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Extending Zeroconf Services: Cache Tuning

Introduction

With the introduction of Cisco mDNS Service Discovery Gateway in IOS, customers that have implemented the solution are observing client behavior they haven’t seen prior to extending services across subnet boundaries. One of the effects is the duplicate name issue seen when devices with enabled services are moved from one L3 subnet to another L3 subnet and these two subnets happen to be connected to the same router/switch running the Service Discovery Gateway (SDG).

Background

When devices (like a Mac OS X computer) offer a service such as Remote Login (SSH) or Screen Sharing (VNC), they will announce these services using mDNS/Bonjour/Zeroconf using their hostname as configured in ‘System Preferences -> Sharing -> Computer Name’ (see Fig. 1).
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Cisco Service Discovery Gateway – Enabling Zeroconf in Enterprise Networks

Cisco Service Discovery Gateway – Enabling Zeroconf in Enterprise Networks

I’ll admit it: I’m what others call an Apple fan boy. One of the many reasons for being one is the polished user experience and the ease-of-use of their products. One of the underlying technologies that enables the user to discover devices and services on the network is Zeroconf or, as Apple calls it, Bonjour.

Zeroconf consists of three major components:

  • Address auto configuration,
  • Naming –and–
  • Service discovery.

If your network doesn’t have a DHCP server or you haven’t statically assigned an IP address to your host, most operating systems will use an automatic private IP address. I’m not going into much detail on address auto configuration except that this is typically done using a technique called APIPA (Automatic Private IP Addressing) for IPv4 the host will use the famous 169.254.0.0/16 addresses or, in case of IPv6, by using link-local addresses only (FE80::/10) which has been designed into IPv6 as a basic functionality from day one. Also, naming is not of much of a concern in the context of this discussion. However, it is worth mentioning that Zeroconf names can contain Unicode characters and whitespace, which can make those names a lot more user friendly and meaningful contrary to pure DNS names.

The more interesting part, as it pertains to Zeroconf, is the service discovery. Read More »

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Route Redistribution – A thing of the past?

This week at CiscoLive Orlando, Cisco made two announcements around Enterprise Routing – Open EIGRP and EIGRP OTP. Originally announced at CiscoLive London, EIGRP has been opened to the community as an IETF Informational Draft “Open EIGRP”, Open EIGRP  provides vendors with technical information on EIGRP and the accumulation of 20 years of development and enhancements. With the publishing of this IETF Draft, vendors can now integrate EIGRP into their appliances and interop with Cisco.

On Tuesday, Cisco also announced a new innovation in Enterprise Routing; “EIGRP Over the Top” (or simply OTP).

EIGRP OTP

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Programmability and SDN are not the same

Network programmability means democracy, means freedom, freedom to program across all layers and entities, software or hardware – depending on your needs. Is SDN required to have network programmability? Not at all. Does the SDN architecture leverage network programmability? Yes, of course.  So, why do many people equate network programmability and SDN? Read More »

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What is a “Controller”? And how many do we need?

Thanks to SDN, the “Controller” word pops up in many network architecture discussions these days. In networking alone, we’re already surrounded by many “controllers” and we’re busy introducing more as we speak:  For example, Session Border Controllers or Wireless LAN Controllers have been around for quite some time, and have recently announced the OpenDaylight Controller, the Cisco XNC, or the Cloupia Unified Infrastructure Controller. So what is a “Controller” in networking terms, and how many do we need in emerging network architectures?

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