Category Archives: IPv6

Well, this is simply IPv6 stuff. Either network and/or security related.

FortiGate Enables NAT for IPv6 by Default 🤦

Fortinet, IPv6, , , , , , ,

Fortinet has a misstep in its IPv6 settings: NAT66 is enabled by default for every policy. Not only does this make no technical sense and go against established best practices, but in my view, there’s an even bigger issue at play here:

Given the widespread use of FortiGate devices and the still limited level of IPv6 expertise among many administrators, this default setting risks creating false knowledge. Many admins may come away believing that NAT for IPv6 is just as normal as it is for IPv4 – after all, it’s enabled out of the box. And as with any default, people will quickly get used to it.

In this blog post, I’ll therefore look at a few practical workarounds to move away from this approach as quickly as possible.

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Basic IPv6 Messages (v2): Wireshark Captures

IPv6, Memorandum, , , , , , , , , , ,

In my IPv6 classes, I always teach the basic IPv6 messages as seen on the wire. There’s so much new stuff, such as Router Advertisements, Duplicate Address Detections, Neighbour Solicitations, and so on. Therefore, I’m using a rather simple packet capture showing the starting process of a client getting its addresses.

For the last 10 years, I used this capture, which I took on a Knoppix Linux along with a German Speedport router, in which SLAAC was used for getting the addresses. However, it turned out that in enterprise-grade networks, stateful DHCPv6 is used more commonly. Hence, I did it again and captured the very first IPv6 messages as seen on an IPv6 node, but this time on a Windows 11 PC and a Debian 13, along with stateful DHCPv6.

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OSPFv3 Authentication on a Palo Alto (Logical Router)

Authentication, IPv6, Palo Alto Networks, Routing, , , , , ,

I had a hard time figuring out how to configure OSPFv3 authentication on a Palo Alto Networks NGFW due to its different configuration formats compared to a Cisco router.

TL;DR: The SPI must be set in hexadecimal, while the actual key (40 chars, hexadecimal) must be grouped in 5 sections, separated with hyphens.

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Bad IPv6 Approaches

IPv6, , , , , , , , , , ,

I just got a few emails from an administrator of a medium-sized company, asking some IPv6 questions. They want to use IPv6 to reach the Internet, using two ISPs, while remaining IPv4-only on their internal networks. For whatever reason, they came across three different ideas that were almost completely wrong, speaking of a sound IPv6 design. But why? Maybe because IPv4 thinking is a bigger problem than we ever thought? Or because admins rely on firewall vendors (like Fortinet) that suggest completely wrong network approaches?

Let’s dig into some misconceptions concerning IPv6:

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Dual-Stack PPPoE on a FortiGate Firewall

Fortinet, Internet Access, IPv6, , , , , , ,

You can use a FortiGate to connect to the Internet (that is: Dual-Stack!) directly in various ways. In my current setup, I’m using a PPPoE residential xDLS connection. It’s not that easy to configure everything correctly since it requires the use of many different protocols such as PPPoE and PPPoEv6 (PPP IPV6CP) along with DHCPv6-PD. But here it is:

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DHCPv6 Prefix Delegation on a FortiGate Firewall

DHCP/DHCPv6, Fortinet, IPv6, , , , , , ,

I got DHCPv6-PD aka prefix delegation up and running on a FortiGate. Yes! ✅ Configuring it is tricky since it’s not always clear which options to use. You cannot see everything in the GUI (it even changes depending on other options made later on or selects hidden and wrong default values), hence, you must set specific options via the CLI. I navigated around some bugs and finally got it running. Here we go:

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Dual-Stack PPPoE on a Palo Alto Firewall

Internet Access, IPv6, Palo Alto Networks, , , , , , ,

If you want to establish an Internet connection (that is: IPv6 and IPv4) right away from your firewall through xDSL connections, you need quite some technologies: PPPoE and PPPoEv6 (PPP IPV6CP) along with DHCPv6-PD. Fortunately, with PAN-OS 11.0 and 11.1, those missing IPv6 links were finally added by PANW to their Strata firewalls. (I have been awaiting them since 2015!)

So, here it is: Connecting a Palo through an xDSL modem to a residential ISP:

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Palo’s Mgmt-Intf is not usable with IPv6 anymore

IPv6, Palo Alto Networks, , ,

Wow, that was unexpected: With PAN-OS 11.1 the out-of-band management interface of Palo Alto Networks firewalls doesn’t accept an IPv6 default route pointing to one of its own data interfaces anymore. That is: In most setups, you can’t use IPv6 for management purposes anymore. “Works as expected.” Wow. Really?

