Category Archives: Network

Change BackupExec server name


How to update media server configuration information, including server name and domain name changes for Backup Exec 2012 and prior versions.



In Backup Exec 2012 and prior versions, the Update Configuration for New Media Server Name option enables an administrator to update the name of a media server if it has been changed, without having to re-install Backup Exec.

The domain name can also be updated if the media server is in a different domain.

Caution: Using Update Configuration for New Media Server Name does not change the media server name in existing backup selection lists. If this task is used to update the media server name, all the selection lists that back up data from that media server must be recreated. Otherwise, the backup jobs will fail. In addition, when creating a restore job that targets the original media server, all data being restored must be redirected to the newly named media server.
You may also make a copy of the Backup Exec Database before running the utility. For that, stop SQL instance service for Backup Exec (SQL Server (BKUPEXEC) and all other BE services. Then from X:\Program Files\Symantec\Backup Exec\Data make a copy of two files bedb_dat.mdf and bedb_log.ldf. After making a copy, start the SQL service first and then start all BE services and follow the below steps.

To use the Update Configuration for New Media Server Name task:

Location of BEUtility : X:\Program Files\Dymantec\Backup Exec, where X is the drive where Backup Exec is installed

1.  Start BEUtility.

2.  Select a media server from either a media server group or from the All Media Servers subnode that has been renamed.

3. On the task pane, under Services Tasks, click Update Configuration for New Media Server Name. (Figure 1)

Figure 1

4. Make changes as appropriate:

Update Configuration for New Media Server Name fields

Item Description
Current domain name The new domain name, of which the media server is now a member.
Current media server name The new computer name of the media server.
Previous domain name The previous domain name, of which the media server was a member
Previous media server name The previous media server name.

5. Click OK.

6. When the operation completes, click Close.

Enable Telnet Access on Cisco Router


Use the following commands to enable telnet access to the router.

First check how many virtual terminal router supports.
(Depending on the router model, the output might be different)

Router#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router(config)#line vty 0 ?
  <1-4>  Last Line number

Enable access to virtual terminals and set the “cisco” as the password to access user mode:

Router(config)#line vty 0 4
Router(config-line)#password cisco

Enable access to virtual terminals and set the “cisco” as the password to access CONFIG mode:

Router(config)#line vty 0 4
Router(config-line)#login local

Will use username and password set at congif level:
Router(config)#username [my_username] privilege 15 password [my_password]


To verify use the following command

Router#show line
   Tty Typ     Tx/Rx    A Modem  Roty AccO AccI   Uses   Noise  Overruns   Int
*     0 CTY              -    -      -    -    -      0       0     0/0       -
     97 AUX   9600/9600  -    -      -    -    -      0       0     0/0       -
     98 VTY              -    -      -    -    -      1       0     0/0       -
     99 VTY              -    -      -    -    -      0       0     0/0       -
    100 VTY              -    -      -    -    -      0       0     0/0       -
    101 VTY              -    -      -    -    -      0       0     0/0       -
    102 VTY              -    -      -    -    -      0       0     0/0       -

Line(s) not in async mode -or- with no hardware support:


Thats it. Now you can access the router remotely using telnet.

Disable telnet:

Router(config)#no line vty 0 4

IPv6 Subnetting – How and Why to Subnet IPv6

by Arani Mukherjee (link)

In the previous tutorials, I went through the need for IPv6, and followed it up by drawing out the salient features which overcomes issues with IPv4. We took the journey of looking inside the headers, the structure and purpose of each and every extension headers. By now I sincerely hope, as readers, you all have got a good grasp of what entails this new protocol.

In this tutorial, I will be talking about subnetting. Subnetting is one of the most talked about, practiced, and supposedly confusing topics encountered by network professionals. In retrospect, all I would say, and do take it as a personal opinion, subnetting is one of the easiest things that can be mastered. The question you might ask is, why do we need to do subnetting if IPv6 already caters to the need for an absurd amount of IP addresses? Yes, I would agree to it at first but because IPv6 does make itself and subnetting two very disjoint terms. I might say, subnetting decreases broadcast traffic, but then you can counter it by saying IPv6 doesn’t have broadcast traffic. It does become difficult to justify.

