Transcript Global Information Systems and Software Technology (GISST)

University of British Columbia
CICS 515 (Part 2) Computer Networks
Lecture 5b-c – IPv6 and Other Protocols
Instructor: Dr. Son T. Vuong
Email: [email protected]
The World Connected
Cics 515 – Summer 2012 © Dr. Son Vuong
1
IPv6


Initial motivation: 32-bit address space soon to
be completely allocated.
Additional motivation:
 header
format helps speed processing/forwarding
 header changes to facilitate QoS
IPv6 datagram format:
 fixed-length 40 byte header
 no fragmentation specified in basic header
Cics 515 – Summer 2012 © Dr. Son Vuong
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IPv6 Header (Cont)
Priority: identify priority among datagrams in flow
Flow Label: identify datagrams in same “flow.”
(concept of“flow” not well defined).
Next header: identify upper layer protocol for data
Cics 515 – Summer 2012 © Dr. Son Vuong
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Other Changes from IPv4



Checksum: removed entirely to reduce
processing time at each hop
Options: allowed, but outside of header,
indicated by “Next Header” field
ICMPv6: new version of ICMP
 additional
message types, e.g. “Packet Too Big”
 multicast group management functions
Cics 515 – Summer 2012 © Dr. Son Vuong
4
Transition From IPv4 To IPv6

Not all routers can be upgraded simultaneous
 no
“flag days”
 How will the network operate with mixed IPv4 and
IPv6 routers?

Tunneling: IPv6 carried as payload in IPv4
datagram among IPv4 routers
Cics 515 – Summer 2012 © Dr. Son Vuong
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Dual
IPv6/IPv4
Router
Tunneling
Logical view:
Physical view:
Dual
IPv6/IPv4
Router
A
B
IPv6
IPv6
A
B
C
IPv6
IPv6
IPv4
Flow: X
Src: A
Dest: F
data
A-to-B:
IPv6
Cics 515 – Summer 2012 © Dr. Son Vuong
E
F
IPv6
IPv6
D
E
F
IPv4
IPv6
IPv6
tunnel
Src:B
Dest: E
Src:B
Dest: E
Flow: X
Src: A
Dest: F
Flow: X
Src: A
Dest: F
data
data
B-to-C:
IPv6 inside
IPv4
B-to-C:
IPv6 inside
IPv4
Flow: X
Src: A
Dest: F
data
E-to-F:
IPv6
6
IPv6 – Peer Instruction – Question 5.2
IPv6 supports the following features:
A. 128-bit IP address
B. Auto-configuration (plug-and-play) (stateless)
as well as dynamic IP address via a DHCPv6
server (stateful)
C. More options via extension headers
including Jumbogram of greater than 64KB
D. Efficient header processing
E. All the above
F. A, B and C
Cics 515 – Summer 2012 © Dr. Son Vuong
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IPv6 – Peer Instruction – Question 5.3
An IPv6 datagram is 80,000 bytes. What extension
header must be used?
A. Destination option
B. Fragmentation
C. Authentication
D. Hop-by-hop
E. None of the above
Cics 515 – Summer 2012 © Dr. Son Vuong
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IPv6 – Peer Instruction – Question 5.4
The IPv6 jumbogram option gives rise to the
following issues:
A. Fragmentation
B. 16-bit length of UDP
C. 16-bit MSS option of TCP
D. Checksum calculation
E. All of the above
F. B and C
Cics 515 – Summer 2012 © Dr. Son Vuong
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Ch 4: Network Layer and Routing

The IP Protocol



Routing







IP Format, Addressing, fragmentation,
Internet Control Protocols (ICMP)
RIP (Routing Information Protocol)
OSPF (Open Shortest Path First)
The Interior Gateway Routing Protocol
BGP – The Exterior Gateway Routing Protocol
IPv6
Internet Multicasting
Mobile IP
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What have we covered?

IPv4, IPv6
What’s next ?





