Given 00101101 00010010 10001100 10100001 11010010 01011110 as a set of address bit received at receiver device, compute the physical address?
Can anyone help me on this?
Related
can you please help me to know what is the 1a after point mean in the following MAC address? Also why it starts from 01 and after that MAC address starts.
Many thanks!
0174.b2ba.c585.1a
That is not a hardware address, but rather a client identifier.
Many DHCP clients will use a client identifier to require an IP address.
Most client software construct this by prepending “01” to the hardware address.
In your example, the 0174.b2ba.c585.1a is 01 and the hardware address 74b2.bac5.851a.
How does contiki os map an IP address to a MAC address, and where is this stored?
I know the basics of ICMPv6 and RPL but once the network is built, when sending an IPv6 packet, how is the MAC address of the next hop known? I assume that a Neighbor Solicitation message is not sent every time. Also, on Cooja, the only ICMPv6 messages I see are RPL messages.
I tried to find the answer by grep, google search and in the doc but I couldn't find it.
There is a uIP neighbor data structure called uip_ds6_nbr_t. These structures are kept in Contiki neighbor tables. When the mapping from an IPv6 address to a MAC address is needed, the code first calls uip_ds6_nbr_lookup(ipv6_address) to find the neighbor, then uses the neighbor to find the link-layer address, by calling the function uip_ds6_nbr_get_ll(nbr).
An ethernet frame header is defined as:
struct ethernet_header {
uint8_t dest_address[6];
uint8_t source_address[6];
uint16_t length_or_ethertype;
};
My understanding is that the 6-octet MAC address format is now formally known as EUI-48. I have also read that there is another format, known as EUI-64, which describes an 8-octet MAC address.
But I'm very confused about the purpose of EUI-64. At face value, the obvious reason for EUI-64 is to deal with address exhaustion when we have more than 2^48 unique devices on Earth. However, all available information I can find Googling about EUI-64 seems to only talk about it in relation to IPv6. That is, EUI-64 provides a way to map a 48-bit MAC address to a IPv6 address.
But, apart from IPv6, does EUI-64 have any other purpose? Was EUI-64 invented purely to solve a problem related to IPv6, or was it also invented to deal with the eventual exhaustion of 48-bit MAC addresses?
I assumed that EUI-64 was primarily designed to deal with eventual exhaustion of 48-bit MAC addresses - meaning that many new hardware devices will be created that have 64-bit MAC addresses (or Extended Unique Identifiers, to use the formally correct term.) But if this is the case, how will any existing networking equipment, such as routers and switches, be able to tell the difference between a packet with a 48-bit source and destination address, and a packet with a 64-bit source and destination address?
Since the first two fields of an Ethernet header are the 2 48-bit source/destination addresses, we can't just replace these fields with 64-bit source/destination addresses, because any software inspecting the packet won't know how to tell the difference, since there is no "type" or "version" field that precedes the addresses. (In the way that, for example, an IP header conveniently has a 4-bit version field as the first 4-bits of the header, so we can easily distinguish between IPv4 and IPv6).
So my question(s):
Is EUI-64 meant to solve 48-bit MAC address exhaustion, or is it
only meant to map MAC addresses to IPv6 addresses?
If EUI-64 is meant to solve eventual 48-bit address exhaustion, how
can networking software distinguish between Ethernet packets
containing 48-bit versus 64-bit MAC addresses?
Since EUI-48 is allocated in 24-bit OUI chunks the address space is running low. Still, it is and will continue to be used for the very popular Ethernet and WiFi networks.
EUI-64 is a superset of EUI-48 and is intended for "new" applications. Currently, it's used for Firewire, ZigBee and, in a EUI-48-derived form, for IPv6.
I am trying to understand the bits which are structured in an IPv4 or CIDR. Reading through RFC documentation I understood that the IP addresses began as 4 octets of made up of 32-bits. I am confused at what a network mask of 255.255.0.0 means?
