Security; Data Center

View solution in original post

Highlighted
L3 Networker

Thanks @reaper @pulukas for your comments 

Highlighted
L2 Linker

Hi, sorry to bring this thread up as I happened to came across  when searching for a solution to my issue. 

 

So, I have a setup as below, I'm having 2 VSYS with overlapping subnet (Network A and B) in the trust interface, however, I also added secondary subnets in that same interface, however, this time, the secondary subnets are non overlapping. 

 

What I did next was, from each VSYS A and VSYS B,  configured Source NAT from Trust to External Zone, translated IP as the secondary subnet interface IP (ie 192.168.3.1 and 192.168.4.1 for VSYS A and B respectively), to reach out to a server in the untrust subnet located in the Main VSYS.

 

I also have routing configured respectively, as you can see from the diagram, however, I could not reach to the untrust subnet from both VSYS A and B. 

 

Session browser showed connected sessions from both VSYS A and B trust zones to the Main VSYS untrust zones, with correct source and destination addresses with NAT-ed IP as well.

 

The following counter global were observed:

Session setup: no destination zone from forwarding

Packets dropped: no route

 

These counters indicated there there were no routing or routing was incorrect, however, fib route lookup from both VSYS A and B to Main VSYS  to destination in untrust zone in main VSYS was successful.  Route lookup from Main VSYS to VSYS A and B to destination of Source NAT-ed IP (192.168.3.1 and 4.1) was successful as well.

 

Therefore, could anyone verified if SourceNAT is supported in such intervsys routing design?

 

Screenshot 2020-03-25 at 3.38.03 PM.png

Like what you see?

Show your appreciation!

Click Like if a post is helpful to you or if you just want to show your support.

Click Accept as Solution to acknowledge that the answer to your question has been provided.

The button appears next to the replies on topics you’ve started. The member who gave the solution and all future visitors to this topic will appreciate it!

These simple actions take just seconds of your time, but go a long way in showing appreciation for community members and the Live Community as a whole!

The Live Community thanks you for your participation!