Routing Layers

 

 

Scheme:

We have two end points and three ISP’s (R2,R3, R4) in between the router R1 and R5. We need to move traffic between R1 and R5  in such away so that traffic  from R1 to R5 should not be monitored  when passing through  ISP’s in between. To achieve this purpose we need tunneling concept through which we can easily move packets back and forth in an efficient and private manner without being noticed by the providers in between the two end points. Today we will use GRE tunnel which is very simple to create and yet very efficient.  To create GRE tunnel decide the source and destination points in such way so that the source ip address or interface from R1 should be destination interface from R5 perspective and vice versa. For Source and destination we can either use loopback interfaces or the real physical interfaces. One important point to note that we will also create a virtual Tunnel interface on both tunnel ends and assign them with IP addresses both the IP addresses assigned to the tunnel interfaces should be on the same subnet so that when traffic will pass through in between R2, R3 and R4 then it will consider it as only one hop away from R1 to R5. Also we need to create the ip route for specific tunnel traffic to forward from both R1 and R5. OK, no worries as the process will be much simpler once I will show you the  configuration and then we will verify our traffic transport as well.

 

 

Bullets

• Establish connectivity between all routers by routing protocol (we used EIGRP).
• Create Tunnel interface R1 and R5 and should be on same subnet.
• Create Tunnel source on each desired router to be in the tunnel.
• Create Tunnel destination on each desired router to be in the tunnel.
• Create IP route to forward tunnel traffic immediately to the outside interface of tunneling routers.

 

 

Configuration:

 

R1

interface Tunnel15

 ip address 192.168.1.1 255.255.255.0

 tunnel source FastEthernet0/0

 tunnel destination 172.16.2.1

!        

interface FastEthernet0/0

ip address 172.16.1.1 255.255.255.0

duplex auto

speed auto

!

router eigrp 100

network 172.16.0.0

network 192.168.1.0

no auto-summary

!

ip route 172.16.2.0 255.255.255.0 FastEthernet0/0

!

 

R2

interface FastEthernet0/0

ip address 172.16.1.2 255.255.255.0

!

interface FastEthernet1/0

ip address 1.1.1.1 255.255.255.0

!

router eigrp 100

network 1.0.0.0

network 172.16.0.0

no auto-summary

!

 

R3

interface FastEthernet0/0

ip address 2.2.2.1 255.255.255.0

duplex auto

speed auto

!

interface FastEthernet1/0

ip address 1.1.1.2 255.255.255.0

duplex auto

speed auto

!

router eigrp 100

network 1.0.0.0

network 2.0.0.0

no auto-summary

!

 

R4

interface FastEthernet0/0

ip address 172.16.2.2 255.255.255.0

duplex auto

speed auto

!

interface FastEthernet1/0

ip address 2.2.2.2 255.255.255.0

duplex auto

speed auto

!

router eigrp 100

network 2.0.0.0

network 172.16.0.0

no auto-summary

!

 

R5

!

interface Tunnel 15

 ip address 192.168.1.2 255.255.255.0

 tunnel source FastEthernet0/0

 tunnel destination 172.16.1.1

!   

interface FastEthernet0/0

ip address 172.16.2.1 255.255.255.0

duplex auto

speed auto

!

interface FastEthernet1/0

no ip address

shutdown

duplex auto

speed auto

!

router eigrp 100

network 172.16.0.0

network 192.168.1.0

no auto-summary

!

ip route 172.16.1.0 255.255.255.0 FastEthernet0/0

!

 

Verification:

 

Verify the tunnel source and destination IP addresses.

 

R1#show interface tunnel 15

Tunnel15 is up, line protocol is up

Hardware is Tunnel

Internet address is 192.168.1.1/24

MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation TUNNEL, loopback not set

Keepalive not set

Tunnel source 172.16.1.1 (FastEthernet0/0), destination 172.16.2.1

Tunnel protocol/transport GRE/IP

Key disabled, sequencing disabled

Checksumming of packets disabled

Tunnel TTL 255

Fast tunneling enabled

Tunnel transmit bandwidth 8000 (kbps)

Tunnel receive bandwidth 8000 (kbps)

Last input 00:00:02, output 00:00:02, output hang never

Last clearing of “show interface” counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/0 (size/max)

5 minute input rate 0 bits/sec, 0 packets/sec

5 minute output rate 0 bits/sec, 0 packets/sec

66 packets input, 5688 bytes, 0 no buffer

Received 0 broadcasts, 0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort

68 packets output, 5876 bytes, 0 underruns

0 output errors, 0 collisions, 0 interface resets

0 output buffer failures, 0 output buffers swapped out

 

Verify how many hops in between the Tunnel to reach the other end and you will see it is only one hop away and will not show the in between routers (R2, R3, R4)

 

R1#trace 192.168.1.2

Type escape sequence to abort.

