2. 2
Internet Control Message Protocol
• The IP (Internet Protocol) relies on several
other protocols to perform necessary control
and routing functions:
• Control functions (ICMP)
• Multicast signaling (IGMP)
• Setting up routing tables (RIP, OSPF, BGP,
PIM, …)
3. 3
• The Internet Control Message
Protocol (ICMP) is ahelper protocol
that supports IP with facility for
– Error reporting
– Simple queries
– ICMP messages are encapsulated as IP
datagrams:
4. 4
Message Format
• 4 byte header:
– Type (1 byte): type of ICMP message
– Code (1 byte): subtype of ICMP message
– Checksum (2 bytes): similar to IP header checksum.
• Checksum is calculated over entire ICMP message
• If there is no additional data, there are 4 bytes set to zero.
• Each ICMP messages is at least 8 bytes long
5. CA528 - Advanced Data
Communications
5
ICMP Query Message
ICMP query:
• ICMP Request sent by host to a router
or host
• ICMP Reply sent back to querying host
6. ICMP Error Message
• ICMP error messages report error
conditions
• Typically sent when a datagram is
discarded
8. 8
Internet Group Management Protocol
• End system to router protocol is IGMP
• The internet group management
protocol(IGMP) is one of the necessary but
not sufficient protocol that is involved in
multicasting.
OBJECTIVE:
• Objective is to keep router up-to-date with
group membership of entire LAN
• Routers need not know who all the members
are, only that members exist
9. 9
How IGMP Works
• On each link, one router is elected the “querier”
• Querier periodically sends a Membership Query message to the all-
systems group
• On receipt, hosts start random timers (between 0 and 10 seconds) for
each multicast group to which they belong
QRouters:
Hosts:
10. How IGMP Works (cont.)
• When a host’s timer for group G expires, it sends a Membership Report to
group G.
• Other members of G hear the report and stop their timers
• Routers hear all reports, and time out non-responding groups
Q
G G G G
Routers:
Hosts:
11. Internet Group Management Protocol
(IGMP)
Each host
responds to the
query with a
random delay. If
one report is
received at the
router, the other
reports will be
suppressed
12. First Question
• How does your computer know which IP
to use?
• How does your computer know that
www.iimcal.ac.in is at IP 202.54.116.3?
• How can you track your network’s health?
13. The Internet and Addressing
• All machines on the Internet are accessed via
their IP address
– Dotted quad: xxx.xxx.xxx.xxx
• Problem: IP addresses are hard to remember
and hard to statically assign on large networks
• Solution: Need to come up with a way to
automatically assign IP addresses and a text
based representation of machine addresses
instead of just 4 numbers
14. Two protocols have been developed to solve these
problems
DHCP – automatic network configuration (including
IP address)
DNS – translates textual based names into IP
addresses and vice versa
15. DHCP(dynamic
Configuration protocol):
• Allows client machines to receive an IP
address, DNS information, etc.
automatically
• Before DHCP came into use, users had
to type in all this information by hand,
which is bad:
– Easy to mistype something when entering by hand
– Manually changing network configuration every time
you move your laptop is a pain
– Bootp resolved some of these issues
16. DHCP:
• Efficient way of assigning computers IP
addresses and delivering configuration
information to those computers
• Does not solve other problem of addressing –
that IP addresses are hard to remember
17. Dynamic IP addresses:
Dynamic assignment of IP addresses is
desirable for several reasons:
• IP addresses are assigned on-demand
• Avoid manual IP configuration
• Support mobility of laptops
18. Static IP Address :
• Static addresses are created
manually.
• A DHCP server has a database that
statically binds physical addresses
to IP addresses.
