Category: Design Principles

IS-IS History

https://en.wikipedia.org/wiki/IS-IS
https://en.wikipedia.org/wiki/OSI_protocols
https://en.wikipedia.org/wiki/Type-length-value

• Created for the OSI Protocol Suite
• Integrated IS-IS: the mutation.
• IS-IS dictionary:
  • IS = Intermediate System  (Routers)
  • ES = End System
  • TLV = Type Length Value
  • NSAP = Network Service Access Point
    • (OSI protocols equivilent of the TCP/IP’s IP Address)
• IS-IS features:
  • Link State Routing Protocol  (Same as OSPF)
  • NSAP address assigned per router
  • Dijkstra SPF powered (Same as OSPF)
    • PRC efficient
  • Hellos Establisch neighbors at Layer 2 ( source MAC, Multicast Mac )
  • Two routing levels ( Level 1 and Level 2 )
  • Area Based Design ( Routers know their area )
  • default link cost = 10

IS-IS High level Design

• Two routing databases
  • Level1 and Level2
    • Level 1 routers find closest Level2 Exit.
  • Area defined by
  • 49.0001  ( Area 1 )
    • 49 private adressing , 0001 is area 1
• Three router types

IS-IS Neighbors and Area Design

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• Wireless Signal Mesured in dBm ( Power referenced against one Milliwatt )
• Range is roughly -30dBm to -90dBm
  • -30dBm = Max Achievable ( not desired ).
  • -67dBm = Mininum for real-time Apps.
  • -80dBm = Minimum for communication.
• Noise is always a challenge
• Signal to Noise Ratio ( SNR ) = ( Signal – Noise ) = Value
  • Mininum SNR of 25 is needed for real-time apps.

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Unicast vs Multicast

• Routed via PIM ( Protocol Independent Multicast ).
• Always UDP-Based ( Video, Audiostreams, some kinds of data ).
• Typical network challenges ( QoS, Security, Bandwidth consumption).
• Began as a ‘speciality’ technology, becoming heavily adopted in modern times.

Multicast Addresses

• Multicast group members receive all data center to a group.
• Multicast IPv4 Range: [ 224.0.0.0  239.255.255.255 ]
  • Filtering tip:
    • Last 23 bits of IP mapped to MAC
      • Can lead to overlapping addresses

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Remote Access VPN design

• For a VPN you need a termination device (vpn concentrator / Firewall), a client and the connecting technology for tunneling.
• Cisco Easy VPN.
• Client options
  • IPSEC VPN client
  • SSLVPN Clientless Access
  • SSLVPN Thin client
  • SSLVPN Thick client

Placement of the VPN Termination Device:

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Core layer

• Cisco 6509.
• Static routing used to ISP ( or basic BGP ).
• FWSM or ACE module used as initial filter.
• Static route down to VIP of aggregation layer FHRP.

Aggregation Layer

• Cisco 6506 ( MSFC ).
• Traffic received from core routed to CSM
  
• CSM load balances to VLANs at the access layer
• Simple Design allows inter-vlan routering ( web, app, db )
  • Inter-vlan routing without a FWSM can lead to access from the VLANs.

Access Layer

• Cisco 6509
• Servers typically devided into web, app, and database VLANS.
• Server gateways set to CSM, FWSM, or VIP of the FHRP on L3.
• Firewall restrictions between layers common.

A design that must stay up

• Public face of an organization
• The place where downtime is incredibily harmful
• The place where budgets are approved\

Ultra Redundant, Ultra secure Firewall Design

• Only Method through layers is via servers
• Option of using different firewall vendors at different layers
• Supports virtual firewall using FWSM (Firewall Services Module) or ACE (Application controle engine) module

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SONET / SDH

Sonet ( Synchronous Optical Networking)

• American National Standards Institute (ANSI)
• Used in US / Canada
• Synchronous transport signals (STS) used for speed

Synchronous Digital Hierarchy

• International Telecommunications union (ITU)
• Used everywhere expect US / Canada
• Synchronoous transport Modules (STM) used for speed)

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EIGRP design principles

• EIGRP works for arbitrary topologies for small to medium networks.
• A flat EIGRP network doesn’t really scale beyond 400 routers and will lead to performance issuse
  • How to solve this?
    • Stub areas, summerization, route filtering limits the query scope
• If EIGRP doesn’t have a feasible successor it will query all it’s neighbours.
  • “I don’t have a route anymore, don’t route through me, give me a viable route”.
• BFD to optimize convergence (100ms wtih 1000 routes).
• 2 second hello timer, 6 second hold timer ( recommended )

Multiple EIGRP design principles

• Used to merge two networks ( Acquisitions )
• Different administrative groups in a company
• a way to devide large networks ( and control queries )
• Routes are distributed between AS ( don’t loop! )

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