Internet Control Message Protocol (ICMP)
Address resolution (ARP)
Getting (dynamic) addresses (DHCP)
DNS
Routing protocols (RIP, OSPF, BGP)
Cics 515 – Summer 2012 © Dr. Son Vuong
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University of British Columbia
CICS 515 (Part 2) Computer Networks
Lecture 5c – ICMP, ARP, DHCP, DNS
Instructor: Dr. Son T. Vuong
Email: [email protected]
The World Connected
Cics 515 – Summer 2012 © Dr. Son Vuong
12
Lect. 5c – Other IP protocols
ICMP, ARP, DHCP (Sect. 4.4.3, 5.4)
DNS (Sect. 2.5 )

Internet Control Message Protocol (ICMP) (Sect 4.4.3)

Address Resolution (ARP) (Sect 5.4)

Dynamic IP address assignment (DHCP) (Sect 5.4)

Domain Name System (DNS) (Sect2.5)
Cics 515 – Summer 2012 © Dr. Son Vuong
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ICMP: Internet Control Message Protocol
RFC 792

Used by hosts & routers to communicate
network-level information
 error
reporting: unreachable host, network, port,
protocol
 echo request/reply (used by ping)

Network-layer “above” IP:
 ICMP

msgs carried in IP datagrams
ICMP message: type (1B), code (1B),
checksum (2B) plus part of IP datagram
causing error (header + first 8 bytes of data)
Cics 515 – Summer 2012 © Dr. Son Vuong
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ICMP datagram structure


ICMP msgs carried in IP datagrams
ICMP data contains part of IP datagram
causing error (IP header + first 8 bytes of data)
Cics 515 – Summer 2012 © Dr. Son Vuong
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ICMP: Internet Control Message Protocol
Type
0
3
3
3
3
3
3
4
5
8
9
10
11
12
Code
0
0
1
2
3
6
7
0
0-3
0
0
0
0
0
description
echo reply (ping)
dest. network unreachable
dest host unreachable
dest protocol unreachable
dest port unreachable
dest network unknown
dest host unknown
source quench (congestion control - not used)
redirect a host to a better router
echo request (ping)
route advertisement
router discovery (solicitation)
TTL expired
bad IP header
Cics 515 – Summer 2012 © Dr. Son Vuong
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“Real” Internet delays and routes


What do “real” Internet delay & loss look like?
traceroute (tracert) program: provides delay
measurement from source to router along endend Internet path towards destination. For all i:
sends three UDP packets that will reach router i on
path towards destination
 router i will return packets to sender
 sender times interval between transmission and
reply.

3 probes
3 probes
3 probes
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Traceroute and ICMP


Source sends series of UDP
segments to dest

When ICMP message arrives,
source calculates RTT
 First has TTL =1

Traceroute does this 3 times
 Second has TTL=2, etc.
Stopping criterion
 Unlikely port number
When nth datagram arrives to  UDP segment eventually
arrives at destination host
nth router:
 Router discards datagram  Destination returns ICMP “port
unreachable” packet (type 3,
 And sends to source an
code 3)
ICMP message (type 11,

When source gets this ICMP,
code 0)
stops.
 Message includes name of
router& IP address
Cics 515 – Summer 2012 © Dr. Son Vuong
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Address Resolution Protocol (ARP)




How do we convert the IP address of each node
(either the destination node, or a router) into the
address on the local network? E.g. IP -> Ethernet.
Each machine keeps a mapping of IP address to
physical addresses in a cache.
E.g. cascade.cs.ubc.ca 08:00:20:79:70:f5
dragon.cs.ubc.ca 08:00:09:27:b4:73
etc…
What if the mapping isn’t known, or has expired?
Send an ARP (Address Resolution Protocol)
broadcast message over the network.
Cics 515 – Summer 2012 © Dr. Son Vuong
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ARP Packet Format
0
8
16
Hardware type = 1
HLen = 48
PLen = 32
31
ProtocolType = 0x0800
Operation
SourceHardwareAddr (bytes 0-3)
SourceHardwareAddr (bytes 4-5)
SourceProtocolAddr (bytes 2-3)
SourceProtocolAddr (bytes 0-1)
TargetHardwareAddr (bytes 0-1)
TargetHardwareAddr (bytes 2-5)
TargetProtocolAddr (bytes 0-3)
Cics 515 – Summer 2012 © Dr. Son Vuong
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ARP Fields

Request format
 HardwareType
- Type of physical network
(e.g., Ethernet)
 ProtocolType - Type of higher layer protocol
(e.g., IP)
 HLEN & PLEN - Length of physical and
protocol addresses (measured in bits)
 Operation - Request for an address, or
response to a request.
 Source/Target Physical/Protocol addresses
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ARP Comments



An ARP packet sits at the same level in the
protocol graph as an IP packet. However ARP
service is used by IP; thus ARP can also be
viewed as a sublayer below IP.
ARP table entries timeout in about 10 minutes
Update the ARP table with information about
the source when you are the target. Hence,
both source/target physical/protocol addresses
are in the packet.
Cics 515 – Summer 2012 © Dr. Son Vuong
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Dynamic Host Configuration Protocol
(DHCP)
How does a host get an IP address?



