The network layer Addressing and routing

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The network layer
Addressing and routing
1. Mobility and addressing
1. What is the DHCP protocol used for?
Assign IP addresses and network conguration of automatic way.
2. What are the advantages of DHCP in comparison with a manual configuration?
Disadvantages of manual conguration:
(A) it is possible to assign an IP address has two different stations,
(B) to err in the conguration (subnet mask, network, default gateway)
(C) generates a high administrative burden in case of "nomadic" users.
Benefits of DHCP server provides all the information conguration TCP / IP with the
customer. The user no longer needs to visit his administrator for information on its
conguration
3. What is the difference between DHCP and the BOOTP or RARP protocols?
DHCP is based on BOOTP and maintains some backward compatibility. The main
difference is that BOOTP was designed for manual pre-conguration of the host
information in a server database, while DHCP allows for dynamic allocation of network
addresses and congurations to newly attached hosts. Additionally, DHCP allows for
recovery and reallocation of network addresses through a leasing mechanism. RARP is a
protocol used by Sun and other vendors that allows a computer to find out its own IP
number, which is one of the protocol parameters typically passed to the client system by
DHCP or BOOTP. RARP doesn’t support other parameters and using it, a server can only
serve a single LAN. DHCP and BOOTP are designed so they can be routed.
4. What is the Client ID used for?
What is termed the Client ID for the purposes of the DHCP protocol is whatever is
used by the protocol to identify the client computer. By default, DHCP implementations
typically employ the client’s MAC address for this purpose, but the DHCP protocol
allows other options. Some DHCP implementations have a setup option to specify the
client ID you want. One alternative to the MAC address is simply a character string of
your choice. In any case, in order for DHCP to function, you must be certain that no other
client is using the client ID you choose, and you must be sure the DHCP server will accept
it.
5. What are the four phases necessary so that a customer DHCP obtains a configuration of a
DHCP server?
(A) Dissemination of IP lease request
(B) Dissemination of a proposed lease IP server in response to the request
(C) The customer selects a lease that suits him (Sending a message to request a rental
lease)
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(D) The server responds originally meant the proposal and other DHCP servers withdraw
their proposal
6. Can a DHCP server be used as backup for another DHCP server?
You can have two or more servers handing out leases for different addresses. If each has a
dynamic pool accessible to the same clients, then even if one server is down, one of those
clients can lease an address from the other server. However, without communication
between the two servers to share their information on current leases, when one server is
down, any client with a lease from it will not be able to renew their lease with the other
server. Such communication is the purpose of the "server to server protocol" (see next
question). It is possible that some server vendors have addressed this issue with their own
proprietary server-to-server communication.
7. Does that have a direction to think that a computer which was already seen allocating an
address by DHCP in request another temporarily to this same server?
There is nothing in the protocol to keep a client that already has a leased or permanent IP
number from getting a(nother) lease on a temporary basis on another subnet (i.e., for that
laptop which is almost always in one oce, but occasionally is plugged in in a conference
room or class room). Thus it is left to the server implementation to support such a feature.
I’ve heard that Microsoft’s NT-based server can do it.
8. How to choose the lease length of an address? Define the standard which appear
important to you.
I’ve asked sites about this and have heard answers ranging from 15 minutes to a year.
Most administrators will say it depends upon your goals, your site’s usage patterns, and
service arrangements for your DHCP server. A very relevant factor is that the client starts
trying to renew the lease when it is halfway through : thus, for example, with a 4 day lease,
the client which has lost access to its DHCP server has 2 days from when it rst tries to
renew the lease until the lease expires and the client must stop using the network. During a
2-day outage, new users cannot get new leases, but no lease will expire for any computer
turned on at the time that the outage commences. Another factor is that the longer the
lease the longer time it takes for client conguration changes controlled by DHCP to
propogate. Some relevant questions in deciding on a lease time : Do you have more users
than addresses ? If so, you want to keep the lease time short so people don’t end up sitting
on leases. Naturally, there are degrees. In this situation, I’ve heard examples cited of 15
minutes, 2 hours, and 2 days. Naturally, if you know you will have 20 users using 10
addresses in within a day, a 2 day lease is not practical. Are you supporting mobile users ?