Tracing the route to 192.168.1.2

 

1 192.168.1.2 468 msec 492 msec *

 

Check how many routes are directly connected.

(Note that 172.16.2.0 is not directly connected at this time but later we will create the static route.)

R1#show ip route

Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP

D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area

N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2

E1 – OSPF external type 1, E2 – OSPF external type 2

i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2

ia – IS-IS inter area, * – candidate default, U – per-user static route

o – ODR, P – periodic downloaded static route

 

Gateway of last resort is not set

 

1.0.0.0/24 is subnetted, 1 subnets

D       1.1.1.0 [90/30720] via 172.16.1.2, 00:06:31, FastEthernet0/0

2.0.0.0/24 is subnetted, 1 subnets

D       2.2.2.0 [90/33280] via 172.16.1.2, 00:06:31, FastEthernet0/0

172.16.0.0/24 is subnetted, 2 subnets

C       172.16.1.0 is directly connected, FastEthernet0/0

D       172.16.2.0 [90/35840] via 172.16.1.2, 00:06:31, FastEthernet0/0

C    192.168.1.0/24 is directly connected, Tunnel15

R1#

 

Add more security by creating static route to immediately forward packets destined for tunnel (172.16.2.0 network) to the f0/0 interface of  R1 Tunnel router.

 

R1#conf t

R1(config)#ip route 172.16.2.0 255.255.255.0 f0/0

R1(config)#end

R1#

 

We can see 172.16.2.0 after creating static route to forward tunnel packets it is now directly connected in our ip route.

 

R1#show ip route

Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP

D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area

N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2

E1 – OSPF external type 1, E2 – OSPF external type 2

i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2

ia – IS-IS inter area, * – candidate default, U – per-user static route

o – ODR, P – periodic downloaded static route

 

Gateway of last resort is not set

 

1.0.0.0/24 is subnetted, 1 subnets

D       1.1.1.0 [90/30720] via 172.16.1.2, 00:08:17, FastEthernet0/0

2.0.0.0/24 is subnetted, 1 subnets

D       2.2.2.0 [90/33280] via 172.16.1.2, 00:08:17, FastEthernet0/0

172.16.0.0/24 is subnetted, 2 subnets

C       172.16.1.0 is directly connected, FastEthernet0/0

S       172.16.2.0 is directly connected, FastEthernet0/0

C    192.168.1.0/24 is directly connected, Tunnel15

R1#

 

Repeat the same process to the other end of Tunnel which is R5 and create an static route to forward 172.16.1.0 tunnel destined traffic to the exit interface of R5 tunnel router.

 

 

R5(config)#ip route 172.16.1.0 255.255.255.0 f0/0

R5(config)#end

R5#

 

We can see below the ip route where 172.16.1.0  is now directly connected in our R5 ip route. (Tunnel router)

 

 

R5#show ip route

Codes: C – connected, S – static, R – RIP, M – mobile, B – BGP

D – EIGRP, EX – EIGRP external, O – OSPF, IA – OSPF inter area

N1 – OSPF NSSA external type 1, N2 – OSPF NSSA external type 2

E1 – OSPF external type 1, E2 – OSPF external type 2

i – IS-IS, su – IS-IS summary, L1 – IS-IS level-1, L2 – IS-IS level-2

ia – IS-IS inter area, * – candidate default, U – per-user static route

o – ODR, P – periodic downloaded static route

 

Gateway of last resort is not set

 

1.0.0.0/24 is subnetted, 1 subnets

D       1.1.1.0 [90/33280] via 172.16.2.2, 00:11:50, FastEthernet0/0

2.0.0.0/24 is subnetted, 1 subnets

D       2.2.2.0 [90/30720] via 172.16.2.2, 00:11:50, FastEthernet0/0

172.16.0.0/24 is subnetted, 2 subnets

S       172.16.1.0 is directly connected, FastEthernet0/0

C       172.16.2.0 is directly connected, FastEthernet0/0

C    192.168.1.0/24 is directly connected, Tunnel15

R5#

 

 

How to remotely access routers and switches through TELNET.

