Download UNIT name: IP protocol

UNIT name: IP routing
o What are the PRIOR knowledge for unit – concepts what must be covered
before
bit/bait
AND ja OR operations in 2-nd system
IP addresses, masks
o AIM of the unit
Understands how IP packets are handled in routers of IP network and is able to
correctly configure router parameters.
o Theory (HTML text - possible with links to outside material and simple
flash)
1. Routing
Look again to ISO/OSI simulation (in unit “ISO/OSI model”, especially Network
Layer in that. Look also another simple picture of routing:
http://www.windowsnetworking.com/articles_tutorials/route.html
Ordinarily routing is hierarchical – there is only one track (road) from one node to
another. In some cases there is different routes available, called multiple routing
networks.
Hierarchical routing, Source: http://www.uga.edu/~ucns/lans/tcpipsem/
Multiple routing, Source - http://www.uga.edu/~ucns/lans/tcpipsem/
Multiple routing is used in backbone systems. Information between routers is
exchanged to clarify best routs in the situation (timeframe).
Source - http://www.ces.net/doc/2004/research/nren.html
INTERESTING SERVICE:
Geological identification of IP addresses based of routing information in the internet:
http://www.ipaddresslocation.org/ and http://www.xkcd.com/c195.html
2. Routing table
In the routing table of the IP network node there is written all the information about IP
networks, the node knows. To remember - IP addresses (as the network protocol of
TCP/IP family) are divided into two logical parts – network address and node address
– by address mask (look more in IP unit).
In the routing table we can see it like follows as an example:
Network Destination
Netmask
0.0.0.0
0.0.0.0
127.0.0.0
255.0.0.0
172.10.0.0
255.255.255.0
172.10.0.187 255.255.255.255
Gateway
172.10.0.1
127.0.0.1
172.10.0.187
127.0.0.1
Interface
172.10.0.187
127.0.0.1
172.10.0.187
127.0.0.1
Metric
30
1
30
30
There is defined networks by “Destination” and “Netmask” connected to “Interface”
by means of Data Link Layer (or Physical) segments which are available for the node
(as LAN, WLAN etc), which has configured IP address.
Then “Gateway” is an address of node, which knows more or which actually
transports packets from one network segment to other. The node defined as gateway
for other IP nodes is called router.
Routers are nodes, which are parts of different IP network segments. These network
segments can be physically in one or different Datalink Layer segment as they are not
interrelated in theory. So, router can define two different IP networks in the same
physical network segment – then nodes (computers etc) in the same physical network
segment, but different IP network segment, are communicating only thorough router
although they are in the same physical network segment. Some network equipments
are connecting different physical segments (ADSL modems, WLAN AP-s, different
bridges etc), but IP network is actually the same over these different networks.
Every router, on the track between source and destination node, is making a transport
“hop” and of course takes some additional time to carry on giving additional latency
for packet delivery. Of course bridges between different physical segments are giving
additional latency too, but they are not visible as hops in the track from source to
destination.
TASK:
Try to figure out with MS Windows command “tracert”, how many hops there is from
your computer to www.google.com.
If node (with source IP address) is willing to send IP packet to other node (destination
IP address), there will be used routing table of the node to calculate, where to send
packet by means of gateway. If the gateway is in the list of interfaces of the node,
packet will be sent straightly to the destination IP address thorough interface (found in
routing table). If the gateway is other IP node, the packet will be sent to the router
(gateway address).
To find the right routing table row for each IP packet, destination address is compared
with each network in routing table starting with smallest (network mask is “bigger”).
If the network address matches, right row is found. Broadest network in every routing
table is called “Default gateway” as there are “all other networks”.
In the example of routing table there is smallest “network segment” with the mask
255.255.255.255. This is actually local interface address of the node itself, not real
network. Second smallest network is 172.10.0.0/24 which is actually LAN connection
in the one building where the node is situated.
Third network 127.0.0.0/8 is special address area for local addressing inside the node,
called “Loopback network”. And last, biggest network, is the default route (gateway)
to other networks.
Actually, sometimes one node can have many different IP addresses defined for one
physical network interface (Network Interface Card – NIC).
Look another example at Microsoft TechNet, article “The IP routing table”:
http://technet2.microsoft.com/WindowsServer/en/library/63158f32-9fcd-42ea-ba2f8008bb7bb5241033.mspx?mfr=true
3. NAT
Network Address Translation (NAT) is used inside organizations for there are not
enough addresses for all nodes in the world, and also it gives some security advances.
