Headers

Frame-Relay LMI

What is LMI?
LMI stands for Local Management Interface.
LMI messages are exchanged between routers(DTE) and frame-relay(DCE) switches.  At its very basic we can say the LMI messages act as keepalives between the router and frame-relay switch.  LMI messages also contain information which allows routers to detect new PVCs dynamically.  Cisco IOS currently supports 3 types of [...]

ISIS header

Below is a diagram of the ISIS header.  The different ISIS packets ie hellos and SNPs have slightly different headers, however the first 8 bytes are identical.

Click here to see a power point show on the isis header.

MPLS Header

This is what an MPLS label looks like.  The MPLS label contains a 20-bit label, dont get confused between the different uses of the word label.

The 3 bit EXP bits are used for QoS purposes.  You can use them to define different tunnel modes, which I’ll talk about on another day.
The S bit identifies the [...]

IP Packet Header

Below is a diagram of the IPv4 header.  The header is 20bytes long in most cases, however this can be extendend using the options field.

Click here to see a power point version of the header.