Fixed – assigned
Dynamic – changeable: via DHCP
why?
Cics 515 – Summer 2012 © Dr. Son Vuong
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Dynamic Host Configuration Protocol
(DHCP)



DHCP allows config info (IP address etc)
stored in DHCP server to be retrieved
automatically by each host when booted or
connected to network (via broadcast
DHCPDiscover message)
that is, special IP address 255.255.255.255
ignored by everyone except the DHCP server
Cics 515 – Summer 2012 © Dr. Son Vuong
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DHCP (cont’d)



DHCP also allows dynamic assignment of IP
addresses to hosts (DHCP server maintains a
pool of available IP addresses to lease to
host and host need to renew lease
periodically).
It is not desirable to have a DHCP server on
every network – instead, uses a relay agent
for each network.
Relay agent unicasts DHCP request to server
Cics 515 – Summer 2012 © Dr. Son Vuong
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DHCP with relay agent
Unicast to server
DHCP
relay
Other networks
DHCP
server
Broadcast
Host
Cics 515 – Summer 2012 © Dr. Son Vuong
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DHCP Packet Format
Operation
HType
HLen
Hops
Transaction ID (Xid)
No. of secs
Flags/unused
Client IP addr
Your IP addr (yiaddr)
Server IP addr
Gateway IP addr
Client hardware addr (chaddr) (16 bytes)
Server name (64 bytes)
file (128 bytes)
options
DHCP is derived from an earlier protocol called BOOTP
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DHCP (cont’d)




Sent using UDP
Client puts hardware address in chaddr
Server replies with IP address in yiaddr (and
other config info, e.g. gateway addr, server IP
address, etc)
Types of DHCP packets (spec’d as options):


Discover, Offer, Request, Decline, Ack,
Nack, Release
Scalability/manageability -- recurring theme
(via relay/proxy)
Cics 515 – Summer 2012 © Dr. Son Vuong
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DHCP Scenario
DHCP Client
DHCP Server
...
...
Cics 515 – Summer 2012 © Dr. Son Vuong
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Layering Relationships between
ICMP, ARP, DHCP and IP, UDP



ICMP/IP
IP calls ARP/Link(Ethernet)
DHCP(BOOTP) / UDP(67/68) (for simple
configinfo)
DHCP(BOOTP) / TFTP/UDP(69) (to get config file)
Cics 515 – Summer 2012 © Dr. Son Vuong
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DNS: Domain Name System
Cics 515 – Summer 2012 © Dr. Son Vuong
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Chapter 2: Application layer








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2.1 Principles of network applications
2.2 Web and HTTP
2.3 FTP
2.4 Electronic Mail
 SMTP, POP3, IMAP
2.5 DNS
2.6 P2P file sharing
2.7 Socket programming with TCP
2.8 Socket programming with UDP
2.9 Building a Web server
Cics 515 – Summer 2012 © Dr. Son Vuong
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Domain Name System (DNS)
Overview

What do names do?
 identify
objects
 help locate objects
 define membership in a group
 specify a role
 convey knowledge of a secret

Name space
 defines
set of possible names
 consists of a set of name to value bindings
Cics 515 – Summer 2012 © Dr. Son Vuong
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Properties







Names versus addresses
Location transparent versus locationdependent
Flat versus hierarchical
Global versus local
Absolute versus relative
By architecture versus by convention
Unique versus ambiguous
Cics 515 – Summer 2012 © Dr. Son Vuong
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Examples

Hosts
cheltenham.cs.princeton.edu
192.12.69.17

80:23:A8:33:5B:9F
Files
/usr/llp/tmp/foo

192.12.69.17
(server, fileid)
Users
Larry Peterson
Cics 515 – Summer 2012 © Dr. Son Vuong
[email protected]
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Summary of “Naming” or identification



