Review of Networking Technologies
Vahid Tabatabaee
Fall 2007
ENTS689L: Packet Processing and Switching
Networking Technologies
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References
 Title: Internetworking with TCP/IP vol. I Principles, Protocols, and
Architecture
Author: Douglas E. Comer
Publisher: Prentice-Hall
 Title: Network Processors Architectures, Protocols, and Platforms
Author: Panos C. Lekkas
Publisher: McGraw-Hill
 Title Computer Networking: A Top-Down Approach
Author: J.F. Kurose, K.W. Ross
Publisher: Addison Wesley
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Networking Technologies
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Connection Oriented Communication
 Connection oriented communication forms a dedicated
connection (circuit, path) between two points.
 E.g. Telephone systems, ATM, Frame Relay
 Potential Advantages:
Easier to make it reliable (note it is not necessarily
more reliable).
Guaranteed/reserved bandwidth.
Identify flows by connection identifier rather than
source/destination address (tag switching)
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Connection-less Communication
 Data is segmented into packets.
 Every packet has identification information that
enables network hardware to send it to the
specified destination.
 E.g. Ethernet, Internet Protocol
 Potential Advantages:
More efficient use of resources
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Networking Technologies
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Network Hierarchy (3 layer)
 Enterprise Network
 Typical networks in companies, universities.
 Based on Ethernet, Fast-Ethernet, WiFi.
 Contains one or more LAN connecting PC, printers, servers
 They can also have faster connections based on Gigabit Ethernet to connect to
server and storage subsystems.
 Gateway and customer access routers provide connection to the rest of the
world
 Access Network (provider network)
 Aggregate customer traffic.
 Send the aggregated traffic through a larger pipe into the WAN.
 We have three kind of routers here:
 Provider Edge Router (infamous last mile connection)
 Provider core router
 The typical speed range OC-3 and OC-48
 WAN
 Interconnect provide or career networks
 The typical speed ranges between OC-12 and OC-192
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Conceptual Hierarchy of Networks
WAN
Access Network
Provider Edge Router
Enterprise Network
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Networking Technologies
Customer Edge Router
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LAN/MAN/WAN
Source:
http://www.crema.unimi.it/didattica/Labsistemi/matagg/Tutorial%20Networking.htm
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MAN
 MAN are large
network spanning a
campus or city.
 MAN (WAN) is
generally less than
(over) 30-50 Km.
 WAN spans central
office facilities, while
a MAN starts and
ends in a central
office
ENTS689L: Packet Processing and Switching
Networking Technologies
Source:
http://www.dbguide.net/know/know103001.jsp?mode=view&pg=1&idx=1038
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4 layer Network Hierarchy
WAN
Core
3
 Core Router Requirements:
 OC-192 wire-speed IP routing and
MPLS
 VPN
 Traffic Engineering
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Networking Technologies
Edge
LAN(s)
Access
2
MAN
CPE
1
 Edge Router Requirements:
 Aggregate multiple access network
interfaces
 Access network uplinks can be GigE
OC-12
 Reliability
 Redundant component
 Hot pluggable line cards
 Multiservice Providing Platform (MSSP)
 TDM OC-3 to OC-192
 GigE, 10GigE LAN, 10GigE WAN
 SAN (Fibre Channel, …)
 IP services
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Sprint Logical Topology
 18 IP routers with 36 bidirectional logical links
Source: A. Nucci, A. Sridharan, N. Taft, “The Problem of Synthetically Generating IP Traffic Matrices:
Initial Recommendations”, ACM Computer Communication Review, vol. 35, no. 3, pp. 19-32 ,July 2005.
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Sprint WDM Technology
 36 OXC with 55 WDM fibers..
 Wa = 40 OC-192 channels, Wb = 40 OC-48 channels, Wc = 40 OC-12 channels
Source: A. Nucci, A. Sridharan, N. Taft, “The Problem of Synthetically Generating IP Traffic Matrices:
Initial Recommendations”, ACM Computer Communication Review, vol. 35, no. 3, pp. 19-32 ,July 2005.
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Networking Technologies
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Ethernet Technology
 Ethernet is the most popular
LAN technology:
Shared media
Carrier Sense Multiple
Access/ Collision
Detection (CSMA/CD)
 There are different variants of
the Ethernet technology:
Coaxial
Thin wire
Twisted Pair (10Base-T)
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10Base-T
 Data rate : 10Mbps
 Broadcast, bus technology
 Best effort delivery: Hardware
provide no information to the
sender that the packet is
delivered
Source:
http://www.webclasses.net/Courses/Intro/6.1/demo/units/unit02/sec04b.html
 Max. Segment length: 100m
 Repeaters relay electrical from one cable to another. At most two
bridges between any two machines.
 Bridges learn addresses and replicate the signal if needed. They isolate
Ethernet segments from each other.
