Studies in Data Center Networking, Virtualization, Computing
Dec 02 2007
One of my accounts had an unfortunate network outage that lasted about an hour. This outage was caused by human error with VTP but not in the classic revision number way we have heard about before.
Here is what happened…
Nov 27 2007
It always helps me to think of the English translation when trying to memorize and understand some the Cisco IOS settings I think are important.
Here are some Cisco IOS switchport configurations translated into English:
‘switchport mode trunk‘ says: “Always trunk on this end, and I will send DTP to attempt to negotiate a trunk on the [...]
Nov 27 2007
IEEE 802.1Q (sometimes referred to as 1Q or DOT1Q) is a industry standards based implementation of carring traffic for multiple VLANs on a single trunking interface between two Ethernet switches. 802.1Q is for Ethernet networks only.
Unlike ISL , 802.1Q does not encapsulate the original Ethernet frame.
For Ethernet V2 frames, 802.1Q inserts a new 4-byte [...]
Nov 26 2007
Inter-Switch Link (ISL) is a Cisco specific implementation of trunking multiple VLANs between two Cisco switches where a single interface will carry traffic for more than one VLAN. ISL was designed to work with Ethernet, FDDI, Token Ring, and ATM.
ISL completely encapsulates the original Ethernet frame by adding a new 26 byte header and [...]
Nov 21 2007
Some notes about VTP (VLAN Trunking Protocol):
Cisco switches running Cisco IOS store VTP and VLAN information in a separate database stored in Flash, in file called vlan.dat.
Cisco switches running CatOS store VTP and VLAN information in the main switch configuration file, stored in NVRAM.
VTP information is only transmitted over trunk ports.
A VTP client does not [...]
Nov 21 2007
Just like there are 3 different Ethernet header types, there are also 3 different types of Ethernet addresses:
Unicast
Broadcast
Multicast
A unicast frame contains the unique MAC address of the destination receiver. A broadcast frame contains all binary 1’s as the destination address (FFFF.FFFF.FFFF). A multicast frame contains the unique multicast MAC address of an application, [...]
Nov 19 2007
There are 3 different Ethernet Header types defined by the IEEE and in use today. So, one question comes to mind: When a Ethernet receiver receives a frame, how does it know what kind of header it is? After all, if a receiver is unable to properly recognize the header type, it will [...]
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