If so, you may be in the situation of having more users than addresses on some particular
IP number range. See above. Do you have a typical or minimum amount of time that you
are trying to support ? If your typical user is on for an hour at minimum, that suggest a
hour lease at minimum. How many clients do you have and how fast are the
communications lines over which the DHCP packets will be run ? The shorter the lease,
the higher the server and network load. In general, a lease of at least 2 hours is long
enough that the load of even thousands of clients is negligible. For shorter leases, there
may be a point beyond which you will want to watch the load. Note that if you have a
communication line down for a long enough time for the leases to expire, you might see
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an unusually high load it returns. If the lease-time is at least double the communication
line outage, this is avoided.
How long would it take to bring back up the DHCP server, and to what extent can your
users live without it ? If the lease time is at least double the server outage, then running
clients who already have leases will not lose them. If you have a good idea of your longest
likely server outage, you can avoid such problems. For example, if your server-coverage
is likely to recover the server within three hours at any time that clients are using their
addresses, then a six hour lease will handle such an outage. If you might have a server go
down on Friday right after work and may need all Monday’s work-day to x it, then your
maximum outage time is 3 days and a 6-day lease will handle it. Do you have users who
want to tell other users about their IP number ? If your users are setting up their own web
servers and telling people how to get to them either by telling people the IP number or
through a permanent DNS entry, then they are looking for an IP number that won’t be
changing. While some sites would manually allocate any address that people expected to
remain stable, other sites want to use DHCP’s ability to automate distribution of relatively
permanent addresses. The relevant time is the maximum amount of time that you wish to
allow the user to keep their machine turned o yet keep their address. For example, in a
university, if students might have their computers turned o for as long as three weeks
between semesters, and you wish them to keep their IP address, then a lease of six weeks
or longer would suffice.
Some examples of lease-times that sites have used and their rationals : 15 minutes : To
keep the maximum number of addresses free for distribution in cases where there will be
more users than addresses. 6 hours : Long enough to allow the DHCP server to be xed, e.g.
3 hours. 12 hours : If you need to take back an address, then you know that it will only take
one night for the users’ lease to expire. 3 days : This is apparently Microsoft’s default,
thus many sites use it. 6 days :Long enough that a weekend server outage that gets xed on
Monday will not result in leases terminating. 4 months : Long enough that students can
keep their IP address over the summer hiatus. I believe this rational is workable if the
summer hiatus is no more than 2 months. One year : If a user has not used their address in
six months, then they are likely to be gone. Allows administrator to recover those
addresses after someone has moved on.
9. Can the server control if the allocated addresses are always used by the clients?
There is no ideal answer : you have to give something up or do some extra work. You
can put all your clients on a subnet of your own along with your own DHCP server. You
can use manual allocation. Perhaps you can nd DHCP server software that allows you to
list which MAC addresses the server will accept. DHCP servers that support roaming
machines may be adapted to such use. You can use the user class option assuming your
clients and server support it : it will require you to congure each of your clients with a user
class name. You still depend upon the other clients to respect your wishes.
10. Can a DHCP server prohibit machines not to allocate itself an IP address that it manages?
This would have to be done using a mechanism other than DHCP. DHCP does not prevent
other clients from using the addresses it is set to hand out nor can it distinguish between a
computer’s permanent MAC address and one set by the computer’s user. DHCP can
impose no restrictions on what IP address can use a particular port nor control the IP
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address used by any client.
11. Explain what would be the problem if an intruder on a network has taken a place
mischievously in a DHCP server?