It is desirable and a very common practice in big organizations to control a large number of devices (mostly routers, switches and servers remotely from one or few terminals located remotely in distant areas in order to troubleshoot, monitor and continuous maintenance for the whole network.  There are number of ways to remotely access devices such as SSH, TELNET, VPNs and today we will discuss the simplest way to connect remote devices which is TELNET.  Here the definition of the word remote can vary from one room to another room or from one country to another country located in another part of the world.

 

Configuration:

R1

conf t

int f0/0

ip address 2.2.2.1 255.255.255.0

no shut

!

router eigrp 100

network 2.2.2.0

no auto

!

!

enable secret special

! to get access privilege to global configuration

! when someone either access locally or

! remotely through TELNET or SSH

!

!

line vty 0 4

login local

! login local is needed if you need to enable password checking at virtual login such as TELNET

user najam password tryme

end

!

 

R2

conf t

int f0/0

ip address 2.2.2.2 255.255.255.0

no shut

router eigrp 100

network 2.2.2.0

no auto

 

• Establish connectivity between routers through routing protocol (we used EIGRP)
• Create username and password for vty line(s) to remotely access through Telnet.
• Enable secret password which is required to remotely access R1’s privileged mode.

Explanation:

The above process is really simple to establish telnet connection from R2 to R1 and VTY indicates Virtual Terminal Lines between the connected routers. Suppose we have five vty lines starts from 0 to 4. so we need line vty 0 4 command and then assigned a username “najam” and password “tryme” to access all these lines remotely through TELNET.  The  “login local” command is used to indicate that we now require password to give access to the user “najam” for telnet access so it is an added security which is beneficial.  Also we used “enable secret special”  and this is used to access the R1’s privileged mode from any other device otherwise without setting any password we will get the message password needed but not set and will only be able to access the user mode  but not the privileged or global configuration mode of R1.

You can access devices through Telnet from any number of routers  in series as long as  routers have  connectivity through any routing discipline.  Please note the example above is a very simple Telnet access procedure however in the real world we also come across with policies and firewalls wherever on purpose Telnet is not allowed for security reasons between any number of specific routes or routing devices.

Verification:

At first PING from R2 to R1 to verify the successful reply and then Initiate the TELNET process from R2 to access R1.

R2#telnet 2.2.2.1

Trying 2.2.2.1 … Open

User Access Verification

Username: najam

Password:  (tryme you will not be able to see the password when typing and it is normal)

R1>enable

Password: (special you will not be able to see the password when typing and it is normal)

R1#

R1#conf term

Enter configuration commands, one per line.  End with CNTL/Z.

R1(config)#

 After typing the correct password tryme you already established the telnet connection between R2 and R1 and now to further access the R1’s next level modes you need to apply the password special and then will be able to access privileged and global configuration mode.  R1(config)# in the above example shows that we are now accessing R1’s global configuration mode remotely from R2.

 

 

 

 

 

 

To setup connectivity and to route packets between the routers we need routing protocols and one of the most famous among them is OSPF (Open Shortest Path First). Today I will show you how quickly we can build an OSPF network between the routers without taking care of our specific network classes or ranges or in other words practically we can apply this default configuration to any number of networks starting from any IP address range and between any number of routers provided we have no restriction to save IP address space or network ranges for other purposes.  In the example we used four routers and single OSPF Area 0 where

 10.10.1.0/24 is the OSPF network between R1 and R2

10.10.2.0/24 is the OSPF network between R1 and R3 and

10.10.3.0/24 is the OSPF network between R1 and R4.

 

Configuration:

R1

int f0/0

ip address 10.10.1.1 255.255.255.0

no shut

exit

router ospf 100

network 0.0.0.0 255.255.255.255 area 0

no auto

!

 

R2

int f0/0

ip address 10.10.1.2 255.255.255.0

no shut

!

int f1/0

ip address 10.10.2.2 255.255.255.0

no shut

!

int f2/0

ip address 10.10.3.2 255.255.255.0

no shut

exit

router ospf 100

network 0.0.0.0 255.255.255.255 area 0

no auto

!

 

R3

int f1/0

ip address 10.10.2.1 255.255.255.0

no shut

exit

router ospf 100

network 0.0.0.0 255.255.255.255 area 0

no auto

!

 

R4

int f0/0

ip address 10.10.3.1 255.255.255.0

no shut

exit

router ospf 100

network 0.0.0.0 255.255.255.255 area 0

no auto

!

