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

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

Boot Sequence

1: Router performs a POST2: Bootstrap looks for & loads the Cisco IOS3: IOS software looks for a valid configuration file4: Startup-config file (from NVRAM) is loaded

– If startup-config file is not found, the router will start the setup mode

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 2Bit number 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0Binary 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

Configuration Meanings

Boot Field Meanings

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

Changing the Configuration Register

Router(config)#config-register 0x0101Router(config)#^ZRouter#sh ver

Configuration register is 0x2102 (will be 0x0101 at next reload)

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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.

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

Encapsulation Process

original IP header original data

new datanew IP header

outer header inner header original data

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.

IP in IP Encapsulation• IP in IP encapsulation (mandatory in RFC

2003)– tunnel between HA and COA

Care-of address COAIP address of HA

TTLIP identification

IP-in-IP IP checksumflags fragment offset

lengthTOSver. IHL

IP address of MNIP address of CN

TTLIP identification

lay. 4 prot. IP checksumflags fragment offset

lengthTOSver. IHL

TCP/UDP/ ... payload

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 COAIP address of HA

TTLIP identification

min. encap. IP checksumflags fragment offset

lengthTOSver. IHL

IP address of MNoriginal sender IP address (if S=1)

Slay. 4 protoc. IP checksum

TCP/UDP/ ... payload

reserved

Generic Routing Encapsulationoriginalheader original data

new datanew header

outer header GRE header original dataoriginal

header

Care-of address COAIP address of HA

TTLIP identification

GRE IP checksumflags fragment offset

lengthTOSver. IHL

IP address of MNIP address of CN

TTLIP identification

lay. 4 prot. IP checksumflags 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

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.