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Optimized NAT46 Config on a FortiGate

Fortinet, Internet Access, IPv6, NAT, Tutorial/Howto, , , , ,

Johannes published a basic NAT46 configuration for a Fortigate firewall with FortiOS 7.0 some time ago. I run such a service (legacy IPv4 access to IPv6-only resources) since FortiOS 5.6, which means more than six years; lastly with FortiOS 6.4. It’s running for more than 100 servers without any other problems as we see them with IPv4 only or dual stack services.

But we weren’t happy with the basic configuration example by Fortinet. We wanted some NAT46 sample configuration with more details, that is: including the original source IPv4 address within the synthesized/SNATted IPv6 address. More in this post, after a short story about my way to a running nat46 configuration with port forwarding in FortiOS 7.2.x.

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DHCPv6 Prefix Delegation on Palo Alto’s NGFW

DHCP/DHCPv6, IPv6, Palo Alto Networks, , , , ,

Finally! With PAN-OS 11.0 a long missing IPv6 feature was introduced: DHCPv6-PD aka prefix delegation. For the first time, we can now operate a PAN-OS firewall directly on the Internet (the IPv6-Internet that is) on many kinds of ISP connections. Remember: To get a routed IPv6 prefix requires DHCPv6-PD (if you’re not a BGP-homed enterprise). Hence, without that feature, we could not connect to the Internet with a Palo directly.

With DHCPv6-PD, the firewall can receive a prefix from the ISP (commonly a /48 or a /56), while handing out /64s to downstream layer 3 interfaces. Here we go:

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DHCPv6 Prefix Delegation

DHCP/DHCPv6, IPv6, Memorandum, , , , , , ,

What is DHCPv6 Prefix Delegation? Coming from IPv4, you’re already familiar with DHCP (for IPv4) which hands out IPv4 addresses to clients. The same applies to (stateful) DHCPv6: it hands out IPv6 addresses to clients.

However, with IPv6 we’re heavily dealing with subnets rather than just single addresses. Again, you’re familiar with IPv4: For an IPv4-based ISP connection, you’re getting either a single public IPv4 address or a small subnet such as a /29, /28, or the like for your WAN interface. For an IPv6-based ISP connection, you’re getting a subnet which includes multiple unique subnets to be used for other layer 3 segments rather than a single address (with NAT on the CPE). This is where DHCPv6 prefix delegation (commonly abbreviated as DHCPv6-PD) kicks in: It hands out IPv6 subnets to routers.

Let’s have a closer look:

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Minor Palo Bug: ICMPv6 Errors sourced from Unspecified Address

IPv6, Palo Alto Networks, , , , ,

During my IPv6 classes, I discovered a (minor) bug at the NGFW from Palo Alto Networks: ICMPv6 error messages, such as “time exceeded” (type 3) as a reply of traceroute, or “destination unreachable” (type 1) as a reply of a drop policy, are not correctly sourced from the IPv6 address of the data interface itself, but from the unspecified address “::”. Here are some details:

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Verbindungsaufbau Deutsche Glasfaser

DHCP/DHCPv6, Internet Access, IPv6, Memorandum, , , , , , , , ,

Als netzwerktechnisches Spielkind beschäftige ich mich nicht nur mit den Netzwerken großer Firmenumgebungen, sondern auch mit meinem eigenen Anschluss daheim. Vor vielen Jahren habe ich dem echten Dual-Stack Anschluss der Deutschen Telekom mal auf die Finger geguckt – heute ist die Variante der Deutschen Glasfaser an der Reihe, welches zwar ein Dual Stack, aber ohne eigene öffentliche IPv4 Adresse ist. Quasi ein halbes DS-Lite. Kernfrage für mich war: Kann ich die Fritzbox (mit ihren mitgelieferten Presets für verschiedene ISPs) durch eine echte Enterprise-Firewall ersetzen, die ja leider nicht unbedingt alle Sprecharten wie PPPoE im Subinterface oder PPP IPv6CP unterstützen.

TL;DR: DHCP, DHCPv6-PD, RA.

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Stateful DHCPv6 Capture (along with Relaying)

DHCP/DHCPv6, IPv6, , , , , , ,

For my IPv6 training classes, I was missing a capture of a stateful DHCPv6 address assignment. That is: M-flag within the RA, followed by DHCPv6 messages handing out an IPv6 address among others. Therefore, I set up a DHCPv6 server on an Infoblox grid and furthermore used a Palo Alto NGFW as a DHCPv6 relay to it. I captured on two points: from the client’s point of view (getting to the relay) and from the server’s point of view (unicast messages from the relay). And since I was already there anyway, I additionally captured the same process for DHCPv4. So, here we go:

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