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Collision Detection and Recovery
 It is possible that two transmitters send data
simultaneously and collision happens.
 Each transceiver monitors the cable to see if
there is a coliision.
 When it detects collision it aborts transmission
and remain idle before trying again.
 They use a binary exponential back-off policy.
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Ethernet Hardware Address
 Ethernet defines a 48-bit addressing scheme.
 Each hardware card has a unique address assigned to it.
 Ethernet addresses are sometimes called hardware or
physical addresses.
 Interface card receives all packets, but only send to the
host that are addressed to it.
 Three types of address:
Physical address of one network interface.
The network broadcast address (all 1s)
Multicast address: some interfaces can be
programmed to recognize multicast addresses.
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Ethernet Frame Format
 Ethernet frame size are between 64 and 1518
bytes (including header, data, and CRC).
 There is also 12 byte gap between Ethernet
frames.
Preamble
7 octets
SFD
1
octet
Destination
Address
6 octets
Source
Address
6 octets
Frame
Type
2 octets
Frame Data
64-1500 octets
CRC
4 octets
10101011
Alternating 0 and 1
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1 GigE and 10 GigE
 It preserves compatibility with legacy software applications
developed for running on 10BaseT.
 The technology has been proposed both for LAN and MAN/WAN.
 The jumbo frames can be up to 9000 bytes data.
 10 GigE is not based on the CSMA/CD technology anymore.
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Internet Architecture
 Networks are connected by routers
 Routers need to know about the topology of the internet beyond
the networks to which they connect.
 Routers use the destination network, not the destination host,
when routing a packet.
Workstation
Host
Net 1
Net 2
Router 1
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Net 3
Router 2
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Questions
 What is the exact form of Internet Addresses?
 How Internet addresses are mapped to the
Hardware addresses such as Ethernet
addresses?
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Host Universal Identifiers
 Host Identifiers are:
 Names: specify what an object is.
 Addresses: Where it is.
 Routes: How to get there.
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Classes of IP Addresses
 Each host has a unique 32 bit internet address.
 Each address is a pair of (netid, hostid).
8
Class A
0
Class B
1 0
Class C
1 1
0
Class D
1 1
1
0
Class E
1 1
1
1




24
16
31
0.0.0.0 --127.255.255.255
hostid
netid
hostid
netid
netid
0
128.0.0.0 --191.255.255.255
hostid
192.0.0.0 --223.255.255.255
multicast address
224.0.0.0 --239.255.255.255
reserved for future use
240.0.0.0 --255.255.255.255
127.0.0.1 is the loopback address in IP. (127.0.0.0 to 127.255.255.255)
0.0.0.0 – 0.255.255.255 (zero addresses should not be used).
255.255.255.255 broadcast to all other nodes on the LAN
In general zeros mean this and ones mean all.
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Classless Inter-Domain Routing
 It replaces the older system
based on classes
 Most sites were too big for class
C and received class B number.
 Depletion of class B addresses
(~16,000 total)
 It looks like a normal IP address
but it ends with a slash and a
number following it.
 It facilitates routing by allowing
blocks of addresses to be
grouped together into single
routing table entries.
Source:
http://en.wikipedia.org/wiki/Classless_Inter-Domain_Routing
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An example for CIDR
 Different CIDR prefixes are used
in different locations for routing
Outside MCI network
Inside MCI network
Inside ARS network
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Weaknesses in Internet Addressing
 If a computer moves from one network to another, its IP address
must change.
 This is the main source of challenge for mobile IP.
 The path used for hosts with multiple IP addresses (multi-homed
hosts) depends on the address used.
 If host B connection to network 1 fails, packets from host A that
uses I3 address can not reach host B.
Network 1
I1
I2
I3
Router
HOST
A
HOST
B
I5
I4
Network 2
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Address Aggregation
ENTS689L: Packet Processing and Switching
Networking Technologies
Source: “Computer Networking: A Top-Down
Approach” by J.F. Kurose, K.W. Ross
25
More specific routes
ENTS689L: Packet Processing and Switching
Networking Technologies
Source: “Computer Networking: A Top-Down
Approach” by J.F. Kurose, K.W. Ross
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Mapping Internet Address to Physical Address
 Consider two machines A and B on the same network.
 IA, IB are internet addresses and PA, PB are physical
addresses of A and B respectively.
 A wants to send a packet to B, but it only has IB
address of B.
 Address Resolution Protocol (ARP) resolves this
problem for networks with static address and broadcast
capability.
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ARP
 Host A has an ARP cache of recently acquired IP-to-physical address bindings.
 If IB is not in the cache, then A broadcasts an ARP request containing IB.
 Host B responds with an ARP reply to A that contains (IB, PB). It also adds (IA,
PA) to its own cache.
 Sender A queues all packets destined to B until it receives ARP reply.
 Expiring timer for the binding entries in the cache.