However if you see it logically, you will still need reduce unnecessary network traffic. Subnetting also will give you an element of security. You can force people to follow a certain route, or even go through a specific router, where you can apply security policies.

For network administrators, subnetting increases flexibility in designing networks, route summarisation becomes easy, routing itself becomes efficient and management of networks improves. If you are given a /48 subnet to work with, you will have more than enough spaces to work with i.e. you get 65536 subnets with 18,446,744,073,709,551,616 hosts per subnet. I think that’s more than enough.

So, in all, subnetting is necessary in IPv6, but not for the reasons why we did it with IPv4.

Before diving into subnetting IPv6, I’d like to present a diagram which illustrates the differences between the IPv4 & IPv6 header. This will help understand the major structural differences between the two protocols. Notice the additional addressing space provided in the IPv6 Source and Destination Address which is now 128bit long (each), compared to 32bits in IPv4:


Courtesy of

Now, let us all exercise our birthright to subnet, and dig deeper into how we go about doing it. I can bet you, there are more than thousands of ways you can do this, and perhaps a similar if not greater number of videos on the web, that teaches you to do this as well. What follows is my personal humble attempt of practicing the dark arts, in perhaps a simple way possible.
An IPv6 subnet mask is written in hexadecimal, but let’s start by explaining that IPv6 uses 128 binary digits for each IP address, as opposed to IPv4’s 32 binary digits, and those 128 binary digits are divided into eight 16-bit words (8 x 16 = 128), like this:


It would be a little difficult to use IPv4’s old octet notation for 128 bits, which might look like this:

So, a hexadecimal representation is used instead, which makes a little bit easier. Hexadecimal is a 16-digit numbering system, as opposed to binary’s 2-digit system and decimal’s 10-digit system. The 16 digits of hexadecimal run from zero to nine, then use the letters A to F: {0123456789ABCDEF}.

One 4-digit hex word represents 16 binary digits, like this:
Bin 0000000000000000 = Hex 0000 (or just 0)
Bin 1111111111111111 = Hex FFFF
Bin 1101010011011011 = Hex D4DB

So, this 128-bit binary address:


…would be represented by 8 hex words, separated by colons:


A full IPv6 subnet mask uses the same 8-hex-word format as an IPv6 address, although some tools allow you to specify only 1 hex word.

Like IPv4, an IPv6 address has a network portion and a device portion. Unlike IPv4, an IPv6 address has a dedicated subnetting portion. Here’s how the ranges are divided in IPv6:

Network Address Range
In IPv6, the first 48 bits are for Internet routing.


Subnetting Range :
The 16 bits from the 49th to the 64th are for defining subnets.


Device (Interface) Range:
The last 64 bits are for device (interface) ID’s.


The diagram below depicts a Global Unicast IPv6 address which has the following characteristics:

  • Address format that enables aggregation upward to the ISP.
  • 48-bit global routing prefix and a 16-bit subnet ID.
  • Allows for organizations to have up to 65535 individual subnets


Courtesy of

Subnetting Example

Let’s say you want to break your corporate network into 64 subnets. The binary mask just for the subnetting range would be1111110000000000 which translates to a hex value of FC00. Some IPv6 masking tools will work with just this one hex word, otherwise a full 128-bit hex mask would be FFFF:FFFF:FFFF:FC00:0:0:0:0.

If you play around with converting values in the Windows Calculator (in scientific mode), remember to convert between binary and hexadecimal, not decimal and hex.