A malicious user could make trouble by putting up an unocial DHCP server. The
immediate problem would be a server passing out numbers already belonging to some
computer yielding the potential for two or more "innocent bystander" nodes ending up
with the same IP number. Net result is problems using the nodes, possibly intermittent of
one or the other is sometimes turned o. A lot of problems are possible if a renegade server
manages to get a client to accept its lease oering, and feeds the client its own version of
other booting parameters. One scenario is a client that loads its OS over the network via
tftp being directed to a different le (possibly on a different server), thus allowing the
perpetrator to take over the client. Given that boot parameters are often made to control
many different things about the computers’ operation and communication, many other
scenarios are just as serious. Note that BOOTP has the same vulnerabilities. The
"broadcast ag" : DHCP includes a way in which client implementations unable to receive
a packet with a specic IP address can ask the server or relay agent to use the broadcast IP
address in the replies (a "ag" set by the client in the requests). The denition of DHCP states
that implementations "should" honor this ag, but it doesn’t say they "must". Some
Microsoft TCP/IP implementations used this ag, which meant in practical terms, relay
agents and servers had to implement it. A number of BOOTP-relay-agent
implementations (e.g. in routers) handled DHCP just ne except for the need for this
feature, thus they announced new versions stated to handle DHCP. Some of the virtual
LAN schemes, i.e., those that use the packet’s IP number to decide which "virtual LAN" a
client-computer is on for the purposes of TCP/IP, don’t work when using DHCP to
dynamically assign addresses. DHCP servers and relay agents use their knowledge of
what LAN the client-station is on to select the subnet number for the client-station’s new
IP address whereas such switches use the subnet number sent by the client-station to
decide which (virtual) LAN to put the station on. Routers are sometimes congured so that
one LAN on one port has multiple network (or subnet) numbers. When the router is
relaying requests from such a LAN to the DHCP server, it must pass along as IP number
that is associated with one of the network (or subnet) numbers. The only way the DHCP
server can allocate addresses on one of the LAN’s other network (or subnet) numbers is if
the DHCP server is specically written to have a feature to handle such cases, and it has a
conguration describing the situation.
The knowledge that a particular IP number is associated with a particular node is often
used for various functions. Examples are : for security purposes, for network
management, and even for identifying resources. Furthermore, if the DNS’s names are
going to identify IP numbers, the numbers, the IP numbers have to be stable. Dynamic
conguration of the IP numbers undercuts such methods. For this reason, some sites try to
keep the continued use of dynamically allocatable IP numbers to a minimum. With two or
more servers serving a LAN, clients that are moved around (e.g. mobile clients) can end
up with redundant leases. Consider a home site with two DHCP servers, a remote site with
DHCP services, and a mobile client. The client rst connects to the home site and receives
an address from one of the two serves. He/she then travels to the remote site (without
releasing the lease at the home site) and attempts to use the acquired address. It is of
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course NAK’ed and the client receives an address appropriate for the remote site. The
client then returns home and tries to use the address from the remote site. It is NAK’ed but
now the client broadcasts a DHCPDISCOVER to get a address.
The server that holds the previous lease will oer the address back to the client but there is
no guarantee that the client will accept that address ; consequently, it is possible for the
client to acquire an address on the other server and therefore have two leases within the
site. The problem can be solved by using only one server per subnet/site and can be
mitigated by short lease lengths. But in a very mobile environment, it is possible for these
transient clients to consume more than their fair share of addresses. If departments, oces,
or individuals run DHCP servers with their own small address pools on LANs shared by
other departments, oces, or individuals, they can nd that their addresses are being used by
anyone on the LAN that happens to set their IP conguration to use DHCP. An easy
mistake to make in setting up a DHCP server is to fail to set all the necessary global
parameters. This can result in some functions working while others are not, or functions
working when the client is set up manually, but failing to work when set to use DHCP.
Long leases can be disadvantageous in cases where you need to change a conguration
parameter or withdraw an address from use. The length of the lease can mean the dierence
between having to go to every aected client and rebooting it, or merely waiting a certain
amount of time for the leases to be renewed. (Note : one workaround is to fool with the
client computer’s clock).
12. A DHCP relay must in theory always use the same server of destination for the
BOOTPREQUEST messages that it receives of a client given. Nevertheless an
implementation of relay agent which was developed proposes to use a mechanism of
Round-Robin for determine towards which DHCP server to send the request. Comment
on the advantages and disadvantages of this solution.
Advantage: allows load balancing among multiple DHCP servers.