Domain name: a name that makes sense to a
human -- e.g. “cascade.cs.ubc.ca”
IP address: an identifier that makes sense to
hosts and routers -- e.g. “142.103.7.7”
Physical address: an identifier that makes sense
to the interface card -- e.g. “8:0:2b:e4:b1:2”
Cics 515 – Summer 2012 © Dr. Son Vuong
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DNS: Domain Name System
People: many identifiers:

SSN, name, passport #
Internet hosts, routers:
IP address (32 bit) used for addressing
datagrams
 “name”, e.g.,
www.yahoo.com - used
by humans

Q: map between IP
addresses and name ?
Cics 515 – Summer 2012 © Dr. Son Vuong
Domain Name System:

distributed database
implemented in hierarchy of
many name servers

application-layer protocol
host, routers, name servers
to communicate to resolve
names (address/name
translation)


note: core Internet function,
implemented as applicationlayer protocol
complexity at network’s
“edge”
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DNS: Domain Name System
DNS services

Hostname to IP address
translation

Host aliasing



Canonical and alias
names
Mail server aliasing
Load distribution

Why not centralize DNS?

single point of failure

traffic volume

distant centralized database

Maintenance

doesn’t scale!
Replicated Web servers:
set of IP addresses for
one canonical name
Cics 515 – Summer 2012 © Dr. Son Vuong
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Examples (cont)

Mailboxes
User
2
vuong @ cs.ubc.ca
cs.ubc.ca
Name
server
1
Mail
program
142.103.7.51
142.103.7.51
4
3
TCP
142.103.7.51
5
IP

Services
nearby ps printer with short queue and 2MB
Cics 515 – Summer 2012 © Dr. Son Vuong
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Domain Naming System

Hierarchy
edu
princeton … mit
cs
com
gov
cisco… yahoo nasa …nsf
mil
org
arpa …navy
acm …ieee
net
uk
fr
ee physics
ux01 ux04

Name
chinstrap.cs.princeton.edu
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Distributed, Hierarchical Database
Root DNS Servers
com DNS servers
yahoo.com amazon.com
DNS servers DNS servers
org DNS servers
pbs.org
DNS servers
edu DNS servers
poly.edu
DNS servers
umass.edu
DNS servers
Client wants IP for www.amazon.com; 1st approx:

Client queries a root server to find com DNS server

Client queries com DNS server to get amazon.com DNS
server

Client queries amazon.com DNS server to get IP address
for www.amazon.com
Cics 515 – Summer 2012 © Dr. Son Vuong
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Name Servers
Partition hierarchy into zones
Root name servers
Top Level Domain
(TLD) Servers

edu
princeton … mit
cs
ee
com
gov
cisco … yahoo nasa … nsf
mil
org
arpa … navy
acm … ieee
uk
fr
physics
ux01 ux04

net
Root
Each zone corresponds to an
admin authority (implemented by
two or more name servers for
redundancy)
Authoritative Servers
CS
name server
UBC
…
name server
name server
…
Cisco
name server
ECE
name server
Local Name Servers (LNS)
Cics 515 – Summer 2012 © Dr. Son Vuong
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DNS: Root name servers


contacted by local name server that can not resolve name
root name server:
contacts authoritative name server if name mapping not known
 gets mapping
 returns mapping to local name server

a Verisign, Dulles, VA
c Cogent, Herndon, VA (also Los Angeles)
d U Maryland College Park, MD
k RIPE London (also Amsterdam, Frankfurt)
g US DoD Vienna, VA
h ARL Aberdeen, MD
i Autonomica, Stockholm (plus 3 other locations)
j Verisign, ( 11 locations)
e NASA Mt View, CA
f Internet Software C. Palo Alto, CA
m WIDE Tokyo
(and 17 other locations)
b USC-ISI Marina del Rey, CA
l ICANN Los Angeles, CA
Cics 515 – Summer 2012 © Dr. Son Vuong
13 root name
servers worldwide
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TLD and Authoritative Servers

Top-level domain (TLD) servers: responsible for com,
org, net, edu, etc, and all top-level country domains uk,
fr, ca, jp.

Verisign controls .com and .net TLDs



Many companies act as intermediaries
Educause for edu TLD
Authoritative DNS servers: organization’s DNS servers,
providing authoritative hostname to IP mappings for
organization’s servers (e.g., Web and mail).

