Category: MPLS

The following design challenge landed in my Inbox not too long ago:

My organization is the in the process of building a completely new data center from the ground up (new hardware, software, protocols ...). We will currently start with one site but may move to two for DR purposes. What DC technologies should we be looking at implementing to build a stable infrastructure that will scale and support technologies you feel will play a big role in the future?

In an ideal world, my answer would begin with “Start with the applications.”

I got an interesting question after writing the Asymmetric MPLS MTU Problem post:

Why does PHP happen only on directly-connected interfaces but not on other non-MPLS routes?

Obviously it’s time for a deep dive into Penultimate Hop Popping (PHP) mysteries (warning label: read the MPLS books if you plan to get seriously involved with MPLS).

Russell Heilling made a highly interesting observation in a comment to my MPLS MTU challenges post: you could get asymmetric MTUs in MPLS networks due to penultimate hop popping.

Imagine our network has the following topology (drawn with the fantastic tools used by the RFC authors):

S---CE---R1===R2---FW---C

@MCL_Nicolas sent me the following tweet:

Finished @packetpushers Podcast show 7 with @ioshints ... I Want to learn more about Mpls+Mtu problem

You probably know I have to mention that a great MPLS/VPN book and a fantastic webinar describe numerous MPLS/VPN-related challenges and solutions (including MTU issues), but if MTU-related problems are the only thing standing between you and an awesome MPLS/VPN network, here are the details.

Network World has published another masterpiece last week: FAQ: What is OpenFlow and why is it needed? Following the physics-changing promises made during the Open Network Foundation launch, one would hope to get some straight facts; obviously things don’t work that way. Let’s walk through some of the points. While most of them might not be too incorrect from an oversimplified perspective, they do over-hype a potentially useful technology way out of proportions.

NW: “OpenFlow is a programmable network protocol designed to manage and direct traffic among routers and switches from various vendors.” This one is just a tad misleading. OpenFlow is actually a protocol that allows a controller to download forwarding tables into one or more switches. Whether that manages or directs traffic depends on what controller is programmed to do.

DJ Spry asked an interesting question in a comment to my MPLS/VPN in DCI designs post: “Why would one choose OTV over MPLS/VPN?” The answer is simple: it depends on what you need. MPLS/VPN provides path isolation between layer-3 domains (routed networks) across MPLS or IP infrastructure whereas OTV providers layer-2 transport (and VLAN-based path isolation) across IP infrastructure. However, it does make sense to compare OTV with VPLS (which was DJ Spry’s next question). Apart from the obvious platform dependence (OTV runs on Nexus 7000, VPLS runs on Catalyst 6500/Cisco 7600 and a few other routers) which might disappear once ASR1K gets the rumored OTV support, there’s a huge gap in functionality and complexity between the two layer-2 transport technologies.

A while ago someone asked me whether I think FC-over-MPLS would be a good PhD thesis. My response: while it’s always a good move to combine two totally unrelated fields in your PhD thesis (that almost guarantees you will be able to generate several unique and thus publishable articles), FCoMPLS might be tough because you’d have to make MPLS lossless. However, where there’s a will, there’s a way ... straight from the haze of the “Just because you can doesn’t mean you should” cloud comes FC-BB_PW defined in FC-BB-5 and several IETF drafts.

My first brief encounter with FCoMPLS was a twitxchange with Miroslaw Burnejko who responded to my “must be another lame joke” tweet with a link to a NANOG presentation briefly mentioning it and an RFC draft describing the FCoMPLS flow control details. If you know me, you have probably realized by now that I simply had to dig deeper.

Just before 2010 disappeared, a tweet by my friend Greg @etherealmind Ferro triggered a minor twitstorm. He wrote:

If we had implemented IPv6 ten years ago, would we have MPLS today? I think not.

His tweet contains two major misconceptions:

• MPLS was designed to implement layer-3 VPN services;
• We wouldn’t need VPNs if everyone would be using global IPv6 addresses.

I’ll focus on the first one today; the inaccuracy of the second one is obvious to anyone who was asked to implement MPLS VPNs in enterprise networks to ensure end-to-end path separation between departments or users with different security levels.

At the time when I was writing my MPLS books and developing MPLS courses for Cisco, everyone was ecstatically promoting GMPLS (Generalized MPLS) as the next unifying technology of everything, making someone so fed up with the fad that he wrote the Electricity over IP RFC.

GMPLS got implemented in high-end routers, but never really took off (at least I’ve never seen or even heard about it). Obviously the transport teams found the idea of routers requesting on-demand lambdas with IP-based protocols too hard to swallow.

I got this question from the SearchTelecom Ask-the-Expert project ... and the engineer asking the question was probably looking for something short and concise. This is my attempt to explain the difference in a few paragraphs. Have I missed anything important? Could it be done better?

Bidirectional Forwarding Detection (BFD) protocol has finally been published as a series of RFCs. BFD gives you quick failure detection between L3 hops (routers) regardless of the underlying technology and equipment (modems, media converters, bridges). It’s been gradually introduced in Cisco IOS during the last few years; release 15.0M and 12.2SRE contain almost everything you’ll ever need (missing: multihop BGP support and MPLS LSP support).

I wrote about BFD in Improve the Convergence of Mission-Critical Networks with Bidirectional Forwarding Detection (BFD) article (you’ll find it somewhere in this list). To learn more, read the RFCs in this order:

Unveiling of the Cisco IOS release 15.1(1)T was the extreme opposite of the CRS-3 and Catalyst 3750-X splashes; the next release of one of the foundations of Cisco’s core business deserved a modest two-paragraph mention in the What's New in Cisco Product Documentation page.

If you’re a voice guru, you’ll probably enjoy the list of 20+ voice-related new features, including the all-important Enhanced Music on Hold. For the rest of us, here’s what I found particularly interesting:

An MPLS Traffic Engineering (MPLS TE) tunnel is a unidirectional Label Switched Path (LSP) established between the tunnel head-end Label Switch Router (LSR) and tail-end LSR. Once the tunnel is established and operational, it’s ready to forward IPv4 data traffic. However, no traffic will enter the tunnel unless the IPv4 routing tables and CEF tables are modified. You can push the traffic into an MPLS TE tunnel with a static route or with policy-based routing (PBR) or modify the behavior of the link-state algorithm used to implement MPLS TE in your network.

The autoroute functionality configured with the tunnel mpls autoroute announce interface configuration command automatically inserts the MPLS TE tunnel in the SPF tree and ensures the tunnel is used to transport all the traffic from the head-end LSR to all destinations behind the tail-end LSR.

The “P-to-P router encryption” post has generated numerous comments. One of the readers suggested using dedicated Ethernet encryption devices, which is probably the best option if you’ve realized you need encryption in the network acquisition phase when there’s still some budget left (too bad the vendor recommended in the comments does not want to admit how expensive the boxes are).

However, assuming you have high-speed IPSec encryption modules and you have to implement P-to-P encryption in existing network, the only option left to you is GRE tunnel. Here’s why: