Open Virtual Network (OVN) is a subproject of Open vSwitch (OVS), a performant, programmable, multi-platform virtual switch. OVN adds to the OVS existing capabilities the support for overlay networks by introducing virtual network abstractions such as virtual switches and routers. Moreover, OVN provides native methods for setting up Access Control Lists (ACLs) and network services such as DHCP. Many Red Hat products, such as Red Hat OpenStack Platform and Red Hat Virtualization, are now using OVN, and Red Hat OpenShift Container Platform will be using OVN soon.
In this article, I’ll cover how OVN ARP/ND_NS actions work, the main limitations in the current implementation, and how to overcome those. First, I’ll provide a brief overview of OVN’s architecture to facilitate the discussion:
Continue reading “IP packet buffering in OVN”
Networks are fun to work with, but often they are also a source of trouble. Network troubleshooting can be difficult, and reproducing the bad behavior that is happening in the field can be painful as well.
Luckily, there are some tools that come to the aid: network namespaces, virtual machines,
netfilter. Simple network setups can be reproduced with network namespaces and
veth devices, while more-complex setups require interconnecting virtual machines with a software bridge and using standard networking tools, like
tc, to simulate the bad behavior. If you have an issue with ICMP replies generated because an SSH server is down,
iptables -A INPUT -p tcp --dport 22 -j REJECT --reject-with icmp-host-unreachable in the correct namespace or VM can do the trick.
This article describes using eBPF (extended BPF), an extended version of the Berkeley Packet Filter, to troubleshoot complex network issues. eBPF is a fairly new technology and the project is still in an early stage, with documentation and the SDK not yet ready. But that should improve, especially with XDP (eXpress Data Path) being shipped in Red Hat Enterprise Linux 8 Beta, which you can download and run now.
Continue reading “Network debugging with eBPF (RHEL 8 Beta)”
In this article, I discuss external connectivity in Open Virtual Network (OVN), a subproject of Open vSwitch (OVS), using a distributed gateway router.
OVN provides external connectivity in two ways:
- A logical router with a distributed gateway port, which is referred to as a distributed gateway router in this article
- A logical gateway router
In this article, you will see how to create a distributed gateway router and an example of how it works.
Creating a distributed gateway router has some advantages over using a logical gateway router for the CMS (cloud management system):
- It is easier to create a distributed gateway router because the CMS doesn’t need to create a transit logical switch, which is needed for a logical gateway router.
- A distributed gateway router supports distributed north/south traffic, whereas the logical gateway router is centralized on a single gateway chassis.
- A distributed gateway router supports high availability.
Note: The CMS can be OpenStack, Red Hat OpenShift, Red Hat Virtualization, or any other system that manages a cloud.
Continue reading “How to create an Open Virtual Network distributed gateway router”