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

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Istanbul, Turkey Apr 16 - 20 R Routing & Switching, Security


Ref: Cisco Doc

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

Protocol overhead

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

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