資管 Lee Lesson 5 IP Packets: Delivery and Routing IP Layer operation.

資管 Lee <Lesson 5-1>

Lesson 5

IP Packets: Delivery and RoutingIP Layer operation


delivery◦Physical forwarding of the packets.◦Connectionless and connection-oriented◦IP protocol is a connectionless protocol.

routing◦Finding the route (next hop) for a datagram.◦Routing methods, types of routing, the

routing table, and the routing module.


Direct delivery Direct delivery

◦ Final destination of the packet is a host connected to the same physical network as the deliverer.

◦ Sender determine by filtering out the destination field of IP packet. IP destination first be masked with the mask field in the routing table compare the destination field in the routing table with the result.

◦ Case for direct delivery,: Case 1: MAC address is known, the sender sent the MAC frame to the

destination Case 2: Otherwise, it use ARP protocol to find the physical address of the

destination.

Network

Router

Host Host

Direct delivery

Direct delivery

To theRest of the Internet


Indirect delivery (by way of router)◦ Case of indirect delivery: [indirect delivery]

final destination of the packet is not connected to the same physical network as the deliverer.

the sender sent the MAC frame to the router’s destination if destination MAC address is available.

{The packet may go from router to router until it reaches the one connected to the same physical network as its final destination.}

Network

Router

Host (source)

Host (destination)

Indirect delivery

Direct delivery

Network


Routing Methods

Next-hop Routing◦ Routing table hold only the address of the next hop

instead of holding the complete route.

R1

Host A (source) Host B (destination)

NetworkNetwork NetworkR2

Destination Route

Host B R1, R2, Host B

Destination Route

Host B R2, Host B

Destination Route

Host B R1

Destination Route

Host B R2

Destination Route

Host B Host B

Destination Route

Host B __


Routing Methods

Network-Specific Routing◦ Instead of having an entry for every host connected to the

same physical networks. Treat all hosts connected to the same network as one single entry.

R1

Host (source)

N1

Destination Next Route

A R1

B R1

C R1

D R1

Destination Route

N2 R1

AB

C

D

N2


Routing Methods

Host-Specific Routing◦ Host address is given in the routing table.

R1Host A

R2

Destination Next Hop

Host B R3

N2 R1

N3 R3

… …

R3

N2

N1

N3

Host B

Routing table for host A


Routing Methods

Default Routing◦ Default entry (network address 0.0.0.0). For example, router

R1 for network N2, others, through router R2.

R1Host A

Destination Next Hop

N2 R1

… …

… …

Default R2

R2

N2

N1

Routing table for host A

Rest of the Internet


Static vs Dynamic Routing

Routing table, entries for all the destination, can be either static or dynamic◦Static routing contains information entered

manually, used in a small internet or in an experimental internet.

◦Dynamic routing table is updated periodically using one of the dynamic routing protocols such as RIP, OSPF, or BGP


Routing Module and Routing Table Design

Basic module for routing and routing table.

… …

… …

Routing module

Routing table

IP packet

IP packet

IP packet

FromIP Processingmodule

Tofragmentationmodule

IP Layer operation

Data Link Layer


Examples

R3

193.14.5.160/27 193.14.5.192/27

111.0.0.0/8

192.16.7.0/24 194.17.21.0/24

RestoftheINternet

R5

R4

193.14.5.165 193.14.5.197

111.25.19.20

R1

m2 m1

m0

R2

111.20.18.14

111.15.17.32

111.30.31.18

192.16.7.5

192.16.7.52 194.17.21.68

Host A:194.17.21.16

194.17.21.14

Host B:193.14.5.163

T0

T1


Routing table design

Seven basic fields:◦ mask, destination address, next-hop address, flags, reference-count,

use, and interface

Mask Dest.address

Next-hopaddress Flags Reference

count Use Interface

255.0.0.0……

124.0.0.0……

145.6.7.23……

UG……

4……

20……

m2……

Flags: 5 flags. U(up), G (gateway), H(host-specific), D(added by redirection), M(modified by redirection):

G flags mean another network or not.H flags means that the entry is a host-specific address.

Reference count: the user number that use this entry.Use: the total packets that use this entry.


