Tag Archives: VPN

IPv6 Renumbering: A Pain in the …

If you’re following my blog you probably know that I am using IPv6 everywhere. Everything in my lab is dual-stacked if not already IPv6-only. Great so far.

A few months ago my lab moved to another ISP which required to change all IP addresses (since I don’t have PI space yet). Shit. While it was almost no problem to change the legacy IPv4 addresses (only a few NATs), it was a huge pain in the … to change the complete infrastructure with its global unicast IPv6 addresses. It turned out that changing the interface IPv6 addresses was just the first step, while many modifications at different services were the actual problem. And this was *only* my lab and not a complete company or the like.

Following is a list of changes I did for IPv6 and for legacy IP. Just an overview to get an idea of differences and stumbling blocks.

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Route- vs. Policy-Based VPN Tunnels

There are two methods of site-to-site VPN tunnels: route-based and policy-based. While some of you may already be familiar with this, some may have never heard of it. Some firewalls only implement one of these types, so you probably don’t have a chance to configure the other one anyway. Too bad since route-based VPNs have many advantages over policy-based ones which I will highlight here.

I had many situations in which network admins did not know the differences between those two methods and simply configured “some kind of” VPN tunnel regardless of any methodology. In this blogpost I am explaining the structural differences between them along with screenshots of common firewalls. I am explaining all advantages of route-based VPNs and listing a table comparing some firewalls regarding their VPN features.

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Network Transfer: 1 Big vs. 100 Small Files

A common mistake when analyzing network speed/bandwidth between different applications and servers is to fully rely on the mere size of the files being transferred. In fact, one big file will transfer much faster than thousands of small files that have the same accumulated size. This depends on the overhead of reading/writing these files, building TCP/IP sessions, scanning them for viruses, etc. Furthermore, it is application dependent.

I built a small lab with an FTP server, switch, firewall, and an FTP client in which I played a bit with different file sizes. In this blog post I am showing the measured transfer times and some Wireshark graphs.

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Considerations about IPsec Pre-Shared Keys

Pre-shared keys (PSK) are the most common authentication method for site-to-site IPsec VPN tunnels. So what’s to say about the security of PSKs? What is its role for the network security? How complex should PSKs be? Should they be stored additionally? What happens if an attacker catches my PSKs?

I am listing my best practice steps for generating PSKs.

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Grep Commands for Cisco ASA Syslog Messages

In a basic environment with a Cisco ASA firewall I am logging everything to a syslog-ng server. As there aren’t any reporting tools installed, I am using grep to filter the huge amount of syslog messages in order to get the information I want to know. In this blog post I list a few greps for getting the interesting data.

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