Can be maintained by organization or service provider
Cics 515 – Summer 2012 © Dr. Son Vuong
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Local Name Server


Does not strictly belong to hierarchy
Each ISP (residential ISP, company,
university) has one.
 Also

called “default name server”
When a host makes a DNS query, query is
sent to its local DNS server
 Acts
as a proxy, forwards query into
hierarchy.
Cics 515 – Summer 2012 © Dr. Son Vuong
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root DNS
server
Example: Iterative queries

2
Host at cis.poly.edu wants IP
address for gaia.cs.umass.edu
3
TLD DNS
server
4
5
iterative query:
contacted server
replies with name of
server to contact
“I don’t know this
name, but ask this
server”
local DNS server
dns.poly.edu
1
8
requesting host
cis.poly.edu
7
6
authoritative DNS server
dns.cs.umass.edu
gaia.cs.umass.edu
Cics 515 – Summer 2012 © Dr. Son Vuong
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Recursive queries
root DNS
server
recursive query:
2

puts burden of name
7
resolution on
contacted name
server
local DNS server

heavy load?
dns.poly.edu
1
3
6
TLD DNS
server
5
4
8
requesting host
cis.poly.edu
authoritative DNS server
dns.cs.umass.edu
gaia.cs.umass.edu
Cics 515 – Summer 2012 © Dr. Son Vuong
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DNS: caching and updating records

once (any) name server learns mapping, it caches
mapping
 cache
entries timeout (disappear) after some time
 TLD servers typically cached in local name servers
 Thus

root name servers not often visited
update/notify mechanisms under design by IETF

RFC 2136

http://www.ietf.org/html.charters/dnsind-charter.html
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DNS records
DNS: distributed db storing resource records (RR)
RR format: (name, value, type, ttl)

Type = A

name is hostname
 value is IP address


Type = CNAME

Type = NS
name is domain (e.g.
foo.com)
 value is IP address of
authoritative name
server for this domain
servereast.backup2.ibm.com

Cics 515 – Summer 2012 © Dr. Son Vuong
name is alias name for some
“cannonical” (the real) name
www.ibm.com is really


value is cannonical name
Type = MX

value is name of
mailserver associated with
name
49
Example: Root Server
(princeton.edu, cit.princeton.edu, NS, IN)
[in the Princeton domain]
(cit.princeton.edu, 128.196.128.233, A, IN)
(cisco.com, thumper.cisco.com, NS, IN)
[in the Cisco domain]
(thumper.cisco.com, 128.96.32.20, A, IN)
…
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Further example: Princeton Server
[within Princeton domain]
(cs.princeton.edu, optima.cs.princeton.edu, NS, IN)
[name server]
(optima.cs.princeton.edu, 192.12.69.5, A, IN)
(ee.princeton.edu, helios.ee.princeton.edu, NS, IN)
[another name server]
(helios.ee.princeton.edu, 128.196.28.166, A, IN)
(jupiter.physics.princeton.edu, 128.196.4.1, A, IN)
(saturn.physics.princeton.edu, 128.196.4.2, A, IN)
(mars.physics.princeton.edu, 128.196.4.3, A, IN)
(venus.physics.princeton.edu, 128.196.4.4, A, IN)
Cics 515 – Summer 2012 © Dr. Son Vuong
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Further example: CS Server
[within the CS domain in the
Princeton domain]
(cs.princeton.edu, optima.cs.princeton.edu, MX, IN)
[mail server]
(cheltenham.cs.princeton.edu, 192.12.69.60, A, IN)
(che.cs.princeton.edu, cheltenham.cs.princeton.edu,
CNAME, IN)
[alias/actual]
(optima.cs.princeton.edu, 192.12.69.5, A, IN)
(opt.cs.princeton.edu, optima.cs.princeton.edu,
CNAME, IN)
[another alias]
(baskerville.cs.princeton.edu, 192.12.69.35, A, IN)
(bas.cs.princeton.edu, baskerville.cs.princeton.edu,
CNAME, IN)
Cics 515 – Summer 2012 © Dr. Son Vuong
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DNS protocol, messages
DNS protocol : query and reply messages, both with
same message format
msg header


identification: 16-bit id for
query, reply to query uses
same id
flags:
query or reply
 recursion desired
 recursion available
 reply is authoritative

Cics 515 – Summer 2012 © Dr. Son Vuong
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DNS protocol, messages
Name, type fields
for a query
RRs in reponse
to query
records for
authoritative servers
additional “helpful”
info that may be used
Cics 515 – Summer 2012 © Dr. Son Vuong
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Inserting records into DNS


