Kapitel 3 fra CCDP ARCH bogen.

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At designe avancerede IP adresserings løsninger

Design en ip adresseplan.

Role-Based addressing

Hvis vi bruger 172.16.cccc cccR.RRhh hhhh til at indele vores netværk, får vi:

7 bit til wireing closets giver 2⁷=128 forskellige krydsfelter eller lag 3 switche
3 bit til Roler giver 2³=8 forskellige roler.
6 bit til hosts hvilket giver 2⁶=64-2 hosts per subnet/VLAN

Samtidig er det vigtigt at netværkene bliver summerbare som i dette eksempel, hvor hvert krydsfelt kan summeres til /23.

Hvis vi kigger på ACL lister til disse netværker har vi 8 forskellige roller(3bit):

000
001
010
011
100
101
110
111

Hvis vi så skal lave en ACL der matcher Role 1 skal vi kun matche på de 3 bit der beskriver rolerne og ignorere alle andre. Det kunne fx se sådan her ud:

access-list 101 pemit ip any 172.16.0.0 0.0.254.63
172.16.xxxxxxx0.00xxxxxx

Hvis access listen bliver placeret på vlan interfacet INGRESS så ville de enkelte vlans ikke kunne snakke med de andre Roler, men kun deres egne i de andre krydsfelter.

NAT

Nat mellem private adresser anbefales ikke
Nat gør netværksfejlfinding mindre overskueligt.
Nat til eksterne partnere.

Content Load-Balancing Device

En enhed der fordeler belastningen mellem flere Servere. For eksempel en enhed der fordeler forespørgsler fra WEB-brugere mellem ti identiske WEB-servere. Det kan være baseret på forskellige faktorer

Antallet af forbindelser til hver server
CPU belastning på Serverne
En kombination af flere faktorer der beskriver servernes belastning

For eksempel Cisco CSS 11500 Series Content Services Switch

Designing avanceret Routning

Inappropriate Transit Traffic

Dont do the job of your ISP

Defensive filtering

Trust no one

Route redistribution

Prefix-list, Route-maps or Tagging of routes

Migrating Between Routing Protocols

Two companies have been merged. Company A are running EIGRP and Company B are running OSPF.
Step 1: Redistribute between A & B
Step 2: Enable OSPF in company A, and make sure it has the highest Administrativ Distance
Step 3: When OSPF is running and is fully converged, Remove EIGRP

Route Summarization og Default Routing

Designing Scalable OSPF Design

OSPF Scalability best practise

Any one Router should have no more than 60 adjacent neighbors
An area should have no more than 50 Routers
Any one Router should not be in more than three areas
Already heavily loaded Routers should not be DR and BDR

Designing Areas

Network topology and addressing should be designed initially with division of areas in mind.

General advice about OSPF design is:

Minimize the routing information advertised into and out of the area.
Experience shows that you should be conservative about adding routers to the backbone area.
Make it simple
Make nonbackbone areas stub or totally stubby areas
Make it summarized

OSPF Areas & Area Summarization

Yada yada OMG OSPF

If hello timers are set to 1/3 second for 300 interfaces, each with 10 neighbors, the router would have to generate 900 hellos per second.
When the 3000 neighbors send 3 hellos per second back to the router, it has to process a total of 9900 hellos per second.

Det er jo ikke realistisk, Cisco tag dig sammen

Incremental SPF

iSPF calculate only the part of the path tree that has changed.
The iSPF feature has been available since Cisco IOS Software Release 12.0(24)S, 12.3(2)T, 12.2(18)S, and 12.2(27)SBC. It is enabled with the iSPF router command under an OSPF process.

SPF & iSPF comparison

Bidirectional forward detection

BFD hjælper med at gøre route failover hurtigere ved at bruge en hurtigere lag 2 hello protokol end almindelige keep-alives. BFD skal også være understøttet af routing protokollen og har support i ospf, eigrp, isis og bgp. BFD kan tune rspons tiden ned til 50ms, hvad man er vant til fra SONET, men bruger ca 2 procent mere CPU.

Designing Scalable BGP Designs

Vis BGP slide...

Scaling iBGP with Route Reflectors

Image text

Scaling BGP with Confederations