Before you ask, yes, it is possible to use bits in the device range for additional subnet masking, but you shouldn’t need it. The 16 binary digits dedicated to subnetting and 64 binary digits available for devices give 65,535 subnets with over 18 quintillion devices per subnet. In addition, if you use some of the 64 bits in the device range for subnetting, then you can’t use autoconfiguration tools because they expect all of the 64 bits on the right side to be dedicated to devices. So don’t use any of the device bits for subnetting if you need IPv6 Autoconfiguration and if you don’t know whether or not you need autoconfiguration, assume you do. And even if you know you don’t need autoconfiguration, it’s a good standard to use a 64-64 split for network/lan vs. device.

Those interested in IP4v Subnetting can read through our extensive IPv4 Subnetting tutorial.

Hope the tutorial quenches your thirst for IPv6 subnetting.

About the Writer

Arani Mukherjee holds a Master’s degree in Distributed Computing Systems from the University of Greenwich, UK and works as network designer and innovator for remote management systems, for a major telecoms company in UK. He is an avid reader of anything related to networking and computing. Arani is a highly valued and respected member of, offering knowledge and expertise to the global community since 2005.

10 things you should know about IPv6 addressing

October 22, 2010, 7:55 AM PDT

Takeaway: Although IPv6 adoption seems to be moving at a snail’s pace, there’s no outrunning it. Brien Posey demystifies some of the addressing issues many admins are still trying to figure out.

[Editor’s note: This article has been revised to correct a couple of errors noted by TechRepublic members. Thanks to everyone who contributed their input.]

Over the last several years, IPv6 has been inching toward becoming a mainstream technology. Yet many IT pros still don’t know where to begin when it comes to IPv6 adoption because IPv6 is so different from IPv4. In this article, I’ll share 10 pointers that will help you understand how IPv6 addressing works.

1: IPv6 addresses are 128-bit hexadecimal numbers

The IPv4 addresses we are all used to seeing are made up of four numerical octets that combine to form a 32-bit address. IPv6 addresses look nothing like IPv4 addresses. IPv6 addresses are 128 bits in length and are made up of hexadecimal characters.

In IPv4, each octet consists of a decimal number ranging from 0 to 255. These numbers are typically separated by periods. In IPv6, addresses are expressed as a series of eight 4-character hexadecimal numbers, which represent 16 bits each (for a total of 128 bits). As we’ll see in a minute, IPv6 addresses can sometimes be abbreviated in a way that allows them to be expressed with fewer characters.

2: Link local unicast addresses are easy to identify

IPv6 reserves certain headers for different types of addresses. Probably the best known example of this is that link local unicast addresses always begin with FE80. Similarly, multicast addresses always begin with FF0x, where the x is a placeholder representing a number from 1 to 8.

3: Leading zeros are suppressed

Because of their long bit lengths, IPv6 addresses tend to contain a lot of zeros. When a section of an address starts with one or more zeros, those zeros are nothing more than placeholders. So any leading zeros can be suppressed. To get a better idea of what I mean, look at this address:


If this were a real address, any leading zero within a section could be suppressed. The result would look like this:


As you can see, suppressing leading zeros goes a long way toward shortening the address.

4: Inline zeros can sometimes be suppressed

Real IPv6 addresses tend to contain long sections of nothing but zeros, which can also be suppressed. For example, consider the address shown below:


In this address, there are four sequential sections separated by zeros. Rather than simply suppressing the leading zeros, you can get rid of all of the sequential zeros and replace them with two colons. The two colons tell the operating system that everything in between them is a zero. The address shown above then becomes:


You must remember two things about inline zero suppression. First, you can suppress a section only if it contains nothing but zeros. For example, you will notice that the second part of the address shown above still contains some trailing zeros. Those zeros were retained because there are non-zero characters in the section. Second, you can use the double colon notation only once in any given address.

5: Loopback addresses don’t even look like addresses

In IPv4, a designated address known as a loopback address points to the local machine. The loopback address for any IPv4-enabled device is

Like IPv4, there is also a designated loopback address for IPv6:


Once all of the zeros have been suppressed, however, the IPv6 loopback address doesn’t even look like a valid address. The loopback address is usually expressed as ::1.

6: You don’t need a traditional subnet mask

In IPv4, every IP address comes with a corresponding subnet mask. IPv6 also uses subnets, but the subnet ID is built into the address.

In an IPv6 address, the first 48 bits are the network prefix. The next 16 bits are the subnet ID and are used for defining subnets. The last 64 bits are the interface identifier (which is also known as the Interface ID or the Device ID).

If necessary, the bits that are normally reserved for the Device ID can be used for additional subnet masking. However, this is normally not necessary, as using a 16-bit subnet and a 64-bit device ID provides for 65,535 subnets with quintillions of possible device IDs per subnet. Still, some organizations are already going beyond 16-bit subnet IDs.

7: DNS is still a valid technology

In IPv4, Host (A) records are used to map an IP address to a host name. DNS is still used in IPv6, but Host (A) records are not used by IPv6 addresses. Instead, IPv6 uses AAAA resource records, which are sometimes referred to as Quad A records. The domain is used for reverse hostname resolution.

8: IPv6 can tunnel its way across IPv4 networks

One of the things that has caused IPv6 adoption to take so long is that IPv6 is not generally compatible with IPv4 networks. As a result, a number of transition technologies use tunneling to facilitate cross network compatibility. Two such technologies are Teredo and 6to4. Although these technologies work in different ways, the basic idea is that both encapsulate IPv6 packets inside IPv4 packets. That way, IPv6 traffic can flow across an IPv4 network. Keep in mind, however, that tunnel endpoints are required on both ends to encapsulate and extract the IPv6 packets.

9: You might already be using IPv6

Beginning with Windows Vista, Microsoft began installing and enabling IPv6 by default. Because the Windows implementation of IPv6 is self-configuring, your computers could be broadcasting IPv6 traffic without your even knowing it. Of course, this doesn’t necessarily mean that you can abandon IPv4. Not all switches and routers support IPv6, just as some applications contain hard-coded references to IPv4 addresses.

10: Windows doesn’t fully support IPv6

It’s kind of ironic, but as hard as Microsoft has been pushing IPv6 adoption, Windows does not fully support IPv6 in all the ways you might expect. For example, in Windows, it is possible to include an IP address within a Universal Naming Convention (\\\C$, for example). However, you can’t do this with IPv6 addresses because when Windows sees a colon, it assumes you’re referencing a drive letter.

To work around this issue, Microsoft has established a special domain for IPv6 address translation. If you want to include an IPv6 address within a Universal Naming Convention, you must replace the colons with dashes and append to the end of the address — for example, FE80-AB00–

Thực hành chia subnet

Bài toán:

Cho địa chỉ IP:
a.  Địa chỉ này thuộc lớp nào? Giải thích.
b.  Tìm địa chỉ mạng và địa chỉ broadcast của mạng chứa địa chỉ IP trên?
c.  Hãy chia mạng con vừa tìm được ở câu b thành 4 mạng con. Liệt kê các địa chỉ mạng, địa chỉ broadcast và dãy địa chỉ host của 4 mạng con này.



Giải: là địa chỉ đã dc chia
với n=3 ->2^3=8 ta có
bước nhảy: 256-224=32
liệt kê lớp Net: -> IP nằm trong lớp Net này vậy
Net ID:
Star IP:
End IP:
Broadcast: chia thành 4 mạng con
2^n>=4 ->n=2 thì ->
Với n=2 thì ta có SM
Vì defaul là /24 =
Khi mượn thêm 3 thì /27 =
Khi mượn thêm 2 nữa thì tức là thành mượn 5 /29 =
Bước nhảy: 256-248=8
Liệt kê:
Net 1  Net ID:
Star IP:
End IP:
Net 2:   Net ID:
Star IP:
End IP:
Net 3:  Net ID
Star IP:
End IP:
Net 4:   Net ID
Star IP:
End IP:


Subnet mask và cách chia

Vì sao cần phải chia Subnet mask?

