Saturday, August 28, 2010

BSCI - OSPF - Network types

From my experience with the Cisco ISCW exam if you try to hide from a subject, hoping your outstanding knowledge in other topics with carry you through, the you're more or less guaranteed that this will come back and bite you in the ass. You can tell what happened to me.

Soooo, OSPF Network types. This is not Area types where we are looking at making the OSPF process more efficient. This is the nature of the network that OSPF is running on.

There are generally 3 broad types of network that OSPF can be used within:
1) Broadcast Access - this is a multi-access network. Ethernet.
2) Point-To-Point - Such as lease lines, T1/T3 connections, ISDN.
3) Non-Broadcast Multi-Access (NBMA) - Any WAN config represented by a Cloud, Frame-Relay, ATM etc

In your lab work you'll generally configure either option 1, fastethernet links in to a switch and all your routers connected to the switch resulting in DR/BDR elections. Alternatively you'll have configured option 2, directly connecting your routers using serial cables resulting in there being only one device at either end, thereby eliminating the need for DR/BDR operations.

It is here that we arrive at our third option and the one I struggle with. Just keep telling yourself 'if it was easy it wouldn't be worth achieving'

There are 5 modes of NMBA network:
1) NBMA - RFC 2328 standard
2) Point-To-Multipoint - RFC 2328 standard
3) Point-To-Point - Cisco propriortary
4) Broadcast - CIsco propriortary
5) Point-To-Multipoint Non-Broadcast - Cisco propriortary

The next articles cover these network modes.

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