 Resending the request (at least once) if did not get a reply.
 In most technologies a single type value is used for ARP frames.
 In Ethernet type field of (0806)16 is for ARP messages.
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RARP
 A machine uses Reverse Address Resolution Protocol
(RARP) to get its IP address from the server at the
startup.
 The server has a list of IP addresses of the machines.
 Machine uses its physical address to communicate on
the network.
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IP Packet (Datagram) delivery
 The maximum size of an IP datagram is 216 octets.
 It is more efficient to carry each IP packet in a network
frame (encapsulation).
 Each technology has a different maximum frame size
Ethernet 1500 octets
FDDI 4470 octets
 IP chooses a appropriate initial datagram size.
 Fragmentation is the process of dividing larger packets
into smaller ones to adhere to the network Maximum
Transfer Unit (MTU).
 Destination uses the Identification, Flags, and Fragment
offset to reassembly the packet.
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Time To Live field
 Time To Live field specifies how long a packet is allowed to be in
the Internet.
 The source sets the maximum time that the datagram should
survive.
 Each router decrement this field by one when it process the
packet.
 To take into account buffering delay, each router records arrival
time and decrement the field by seconds that packet stays in the
router.
 When TTL reaches zero, the router discards the packet.
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IP routing
 Direct Delivery:
Transmission of packets from one machine across a SINGLE
physical network to another.
 Indirect Delivery:
Destination is not connected directly to the network of the sender,
hence sender should pass the packet to a router for delivery.
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Direct Delivery
 Does not involve the router.
 Sender encapsulates the datagram in a single
physical frame.
 Binds the destination IP address to a physical
hardware address using ARP (if needed).
 How does the sender know if the destination is
directly connected to the same network?
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Indirect Delivery
 Host (sender):
Encapsulates the datagram in a physical network frame and send it
to a router attached to the network.
 Router:
Extracts the encapsulated datagram,
Decides the next router to send the datagram to.
Encapsulates the Datagram for transmission over the next network.
 Question:
How a router and host decide next router to send the datagram to?
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IP Routing Table
 Every host and router has a routing table
 Routing table has information about destination and how to reach them.
 We can not have a separate entry for every possible destination.
 First refinement: We can have a single entry for all hosts connected to the
same network and only check the netid part of the internet address.
 Second refinement: We only need to keep the information for the next hop
not the entire path for each destination.
 All next hop routers listed in router M routing table must lie on networks to
which M connects directly.
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Routing Table
Longest Prefix Match:
 Recall that in CIDR more than one table entry may match
the destination address.
 The one with largest prefix number is used for routing.
 Routing Table Entries:
Both entries match the destination
 192.168.0.0/16
address 192.168.20.19, but the second
 192.168.20.16/28
one with larger prefix number is used.
Default Routes:
 A default route is used by a router or a server when no
other known route works for a packet destination address.
 The default route in CIDR is 0.0.0.0/0
 Hosts and routers in an organization generally point the
default route towards the router that has connection to a
network service provider
Source: Wikipedia
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Example: Route Selection in Cisco Routers
 This example is based on the “Route Selection
in Cisco Routers, Document ID: 8651 available
at:
http://www.cisco.com/en/US/tech/tk365/tec
hnologies_tech_note09186a0080094823.
shtml
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Routing Table
There are three process involved in building and maintaining the
routing table:
Various Routing Process, which run a routing protocol such as:
 Enhanced Interior Gateway Routing Protocol (EIGRP)
 Border Gateway Protocol (BGP)
 Intermediate System-to-Intermediate System (IS-IS)
 Open Shortest Path First (OSPF)
The routing table, which accepts information from routing process
and replies to requests from the forwarding process.
The forwarding process, which requests information from the routing
table for packet forwarding.
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Building the Routing Table
Main considerations in building the routing table:
 Administrative Distance: This indicates how much we trust source
of the route.
 Metric: This is a measure used by the routing protocol to calculate
the best path to a given destination.
 Prefix length
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Routing Table Entry Update
Assume there are four routing process
running:
 EIGRP, OSPF, RIP, IGRP
 All 4 process learned various routes
to 192.168.24.0/24 and each has
chosen its best path to that network
using its internal metrics and
process.
 Each routing process attempts to
install their route in the routing
table.
 The one with lowest administrative
distance (EIGRP here) can install
its route in the routing table
 Other routes may be used as
backup routes
ENTS689L: Packet Processing and Switching
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Default Administrative Distances
Connected
0
Static
1
eBGP
20
EIGRP (internal)
90
IGRP
100
OSPF
110
IS-IS
115
RIP
120
EIGRP (external)
170
iBGP
200
EIGRP summary
route
5
40
Prefix Lengths
 Assume the three routing process
have received these routes:
 EIGRP (internal): 192.168.32.0 /
26
 RIP: 192.168.32.0 / 24
 OSPF: 192.168.32.0 / 19
 ALL these routes will be installed in
the routing table, since they have
different prefix length.