Disadvantages: Each time it receives a new BOOTREQUEST message,it relays the
message to the next BOOTP server in a list of servers. Thus, with this relay agent,
multiple consecutive BOOTREQUEST messages from a given client will be delivered
todifferent servers. Unfortunately, this well-intentioned scheme reacts badly with DHCP
[3] and perhaps other variations of the BOOTP protocol which depend on multiple
exchanges of BOOTREQUEST and BOOTREPLY messages between clients and servers.
Therefore, al BOOTREQUEST messages from a given client MUST be relay d to the
same destination (or set of destinations). One way to meet this requirement while
providing some load-balancing benet is to hash the client’s link-layer address (or some
other reliable client-identifying information) and use the resulting hash value to select the
appropriate relay destination (or set of destinations). The simplest solution, of course, is to
not use a load-balancing scheme and just relay ALL received BOOTREQUEST messages
to the same destination (or set of destinations). When transmitting the request to its next
destination, the relay agent may set the IP Time-To-Live eld to either the default value for
new datagrams originated by the relay agent, or to the TTL of the original
BOOTREQUEST decremented by (at least) one.
13. It is supposed that 2 IP sub-network share physically the same LAN. The stations on each
sub-network then will see circulating all the packets diffused on the physic network.
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a) Which problem can occur if two DHCP servers coexist on this shared LAN?
Suppose that two sub-IP networks share physically in a same physical support (2 VLANs
coexist on the same Ethernet). The stations on each subnet will then see all the packets
travel over the network physical dius. A computer can be assigned an address of a subnet
but does not know a priori which one. There may be conflicts during? Access to local
resources, such as name servers, NIS server?
b) Can one solve the problem? Propose a solution.
We can define the level of the server (or client for some implementations) the MAC
address associated with each IP address and thus define what address will be attributed to
a particular machine.
14. Why does one define the number of associations (MAC address – IP address) in the of
configuration files of DHCP server?
Because this limits the number of machines that can transit on the network.
15. By basing you on the extract of RFC 1542 whose extracts are given to you in appendix,
explain how a DHCP server managing several ranges of addresses will know to choose
the IP address in answer to a request.
Problem
A network administrator must reconsider the network plan of his company. He must conceive
the new network plan detail who will have to allow the automatic attribution of TCP/IP
configurations. The IP address of the network is 194.12.230.0, but the structure of the network
must reflect the organization in 3 distinct departments: Direction and Administrative
Departments, Engineer and R&D, Marketing and Commercial Service. These 3 domains are
connected to a router who is used as link towards the Internet. The IP address of this router is
fixed and does not belong with any the precedents domain. These three departments have
currently and respectively of 15, 45 and 12 workstations but the number of workstations is
brought to increase in the future. Each sub-network will have to allocate the configurations with
assistance of distinct DHCP servers. In order to make functionary the network in the same
breakdown case of one of DHCP servers, the other server must be able to take the relay. They
must if possible ensure that at least 25 % of the machines will be able to obtain a valid
configuration in their sub-network.
The configurations will have to be static in the case of some machines (server, router…) and
dynamic for the others. The DHCP servers will have to always obtain highest IP address available
in each sub-network, while the links will have the lowest IP address.
MAC address list of hosts which a fixed address must be allocate:
- Administrative DNS Server: 00-32-DE-5A-78-9C
- Administrative network link: 1F-7A-90-02-F0-F0
- Administrative network link towards the external router: 1F-7A-90-02-5F-4G
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- Engineers network link: 2B-14-62-91-C9-B1
- Engineers network link towards the external router: 2B-14-62-3F-39-21
- Commercial network link: 1C-96-AA-F4-C2-91
- Commercial network link towards the external router: 1C-96-AA-14-62-3F
- Router towards the Internet: 82-F0-06-01-9B-7A
In the Administrative department, 5 workstations will have their fixed address.
An address range of Commercial domain is allocated for the outside connections or the clients
visiting in the company. This reserved addresses range cover the going addresses from
194.12.230.130 to 194.12.230.140.
1. Propose a mask of sub-network for the network of company.
194.12.230.0 is a Class C address, the last byte must be used to encode the numbers of
sub-network and the numbers of hosts in each subnet. It is necessary to use two bits for
three sub-networks the subnet mask is complete: 255.255.255.192.
