Category Archives: Vendor/Device/OS

DHCPv6 Relay Issue with Cisco ASA and Ubuntu

Cisco ASA, DHCP/DHCPv6, IPv6, Linux, , , ,

Some months ago, my co-worker and I ran into an interesting issue: a notebook with a newly installed Ubuntu 20.04 does only work with IPv4, but this office network is dual-stacked (IPv4 and IPv6). Other Linux clients as well as Windows and Mac systems still work fine. They all get an IPv4 configuration by DHCPv4 and an IPv6 configuration by stateful DHCPv6 from the same DHCP server, relayed by a Cisco ASA 5500-X. What’s wrong with Ubuntu 20.04?

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Publishing IPv6 NTP Servers with DHCPv6

DHCP/DHCPv6, Fortinet, IPv6, Network, NTP, , , , , , , , ,

During the last weeks, I had an interesting request to publish NTP servers to client systems by using DHCPv6 in an IPv6 only network. Our Fortigate (or me?) had to learn how to publish the information. Hence this post is not only about NTP and IPv6, but a small guide on how to walk through RFCs and how to get out the relevant information. I’m very happy I got the possibility to share my experience here. Thank you, Johannes!

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Pi-hole Installation Guide

DNS/DNSSEC, Internet Access, Raspberry Pi, Tutorial/Howto, , , , , ,

You probably know already the concept of the Pi-hole. If not: It’s a (forwarding) DNS server that you can install on your private network at home. All your clients, incl. every single smartphone, tablet, laptop, and IoT devices such as smart TVs or light bulb bridges, can use this Pi-hole service as their DNS server. Now here’s the point: it not only caches DNS entries, but blocks certain queries for hostnames that are used for ads, tracking, or even malware. That is: You don’t have to use an ad- or track-blocker on your devices (which is not feasible on smart TVs or smartphone apps, etc.), but you’re blocking this kind of sites entirely. Nice approach!

Yes, there are already some setup tutorials for the Pi-hole out there. However, it’s not only about installing the mere Pi-hole, but setting it up with your own recursive DNS server (since the default installation forwards to public DNS servers), using DNSSEC, and adding some more adlists. That’s why I am listing my installation procedure here as well. However, it’s not a complete beginners guide. You’ll need some basic Linux know-how.

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Palo Alto Syslog via TLS

Palo Alto Networks, Syslog, , , , ,

As we have just set up a TLS capable syslog server, let’s configure a Palo Alto Networks firewall to send syslog messages via an encrypted channel. While it was quite straightforward to configure I ran into a couple of (unresolved) problems as I added and deleted some syslog servers and their certificates. Uhm.

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syslog-ng with TLS: Installation Guide

Linux, Syslog, Tutorial/Howto, , , , , ,

Some years ago I wrote a blog post called “Basic syslog-ng Installation“. While I used it myself quite often in my labs or at the customers’ sites, it shows only basic UDP transport which is both unreliable and insecure. So, let’s have a look at a fresh installation of syslog-ng with TLS support for security reasons. However, TCP and UDP as transport are covered as well for the support of legacy systems.

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Palo Alto: User Group Count Exceeds Threshold

Palo Alto Networks, , , ,

We have run into an annoying situation: A hardware-dependent limit of user groups on a Palo Alto Next-Generation Firewall. That is: We cannot use more Active Directory groups at our firewalls. The weird thing about this: We don’t need that many synced groups on our Palo, but we have to do it that way since we are using nested groups for our users. That is: Palo Alto does not support nested groups out of the box, but needs all intermediary groups to retrieve the users which results in a big number of unnecessary groups.

I am asking you to give me some input on how you’re using user groups on the Palo. How are you using group filters? What count of AD groups do you have? Are you using nested groups (which is best practice)?

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Cisco ESA: Mail Flow for Encryption Appliances

Cisco ESA, , , , , , , ,

The Cisco Email Security Appliance (ESA) is well-known for its very good Anti-Spam features. But it completely lacks a usable implementation for mail encryption with S/MIME or OpenPGP. That is: We are using other appliances for that such as Zertificon, SEPPmail, or totemo.

However, the Cisco ESA still remains the main MTA for incoming and outgoing mails, hence mails must be routed to the encryption appliance of your choice for signing/encrypting (outgoing) or verifying/decrypting (incoming) mails. Such mail routings should be done with CLI-only message filters, rather than content filters. Here we go:

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Palo Alto Networks Cluster “not synchronized”

Palo Alto Networks, , , ,

For whatever reason, I had a Palo Alto Networks cluster that was not able to sync. A manual sync was not working, nor did a reboot of both devices (sequentially) help. Finally, the PAN support told me to “Export device state” on the active unit, import it on the passive one, do some changes, and commit. Indeed, this fixed it. A little more details:

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Capturing – because I can: IS-IS, GLBP, VRRP

Cisco Systems, Internet Access, Network, Routing, , , , , , , , ,

I am constantly trying to add more protocols to the Ultimate PCAP. Hence I used some time in my (old) Cisco lab to configure and capture the following protocols: IS-IS, GLBP, and VRRP. And since Alexis La Goutte sent me some CAPWAP traffic, this protocol is also added. All packets are now found in another update of the Ultimate PCAP. Here are some details:

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Route-Based VPN Tunnel FortiGate <-> Cisco ASA

Cisco ASA, Fortinet, IPsec/VPN, , , , , ,

More than 6 years ago (!) I published a tutorial on how to set up an IPsec VPN tunnel between a FortiGate firewall and a Cisco ASA. As time flies by, ASA is now able to terminate route-based VPN tunnels (which is great!), we have IKEv2 running everywhere and enhanced security proposals. Hence, it’s time for an update:

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Route-Based VPN Tunnel Palo Alto <-> Cisco ASA

Cisco ASA, IPsec/VPN, Palo Alto Networks, , , , ,

More than 6 years ago (!) I published a tutorial on how to set up an IPsec VPN tunnel between a Palo Alto Networks firewall and a Cisco ASA. As time flies by, ASA is now able to terminate route-based VPN tunnels (which is great!), we have IKEv2 running everywhere and enhanced security proposals. Hence, it’s time for an update:

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FortiGate bug: firewalls sending excessive requests to the NTP Pool

Fortinet, NTP, , , , , ,

The NTP Pool is a volunteer organization that provides time synchronization service to hundreds of millions of computers worldwide. A typical client might query a particular NTP Pool server ~10-60 times/hour. Wikipedia lists some abusive clients that far exceeded the normal rate. This wastes NTP server resources, may interfere with other clients, and can trigger DDoS protections. In late 2019, a software update made some FortiGate firewalls very unfriendly to the NTP Pool.

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iperf3 on a FortiGate

Bandwidth/Delay, Fortinet, Internet Access, Monitoring, , , ,

This is a really nice feature: you can run iperf3 directly on a FortiGate to speed-test your network connections. It’s basically an iperf3 client. Using some public iperf servers you can test your Internet bandwidth; using some internal servers you can test your own routed/switched networks, VPNs, etc. However, the maximum throughput for the test is CPU dependent. So please be careful when interpreting the results. Here we go:

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A Little Printing Please – Packet Capture

iPhone/iPad, Network, , , , , ,

Uh, I wasn’t aware of so many different printing protocols. Do you? While I was trying to solve a little printing problem I took a packet capture of three different printing variants over TCP/IP: Raw via TCP port 9100, LPD/LPR via TCP port 515, and Apple’s AirPrint which uses the Internet Printing Protocol IPP. As always, you can download this pcap and have a look at it by yourself.

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