Re: [Ilugc] IP address and netmask
On Tue, Jun 12, 2012 at 11:51 AM, Manokaran K manoka...@gmail.com wrote: On Tue, Jun 12, 2012 at 11:23 AM, Suraj Kumar su...@careergear.in wrote: On Sat, Jun 9, 2012 at 2:22 PM, Girish Venkatachalam girishvenkatacha...@gmail.com wrote: We should learn 3 special network blocks , 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 which are not globally unique. This is not technically mandatory anymore. CIDR replaced the class-based network addressing scheme a long time ago. AFAIK, CIDR only dispenses with the need to have rigid network address space and make it network admin definable for his/her convenience. The pvt network blocks still exist and packets meant for it are not allowed to enter the internet. Or am I wrong? You are right. classful addressing still exists in various parts of the Internet. CIDR is technically backwards compatible and hence allows this to exist. Hence I used the phrase this is not *technically mandatory* anymore (ie., the choice is upto you to implement CIDR / classful routing). This can be compared to IPv4 vs IPv6: even if IPv6 becomes widely used, it may still help to learn about our history by knowing about IPv4. Yet, if one is expected to setup a network, it would be short-sighted/foolish to setup an IPv4-only network. This is all I wanted to point out. cheers, -Suraj -- Career Gear - Industry Driven Talent Factory http://careergear.in/ ___ ILUGC Mailing List: http://www.ae.iitm.ac.in/mailman/listinfo/ilugc
Re: [Ilugc] IP address and netmask
On Tue, Jun 12, 2012 at 11:23 AM, Suraj Kumar su...@careergear.in wrote: On Sat, Jun 9, 2012 at 2:22 PM, Girish Venkatachalam girishvenkatacha...@gmail.com wrote: We should learn 3 special network blocks , 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 which are not globally unique. This is not technically mandatory anymore. CIDR replaced the class-based network addressing scheme a long time ago. AFAIK, CIDR only dispenses with the need to have rigid network address space and make it network admin definable for his/her convenience. The pvt network blocks still exist and packets meant for it are not allowed to enter the internet. Or am I wrong? thanks, mano ___ ILUGC Mailing List: http://www.ae.iitm.ac.in/mailman/listinfo/ilugc
Re: [Ilugc] IP address and netmask
AFAIK, CIDR only dispenses with the need to have rigid network address space and make it network admin definable for his/her convenience. The pvt network blocks still exist and packets meant for it are not allowed to enter the internet. Or am I wrong? RFC 1918 address in whatever form will not be allowed/routable over the internet, except when it is going across a VPN tunnel to another Private LAN. -- Regards, Balasubramaniam Natarajan www.etutorshop.com/moodle/ ___ ILUGC Mailing List: http://www.ae.iitm.ac.in/mailman/listinfo/ilugc
Re: [Ilugc] IP address and netmask
On Sat, Jun 9, 2012 at 2:22 PM, Girish Venkatachalam girishvenkatacha...@gmail.com wrote: We should learn 3 special network blocks , 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 which are not globally unique. This is not technically mandatory anymore. CIDR replaced the class-based network addressing scheme a long time ago. cheers, -Suraj -- Career Gear - Industry Driven Talent Factory http://careergear.in/ ___ ILUGC Mailing List: http://www.ae.iitm.ac.in/mailman/listinfo/ilugc
[Ilugc] IP address and netmask
An IP address is composed of 32 bits which is 4 bytes usually written in the form a.b.c.d. Using a tiny sample space of 2^32 possibilities we have been able to successfully networking all electronic items. I wonder what is going to be the timeline for IPv6 rollout. An IP address is composed of 4 octets or 4 bytes written in a human readable form with dots in between. But computers see it differently. It sees it as a hexadecimal quantity, an unsigned long integer. It is also represented differently and written differently if the machine is little endian or big endian. The network byte order or the alignment for networking by convention is always big endian. That way people talk a common language on the wire. Anyway an IP address looks like this internally(0xC0A80103 or 3232235779) which is what we write as 192.168.1.3. $ sipcalc 192.168.1.3/24 -[ipv4 : 192.168.1.3/24] - 0 [CIDR] Host address- 192.168.1.3 Host address (decimal) - 3232235779 Host address (hex) - C0A80103 Network address - 192.168.1.0 Network mask- 255.255.255.0 Network mask (bits) - 24 Network mask (hex) - FF00 Broadcast address - 192.168.1.255 Cisco wildcard - 0.0.0.255 Addresses in network- 256 Network range - 192.168.1.0 - 192.168.1.255 Usable range- 192.168.1.1 - 192.168.1.254 Using IP addresses we can do a lot of things. In fact everything in networking and Internet is actually IP addresses. We should learn 3 special network blocks , 10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16 which are not globally unique. You use them for computers in a local LAN and they never go out to the Internet that way. Only possibility is either NAT them with a globally unique IP address which rewrites the packet header or you should use a VPN to talk to another LAN that is remote. In which case the IP address should be unique across all the LANs connected by VPN. Certain IP addresses are used for broadcast purposes. I have never had to worry about them so far. The concept of netmask is closely linked with the idea of network and host ranges. An IP address always starts with a network part and then a host part. This is very simple. All names in a family end with a certain surname. Similarly all IP addresses in a network start with a certain pattern, say 10. or 192.168. or 172.16... or some such thing. The host part can change to identify each machine like we identify each family member by a name. The netmask is nothing but a simple electronics concept of applying bitmask over the IP address written in binary which does not change for all computers in a network. You specify a network in many ways. Like this usually called CIDR, 192.168.1.0/24 which means that 24 bits of the IP addresses do not change. Or you say, 192.168.1.0 255.255.255.0 which means that the mask is of length 8 + 8 + 8 = 24 bits You can also say 255.240.0.0 which is same as 8+4 = 12 bits It is not very hard. Only networks have masks. IP addresses don't have them. Which means that you cannot have two different IP addresses just by changing the mask. That won't work. Mask is a feature of the IP address space. -Girish -- Gayatri Hitech http://gayatri-hitech.com ___ ILUGC Mailing List: http://www.ae.iitm.ac.in/mailman/listinfo/ilugc
