[j-nsp] NAT on SRX with routed IP range

[Jonathan Call]

I've been reading the Juniper documentation and confirmed that the proxy-arp statement is only needed when the  NAT IP falls within the subnet range of the external IP address of the egress interface. It will automatically proxy-arp for all else. It also doesn't matter if it is a source, a destination or a static NAT.
In my case, the problem turned out to be a missing route on a third party device preventing the traffic from even reaching the SRX.
Thanks!Date: Wed, 4 Feb 2015 14:16:02 -0800
Subject: Re: [j-nsp] NAT on SRX with routed IP range
From: tyler at adap.tv
To: lordsith49 at hotmail.com
CC: juniper-nsp at puck.nether.net

Nope.  It's been a while, but I just reviewed our configuration, we removed proxy-arp at some point.  Suppose it turns out proxy-arp wasn't needed.
We also have security policy configuration like this:
> show configuration security policies from-zone untrust to-zone trust policy <name> {
    match {        source-address <Allowed external address>;        destination-address <internal RFC1918 IP>;        application [ <list of ports/applications> ];    }    then {        permit;    }}
If you want to make the NAT work for any outside source, you could just set source-address to any.


On Wed, Feb 4, 2015 at 2:00 PM, Jonathan Call <lordsith49 at hotmail.com> wrote:
I'm in the process of rewriting it all as a static NAT right now.

Are you applying any IP from routed block to your external interface? Reading the rules of proxy-arp suggests that IP range needs to reside on the external interface.

Thanks,

JonathanDate: Wed, 4 Feb 2015 13:52:00 -0800

Subject: Re: [j-nsp] NAT on SRX with routed IP range

From: tyler at adap.tv

To: lordsith49 at hotmail.com

CC: juniper-nsp at puck.nether.net



Ah, sorry, I misunderstood.  We're using static NAT.  Here's a short example.

> show configuration security nat static rule-set static-NATs    from zone untrust;rule <name> {    match {        destination-address <external routed destination>;        destination-port <external port>;    }    then {        static-nat {            prefix {                <real host>;                mapped-port <real port>;            }        }    }}







On Wed, Feb 4, 2015 at 1:08 PM, Jonathan Call <lordsith49 at hotmail.com> wrote:







I added a proxy-arp enty:

source {rule-set my-lab-internal {from zone lab-internal;to zone untrust;rule my-lab-inet {match {source-address192.168.2.0/26;}then {source-nat {interface;}}}}}destination {pool lab-plasma {address 192.168.2.2/32 port 8080;}rule-set lab-nats {from zone untrust;rule lab-plasma-1 {match {destination-address 4.5.32.16/32;destination-port 8080;} then {destination-nat pool lab-plasma;}}}}proxy-arp {interface reth0.0 {address {4.5.32.16/32;}}}

The translation hit counter from 'show security nat destination rule all' does not increment so I'm still not hitting the NAT rule. I have the appropriate security policy rules between the untrust and lab-internal zones to allow 8080 inbound and anything outbound.

Jonathan



Date: Wed, 4 Feb 2015 11:45:26 -0800

Subject: Re: [j-nsp] NAT on SRX with routed IP range

From: tyler at adap.tv

To: lordsith49 at hotmail.com

CC: juniper-nsp at puck.nether.net



We use routed ranges to NAT a few hosts.  The key for us was configuring proxy-arp on the untrust interface for the IPs.

On Wed, Feb 4, 2015 at 11:24 AM, Jonathan Call <lordsith49 at hotmail.com> wrote:

I've seen plenty of examples of a static NAT where the SRX has a public IP range on the untrusted interface. I have not found a good one for when the SRX has an IP range routed to it.



SRX Public IP: 4.5.6.60/30Routed IP range (via the public interface) 4.5.32.16/28Trusted zone: 192.168.2.1/26



show configuration security nat (hopefully this will display properly)



source {    rule-set my-lab-internal {        from zone lab-internal;        to zone untrust;        rule my-lab-inet {            match {                source-address 192.168.2.0/26;            }            then {                source-nat {                    interface;                }            }        }    }}destination {    pool lab-plasma {        address 192.168.2.2/32 port 8080;    }    rule-set lab-nats {        from zone untrust;        rule lab-plasma-1 {            match {                destination-address 4.5.32.16/32;                destination-port 8080;            }            then {                destination-nat pool lab-plasma;            }        }    }}



The result of this configuration is that no NAT occurs. But if I change the destination-address to the SRX's external IP (4.5.6.60) it works just fine.



Jonathan



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