Routing Module operation

Routing Module operationReceive: an IP packet 1. For each entry in the routing table

1. Apply the mask to packet destination address 2. If (the result matches the value in the destination field) 1. If (the G flags is absent) /* direct delivery */

use packet destination address as next hop address

else value in next hop fields as next hop address 2. Send packet to fragmentation module with next hop address

and interface ID.3. Return

2. If no match is found for all entries in the routing table , send an ICMP error message

3. return


Mask Dest.address

Next-hopaddress

Flags RC Use Interface

255.0.0.0 111.0.0.0 - U 0 0 m0

255.255.255.224 193.14.5.160 - U 0 0 m2

255.255.255.224 193.14.5.192 - U 0 0 m1

… … … … … … …

255.255.255.255 194.17.21.16 111.20.18.14 UGH 0 0 m0

255.255.255.0 192.16.7.0 111.15.17.32 UG 0 0 m0

255.255.255.0 194.17.21.0 111.20.18.14 UG 0 0 m0

0.0.0.0 0.0.0.0 111.30.31.18 UG 0 0 m0

Routing table for router R1

Example: Router R1 receives 500 packets for destination 192.16.7.14; the algorithm applies:1. Direct delivery a. 192.16.7.14& 255.0.0.0 192.0.0.0 no match b. 192.16.7.14& 255.255.255.224 192.16.7.0 no match c. 192.16.7.14& 255.255.255.224 192.16.7.0 no match2. Host-specific a.192.16.7.14& 255.255.255.255 192.16.7.14 no match3. Network-specific a. 192.16.7.14& 255.255.255.0 192.16.7.0 match

{ the router sends the packet through interface m0 along with the next-hop IP address (111,15.17.32) to the fragmentation module for further processing. It increments the use field by 500 and RC by 1. }


Example 2: Router R1 receives 100 packets for destination 193.14.5.176; the algorithm applies:

1. Direct delivery 2. Host-specific

3. Network-specific

Example 3: Router R1 receives 20 packets for destination 200.34.12.34: the algorithm applies:

1. Direct delivery 2. Host-specific

3. Network-specific


Practice Quiz(3)S1: Show the routing table for router R3S2: Router R3 receives 100 packets for destination 193.14.5.176;

the algorithm applies?


IP layer operation


An simplified, bare-bones design of IP

Eight components:

◦ 5 modules: header-adding module, a processing module, a routing module, a

fragmentation module, and reassembly module.

◦ 3 tables: routing table, MTU table, and a reassembly table.


Routing Module and Routing Table Design

… …Routing module

Routing table

IP packet

Reassembly module

Processingmodule

… …

Reassemble table

…

MTU table

IP packet IP packet

Header-addingmodule

IP packetIP packet

Fragmentationmodule

IP packet IP packet

DataDataaddress

From upper layer protocol

From data link layer To data link layer

To upper layer protocol

IP layer operation


Header-Adding Module

Header-Adding Module operation

Receive: data, destination address { 形成 IP 封包 } 1. Encapsulate the data in an IP datagram 2. Calculate the checksum and insert it in the checksum field. 3. Send the data to the corresponding input queue. 4. Return.

Processing Module operation 1. Remove one datagram from one of the input queues. 2. If (destination address is 127.X.Y.Z or matches one of the local addresses)

1) Send the datagram to the reassembly module, 2) Return 3. If (machine is a router)

Decrement TTL. 4. If (TTL less than or equal to zero)

1) discard the data gram, 2) Send an ICMP error message, 3) Return 5. Send the datagram to the routing module. 6. Return.

資管 Lee <Lesson 5-21> 資管

Fragmentation Module operation

Receive: an IP packet from routing module 1. Extract the size of the datagram. 2. If (size>MTU of the corresponding network)

1) If (D bit is set), discard the datagram, send an ICMP message, return.2) Else, Calculate the maximum size, Divide the datagram into fragments, add header to each fragments, send the datagram, return.

3. Else,1) Send the datagram.

4.Return.

Interface Number MTU

………

………

MTU table

資管 Lee <Lesson 5-22> 資管

Reassembly Module operationReceive: an IP datagram from the processing module 1. If (offset value is zero and the M bit is 0)

1) Send the datagram to the appropriate queue, return. 2. Search the reassembly table for the corresponding entry. 3. If (not found)

1) create a new entry. 4.Insert the fragment at the appropriate place in the link list.

1) If (all fragments have arrived), Reassemble the fragements, delivery the datagram to the corresponding upper layer protocol, return.2) Else, check the time-out, if (time-out expired), discard all fragments, send an ICMP error message

5. Return.

State Source Addr. Data ID Time out Fragments

Reassemble table

資管 Lee Lesson 5 IP Packets: Delivery and Routing IP Layer operation.

Documents

Transcript of 資管 Lee Lesson 5 IP Packets: Delivery and Routing IP Layer operation.

資 管 Lee Lesson 5 IP Packets: Delivery and Routing IP Layer operation.

Documents

Transcript of 資 管 Lee Lesson 5 IP Packets: Delivery and Routing IP Layer operation.

資管 Lee Lesson 5 IP Packets: Delivery and Routing IP Layer operation.

Transcript of 資管 Lee Lesson 5 IP Packets: Delivery and Routing IP Layer operation.