 

Verification:

We need to verify if we successfully established neighbor relationship between the routers.

 

R1#show ip ospf nei

 

Neighbor ID     Pri   State           Dead Time   Address         Interface

10.10.3.2         1   FULL/DR         00:00:31    10.10.1.2       FastEthernet0/0

 

 

R2#show ip ospf nei

 

Neighbor ID     Pri   State           Dead Time   Address         Interface

10.10.3.1         1   FULL/BDR        00:00:38    10.10.3.1       FastEthernet2/0

10.10.2.1         1   FULL/BDR        00:00:39    10.10.2.1       FastEthernet1/0

10.10.1.1         1   FULL/BDR        00:00:38    10.10.1.1       FastEthernet0/0

 

R3#show ip ospf nei

 

Neighbor ID     Pri   State           Dead Time   Address         Interface

10.10.3.2         1   FULL/DR         00:00:34    10.10.2.2       FastEthernet1/0

 

Neighbor ID     Pri   State           Dead Time   Address         Interface

10.10.3.2         1   FULL/DR         00:00:36    10.10.3.2       FastEthernet0/0

 

 

PING from R1 to R3

R1#ping 10.10.2.1

 

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.10.2.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 152/161/172 ms

 

PING from R4 to R1

R4#ping 10.10.1.1

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 10.10.1.1, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 132/159/196 ms

 

Explanation:

Same like in my previous article for EIGRP over here we have OSPF routing process with Area 0 and (network 0.0.0.0 255.255.255.255 area 0). This is the simplest and quickest way with least calculations to connect OSPF neighbors with each other. In the OSPF 100 process the 0.0.0.0 indicates from where to start this network and no auto summary indicates the network is not limited to xx.xx.xx.xx – xx.xx.xx.255 as a result it covers all the networks with ip addresses starts from 0.0.0.0 to 255.255.255.254. The above example is just to establish the simplest OSPF routing process however in the real world where we have number of routing protocols between routers and where we need to be careful about the network ranges there we  define the specific network numbers and the range as well. For example  in the above OSPF process in order to save our IP address space we may define the OSPF process 100 between R1 and R2 by using network 10.10.1.0 0.0.0.255 area 0  instead of network 0.0.0.0 255.255.255.255 area 0 so we may save IP address space and number of unused networks for other purposes.

 

To setup connectivity and to route packets between the routers we need routing protocols and one of the most famous among them is EIGRP. Today I will show you how quickly we can build an EIGRP network between the routers without taking care of our specific network classes or ranges or in other words practically we can apply this default configuration to any number of networks starting from any IP address and between any number of routers provided we have no restriction to save IP address space or network ranges for other purposes.  In the example we used three routers and single EIGRP process where 192.168.1.0/24 is the network between R1 and R2 and 192.168.2.0 between R2 and R3. We used EIGRP process 100 to route packets between the routers.

 

Configuration:

R1

interface FastEthernet0/0
ip address 192.168.1.1 255.255.255.0
no shut
!
router eigrp 100
network 0.0.0.0
no auto-summary
!

 

R2

interface FastEthernet0/0
ip address 192.168.1.2 255.255.255.0
no shut
!
interface FastEthernet1/0
ip address 192.168.2.2 255.255.255.0
no shut
!
router eigrp 100
network 0.0.0.0

no auto-summary
!

 

R3

interface FastEthernet0/0
ip address 192.168.2.1 255.255.255.0
no shut
!
router eigrp 100

network 0.0.0.0
no auto-summary

Verification:

Verify EIGRP neighbors through show commands.

 

 R1#show ip eigrp neighbors

IP-EIGRP neighbors for process 100
H   Address                 Interface       Hold Uptime   SRTT   RTO  Q  Seq
(sec)         (ms)            Cnt Num
0   192.168.1.2             Fa0/0             11 00:01:27  128    768     0  3

 

 

R2#show ip eigrp neighbor

 IP-EIGRP neighbors for process 100

 H   Address                 Interface       Hold Uptime     SRTT           RTO      Q   Seq

 

                                                                            (sec)             (ms)                        Cnt  Num

 

1   192.168.2.1             Fa1/0             11 00:02:55      114            684          0    6

 

0   192.168.1.1             Fa0/0             12 00:03:25     134           804          0     5

 

 

 

R3#show ip eigrp neighbor

 IP-EIGRP neighbors for process 100

 H   Address                 Interface       Hold Uptime     SRTT       RTO            Q      Seq

                                                                            (sec)            (ms)                          Cnt    Num

0   192.168.2.2             Fa0/0             11 00:05:36    851       5000          0         8

 

——————————————————————————————————————-

PING from R1 to R3 to ensure there is an end to end connectivity between the routers.