2. Calculate the total number of host which can contain each sub-network.
62 hosts per subnet
3. Affect a number of sub-networks to each department. Define the address ranges usable in
each sub-network.
- 194.12.230.0/255.255.255.192 Administrative sub network address range: 194.12.230.1
(00 000001) has 194.12.230.62 (00 111110)
- Engineers in 194.12.230.64/255.255.255.192 network address range: 194.12.230.65 (01
000001) has 194.12.230.126 (01 111110)
- Commercial network in 194.12.230.128/255.255.255.192 address range:
194.12.230.129 (10 000001) has 194.12.230.190 (01 111 110)
- 194.12.230.192/255.255.255.192 in interconnection network address range:
194.12.230.193 (10 000001) has 194.12.230.254 (01 111110)
4. Trace a network diagram of the company by making appear the host of the network and
their IP address.
5. Define how will be assured the attribution of the IP configurations following a breakdown
on one of DHCP servers. Argument in particular over the duration of beams. Note the
possible contradictions with respect to the specification document.
In case of failure of a DHCP server, hosts must be able to apply a configuration from
another DHCP server on a different subnet, the applications in broadcasting sent by these
hosts must be able to pass the routers. Also, the routers R1 and R2 must be able to route
datagrams DHCP (BOOTP) or DHCP relay agent running in each subnet. Each DHCP
server is assigned a second extended address in another subnet which it provides a kind of
replacement in case of failure. These tracts "security" must not conflict (have identical
addresses) with ranges of addresses from the DHCP server "owner" in the subnet as a risk
to award a duplicate address exists. Here is a proposal for award of these tracts of security:
The Department of Administrative DHCP server provides redundancy for the Department
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of Commercial. The DHCP server provides redundancy department Engineers for the
Administrative Department. of. The DHCP server provides redundancy department
Commercial department for Engineers. from .107 to .125 (or 18 places or 50% of the total
stations). In such a configuration (very limited number of addresses) the length of the
leases will be rather long way to limit the number of guests may request a new
configuration at a given time. The duration can be fixed at 24 hours so as to leave time to
reopen the DHCP server.
Unlike the length of the lease tracts of relief will be rather short to minimize the use of
backup servers.
6. Define the configuration of servers DHCP for each sub-network:
- Extent (beginning and ending addresses, mask)
- Lease duration
- DHCP options (link by defect, server DNS address)
- Addresses to be excluded (+comment)
- Reservations to be envisaged (MAC address/ IP address)
- Rescue extent of the sub-networks of the department Y
- Beginning and ending addresses
- Mask
- Lease duration
- …
2. IP Mobility
2.1 IP Mobile
1. Let a network be constituted of IP mobile terminals which can move in cells. A customer
is registered in the cell where it took its subscription.
a) Why its IP address is not sufficient so that the network finds it when it moves?
Its IP address is not sufficient because it indicates a sub-network in which the
client connects. If it moves, its IP address can no longer locate it.
b) If one gives a new IP address to a user who is not in the cell where it is registered,
how can one establish the link between its basic address and its new address?
It is called a local agent or home agent, to make the correlation between the local
address and the new client's IP address (called address visitor or
care-of-address). When a message arrives in the local subnet, the local agent,
modifies the destination address indicating the destination address field the
address of the care-of-address.
c) If the user emits a packet, it must use its basic address or the address that the
network affected to it?
When a client emits a packet must indicate its local address because it changes a
new network of visitor, it will not forward the message.
d) In which case could it be interesting to give a user who wishes to join our customer
his temporary address, decreed by the cell in which it is?
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Rather than always going through the local agent, it may be interesting to give
visitors al'emetteur address of the recipient. This solution is acceptable if the
recipient is not moving and there is enough time in the network access.
2. IP Mobile was conceived to function with the non-mobile nodes or the applications of the
transparent manner. However improvements can be brought to the protocol when the
corresponding nodes are informed of the node mobility. If a correspondent is able to make
the decapsulation IP- in - IP, it could communicate in manner more efficacies with the
mobile node and this despite the presence to firewall. Why?
3. A mobile node has as principal address 192.68.37.13 and moves in a reception network
where the address of its "care of address" will be 145.48.46.123. The "foreign agent "
address is 145.48.46.79 and that of its mother agent is 192.68.37.2
a) How the mobile node will detect that it is not any more in its mother network?