 Routing Table:
....
D 192.168.32.0/26 via 10.1.1.1
R 192.168.32.0/24 via 10.1.1.2
O 192.168.32.0/19 via 10.1.1.3
....
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A packet destined for 192.168.32.1 is forwarded
to 10.1.1.1, which has the longest prefix match
(26 bits verses 24 or 19 bits).
A packet destined for 192.168.32.100 is
forwarded to 10.1.1.2, because it does NOT fall
within 192.168.32.0/26 (192.168.32.0—
192.168.32.63).
But it falls within the 192.168.32.0/24
destination (192.168.32.0-192.168.32.255)
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Forwarding Decision Process
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Dynamic Host Configuration Protocol (DHCP)
 The router IP addresses are typically configured manually, often
remotely with a network management tool.
 Host addresses is typically configured using the DHCP protocol.
 DHCP can give a host the same IP address each time it connects
to the network or assign a temporary IP address that will be
different each time the host connects to the network
 DHCP also provides additional information such as subnet mask,
address of the first hop router (default gateway) and address of the
local DNS server.
 DHCP is also used commonly in residential access networks and
in wireless LANs.
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DHCP architecture





DHCP is a client-server protocol
Newly arriving hosts are clients
DHCP server has the information requested by the clients
Subnets may have a DHCP server
If there is no server in a subnet, a DHCP relay agent knows the
address of a DHCP server for that network
Source:http://www.windowsitpro.com/Files/5181/Figure_02.gif
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DHCP 4-step process
 DHCP server discovery: Newly
arriving host sends
DHCPDISCOVER message a
UDP packet to port 67. This
message is broadcasted.
 DHCP sservers respond with
DHCPOFFER, which is again
broadcasted. The message
cotains the transaction ID, the
proposed IP address, the
network mask, lease time.
 The client will choose one
server offer and respond to that
server with a DHCPrequest
message.
 The server responds with
DHCPACK
When the renewal
timer expires
When the rebinding
timer expires
Source:http://www.windowsitpro.com/Files/5181/Figure_01.gif
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Mobility Management
 Home Network: The permanent home of a mobile node.
 Home Agent: The entity within the home network that performs the
mobility management functions.
 Foreign Network: The network where the mobile node is currently
residing.
 Foreign Agent: The entity in the foreign network that help the
mobile node with the mobility management functions.
 Correspondent: The entity that wants to communicate with the
mobile node
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Mobile Network Architecture
ENTS689L: Packet Processing and Switching
Networking Technologies
Source: “Computer Networking: A Top-Down
Approach” by J.F. Kurose, K.W. Ross
47
Addressing (Naïve Approach)
 Foreign Network advertises to its neighbors that it has a
highly specific route to the mobile node permanent IP
address.
 When mobile node leaves one foreign network and
joins another the new foreign network, the new foreign
agent would advertise that it has a specific route and
the old one eould withdraw its routing information.
 Drawback: Scalability; it completely destroys the
hierarchical structure of IP addresses.
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Addressing for mobile
 Foreign agent is located at the edge of the foreign network.
 Foreign agent creates a care-of address (COA) for the mobile
node, with the network portion of the COA matching that of the
foreign network.
 Note that there are two addresses for the mobile node:
 Permanent address
 Foreign address
 The foreign agent informs the home agent that the mobile node is
in its network and has the given COA.
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Indirect Routing to a Mobile Node
 The correspondent addresses the packet to the mobile node’s
permanent address.
 The packet is first routed to the mobile node home agent.
 The home agent forwards the packet to a mobile node in two steps:
 The packet is first forwarded to the foreign agent using the COA
 From the foreign agent to the mobile node.
 Mobile node can address directly its packets to the correpondent.
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Indirect Forwarding
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Networking Technologies
Source: “Computer Networking: A Top-Down
Approach” by J.F. Kurose, K.W. Ross
51
Encapsulation and Decapsulation
 Home agent encapsulates packets
 Foreign agent decapsulates packets
ENTS689L: Packet Processing and Switching
Networking Technologies
Source: “Computer Networking: A Top-Down
Approach” by J.F. Kurose, K.W. Ross
52
Network Layer Functionality to Support Mobility
 Mobile Node to Foreign Agent: The mobile node registers with the
foreign agent and deregisters when it leaves the network.
 Foreign Agent to Home Agent: Foreign agent registers the mobile
node ‘s COA with the home agent. Does it need to deregister the
COA when the mobile node leaves its network?
 Home Agent Packet Encapsulation: Encapsulation and forwarding
of the original packets within a packet with the COA address
 Foreign Agent Decapsulation: Extraction of the correspondent’s
original packet and forwarding of it to the mobile node.
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