local broadcast adresse

[ilyas001]

hi guys i know that this adresse is used with dhcp so you automatically have 255.255.255.255  until you got your new address if i'm correct but i don't understand the thing with dhcp forwarding or dhcp relay  i can't understand this ? and so we have a ipv6 broadcast address ? and i don't get ipv4 link - local adressing it's her for when we can't reach the dhcp server the pc choose automatically a value in the 169.254.0.0/16 ok i get that but if it's random and we have a local network so it's possible that two pc's choose randomly the same value ? 

[Electronics Wizardy]

Dhcp doesn't use a address, esp not 255.255.255.255 as its not a local ip

 

You can't have 2 pcs with the same ip. The dhcp server is smart enough not to do that. Its not random

 

Is there a problem with your network?

[ilyas001]

1 hour ago, Electronics Wizardy said:

Dhcp doesn't use a address, esp not 255.255.255.255 as its not a local ip

 

You can't have 2 pcs with the same ip. The dhcp server is smart enough not to do that. Its not random

 

Is there a problem with your network?

you didn't understood my question at all i know 2 pc's can't have the same ip read well it's when we can't reach the dhcp server and the pc don't have a ip adress it automaticlly choose randomly by itself a ip in the range of 169.254.0.0/16 so you get it now ? and i didn't talk at all about normal ip i'm talking about broadcast adress the broadcast adress is 255.255.255.255 it's a random adress that the pc uses to go to the internet knowing he still don't an ip he use this one to contacte the dhcp server but when the dhcp server is not at the same network there is a thing named dhcp relay to get through this how it world ? do you get it now 

[Electronics Wizardy]

37 minutes ago, ilyas001 said:

automaticlly choose randomly by itself a ip in the range of 169.254.0.0/16 so you get it now

Dhcp server has settings that let you pick what ip ranges to give out.

 

 

[ilyas001]

13 minutes ago, Electronics Wizardy said:

Dhcp server has settings that let you pick what ip ranges to give out.

 

 

ohhh my god do you even read what i write with all respect i said when the dhcp server is doooooooooooooooown there is no dhcp server you can't have an adresse you will randomly take a ip in that rage basiclly i don't think that you know what i'm searching for anyway 

[brwainer]

When a computer is configured for DHCP but can't reach a DHCP server, it will assign itself an APIPA address - this is the range of 169.254.0.0/16. The computer will randomly pick an address, and will use ARP requests to make sure there isn't another device on the subnet already using that address - if it finds another computer on that address, it will pick another adress and check again. Does that answer your question? If you were just looking for what this is called, again it's APIPA

[ilyas001]

6 hours ago, brwainer said:

When a computer is configured for DHCP but can't reach a DHCP server, it will assign itself an APIPA address - this is the range of 169.254.0.0/16. The computer will randomly pick an address, and will use ARP requests to make sure there isn't another device on the subnet already using that address - if it finds another computer on that address, it will pick another adress and check again. Does that answer your question? If you were just looking for what this is called, again it's APIPA

thanks mate no i was searching for the arp thing that what i was wanting thanks me alot now if you can  explai nto me the  ipv4 link - local adressing  it's when the dhcp is not at the same network as the pc so we will need to use a dhcp relay to get through the problem that's what i don't get at all can you explain a little more about it  ? how does it work and why do we need it ? 

[brwainer]

Link local address and APIPA are the same thing. 

 

DHCP relays are usually a function built into smart or managed switches. They're usually only used when you are setting up multiple VLANs

[Lurick]

DHCP relay is used to tell the router or switch where to send a packet when the DHCP server isn't local to that switch. It's used because you aren't going to connect a DHCP server to every switch and you also aren't going to setup local DHCP on every switch either, especially in a large organization. You need a centralized area to hand out DHCP addresses so you have a few living in one part of the network and the DHCP Relay address tells the router/switch where to send those packets.

[brwainer]

2 minutes ago, Lurick said:

DHCP relay is used to tell the router or switch where to send a packet when the DHCP server isn't local to that switch. It's used because you aren't going to connect a DHCP server to every switch and you also aren't going to setup local DHCP on every switch either, especially in a large organization. You need a centralized area to hand out DHCP addresses so you have a few living in one part of the network and the DHCP Relay address tells the router/switch where to send those packets.

It doesn't matter if the DHCP server isn't on the same switch, it matters if the DHCP server is not in the same broadcast domain. Which is usually only an issue when VLANs are in use

[Lurick]

Just now, brwainer said:

It doesn't matter if the DHCP server isn't on the same switch, it matters if the DHCP server is not in the same broadcast domain. Which is usually only an issue when VLANs are in use

Yah, i look at stuff from a design perspective where you generally don't want to extend VLANs across a bunch of switches. You are correct though and I should have clarrified.

[brwainer]

4 hours ago, Lurick said:

Yah, i look at stuff from a design perspective where you generally don't want to extend VLANs across a bunch of switches. You are correct though and I should have clarrified.

I'm not sure what you mean. VLANs exist expressly for the purpose of separating traffic across an entire switched network, and can even be used to take control of switching and forwarding in some situations.

[Sir Asvald]

On 8/7/2016 at 0:47 AM, ilyas001 said:

you didn't understood my question at all i know 2 pc's can't have the same ip read well it's when we can't reach the dhcp server and the pc don't have a ip adress it automaticlly choose randomly by itself a ip in the range of 169.254.0.0/16 so you get it now ? and i didn't talk at all about normal ip i'm talking about broadcast adress the broadcast adress is 255.255.255.255 it's a random adress that the pc uses to go to the internet knowing he still don't an ip he use this one to contacte the dhcp server but when the dhcp server is not at the same network there is a thing named dhcp relay to get through this how it world ? do you get it now 

Well if the server isn't on the same network the PC won't be able to get an IP address.  That's why you get the 169.254.0.0 IP address. Also what are you using for your DHCP relay?`