Networking and IT Notes

IT Industry Observations

Comments on the IT industry which perpetuate an ongoing cycle of expenditure:

• Trust no one
• Maintain the paranoia
• It will eventually fail

Cost vs Support

Inequities of equipment Cost vs Support + Maintenance:

Cost vs Availability

SNA Traffic

SNA: 1200 bytes mainframe to screen, 300 bytes back to mainframe.

1200 bytes = 1 second @ 9600 bits/sec.

Formulae & Methodology

Calculate average frame size and then calculate PPS on an Ethernet and across a router:

• Percentage broadcasts/multicasts vs unicasts
• On-net and off-net ratio will give the 80/20 rule for router utilisation

The Economics Triangle

From a Networkers Presenter:

Any to Any Formula

The number of connections in an any-to-any topology:

Communities of Interest

Communities of Interest = VLANs

Broadcast Statistics

AppleTalk

• 1 cable range for every 50 MAC addresses
• Meaningful names
• Regions
• "Twilight Zone" — catch-all for unconfigured devices

IPX Notes

• FEEDFACE
• COFFEE
• Number of SAPs per packet = 7 (480 bytes)
• Number of RIPs per packet = 50 (432 bytes)
• Tick counts for IPXWAN on 2-12 CID
• novell-ether = 802.3
• FFFF = 802.3 RAW
• ETHERNET_802.2

Other Topics

• Internetwork Design Guidelines — Methodology
• Standardising Naming and Addressing structures
• Phased implementation vs cutover
• Change Management
• Problem Solving
• Risk Management
• Economies of Scale
• Bit-flipping for Token Ring to Ethernet conversions
• Browsers not caching DNS names for the same URLs — browser will perform multiple DNS lookups for subsequent URLs