Even more over if we look at an IP associated with cnn.com
151.101.65.67
Are the individual bits of the IP listed above
01101001.01000001.00110101.00110111
?
Or am I not thinking about this correctly. The network mask has 255.255.0.0 as an example but how would I look at the actuals bits represented in the octets?
The IPv4 address 151.101.65.67 corresponds to the number that can be represented as hexadecimal 0x97654143 or decimal 2539995459. In binary it would be 0b10010111011001010100000101000011. It is shown as 151.101.65.67 for the sake of human readers (decimal 151 = hexadecimal 97 = binary 10010111, etc., notice that you can simply concatenate the hexadecimal or binary representations to form the full number, but not the decimal!)
A network mask determines which part of an IP address corresponds to the network and which part is a host. It "shows" the network part with a binary '1's and "hides" the client part with binary '0's.
The network mask is 'anded' to an IP address and results in the network address. In your example:
IP address (10010111011001010100000101000011) & mask (11111111111111110000000000000000)
is = 10010111011001010000000000000000, or 151.101.0.0
The network mask is usually only relevant locally. Consider a client with IP address 151.101.66.45 and network mask 255.255.255.0 that wants to view a page on your example IP.
The first decision the client needs to make is: can it connect to the address directly (i. e. is it in the same local network?) or does it need to send the request to the router (gateway). By "&"ing its own IP with its own newtwork mask (result = 151.101.66.0) and comparing it with the remote address & its own network mask (result = 151.101.65.0) it determines that both values are not equal, so the request goes to the router for further communication.
i already have studied about the internet IP and all those stuff, but i'm still confused about how to identify network ID from an given IP address, for example, if i have given an IP address: 192.168.250.0/24, so what will be the network ID?
can you guys help me?? and explain the method?
Thank you in advance
You need to convert the IP address and mask to binary, then logically AND them, then convert back to decimal:
192.168.250.0 -----> 11000000.10101000.11111010.00000000
24 bit mask -------> 11111111.11111111.11111111.00000000
=================================== <--- Logical AND
Network address ---> 11000000.10101000.11111010.00000000 ---> 192.168.250.0
This answer on Network Engineering describes how to do all your IP operations.
It s simple, your IP address is 192.168.250.0/24 and you should know that IP address is in a fact 32 bits value of zeros and ones. So it s easy for human to say listen this first 24 bits are network ID (network part) and remaining 8 bits are host ID (host part), but machines need parameter that will use to determine what bits are in network and what bits are ih host part. That s why we have subnet mask, that map IP address in a way that binary ones "1" map bits that belongs to network part and binary zeros "0" map bits that belongs to host part.
So your IP address in binary form is
11000000.10101000.11111010.00000000 when we add subnet mask then you have
11111111.11111111.11111111.00000000 or 255.255.255.0 in decimal form
-------------------------------------
11000000.10101000.11111010. bits maped by binary ones (network part)
.00000000 bits maped by binary zeros (host part)
If you count number of ones in subnetmask you will see that there are 24 binary ones, and that s why we use other notations for presenting subnet mask, and that is by something we call network prefix or "/24".
When host want to send packets he first must determine network address, but how he do that? Every host have IP address and subnet mask let say
192.168.250.6 and subnetmask /24 == 255.255.255.0 or in binary
11000000.10101000.11111010.00000110
11111111.11111111.11111111.00000000
------------------------------------- network hosts use logical AND operation
11000000.10101000.11111010.00000000
(notice that network address is address that have binary zeros in host part of IP address. Logical AND use two values (0 or 1), results of this logical operation is "1" only when both values are "1" (or you can easily rememmber it has to be "1" AND "1" to get "1" as result :) ).
After this host examine destination IP let s say 192.168.10.6, and host use again same operation and if result show that network part is identical with his IP than thay communicate directly or if they have different networkID hosts use gateway since destination is at another network.