Active / Active NAT question

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L4 Transporter

Active / Active NAT question

Hi

 

To all the A/A users. How have you / Or can you setup SNAT so that all traffic is SNAT'ed to 1 ip .

 

very basic example

 

Eth1 - connect to 1.2.3.0/24 - interface address is 1.2.3.2/24 & 1.2.3.3/24 (A/A)  1.2.3.1 arp load balanced

eth2 - connecs to 10.10.10.0/24 interface addrss is 10.10.10.2/24  & 10.10.10.3/24 ( A/A) 10.10.10.1 arp load balanced

 

Policy that say every thing from eth2 leaving eth1 get SNAT to 1.2.3.1. how do I do this on A/A

 

A

 

L4 Transporter

Re: Active / Active NAT question

Hello

 

I really believe that for HA A/A you need to have L2 switches upstream/downstream the FWs.

The arp load sharing config allows for a single IP to be shared by both FWs, hence 2 virtual mac addresses.

So the arp table on the L3 switch is going to have 2 entries for the same IP, but with 2 different mac address?

How is that possible?

 

clipboard_image_2.png

 

Based on the parity of the source IP, the FWs will load share (not balance) the sessions.

Yet, if the router has a static IP that is even, then only 1 FW would technically handle the inbound traffic.

 

I mean you could program the FW to use a SNAT of 1.2.3.1, but I believe that the response traffic would only go to a single FW.

 

What other questions can I answer for you.

 

 

 

L4 Transporter

Re: Active / Active NAT question

Hi

 

I get the L2 stuff. this is more around the NAT.

 

if I have 1 SNAT and say it associated with device 0 ( if I have device 0 and device 1).

 

if traffic enters device 1 and the rules state to use NAT, it will go to device 0 via the cross connect and then be NAT'ed and then sent out .

 

if the reverse if a return pack comes in and goes to device 1 it will go to device 0 and be un SNAT and then sent inside

 

so if device 0 fails - that nat will move to device 1 and just work there.

 

Is that how it works ?

L4 Transporter

Re: Active / Active NAT question

@Alex_Samad

 

If you have configured arp load sharing on your FWs, then both device 0 and device 1 would be sending the SNAT through their respective eth1/1 interface.   It would not (to the best of my knowledge) use the HA3 to perform asynchronous routing.

 

If device 0 fails, then device1 will still have the SNAT on it. 

 

What other questions can we answer for you?

 

L4 Transporter

Re: Active / Active NAT question

Let me expand

clipboard_image_0.png

 

Hi

So I have added a diagram - might help.
So A/A cluster Device0 & Device1
The relevant link to the doco
https://docs.paloaltonetworks.com/pan-os/8-1/pan-os-admin/high-availability/set-up-activeactive-ha/d...

so my aim is to have 1 SNAT for all traffic that comes from inside (192.168.0.0/16) to outside (eth1).
The SNAT is 10.0.0.1/32 - I think just having it as a SNAT will make the PA respond to arp requests for it on eth1


on the inside I have 3 vlans 192.168.1.0/24, 192.168.2.0/24, 192.168.3.0/24. With .1 being the DGW for each lan setup as Arp loading sharing

so if the NAT policy is attached to device 0 my expaction would be for 192.168.1.250 -> 10.10.10.250
192.168.1.250 -> 192.168.1.1 (goes to device 0)
device 0 has the NAT pool
SNAT 10.0.0.1 -> 10.10.10.250
then response would be 10.10.10.250 -> 10.0.0.1
so when one of the routers on the internet site does arp 10.0.0.1 device 0 will respond because it has the SNAT policy
deSNAT 10.10.10.250->192.168.1.250

That all works fine

So lets look at 192.168.3.250 -> 10.10.10.250
192.168.1.250 -> 192.168.1.1 (goes to device 1)
?? What happens here. NAP policy is only active on device 0
does the packet get send to device 0 via the HA link or ??

 

 

 

 

L4 Transporter

Re: Active / Active NAT question

Hello again.

 

Thanks for the picture and the detail.

 

There are some assumptions you made, that I want to clear up.

With ARP Load sharing, you really cannot force device 0 to own the virtual IP.

 

clipboard_image_0.png

By definition,  arp load sharing means BOTH FWs will own the 192.168.1.1 address

 

clipboard_image_1.png

 

If you wanted to do Floating IP, then yes, you could have device 0 own the IP.

 

clipboard_image_2.png

 

You would need to configure Floating IP for your outside interfaces, so that 10.0.0.1 is associated with device 0 (as you want).

How would 192.168.3.x get out?  You would need to config a 2nd Floating IP for the device1 FW.

 

Something like this.... (IPs are not the same) but you would get the gist of it... 

 

clipboard_image_3.png

 

The idea (according to the picture) is that BOTH FWs are configured with a weighted configuration, so that each device0 or device1 FW could fail, and the other FW outside interfaces would "float" to the other FW.

 

clipboard_image_0.png

L4 Transporter

Re: Active / Active NAT question

HI

 

Just for clarity - yes I understand how arp loading sharing work and depending on which method you use you can predict which device responsed.  From memory an increment of 1 in the 4th oct will change the device. this is similar to how arp ip load sharing work in linux - last time i looked. so yes its active on both and the pack actual gets to both its a matter of whcih device responds.

 

But basically you are confirming my original thought. with A/A you can't share 1 SNAT addresses. because if  a packet traverses the device that doesn't have the active NAT rule - no NAT Rule would apply.   That to me seems like a very big deficiency ...

 

Lines up with the doco though and what I got from support and from the SE - I went through this exercise nearly 2 years ago.

 

 

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