I am currently working on a network & security training, module “OSI Layer 4 – Transport”. Therefore I made a very basic demo of a TCP and UDP connection in order to see the common “SYN, SYN-ACK, ACK” for TCP while none of them for UDP, “Follow TCP/UDP Stream” in Wireshark, and so on. I wanted to show that it’s not that complicated at all. Every common application/service simply uses these data streams to transfer data aka bytes between a client and a server.
That is: Here are the Linux commands for basic lab, a downloadable pcap, and, as always, some Wireshark screenshots:
Continue reading Basic TCP and UDP Demos w/ netcat and telnet
During my analysis of NTP and its traffic to my NTP servers listed in the NTP Pool Project I discovered many ICMP error messages coming back to my servers such as port unreachables, address unreachables, time exceeded or administratively prohibited. Strange. In summary, more than 3 % of IPv6-enabled NTP clients failed in getting answers from my servers. Let’s have a closer look:
Continue reading Incorrect Working IPv6 NTP Clients/Networks
Wherever you’re running an NTP server: It is really interesting to see how many clients are using it. Either at home, in your company or worldwide at the NTP Pool Project. The problem is that ntp itself does not give you this answer of how many clients it serves. There are the “monstats” and “mrulist” queries but they are not reliable at all since they are not made for this. Hence I had to take another path in order to count NTP clients for my stratum 1 NTP servers. Let’s dig in:
Continue reading Counting NTP Clients
During my work with a couple of NTP servers, I had many situations in which I just wanted to know whether an NTP server is up and running or not. For this purpose, I used two small Linux tools that fulfil almost the same: single CLI command while not actually updating any clock but only displaying the result. That is: ntpdate & sntp. Of course, the usage of IPv6 is mandatory as well as the possibility to test NTP authentication.
Continue reading Basic NTP Client Test: ntpdate & sntp
Since my last blogposts covered many 6in4 IPv6 tunnel setups (1, 2, 3) I took a packet capture of some tunneled IPv6 sessions to get an idea how these packets look like on the wire. Feel free to download this small pcap and to have a look at it by yourself.
A couple of spontaneous challenges from the pcap round things up. ;)
Continue reading 6in4 Traffic Capture
Yes, I know I know, the Juniper ScreenOS devices are Out-of-Everything (OoE), but I am still using them for a couple of labs. They simply work as a router and VPN gateway as well as a port-based firewall. Perfect for labs.
For some reasons I had another lab without native IPv6 Internet. Hence I used the IPv6 Tunnel Broker one more time. Quite easy with the SSGs, since HE offers a sample config. But even through the GUI it’s just a few steps:
Continue reading Juniper ScreenOS with a 6in4 Tunnel
Of course, you should use dual-stack networks for almost everything on the Internet. Or even better: IPv6-only with DNS64/NAT64 and so on. ;) Unfortunately, still not every site has native IPv6 support. However, we can simply use the IPv6 Tunnel Broker from Hurricane Electric to overcome this time-based issue.
Well, wait… Not when using a Palo Alto Networks firewall which lacks 6in4 tunnel support. Sigh. Here’s my workaround:
Continue reading Workaround for Not Using a Palo Alto with a 6in4 Tunnel
For some reason, I am currently using a FortiGate on a location that has no native IPv6 support. Uh, I don’t want to talk about that. ;) However, at least the FortiGate firewalls are capable of 6in4 tunnels. Hence I am using the IPv6 Tunnel Broker from Hurricane Electric again. Quite easy so far.
But note, as always: Though FortiGate supports these IPv6 features such as a 6in4 tunnel or stateful/-less DHCPv6 server, those features are NOT stable or well designed at all. I had many bugs and outages during my last years. Having “NAT enabled” on every new IPv6 policy is ridiculous. Furthermore, having independent security policies for legacy IP and IPv6 is obviously a really bad design. One single policy responsible for both Internet protocols is a MUST. Anyway, let’s look at the 6in4 tunnel:
Continue reading Using a FortiGate with a 6in4 Tunnel
IPv6 brings us enough addresses until the end of the world. Really? Well… No. There was an interesting talk at RIPE77 called “The Art of Running Out of IPv6 Addresses” by Benedikt Stockebrand that concludes that we will run out of IPv6 addresses some day.
Luckily Palo Alto Networks has already added one feature to expand the IPv6 address space by making them case sensitive. That is: you can now differentiate between upper and lower case values “a..f” and “A..F”. Instead of 16 different hexadecimal values you now have 22 which increases the IPv6 space from to about . Here is how it works on the Palo Alto Networks firewall:
Continue reading Using Case Sensitive IPv6 Addressing on a Palo Alto
As you hopefully already know, you should use at least three different NTP servers to get your time. However, there might be situations in which you can configure only one single NTP server, either via static IP addresses or via an FQDN. To overcome this single point of failure you can use an external load balancing server such as F5 LTM (in HA of course) to forward your NTP queries to one of many NTP servers. Here are some hints:
Continue reading Load Balancing NTP via F5 BIG-IP LTM
This post shows how to use a GPS receiver with a Raspberry Pi to build a stratum 1 NTP server. I am showing how to solder and use the GPS module (especially with its PPS pin) and listing all Linux commands to set up and check the receiver and its NTP part, which is IPv6-only in my case. Some more hints to increase the performance of the server round things off. In summary, this is a nice “do it yourself” project with a working stratum 1 NTP server at really low costs. Great. However, keep in mind that you should not rely on such projects in enterprise environments that are more focused on reliability and availability (which is not the case on self soldered modules and many config file edits).
Continue reading NTP Server via GPS on a Raspberry Pi
In this tutorial, I will show how to set up a Raspberry Pi with a DCF77 receiver as an NTP server. Since the external radio clock via DCF77 is a stratum 0 source, the NTP server itself is stratum 1. I am showing how to connect the DCF77 module and I am listing all relevant commands as a step by step guide to install the NTP things. With this tutorial, you will be able to operate your own stratum 1 NTP server. Nice DIY project. ;) However, keep in mind that you should only use it on a private playground and not on an enterprise network that should consist of high reliable NTP servers rather than DIY Raspberry Pis. Anyway, let’s go:
Continue reading NTP Server via DCF77 on a Raspberry Pi
What’s the first step in a networker’s life if he wants to work with an unknown protocol: he captures and wiresharks it. ;) Following is a downloadable pcap in which I am showing the most common NTP packets such as basic client-server messages, as well as control and authenticated packets. I am also showing how to analyze the delta time with Wireshark, that is: how long an NTP server needs to respond to a request.
Continue reading Packet Capture: Network Time Protocol (NTP)
I got an email where someone asked whether I know how to change the link-local IPv6 addresses on a FortiGate similar to any other network/firewall devices. He could not find anything about this on the Fortinet documentation nor on Google.
Well, I could not find anything either. What’s up? It’s not new to me that you cannot really configure IPv6 on the FortiGate GUI, but even on the CLI I couldn’t find anything about changing this link-local IPv6 address from the default EUI-64 based one to a manually assigned one. Hence I opened a ticket at Fortinet. It turned out that you cannot *change* this address at all, but that you must *add* another LL address which will be used for the router advertisements (RA) after a reboot (!) of the firewall. Stupid design!
Continue reading Trying to change an IPv6 Link-Local Address on a FortiGate
I did a session at SharkFest’18 Europe in Vienna with the title of “Crash Course: IPv6 and Network Protocols“. Since the presentation slides + audio were recorded you can listen to the talk, too. Here are some notes about the motivation for this session as well as feedback from the attendees.
Continue reading SharkFest’18 Europe: Crash Course: IPv6 and Network Protocols