As defined in RFC 1631 (http://tools.ietf.org/html/rfc1631) NAT gives possibility to
use same address space (private addresses) in different organizations at the same time.
NAT is additional functionality of a router. NAT translates private addresses to
another (public) address and remembers this translation for feedback packets
(connection tracking data). Because of NAT can not provide connectivity from
“outside world” to “inside”, it is giving natural firewall functionality by that way. All
the nodes behind NAT are visible to outside world as one node.
There is simulation of NAT (in estonian): http://iva.tpt.edu.ee/opiobjektid/nat/
Because of translation only in IP packet header NAT can be problem for some
applications, when IP address is used in higher level too (FTP active connections
etc.).
Read more: http://en.wikipedia.org/wiki/Network_address_translation
4. Calculations
Every node and router needs to calculate for every IP address in every IP packet it
handles, in which IP network it belongs eg. where to send it.
Let’s look over again masks to remember:
Net bits
Subnet mask
total-addresses
/20
255.255.240.0
4096
/21
255.255.248.0
2048
/22
255.255.252.0
1024
/23
255.255.254.0
512
/24
255.255.255.0
256
/25
255.255.255.128 128
/26
255.255.255.192 64
/27
255.255.255.224 32
/28
255.255.255.240 16
/29
255.255.255.248 8
/30
255.255.255.252 4
(Source: http://xtronics.com/reference/ip-subnetmasks.htm)
If node needs to calculate network address from IP address, it takes a logical
operation AND between IP address and Mask as follows:
ip = 10000000 11000000 11111110 01100100 (128.192.254.100)
netmask = 11111111 11111111 00000000 00000000 (255.255.0.0)
AND operation
----------------------------------network = 10000000 11000000 00000000 00000000 (128.192.0.0)
If network administrator needs to calculate network addresses or choose correct
address values for nodes there is need to modify numbers from decimal system to
binary and vice versa. There are different possibilities for that. For example to modify
10-system number to binary, you can use division by 2 like follows:
Task:
There is IP defined in the documentation: IP=213.168.16.220/28
Administrator needs to calculate right network address for routing information.
Solution:
Mask /28 means, that there are 28 ones and 4 zeros in the end. It means last octet is
11110000 and other octets are 1 in the binary view:
MASK=11111111.11111111.11111111.11110000 (2)
So we need to calculate actually only last octet for IP address because of first three
octets are representing fully network address.
220 (10) =?
220/2, 0
110/2, 0
55/2, 1
27/2, 1
13/2, 1
6/2, 0
3/2, 1
1/2, 1
220 (10) = 11011100 (2)
Then we do AND operation, as follows:
11011100
11110000
-------11010000
(2) IP
(2) MASK
AND
(2) NETWORK
Now we modify this back to decimal system using exponents of two for each position
starting 0 to 7. 2 exponent 0 we multiply with last position (right side), 2 exponent 1
with second position etc until 2 exponent 7 with last (eight from right side, first one
from left) position.
2exp0*0+2exp1*0+2exp2*0+2exp3*0+2exp4*1+2exp5*0+2exp6*1+2exp7*1
It means, in these positions, where is 0, we actually do not need to calculate exponent:
2exp4*1+2exp6*1+2exp7*1
All the IT administrators have exponents of 2 in the head :) – so we quickly
summarize it:
16+64+128=208 (10)
Answer:
And there is the solution for network address for IP=213.168.16.220/28
NETWORK=213.168.16.208/28
or NETWORK=213.168.16.208/255.255.255.240
Look for the simulation too as next example:
We use attachment here hopefully! If not, then delete it.
If there is need to calculate broadcast address, it is the same like networks address in
binary view, only the positions, where mask has zeros, in the broadcast address there
are ones:
11011100
11110000
-------11010000
11011111
(2)
(2)
AND
(2)
(2)
IP
MASK
operation
NETWORK
BROADCAST
Of course administrators can use special IP subnet calculators or calc.exe :)
- http://www.google.com/search?q=ip+subnet+calculator
- www.wildpackets.com (downloadable program)
5. Additional material (Maybe not to include?):
- Fragmentation? - http://lin2.tlu.ee/~matsak/telecom/3.html and
http://en.wikipedia.org/wiki/IPv4#Fragmentation_and_reassembly )
- Configuring router boxes (example pictures?)
o Linux routers (example pictures)
o “Routing” with Layer 2 (with ARP)
o “Routing” with upper layers - Proxy
- Detecting packet loss and latency (explain router buffers besides of datalink layer
latency)
o ping
o tracert (traceroute)
- Direct routing schemes (read abut: http://en.wikipedia.org/wiki/Routing):
o unicast
o multicast (IGMP)
o broadcast
Links:
- http://cable-dsl.home.att.net/
o Attachments (Videos, Simulations etc – describe!!!)