By receiving prompts foreign agent or no longer receiving messages from his
agent mother.
b) Describe summarily the exchange of frames allowing this detection: The message
exchange allowing the mobile node to detect that it is in a reception network is
made between ____________________ _____________________ The message
allowing the detection are put in packets __________ (IP/ICMP/UDP)
The exchange of messages to the mobile node to detect that it is in a home network
is between the foreign agent and mobile node. The message can be placed in the
detection of UDP packets.
c) Give the format of the exchanged frames in specifying the @ MAC source and
destination (ex: @MAC NM (node mobile) and) and the @ IP source and
destination of these messages which allow a mobile node to detect that it is not
any more in its mother network:
First message
MAC Source Address: _______________ Destination _______________
IP Source Address: ________________ Destination _______________
Second message
MAC Source Address: _______________ Destination _______________
IP Source Address: ________________ Destination _______________
4. Care-of-address
a) How could the mobile node be its own Care - of - Address?
He received an address of thanks to the DHCP server network Home, but the
foreign agent is always present to send messages of Warning.
b) What are the advantages and disadvantages of this solution?
Benefits: routing via the FA, NM dialogue directly via its HA.
Disadvantages: if there are many mobile node requires that the DHCP server has
an IP address range considerably, which is not always possible. That is why in the
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case of management of mobility with IPv4, it uses the IP address of the FA.
c) In your opinion, must there thus be necessarily a server DHCP by network and
must there have an IP address in the same class which constitutes its range of
addresses?
Not necessarily. They have slightly observes their environment.
d) How can the negotiation be done?
The applications should reach the DHCP server that is located on another network,
they must pass the routers, which is theoretically not possible. It is then necessary
to install one or more routers on a relay agent that will intercept requests for the
broadcast and transmit a DHCP server known to the agent. This relay agent
located on the bridge will be the intermediary and the client still managed to obtain
an address given by DHCP on a different network, but relayed by the relay agent.
2.2 IP version 6 and the mobility management
1. What is the difference between the "traffic class" and "flow label" fields in the IPv6
header?
RFC 2460
Label Flow 20 bits in the IPv6 header may be used by a source naming sequences of
packets for which special treatment by IPv6 routers request. This special treatment could
be a different quality of service the default service or service "real time". This aspect of
IPv6 is still experimental. The hosts or routers that do not support the functions of field
Label Flow xer have the required field to zero when they are originally meant the package,
to pass the field as it stood when they transmit a packet and to ignore the field when they
receive a packet.
Classes trac Trac The Class field of 8 bits in the IPv6 header was created to be used by
bare roots and / or routers and transmitters for identication distinguish different classes or
priorities of IPv6 packets. The Class field Trac offers functionality similar to that of the
ToS can be supported by IPv6. It is hoped that these experiments will eventually arrive at
an agreement on the kinds of conventional traffic that are most useful for IPv6 packets.
The following general requirements apply to the Traffic Class field:
The service interface of an IPv6 service node must provide a means to an upper layer
protocol Plasser bit value Traffic Class for packets from the upper layer protocol. The
default value should be zero for all 8 bits.
The service interface of an IPv6 service node must provide a means to an upper layer
protocol Plasser bit value Traffic Class for packets from the upper layer protocol. The
default value should be zero for all 8 bits.
The nodes that support use specic (possibly experimental or standard) of all or part of the
Traffic Class bits are permitted to change the value of these bits in the packets they create,
transmit or receive, as required by this use specic. The nodes should ignore and leave
unchanged any bits of the Traffic Class field for which they do not support use specic.
An upper layer protocol must not assume that the value of bits of the class of traffic in a
packet received is the same as the value sent by the source package.
Trafic Class (8 bits) : Available for use by originating nodes and/or forwarding routers to
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identify and distinguish between different classes or priorities of IPv6 packets. The rst six
bits of the trafic class eld are referred to as the DS (differentiated services) field, discussed
in Chapter 19. The remaining 2 bits are reserved for an ECN (explicit congestion
notication) field, currently in the process of standardization. Flow Label (20 bits) : May be
used by a host to label those packets for which it is requesting special handling by routers
within a network. All packets that are to be part of the same flow are assigned the same
flow label by the source.
