It’s not always this simple DNS thing such as “single query – single answer, both via UDP”. Sometimes you have some more options or bigger messages that look and behave differently on the network. For example: IP fragmentation for larger DNS answers that do not fit into a single UDP datagram (hopefully not after the DNS flag day 2020 anymore), or DNS via TCP, or some newer options within the EDNS space such as “EDNS Client Subnet” (ECS) or DNS cookies.
I won’t explain any details about those options, but I am publishing a pcap with that kind of packets along with some Wireshark screenshots. Feel free to dig into it.
Continue reading DNS Capture: UDP, TCP, IP-Fragmentation, EDNS, ECS, Cookie
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
When configuring a pool of NTP servers on a F5 BIG-IP load balancer you need to choose how to check if they are still up and running. There is no specific NTP monitor on a F5 BIG-IP that does an application layer health check (like there is for http or radius). The out-of-the-box options that can be used are only ICMP and UDP monitoring. Let’s first look at the pros and cons of using either (or both) of these monitors. Then let’s build a custom UDP monitor that does a better job at checking whether the NTP servers are still healthy.
Continue reading F5 BIG-IP Application Level NTP Health Checks
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 was interested in how a recursive DNS server resolves DNS queries in detail. That is, not only the mere AAAA or A record, but also DNSSEC keys and signatures, the authority and additional section when testing with
dig , and so on. For this I made two simple DNS queries to my recursive DNS server which resulted in more than 100 DNS packets at all. Wow.
In the following I am publishing a downloadable pcap so that you can analyse it by yourself. Furthermore I am showing some listings and screenshots to get an idea of the DNS resolution process.
Continue reading Single DNS Query – Hundreds of Packets
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
And again: Here comes a pcapng capture taken for the dynamic routing protocol EIGRP. If you want to dig into EIGRP messages, download the trace file and browse around it with Wireshark. Since I used both Internet Protocols (IPv6 and legacy IP), MD5 authentication, route redistribution, etc., you can find many different messages in it.
Continue reading EIGRP Capture
Here comes a small lab consisting of three Cisco routers in which I used OSPFv3 for IPv6 with IPsec authentication. I am listing the configuration commands and some show commands. Furthermore, I am publishing a pcapng file so that you can have a look at it with Wireshark by yourself.
Continue reading OSPFv3 with IPsec Authentication
For those who are interested in analyzing basic BGP messages: I have a trace file for you. ;) It consists of two session establishments as I cleared the complete BGP session on two involved routers for it. Refer to my previous blogpost for details about the lab, that is: MP-BGP with IPv6 and legacy IP, neighboring via both protocols as well, with and without password. The involved routers were 2x Cisco routers, one Palo Alto Networks firewall, and one Fortinet FortiGate firewall.
Continue reading MP-BGP Capture
Some time ago I published a pcap that can be used to study basic IPv6 protocol messages such as ICMPv6 for Router Advertisements, Neighbor Solicitations, etc.: “Basic IPv6 Messages: Wireshark Capture“. You can use it to learn the basic IPv6 address assignment and layer 2 address resolution. However, that pcap does not include any upper layer protocols.
This time I captured a few application layer protocols that I used over IPv6 rather than over legacy IP. Common user protocols such as DNS, HTTP/S, IMAP, SMTP, as well as some network administration protocols: SSH, SNMP, and Ping. It is not that interesting at all ;) though you can use it to have some examples for Wireshark to prove that those application protocols are almost the same when run above IPv6 compared to IPv4.
Continue reading IPv6 Upper Layer Protocol Samples
Last but not least I was interested which “home-calling” connections my Yamaha R-N500 Network Receiver initiates. In my previous post I already analyzed the open ports within the network, while I showed a complete Apple AirPlay capture here. This time I was only interested in outgoing TCP/UDP connections to the Internet as well as how the Yamaha App “NP Controller” communicates with the receiver.
It turned out that it was not easy for me to fully analyze such a packet trace even though only a couple of connections were made. It consists of many protocols that I am not familiar with such as UPnP, MDNS, SSDP, and RTP. Anyway, ere we go:
Continue reading Yamaha R-N500 Network Receiver Packet Capture
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.
Continue reading Internet’s Noise
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.
Continue reading SSHFP: FQDN vs. Domain Search/DNS-Suffix
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:
Continue reading SSHFP behind CNAME