cicco router components

1. Cisco Router Components
• Bootstrap
– Brings up the router during initialization
• POST
– Checks basic functionality; hardware &
interfaces
• ROM monitor
– Manufacturing testing & troubleshooting
• Mini-IOS
– Loads Cisco IOS into flash memory
• RAM
– Holds packet buffers, routing tables, & s/w
– Stores running-config

2. Cisco Router Components
• ROM
– Starts & maintains the router
• Flash Memory
– Holds Cisco IOS
– Not erased when the router is reloaded
• NVRAM
– Holds router (& switch) configurations
– Not erased when the router is reloaded
• Configuration Register
– Controls how the router boots up

3. Boot Sequence
1: Router performs a POST
2: Bootstrap looks for & loads the Cisco
IOS
3: IOS software looks for a valid
configuration file
4: Startup-config file (from NVRAM) is
loaded
– If startup-config file is not found, the router will start the
setup mode

4. Configuration Registers
• Register
– 16-bit software written into NVRAM
– Loads from flash memory & looks for the startup-config
file
• Configuration Register Bits
– 16 bits read 15-0, from left to right
– default setting: 0x2102
Register 2 1 0 2
Bit number 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
Binary 0 0 1 0 0 0 0 1 0 0 0 0 0 0 1 0
NOTE: 0x means the digits that follow are in hexadecimal

5. Configuration Meanings

6. Boot Field Meanings

7. Changing the Configuration
Register
• Force the system into the ROM monitor
mode
• Select a boot source & default boot
filename
• Enable or disable the Break function
• Set the console terminal baud rate
• Load operating software from ROM
• Enable booting from a TFTP server

8. Changing the Configuration
Register
Router(config)#config-register 0x0101
Router(config)#^Z
Router#sh ver
Configuration register is 0x2102 (will be
0x0101 at next reload)

9. Leased Line
Used to provide point-to-point dedicated network
connectivity.
Analog leased line can provide maximum bandwidth of 9.6
Kbps.
Digital leased lines can provide bandwidths :
64 Kbps, 2 Mbps (E1), 8 Mbps (E2), 34 Mbps (E3) ...

10. Leased Line Internet Connectivity
ISP
Broadba
nd
Internet
Connecti
vity
ISP
Router
Interface
Converter
LL
Modem
G.703
LL
Modem
V.35
Router
ISP PREMISES CUSTOMER PREMISES
PSTN

11. 11
CSU/DSU and Digital Local Loops
• The communications link needs signals in an appropriate format.
• The Channel Service Unit (CSU) receives and transmits signals from and to the
WAN line and provides a barrier for electrical interference from either side of the
unit. The CSU can also echo loopback signals from the phone company for testing
purposes.
• The Data Service Unit (DSU) manages line control, and converts input and output
between RS-232C, RS-449, or V.xx frames from the LAN and the time-division
multiplexed (TDM) DSX frames on the T-1 line. The DSU manages timing errors and
signal regeneration. The DSU provides a modem-like interface between the
computer as Data Terminal Equipment (DTE) and the CSU.

12. 12

13. 13
The CSU/DSU may also be built into the interface card of the
router.

14. Encapsulation Process
original IP header original data
new datanew IP header
outer header inner header original data

15. Types of Encapsulation
• Three types of encapsulation protocols are specified for Mobile IP:
– IP-in-IP encapsulation: required to be supported. Full IP header added to the
original IP packet. The new header contains HA address as source and Care of
Address as destination.
– Minimal encapsulation: optional. Requires less overhead but requires changes
to the original header. Destination address is changed to Care of Address and
Source IP address is maintained as is.
– Generic Routing Encapsulation (GRE): optional. Allows packets of a different
protocol suite to be encapsulated by another protocol suite.
• Type of tunneling/encapsulation supported is indicated in registration.

16. IP in IP Encapsulation
• IP in IP encapsulation (mandatory in RFC
2003)
– tunnel between HA and COA
Care-of address COA
IP address of HA
TTL
IP identification
IP-in-IP IP checksum
flags fragment offset
lengthTOSver. IHL
IP address of MN
IP address of CN
TTL
IP identification
lay. 4 prot. IP checksum
flags fragment offset
lengthTOSver. IHL
TCP/UDP/ ... payload

17. Minimum Encapsulation
• Minimal encapsulation (optional)
– avoids repetition of identical fields
– e.g. TTL, IHL, version, TOS
– only applicable for unfragmented packets, no
space left for fragment identification
care-of address COA
IP address of HA
TTL
IP identification
min. encap. IP checksum
flags fragment offset
lengthTOSver. IHL
IP address of MN
original sender IP address (if S=1)
Slay. 4 protoc. IP checksum
TCP/UDP/ ... payload
reserved

18. Generic Routing Encapsulation
original
header
original data
new datanew header
outer header
GRE
header
original data
original
header
Care-of address COA
IP address of HA
TTL
IP identification
GRE IP checksum
flags fragment offset
lengthTOSver. IHL
IP address of MN
IP address of CN
TTL
IP identification
lay. 4 prot. IP checksum
flags fragment offset
lengthTOSver. IHL
TCP/UDP/ ... payload
routing (optional)
sequence number (optional)
key (optional)
offset (optional)checksum (optional)
protocolrec. rsv. ver.C R K S s

19. Routing techniques
• Triangle Routing: tunneling in its simplest form has all packets go to home network
(HA) and then sent to MN via a tunnel.
– This involves two IP routes that need to be set-up, one original and the second
the tunnel route.
– Causes unnecessary network overhead and adds to the latency.
• Route optimization: allows the correstpondent node to learn the current location
of the MN and tunnel its own packets directly. Problems arise with
– mobility: correspondent node has to update/maintain its cache.
– authentication: HA has to communicate with the correspondent node to do
authentication, i.e., security association is with HA not with MN.