2. Explain briefly three types of IPv6 addresses.
- Unicast : An identifier for a single interface. A packet sent to a unicast address is
delivered to the interface identied by that address.
- Anycast : An identifier for a set of interfaces (typically belonging to different nodes). A
packet sent to an anycast address is delivered to one of the interfaces identied by that
address (the "nearest" one, according to the routing protocols’ measure of distance).
- Multicast : An identifier for a set of interfaces (typically belonging to different nodes). A
packet sent to a multicast address is delivered to all interfaces identied by that address.
3. The IPv6 addresses are long, that will increase the size of the headers and affect the
processing time of the IPv6 packets. By what these disadvantages are offset in IPv6?
With an increase from 32 to 128 bits for IP addresses, an IPv6 header is actually longer
than one for IPv4 (40 bytes compared to 20). However, this is greatly offset by the
improvements IPv6 offers :
- In IPv6, optimization of headers by using optional extension improves packet
processing.
- Prioritizing IPv6 routing reduces the size of routing tables and thus improves router
processing times.
- IPv6 avoids going through NAT type mechanisms and associated proxies.
- If the problem of the header continues to be important when bandwidth is scarce
(case of the radio), it is possible to apply a standardized header compression mechanism.
When the problem is analyzed as a whole, it appears that with an equivalent processing
type (hardware or software) the processing and routing performances are better in IPv6.
4. Are the IPv6 routers more or less efficacy than the IPv4 routers?
Router performance primarily depends on the capacity of the router to process packets
(forwarding) in hardware. There are routers that process IPv6 forwarding in hardware ;
their performance is similar to that of IPv4. In addition, header optimization improves
performance in IPv6. And, it is not always necessary to process forwarding in hardware,
particularly for access routers. Processing forwarding in software is possible with current
processors, resulting in equivalent performance for IPv4 and IPv6. So IPv4 and IPv6
performances are similar.
5. What is each type of IPv6 header used for?
Hop-by-Hop Options header : Defines special options that require hop-by-hop processing.
Routing header : Provides extended routing, similar to IPv4 source routing. Fragment
header : Contains fragmentation and reassembly information. Authentication header :
Provides packet integrity and authentication. Encapsulating Security Payload header :
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Provides privacy. Destination Options header : Contains optional information to be
examined by the destination node.
6. All these notations being equivalent.
a) Deduce the notation rules of the IPv6 addresses into hexadecimal.
# raw ipv6 address
2001:0000:0234:C1AB:0000:0000:AABC:003F
#
2001:0:234:C1AB:0:0:AABC:3F
2001:0:0234:C1ab:0:0:aabc:3F
2001::0234:C1ab:0:0:aabc:003F
2001:0:0234:C1ab::aabc:003F
Or even
# loopback address
0:0:0:0:0:0:0:1
# can be written as
::1
# all zeros (unspecified a.k.a unassigned IP)
0:0:0:0:0:0:0:0
# can be written as
::
b) Can the address 2001:0:0:1:0:0:0:3F be reduced to:
2001::1::3F or 2001:0:0:1::3F?
7. Which differences exist between Mobile IPv4 and Mobile IPv6?
The design of Mobile IP support in IPv6 (Mobile IPv6) benefits both from the experiences
gained from the development of Mobile IP support in IPv4 (Mobile IPv4) [22, 23, 24], and
from the opportunities provided by IPv6. Mobile IPv6 thus shares many features with
Mobile IPv4, but is integrated into IPv6 and offers many other improvements. This
section summarizes the major differences between Mobile IPv4 and Mobile IPv6 :
- There is no need to deploy special routers as "foreign agents", as in Mobile IPv4. Mobile
IPv6 operates in any location without any special support required from the local router. o
Support for route optimization is a fundamental part of the protocol, rather than a
nonstandard set of extensions.
- Mobile IPv6 route optimization can operate securely even without pre-arranged security
associations. It is expected that route optimization can be deployed on a global scale
between all mobile nodes and correspondent nodes.
