Main components of a router
1) CPU
2) ROM (Permanent)
3) RAM (Erase upon reboot)
4) NVRAM (Erase by user)
5) Flash (Erase by user)
Type of interfaces
1) Management ports - console and auxiliary
2) LAN interfaces - serial (DB60, smart serial)
3) WAN interfaces - fastethernet, ethernet (RJ45)
Contents of a router
1) ROM - Bootstrap, diagnostic and mini IOS
2) RAM - routing table, arp cache, running config, packet buffer
3) NVRAM - startup config
4) Flash - compressed IOS
Boot up sequence
1) POST
2) Bootstrap
3) Locate and load IOS
- Flash
- TFTP
- Mini IOS
4) Locate and load startup config
- NVRAM
- TFTP
- Setup mode
5) Startup config in NVRAM is copied as running config in RAM
Main functions of a router
1) Best path determination
2) Packet switching - decapsulate (Remove old mac addresses), lookup routing table, encapsulate (Add new mac addresses)
3) IP addresses remains the same throughout.
