27 Nov 2011

Microsoft NLB weirdness

NLB (Network Load Balancing) is a clustering tech. used by Microsoft products. There are two NLB methods:
  • Unicast NLB
  • Multicast NLB
NLB is a software clustering tech. and should be avoided. You are better off using Hardware load balancers such as Citrix Netscaler.

NLB has a bad design and using it causes switch flooding. The reason to this is it's ARP/MAC address usage.

To avoid problems where NLB must be used, check configuration examples for Cisco Devices. Catalyst Switches for Microsoft Network Load Balancing Configuration Example


Cisco Mobile to be in Istanbul in April

This is a chance to take the CCIE exams without traveling abroad.
Istanbul, Turkey Apr 16 - 20 R Routing & Switching, Security


Ref: Cisco Doc

23 Nov 2011

TwinGig Convertor configuration

These Cisco convertors are pretty handy I must say. It's an X2 Convertor module that is able to take 2 SFP modules; Allowing you to convert an X2 slot to twin SFP slots. Anyway, when you insert a TwinGig to a switch without first doing the pre-configuration, you're most likely to get an error like this:

%C4K_GLMMAN-3-X2PLUGGABLESEEPROMREADFAILED: Failed to read seeprom on port Te2/8. Reinsert X2 module or configure GigabitEthernet port group if TwinGigConverter is installed.

It's because the X2 slot you used is configured as a TenGig slot. It should be set to Gigabit for the TwinGig to be detected. The way it's done on an 4900M is:

hw-module module 2 port-group 4 select gigabitethernet

The catch is that the 8 port TenGig module used on the 4900M is over-subscribed and you will have to set a "port-group" which represents 2 ports, as "gigabit" to get the TwinGig to work.

After setting our port-group, the log will show the TwinGig is detected:

Nov 23 10:32:06.501: Port Te2/8: TwinGig Converter inserted: vendor: CISCO SYSTEMS, p/n: 800-27645-02, s/n: FDO14290SE5


Here are some references for more info:
Installation Notes for the Cisco TwinGig and OneX Converter Modules
Selecting X2/TwinGig Convertor Mode
SFP Interfaces of X2/Twin Gigabit Converter Do Not Come Up

27 Jun 2011

Protocol overhead

Various protocols introduce overhead to packet networks.
Good explanations here:
Protocol Overhead
Overhead in Packet Networks

20 Mar 2011

Fiber Optic Cable specs

Multi Mode

850nm and 1300nm
OM1: 62.5/125 µm
OM2: 50/125 µm
OM3: 50/125 µm Laser optimized. 10GbE for 300m (quality cables support 550m length)
OM4: Cable will support 125m links at 40 and 100 Gbit/s.


Single Mod
20km, 1 Gbps