R1#ping 192.168.2.1

Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.2.1, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 56/96/188 ms

—————————————————————————————————————-

Explanation:

In the EIGRP 100 process (network 0.0.0.0) is the simplest and quickest way with least calculations to connect EIGRP neighbors with each other. In the process the network 0.0.0.0 indicates from where we start to look neighbors and no auto summary indicates the network is not limited to xx.xx.xx.xx – xx.xx.xx.255 as a result it covers all the networks with IP addresses starts from 0.0.0.0 to 255.255.255.254. The above example is just to establish the simplest EIGRP process however in the real world where we may have number of routing protocols between routers we  need to be careful about the network ranges to define the specific network in our EIGRP process for example in order to save our IP address space we may define network 192.168.1.0 between R1 and R2 in the EIGRP 100 process instead of network 0.0.0.0 just so we save IP address space and number of unused networks for other purposes.

 

Protocol	RIPng	EIGRPv6	OSPFv3
Global Commands	ipv6 unicast-routing ipv6 router Ripng name	ipv6 unicast-routing ipv6 router eigrp asn	ipv6 unicast-routing ipv6 router ospf process-id
Interface Commands	Configure IPv6 address	Configure IPv6 address	Configure IPv6 address
	ipv6 enable	ipv6 enable	ipv6 enable
	ipv6 rip name enable	ipv6 eigrp asn	ipv6 ospf process-id area areanumber
If router ID not automatically chosen		eigrp router-id rid	router-id rid

EIGRP for IPv6 uses the neighbor’s link local address as the next-hop and similar to RIPng in EIGRPv6 there are no classful networks so for obvious reason it cannot perform any auto summarization. A very interesting feature introduced in EIGRPv6 that EIGRP v6 does not require neighbors to be in the same subnet as a requirement to become neighbors so to form neighbor relationship In IPv6 instead of subnet mask it advertises IPv6 prefixes/length.

2002::/56 has the prefix length of  72  as (128-56) =  72 and 56 bits left for host/interface assignments.

EIGRP for IPv6 has almost same configuration procedure as for RIPng we discussed earlier.

Global Commands

 ipv6 unicast-routing

ipv6 router eigrp {1 – 65535}

Interface Commands

 IPv6 address xxxx.xxxx.xxxx.xxxx.xxxx.xxxx.xxxx.xxxx

Or

IPv6 address xxxx::/64 eui-64

no shut

 ipv6 eigrp asn    (asn is Autonomous System Number)

eigrp router-id rid

Note: In EIGRP configuration mode,.we need to configure an EIGRP router id provided there is none of IPv4 interface otherwise even if there is even one IPv4 interface then router itself create his own Router ID to use.

Selection of Router-id: The first priority would be manually assigned router-id through eigrp router-id xxxx  command if it is not available then highest IP address of loopback interface and the third default priority is the highest IP address of non loopback interface also for selection all the interfaces should be in active/up state.

RIP NEXT GENERATION (RIPng)

RIP next generation is very similar to the RIP-2 version in IPv4 however there is no such concept of auto-summarization in RIPng by default in IPv6.

We can adopt following procedure to enable RIPng on Global and then on interface level.

Global Commands

ipv6 unicast-routing

It tells router that IPv6 routing is enabled on this router.

 

ipv6 router rip name

It defines the RIP process  and (name) should be unique on that particular router atleast.

 

Interface level commands

IPv6 address xxxx.xxxx.xxxx.xxxx.xxxx.xxxx.xxxx.xxxx.xxxx

Or

IPv6 address xxxx.xxxx.xxxx.xxxx::/64 eui-64

either use simple IPv6 unicast addressing as in the above line or assign it through eui-64 process..

 

ipv6 rip name enable

Name should be same as defined earlier when defined the RIP process globally.

 

Verification:

To the simplest level you can verify RIPng configuration through the following commands.

Show running-config

which will show the RIPng  process and if already enabled on interface.

PING IPv6  address

Will verify if IPv6 routing is being responsive.

