Anyone serious about high-availability connects servers to the network with more than one uplink, more so when using converged network adapters (CNA) with FCoE. Losing all server connectivity after a single link failure simply doesn’t make sense.

If at all possible, you should use dynamic link aggregation with LACP to bundle the parallel server-to-switch links into a single aggregated link (also called bonded interface in Linux). In theory, it should be simple to combine FCoE with LAG – after all, FCoE runs on top of lossless Ethernet MAC service. In practice, there’s a huge difference between theory and practice.

Every time I write about IPv6 multihoming issues and the need for NPT66, I get a comment or two saying:

But I thought this is already part of IPv6 stack – can’t you have two or more IPv6 addresses on the same interface?

The commentators are right, you can have multiple IPv6 addresses on the same interface; the problem is: which one do you choose for outgoing sessions.

The source address selection rules are specified in RFC 3484 (Greg translated that RFC into an easy-to-consume format a while ago), but they are not very helpful as they cannot be influenced by the CPE router. Let’s look at the details.

Isn’t it amazing that we can build the Internet, run the same web-based application on thousands of servers, give millions of people access to cloud services … and stumble badly every time we’re designing virtual networks. No surprise, by trying to keep vSwitches simple (and their R&D and support costs low), the virtualization vendors violate one of the basic scalability principles: complexity belongs to the network edge.

DHCPv6 server on Cisco IOS got several highly useful enhancements since the first time I started looking into its behavior. Seems like most of them are implemented only in 15.xS trains (where they are most badly needed one would assume), but there’s hope those changes will eventually trickle down into mainstream IOS.

My friend Tom Hollingsworth has written another NAT66-is-evil blog post. While I agree with him in principle, and most everyone agrees NAT as we know it from IPv4 world is plain stupid in IPv6 world (NAPT more so than NAT), we just might need NPT66 (Network Prefix Translation; RFC 6296) to support small-site multihoming ... and yet again, it seems that many leading IPv6 experts grudgingly agree with me.

In the VMware vSwitch – the baseline of simplicity post I described simple layer-2 switches offered by most hypervisor vendors and the scalability challenges you face when trying to build large-scale solutions with them. You can solve at least one of the scalability issues: VM-aware networking solutions available from most data center networking vendors dynamically adjust the list of VLANs on server-to-switch links.

Let’s start with people who are trying to fix real-life problems. Browser and OS vendors are working around the lack of session layer – happy eyeballs approach solves dual-stack problem in either OS stack (Apple) or in the browsers (Chrome, Firefox). The results are ... interesting ;) ... but it seems most implementations are on the right track.

When I started making my first wobbling steps into the Junos MPLS world, Dan (@Johansfo) Backman took time to explain the differences between Cisco IOS and Junos MPLS implementations (and some of the reasons they are so different). This is my feeble attempt at describing what I understood he told me.

If you’re looking for a simple virtual switch, look no further than VMware’s venerable vSwitch. It runs very few control protocols (just CDP or LLDP, no STP or LACP), has no dynamic MAC learning, and only a few knobs and moving parts – ideal for simple deployments. Of course you have to pay for all that ease-of-use: designing a scalable vSwitch-based solution is tough (but then it all depends on what kind of environment you’re building).

For whatever reason I decided to start my Junos experience with a very simple IS-IS network – four core routers from my Building IPv6 Service Provider Core webinar. As Junosphere doesn’t support serial or POS interfaces, I migrated all links to Gigabit Ethernet and added a point-to-point GE link between PE-A and PE-B.