The IP address (193.40.136.67) and Mask (255.255.255.240) is in the Computer
X. Another IP (192.40.136.57) and Mask (255.255.255.240) is in the Computer Y.
Question mark in the middle with sequentially showing :
- are the computers in the same network?
-
How can we (computers themselves) find it out?
Solution: lets calculate network addresses for both computers and compare, are
they equal (are they in the same IP network)?
1. Computer X Mask is zoomed and modified to 2-system
We start with modifying last part - it means, if mask is 255.255.255.240, then 240:
240 (10) =?
240/2, 0
120/2, 0
60/2, 0
30/2, 0
15/2, 1
7/2, 1
3/2, 1
1/2, 1
240 (10) = 11110000 (2)
Additionally explained, that 255 (10) means 11111111 (2).
2. Next same with IP address of Computer X
67 (10) =?
67/2, 1
33/2, 1
16/2, 0
08/2, 0
04/2, 0
02/2, 0
01/2, 1
67 (10) = 01000011 (2)
Same with:
193 (10) =?
40 (10) =?
136 (10) =?
3. Next Computer Address and Mask are put together with AND operation, like:
193.040.136.067 = 11000001.00101000.10001000.01000011
255.255.255.240 = 11111111.11111111.11111111.11110000
193.040.136.064 = 11000001.00101000.10001000.01000000 (net)
And there it is – network address for Computer X.
There can be marked with BOLD (or little flash) the network part of the IP address as
it is the same with Network address (area of 1-s in the mask).
4. There can be modifying from binary to 10-systema again in the way of exponents:
11000001 (2) = 2exp0+2exp6+2exp7 = 1+64+128 = 193 (10)
4. Next same with IP address of Computer Y
57 (10) =?
57/2, 1
28/2, 0
14/2, 0
07/2, 1
03/2, 1
01/2, 1
57 (10) = 00111001 (2)
5. Next Computer Address and Mask are put together with AND operation, like:
193.040.136.057 = 11000001.00101000.10001000.00111001
255.255.255.240 = 11111111.11111111.11111111.11110000
193.040.136.048 = 11000001.00101000.10001000.00110000 (net)
And there it is – network address for Computer Y.
As the answer there you can see, that network address for X and Y are different, and
they can not communicate with each other.
o Quiz (best is 1…x right answers of 3…6 choices, may be different quizzes –
for self-learning and grading)
1. IP address is usually presented like:
a. x.y.z
b. xx-xx-xx-xx-xx-xx
c. x.y.z.w (x)
d. domain.com
2. IP address and Mask are defining:
a. network address (x)
b. gateway address
c. broadcast address (x)
d. unicast address
e. node address (x)
f. source address
3. Please calculate Network, Broadcast and Gateway address for node
219.213.168.226/30 (can use MS windows calc or else)
a. right answer is:
i. network=219.213.168.224
ii. broadcast=219.213.168.227
iii. gateway=219.213.168.225
4. Routing table is giving information about:
a. IP networks nearby node (x)
b. All networks in the internet
c. All node interfaces available
d. Node interfaces using IP (x)
e. Network speed
5. Which MS Windows command you can use, to see IP network hops to
destination host:
a. ping
b. tracert (x)
c. ipconfig
d. cmd
6. Routers are working in ISO/OSI
a. Layer 1
b. Layer 2
c. Layer 3 (x)
d. Layer 4
e. Layer 5
7. How many different IP addresses can be defined to a network interface
a. 1
b. 2
c. 5
d. no limits (x)
8. How many nodes can be defined in IP network, with mask 255.255.255.252
a. 2 (x)
b. 4
c. 8
d. 16
9. Broadcast address is
a. first address in IP network address area
b. last address in IP network address area (x)
c. special address outside IP network definition
10. What is the gateway for IP network node 219.201.46.125, if IP-s are between
219.201.46.124-219.201.46.127.
a. 219.201.46.124
b. 219.201.46.125
c. 219.201.46.126 (x)
d. 219.201.46.127