- Support is also integrated into Mobile IPv6 for allowing route optimization to coexist
efficiently with routers that perform "ingress filtering" [26]. –
- The IPv6 Neighbor Unreachability Detection assures symmetric reachability between
the mobile node and its default router in the current location.
- Most packets sent to a mobile node while away from home in Mobile IPv6 are sent using
an IPv6 routing header rather than IP encapsulation, reducing the amount of resulting
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overhead compared to Mobile IPv4.
- Mobile IPv6 is decoupled from any particular link layer, as it uses IPv6 Neighbor
Discovery [12] instead of ARP. This also improves the robustness of the protocol.
- The use of IPv6 encapsulation (and the routing header) removes the need in Mobile IPv6
to manage "tunnel soft state".
- The dynamic home agent address discovery mechanism in Mobile IPv6 returns a single
reply to the mobile node. The directed broadcast approach used in IPv4 returns separate
replies from each home agent.
8. Anycast Addressing
In addition to supporting unicast addressing and multicast addressing, IPv6 supports a
new type of anycast addressing in the first considering. This technique is similar to the
multicast in the direction where the destination address is a group of addresses, but instead
of trying delivering the datagram to all the members of the group, it tries to deliver to only
one member of the group, which is nearest or most capable to receive it.
You will use a routing algorithm of the OSPF type (state of the links) to build a routing
table of the router R3. The metric used represent the availability link (loss, occupancy rate
…). More it is raised, less the link is available.
a) Build the routing table of R3 by taking the data of links on the figure 8.
b) In considering now that one wants to introduce the concept of Anycast routing into
these tables of routing. The idea consists of taking into account the availability of
Anycast servers and of automating the choice of the server in allocating them to each
one the same Anycast address. The availability represents (number of users connected,
the memory available, the load CPU…). What will be the consequence on routing the
tables?
c) Reconstruct the routing table of R3 in order that the access with the server is made on
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the principal criteria of the availability of the server.
3. Annexes
3.0.1 Extract of the RFC 1542
Extract of the RFC 1542
4. BOOTP Relay Agents
In many cases, BOOTP clients and their associated BOOTP server(s) do not
reside on the same IP network or subnet. In such cases, some kind of third-
party agent is required to transfer BOOTP messages between clients and
servers. Such an agent was originally referred to as a "BOOTP forwarding
agent." However, in order to avoid confusion with the IP forwarding function
of an IP router, the name "BOOTP relay agent" is hereby adopted instead.
( )
4.1 General BOOTP Processing for Relay Agents
All locally delivered UDP messages whose UDP destination port number
is BOOTPS (67) are considered for special processing by the host or
router’s logical BOOTP relay agent.
( ) Hosts and routers are usually required to silently discard incoming
datagrams containing illegal IP source addresses. This is generally
known as "Martian address filtering." One of these illegal addresses
is 0.0.0.0 (or actually anything on network 0). However, hosts or
routers which support a BOOTP relay agent MUST accept for local
delivery to the relay agent BOOTREQUEST messages whose IP source
address is 0.0.0.0. BOOTREQUEST messages from legal IP source
addresses MUST also be accepted.
( )
4.1.1 BOOTREQUEST Messages
Some configuration mechanism MUST exist to enable or disable the
relaying of BOOTREQUEST messages. Relaying MUST be disabled by
default.
( )
If the relay agent does decide to relay the request, it MUST examine
the ’giaddr’ ("gateway" IP address) field. If this field is zero, the
relay agent MUST fill this field with the IP address of the interface
on which the request was received. If the interface has more than one
IP address logically associated with it, the relay agent SHOULD choose
one IP address associated with that interface and use it consistently
for all BOOTP messages it relays. If the ’giaddr’ field contains some
nonzero value, the ’giaddr’ field MUST NOT be modified.
( )
A relay agent MUST use the same destination (or set of
destinations) for all BOOTREQUEST messages it relays from a given
client.
( )
4.1.2 BOOTREPLY Messages
BOOTP relay agents relay BOOTREPLY messages only to BOOTP clients. It
is the responsibility of BOOTP servers to send BOOTREPLY messages

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