 

Example:

Show running-config

interface FastEthernet0/0

no ip address      (this line shows if the IPv4 address is also configured)

ipv6 address 3002::3/64

 

show ipv6 int brief

FastEthernet0/0            [up/up]

FE80::C000:D5FF:FED8:0      (its the link local address )

3002::3                                    (this is the IPv6 address)

show ipv6 int f0/0 

FastEthernet0/0 is up, line protocol is up

IPv6 is enabled, link-local address is FE80::C000:D5FF:FED8:0

No Virtual link-local address(es):

Global unicast address(es):

    3002::3, subnet is 3002::/64

Joined group address(es):

FF02::1

FF02::2

FF02::1:FF00:3

FF02::1:FFD8:0

MTU is 1500 bytes

 

 

Now from another connected router where the RIPng protocol is also enabled

 

ping ipv6 3002::3

Type escape sequence to abort.

Sending 5, 100-byte ICMP Echos to 3002::3, timeout is 2 seconds:

!!!!!

Success rate is 100 percent (5/5), round-trip min/avg/max = 0/4/8 ms

 

Successful  reply from another  router will ensure  the IPv6 routing and the RIPng  processes between two between two routers are functional.

Understanding IPv6 Addressing:

Due to the fact that we are running out of 32bits IPv4 addresses in a very near future scientists suggested another efficient way to assign the IP addresses and this is IP version 6 on in short IPv6 addressing.

• An IPv6 address consist of 128 bits written in Hexadecimal format.
• These 128 bits are subdivided in 8 groups or quartets.
• There are 16 bits in each quarter.

If all the bits are 1 in an IPv6 address then we can write it as follows

in binary format
1111111111111111.1111111111111111.1111111111111111.1111111111111111.1111111111111111.

1111111111111111.1111111111111111.1111111111111111

In IPv6 Hex format
FFFF.FFFF.FFFF.FFFF.FFFF.FFFF.FFFF.FFFF   where FFFF represents one quartet or 16 bits.

Ways to write IPv6 address:

An IPv6 address FEC2.0000.0000.0000.05CD.0000.0000.04D0 can be rewritten in several ways.

FEC2::05CD.0000.0000.04D0
In IPv6 if an IP address has all consecutive 0′s in a hex quarter then we can use “::” (double column) to save some space.
Note: you can use “::” only once in an IPv6 address so it cannot be written as FEC2::05CD::04D0

FEC2::5CD.0.0.4D0
We can eliminate all the leading 0,s from the left so instead of writing fully zeroed quartet as 0000 we can use just  one ‘0‘ only and 05CD and 04D0 as 5CD and 4D0.

Atlast, if the network and subnet address (prefix) is FEC2.0000.0000.0000.0000.0000.0000.0000 then to make it shorter we can write all 0′s or remaining 112 bits as follows
FEC2::/112 which is equivalent to FEC2.0000.0000.0000.0000.0000.0000.0000

Basic structure of IPv6 address:

IPv6 address consist of two parts very similar to the IPv4 address
IPv6 address = Prefix + Host id
Prefix = Network address + Subnetmask

Network address = Regionally unique bits + countrywide + ISP

For example if for Asian region assigned with first two Hex digits FE then all the IPv6 addresses in Asian region starts with FE::/120 or FE00.0000.0000.0000.0000.0000.0000.0000

Means we have 120 bits left for country wide division.

Now we suppose inside Asian region a country XYZ assigned with FEBC::/112 address where ‘BC‘ represents that particular country. Every address in that particular country should be started with FEBC.

Now we have 112 bits left for ISP’s or big governmental organizations wide division.

Lets suppose inside the country XYZ an ISP assigned with FEBC:2000::/96 so every address in that particular ISP will be started with FEBC:2000 and still we have 96 bits left for ISP wide users that is enough for 2 raise to the power 96 or 2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2x2 = 79228162514264337593543950336  number of users or 11318308930609191084 globally unique addresses for each single user anywhere in the world.

These are all hypothetical calculations although very few exceptions with some specifically assigned addresses for multicast and other purposes are reserved but in general IPv6 addresses have no shortage at-least for several centuries so there is even no need to assign any private address for end users and anyone would be able to use his own globally unique IPv6 addresses even for their own sub-networks. IPv6 is not only easier to configure than IPv4 addresses but it also almost eliminated the concept of NAT inside/outside Network Address Translation as mostly the IPv6 addresses are unique all over the world. Broadcast concept is also completely eliminated and instead it uses multicast to advertise the packet to several or all users. I will discuss the IPv6 types of packets and how to assign the host portion of IPv6 addresses in the upcoming articles very soon.