Như ta đã biết mạng Internet sử dụng địa chỉ IPv4 32 bit và phân chia ra các lớp A,B,C,D , tuy nhiên, với một hệ thống địa chỉ như vậy việc quản lý vẫn rất khó khăn . Nếu như một mạng được cấp một địa chỉ lớp A thì có nghĩa nó có thể chứa tới 16*1.048.576 địa chỉ ( máy tính ) .Với số lượng máy tính lớn như vậy rất ít công ty hoặc tổ chức dùng hết được điều đó gây lãng phí địa chỉ IP. Để tránh tình trạng đó các nhà nghiên cứu đưa ra một phương pháp là sử dụng mặt nạ mạng con ( Subnet mask ) để phân chia mạng ra thành những mạng con gọi là Subnet. Subnet mask là một con số 32 bit bao gồm n bit 1 ( thường là các bit cao nhất ) dùng để đánh địa chỉ mạng con và m bit 0 dùng để đánh địa chỉ máy trong mạng con với n+m=32 .
Subnet mask phải được cấu hình cho mỗi máy tính trong mạng và phải được định nghĩa cho mỗi giao diện Router. Như vậy, ta phải dùng cùng một Subnet mask cho toàn bộ mạng vật lý cùng chung một địa chỉ Internet. Trong thực tế, để dễ dàng cho hoạt động quản lý các máy trong mạng, thường chia nhỏ các mạng lớn trong các lớp mạng (A, B, C) thành các mạng nhỏ hơn. Quá trình này được thực hiện bằng cách lấy một số bit ở phần định danh host để sử dụng cho việc đánh địa chỉ mạng. Tuỳ theo cách sử dụng của người quản trị mạng ( số subnet và số host trên mỗi subnet ) mà số lượng bit lấy ở phần host nhiều hay ít.
Để tách biệt giữa địa chỉ mạng và địa chỉ host người ta dùng netmask. Để tách biệt giữa Subnet address và địa chỉ host người ta dùng Subnet mask.

Theo quy ước, các địa chỉ IP được chia ra làm ba lớp như sau:
Class  Subnet mask trong dạng nhị phân              Subnet mask
Lớp A 11111111 00000000 00000000 00000000
Lớp B 11111111 11111111 00000000 00000000
Lớp C 11111111 11111111 11111111 00000000

Như ta đã biết, lớp A sử dụng 1 octet đầu tiên làm Network ID. Sử dụng 8 bit đầu được set  giá trị thành 1, và 24 bit sau set giá trị 0 => có Subnet Mask Tương tự với các lớp kia.
Ví dụ IP:
Đây là địa chỉ thuộc lớp C. Và con số 24 có nghĩa là ta sử dụng 24 bit cho phần Network ID, và còn lại 8 bit cho Host ID.

Chia Subnet Mask như thế nào?

Ở đây, mình sẽ trình bày cách ngắn gọn giúp bạn có thể tính nhẩm được. Lấy ví dụ cụ thể như sau:
Công ty thuê một đường IP là Bây giờ ông giám đốc yêu cầu phân làm chia làm 3 mạng con cho ba phòng ban trong công ty. Hãy thực hiện việc chia subnet này.

Trước hết ta phân tích cấu trúc của địa chỉ: như sau:
+ Địa chỉ NetMask:
+ Network ID: 11111111.11111111.11111111
+ HostID: 00000000

Trong ví dụ này ta cần chia làm 3 mạng con (3 subnet) nên ta cần sử dụng 2 bit ở phần Host ID để thêm vào Network ID. Làm sao để biết được số bit cần mượn thêm? Ta có công thức : 2^n>=m (với m là số subnet cần chia, n là số bit cần mượn). Ở đây 2^2>=3.
Sau khi mượn 2 bit, ta có cấu trúc mới ở dạng nhị phân là (bit mượn ta set giá trị bằng 1 nhé):
+ Địa chỉ NetMask:: 11111111.11111111.11111111.11000000
+ Network ID: 11111111.11111111.11111111.11
+ Host ID: 000000
=> Ở dạng thập phân là:

Địa chỉ IP mới lúc này là: (con số 26 là 24 + 2 bits mượn).
Ta xác định “bước nhảy” cho các subnet:
Bước nhảy k=256-192=64
=> Ta có các mạng con sau:
Ip:         Netmask:
Ip:        Netmask:
Ip:      Netmask:
Ip:      Netmask:

Như vậy số máy trên mỗi mạng bằng bao nhiêu?
Số bits của Host ID còn lại sau khi đã bị Network ID mượn: x = 32-26 = 6
=> Số máy trên mỗi mạng: 2^n-2 = 2^6-2 = 62 máy


Something about IP

IP (Internet Protocol) is an address of a computer or other network device on a network using IP or TCP/IP. For example, the number “” is an example of such an address. These addresses are similar to an addresses used on a house and is what allows data to reach the appropriate destination on a network and the Internet.

There are five classes of available IP ranges: Class A, Class B, Class C, Class D and Class E, while only A, B, and C are commonly used. Each class allows for a range of valid IP addresses. Below is a listing of these addresses.

Class Address Range Supports
Class A to Supports 16 million hosts on each of 127 networks.
Class B to Supports 65,000 hosts on each of 16,000 networks.
Class C to Supports 254 hosts on each of 2 million networks.
Class D to Reserved for multicast groups.
Class E to Reserved for future use, or Research and Development Purposes.

Ranges 127.x.x.x are reserved for the loopback or localhost, for example, is the common loopback address. Range255.255.255.255 broadcasts to all hosts on the local network.

IP address breakdown

Every IP address is broke down into four sets of octets that break down into binary to represent the actual IP address. The below table is an example of the IP If you are new to binary, we highly recommend reading our binary and hexadecimal conversions section to get a better understanding of what we’re doing in the below charts.

IP: 255 255 255 255
Binary value: 11111111 11111111 11111111 11111111
Octet value: 8 8 8 8

If we were to break down the IP “”, you would get the below value. In the below table, the first row is the IP address, the second row is the binary values, and the third row shows how the binary value equals the section of the IP address.

166 70 10 23
10100110 01000110 00001010 00010111
128+32+4+2=166 64+4+2=70 8+2=10 16+4+2+1=23

Automatically assigned addresses

There are several IP addresses that are automatically assigned when you setup a home network. These default addresses are what allow your computer and other network devices to communicate and broadcast information over your network. Below is the most commonly assigned network addresses in a home network. 0 is the automatically assigned network address. 1 is the commonly used address used as the gateway. 2 is also a commonly used address used for a gateway. – 254 Addresses beyond 3 are assigned to computers and devices on the network. 255 is automatically assigned on most networks as the broadcast address.

If you have ever connected to your home network, you should be familiar with the gateway address or, which is the address you use to connect to your home network router and change its settings.

Getting an IP address

By default the router you use will assign each of your computers their own IP address, often using NAT to forward the data coming from those computers to outside networks such as the Internet. If you need to register an IP address that can be seen on the Internet, you must register through InterNIC or use a web host that can assign you addresses.

Anyone who connects to the Internet is assigned an IP address by their Internet Service Provider (ISP) who has registered a range of IP addresses. For example, lets assume your ISP is given 100 addresses, This means the ISP owns addresses to and is able to assign any address in that range to its customers. So, all these addresses belong to your ISP address until they are assigned to a customers computer. In the case of a dial-up connection, you are given a new IP address each time you dial into your ISP. With most broadband Internet service providers because you are always connected to the Internet your address rarely changes and will remain the same until the service provider requires it to be changed.

Connecting to the Internet

The above picture is taken from our “How do computers connect to each other over the Internet?” document and gives a good overview of how a computer can talk to another computer over the Internet using an IP address.