Tag Archives: Wireshark

Internet’s Noise

If you are following the daily IT news you have probably seen many articles claiming they have scanned the whole Internet for this or that. Indeed there are tools such as the ZMap Project “that enable researchers to perform large-scale studies of the hosts and services that compose the public Internet”.

This time I was not interested in scanning something, but in the question about “how many scans happen during one day on my home ISP connection?” Or in other words: What is the Internet background noise as seen by almost any customer? For this I sacrificed my Internet connection at home for 24 hours, while a factory-resetted router established a fresh Internet connection (IPv6 & IPv4) without any end devices behind it. No outgoing connections that could confuse or trigger any scans. That is: All incoming connections are really unsolicited and part of some third-party port scans, worm activities, or whatever. Using a network TAP device I captured these 24 hours and analyzed them with Wireshark.

In this blogpost I will present some stats about these incoming port scans. Furthermore I am publishing the pcap file so you can have a look at it by yourself.

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SSHFP: FQDN vs. Domain Search/DNS-Suffix

This is actually a bad user experience problem: To generally omit the manual verification of SSH key fingerprints I am using SSHFP. With fully qualified domain names (FQDN) as the hostname for SSH connections such as ssh nb10.weberlab.de this works perfectly. However, admins are lazy and only use the hostname without the domain suffix to connect to their servers since the domain search does the rest: ssh nb10. Not so for SSHFP which fails since the default OpenSSH client does not use canonicalization for its DNS queries. Hence you must explicitly enable canonicalization for OpenSSH.

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I am intensely using the SSH Public Key Fingerprint (SSHFP, RFC 4255) in all of my environments. Since my zones are secured via DNSSEC I got rid of any “authenticity of host ‘xyz’ can’t be established” problems. As long as I am using my central jump host with OpenSSH and the “VerifyHostKeyDNS yes” option I can securely login into any of my servers without any warnings. Great!

However, I encountered a couple of daily problems when using SSHFP. One of them was the question whether SSHFP works behind CNAMEs, that is, when connecting to an  alias. Short answer: yes. Some more details here:

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Apple AirPlay Capture

I was interested in how Apple AirPlay works in my network. I am using an iPad to stream music to a Yamaha R-N500 network receiver. There is a great Unofficial AirPlay Protocol Specification which already shows many details about the used protocols. But since I am a networking guy I captured the whole process in order to analyze it with Wireshark.

Following is a downloadable pcap if you want to have a look at it by yourself as well as some Wireshark and NetworkMiner screenshots for a first glance.

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Nmap Packet Capture

I am using Nmap every time I installed a new server/appliance/whatever in order to check some unknown open ports from the outside. In most situations I am only doing a very basic run of Nmap without additional options or NSE scripts.

Likewise I am interested in how the Nmap connections appear on the wire. Hence I captured a complete Nmap run (TCP and UDP) and had a look at it with Wireshark. If you’re interested too, feel free to download the following pcap and have a look at it by yourself. At least I took some Wireshark screenshots to give a first glance about the scan.

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IKE Solutions

Almost 4 weeks ago I published a pcap file with some challenges – this time four falsified configured IPsec VPN connections. If you have not solved it by now you should first download the pcap file and should give it a try.

Remember the scenario: You need to prove that the wrong VPN settings are not on your side (the four routers) but on the headquarters firewall side. Not an easy job. Now here are the solutions:

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IKEv1 & IKEv2 Capture

It is probably one of the most used protocols in my daily business but I have never captured it in detail: IKE and IPsec/ESP. And since IKEv2 is coming I gave it a try and tcpdumped two VPN session initiations with IKEv1 main mode as well as with IKEv2 to see some basic differences.

Of course I know that all VPN protocols are encrypted – hence you won’t see that much data. But at least you can see the basic message flow such as “only 4 messages with IKEv2” while some more for legacy IKEv1. I won’t go into the protocol details at all. I am merely publishing two pcap files so that anyone can have a look at a VPN session initiation. A few Wireshark screenshots complete the blogpost.

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Wireshark Layer 2-3 pcap Challenge Answers

A few weeks ago I published a pcap file along with many challenges in order to invite anyone to download and to solve it. Though there are not that many answers posted in the comment section I hope that the trace file will help many people understanding the layer 2/3 protocols or to work with it during CCNP exam preparation.

Following are my answers to the 46 challenges I posted back then. I’ll not only give you the mere results but many Wireshark screenshots with some notes on how to get them. Here we go:

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Wireshark Layer 2-3 pcap Analysis w/ Challenges (CCNP SWITCH)

While preparing for my CCNP SWITCH exam I built a laboratory with 4 switches, 3 routers and 2 workstations in order to test almost all layer 2/3 protocols that are related to network management traffic. And because “PCAP or it didn’t happen” I captured 22 of these protocols to further investigate them with Wireshark. Oh oh, I remember the good old times where I merely used unmanaged layer 2 switches. ;)

In this blogpost I am publishing the captured pcap file with all of these 22 protocols. I am further listing 46 CHALLENGES as an exercise for the reader. Feel free to download the pcap and to test your protocol skills with Wireshark! Use the comment section below for posting your answers.

Of course I am running my lab fully dual-stacked, i.e., with IPv6 and legacy IP. On some switches the SDM template must be changed to be IPv6 capable such as sdm prefer dual-ipv4-and-ipv6 default .

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Detect DNS Spoofing: dnstraceroute

Another great tool from Babak Farrokhi is dnstraceroute. It is part of the DNSDiag toolkit from which I already showed the dnsping feature. With dnstraceroute you can verify whether a DNS request is indeed answered by the correct DNS server destination or whether a man-in-the-middle has spoofed/hijacked the DNS reply. It works by using the traceroute trick by incrementing the TTL value within the IP header from 1 to 30.

Beside detecting malicious DNS spoofing attacks, it can also be used to verify security features such as DNS sinkholing. I am showing the usage as well as a test case for verifying a sinkhole feature.

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DNSSEC Validation with Unbound on a Raspberry

To overcome the chicken-or-egg problem for DNSSEC (“I don’t need a DNSSEC validating resolver if there are no signed zones”), let’s install the DNS server Unbound on a Raspberry Pi for home usage. Up then, domain names are DNSSEC validated. I am listing the commands to install Unbound on a Raspberry Pi as well as some further commands to test and troubleshoot it. Finally I am showing a few Wireshark screenshots from a sample iterative DNS capture. Here we go:

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Basic BIND Installation

This is a basic tutorial on how to install BIND, the Berkeley Internet Name Domain server, on a Ubuntu server in order to run it as an authoritative DNS server. It differs from other tutorials because I am using three servers (one as a hidden primary and two slaves as the public accessible ones), as well as some security such as denying recursive lookups and public zone transfers, as well as using TSIG for authenticating internal zone transfers. That is, this post is not an absolute beginner’s guide.

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