Example: just created startup “Network Utopia”
Register name networkuptopia.com at a registrar (e.g.,
Network Solutions)
Need to provide registrar with names and IP addresses of
your authoritative name server (primary and secondary)
 Registrar inserts two RRs into the com TLD server:

(networkutopia.com, dns1.networkutopia.com, NS)
(dns1.networkutopia.com, 212.212.212.1, A)


Put in authoritative server Type A record for
www.networkuptopia.com and Type NS record for
networkutopia.com
How do people get the IP address of your Web site?
Cics 515 – Summer 2012 © Dr. Son Vuong
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Dig www.telus.ca
;; QUESTION SECTION:
;www.telus.ca.
IN
A
;; ANSWER SECTION:
www.telus.ca.
86400 IN
CNAME www.telus.com.
www.telus.com.
600
IN
A
205.206.163.16
;; AUTHORITY SECTION:
telus.com.
600
IN
NS
dns1.cidc.telus.com.
telus.com.
600
IN
NS
dns2.cidc.telus.com.
;; ADDITIONAL SECTION:
dns1.cidc.telus.com. 59695 IN
A
216.123.224.131
dns2.cidc.telus.com. 59695 IN
A
66.203.199.203

DNS DDoS, Poisoning and Hijacking
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Layering Relationships between
ICMP, ARP, DHCP, DNS and IP, UDP




ICMP/IP, ICMPv6/IPv6
IP calls ARP/Link(Ethernet)
DHCP(BOOTP) / UDP(68) (for simple configinfo)
DHCP(BOOTP) / TFTP/UDP(69) (to get config file)
DNS / UDP(53)
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What have we covered?



IPv4, IPv6
Internet Control Message Protocol (ICMP)
Address resolution (ARP) and getting
(dynamic) addresses (DHCP)
What’s next ?

Routing protocols (RIP, OSPF, BGP)
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IPv6


Initial motivation: 32-bit address space soon to
be completely allocated.
Additional motivation:
 header
format helps speed processing/forwarding
 header changes to facilitate QoS
IPv6 datagram format:
 fixed-length 40 byte header
 no fragmentation specified in basic header
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IPv6 Header (Cont)
Priority: identify priority among datagrams in flow
Flow Label: identify datagrams in same “flow.”
(concept of“flow” not well defined).
Next header: identify upper layer protocol for data
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Other Changes from IPv4



Checksum: removed entirely to reduce
processing time at each hop
Options: allowed, but outside of header,
indicated by “Next Header” field
ICMPv6: new version of ICMP
 additional
message types, e.g. “Packet Too Big”
 multicast group management functions
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Transition From IPv4 To IPv6

Not all routers can be upgraded simultaneous
 no
“flag days”
 How will the network operate with mixed IPv4 and
IPv6 routers?

Tunneling: IPv6 carried as payload in IPv4
datagram among IPv4 routers
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Dual
IPv6/IPv4
Router
Tunneling
Logical view:
Physical view:
Dual
IPv6/IPv4
Router
A
B
IPv6
IPv6
A
B
C
IPv6
IPv6
IPv4
Flow: X
Src: A
Dest: F
data
A-to-B:
IPv6
Cics 515 – Summer 2012 © Dr. Son Vuong
E
F
IPv6
IPv6
D
E
F
IPv4
IPv6
IPv6
tunnel
Src:B
Dest: E
Src:B
Dest: E
Flow: X
Src: A
Dest: F
Flow: X
Src: A
Dest: F
data
data
B-to-C:
IPv6 inside
IPv4
B-to-C:
IPv6 inside
IPv4
Flow: X
Src: A
Dest: F
data
E-to-F:
IPv6
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Ch 4: Network Layer and Routing

The IP Protocol



Routing







IP Format, Addressing, fragmentation,
Internet Control Protocols (ICMP)
RIP (Routing Information Protocol)
OSPF (Open Shortest Path First)
The Interior Gateway Routing Protocol
BGP – The Exterior Gateway Routing Protocol
IPv6
Internet Multicasting
Mobile IP
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What have we covered?




IPv4, IPv6
Internet Control Message Protocol (ICMP)
Address resolution (ARP) and getting
(dynamic) addresses (DHCP)
DNS
What’s next ?

Routing protocols (RIP, OSPF, BGP)
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