Category: Workshop

Data Center Ethernet (or DCB or CEE, depending on who you are) is a hot story these days and it’s no wonder that misconceptions galore. However, when I hear several CCIEs I highly respect talk about “Priority Flow Control can be used to stop all the other traffic when storage needs more bandwidth”, I get worried. Exactly the opposite is true: you use PFC to stop the overzealous storage traffic (primarily FCoE, but also iSCSI) to make sure you don’t drop it.

During my last Building IPv6 Service Provider Core webinar I got a lot of questions about IPv6 over PPPoE (obviously we’re close to widespread IPv6 implementation; I never got PPPoE questions before). I wanted to test various scenarios in my IPv6 lab and thus enabled PPPoE on an Ethernet link between CE and PE routers.

This time I wanted to test multiple configurations in parallel ... no problem thanks versatile PPPoE implementation in Cisco.

Enhanced Transmission Selection (ETS) is the second part of the Data Center Bridging puzzle (I’ve already described Priority Flow Control). It specifies two different technologies:

• Queuing mechanisms in bridges
• Data Center Bridging eXchange protocol: a Control/Negotiation protocol that allows bridges and hosts to negotiate QoS parameters in a bridged network.

Although some bridges from some vendors supported numerous QoS mechanisms in the past, 802.1Qaz is the first attempt to standardize a richer set of QoS behaviors than the strict priority queuing defined in 802.1p.

A few weeks ago I wrote about the multihop FCoE basics and the two fundamentally different ways an FCoE network could be designed: FCoE on every switch or FCoE on the edges with DCB-extended bridging in the middle.

There are two other configurations you’ll likely see in access parts of an FCoE network: FCoE VN_port proxying and FIP snooping.

Few days ago I wrote about the impact of vMotion on a Data Center network and the traffic flow issues. Now let’s walk through what happens when you move a running virtual machine (VM) between two data centers (long-distance vMotion). Imagine we’re moving a web server that is:

• Serving a few Internet clients (with firewall/NAT and/or load balancing somewhere in the path);
• Getting most of its data from a database server sitting nearby;
• Reading and writing to a local disk.

The traffic flows are shown in the following diagram:

The attendees of my Building IPv6 Service Provider Core webinar get several sets of complete router configurations for a six router lab that emulates a typical Service Provider network with a residential customer and an enterprise BGP customer. The configurations can be used on any hardware (real or otherwise) supporting recent Cisco IOS software, allowing you to test and modify the design scenarios discussed in the webinar.

A while ago I had a chat with a fellow CCIE (working in a large enterprise network with reasonably-sized Data Center) and briefly described vMotion to him. His response: “Interesting, I didn’t know that.” ... and “Ouch” a few seconds later as he realized what vMotion means from bandwidth consumption and routing perspectives. Before going into the painful details, let’s cover the basics.

Yesterday I wrote that you don’t need DCB technologies to implement FCoE in your network. The FC-BB-5 standard is quite explicit (it also says that 802.1Qbb is the other option):

Lossless Ethernet may be implemented through the use of some Ethernet extensions. A possible Ethernet extension to implement Lossless Ethernet is the PAUSE mechanism defined in IEEE 802.3-2008.

The PAUSE mechanism (802.3x) gives you lossless behavior, but results in undesired side effects when you run LAN and SAN traffic across a converged Ethernet infrastructure.

The emerging Ethernet bridging technologies have been hyped to an extent where the lines between them completely blurred, resulting in statements like “we need DCB and TRILL for FCoE”. Actually, none of that is true, but let’s focus on DCB and TRILL first.

The FCoE confusion spread by networking vendors has reached new heights with contradictory claims that you need TRILL to run multihop FCoE (or maybe you don’t) and that you don’t need congestion control specified in 802.1Qau standard (or maybe you do). Allow me to add to your confusion: they are all correct ... depending on how you implement FCoE.