How does setting a static IP on a mobile device prevent linux router from assigning that IP address?

On 09/06/2019 10.38, Melzzzzz wrote:
On 2019-06-09, Johann Beretta wrote:
On 4/11/17 3:22 PM, Mike Easter wrote:
snip

For the same reason that when a cable modem releases its leased IP,
waits a short while, and then renews its lease with the DHCP, it gets
the exact same dyanmic IP back again.Â* Normally.

snip
Not entirely accurate. Generally any device on a network, if it follows
the RFCs, will request a renewal of a lease at the 1/2 way point of the
lease.

i.e. if the lease is valid for 10 hours, then the device will attempt to
renew the lease after 5 hours.

If the renewal is denied, the current lease is still valid for the
remaining 5 hours at which point the device will generally request the
new address at some point before the current lease has actually expired.

If a device (cable modem included) released an IP address before getting
a new one, there would be a break in traffic.

I noticed that on cable they associate IP address with MAC and then if
you change MAC you get different address. Return MAC, and you get
previous address :P


That is not a property of cable: it is just an option that management
has. The dhcp server daemon can do that.

--
Cheers, Carlos.

On 09/06/2019 09.26, Johann Beretta wrote:
On 4/11/17 3:10 PM, Tomos Davies wrote:
How does setting a static IP on a linux Android mobile device prevent the
linux router from assigning that IP address to another device?

snip

It doesn't and if you set a static IP on your device, without telling
the router, you risk an IP address conflict and can end up with
colliding packets, or packets addressed for one device that are
sporadically routed to two different devices. IP address conflicts are
miserable to work with.

While your post is interesting, why write now, after the thread died two
years ago? :-)


--
Cheers, Carlos.

Le 09/06/2019 Ã* 09:26, Johann Beretta a écritÂ*:
On 4/11/17 3:10 PM, Tomos Davies wrote:
How does setting a static IP on a linux Android mobile device prevent the
linux router from assigning that IP address to another device?

It doesn't

From dhcpd.conf manpage :
================================================== ======================
IP ADDRESS CONFLICT PREVENTION
The DHCP server checks IP addresses to see if they are in use before
allocating them to clients. It does this by sending an ICMP Echo request
message to the IP address being allocated. If no ICMP Echo reply is
received within a second, the address is assumed to be free.
================================================== ======================

Of course this works only if the device with the static address is
online and replies to ICMP echo (aka ping) requests.

and if you set a static IP on your device, without telling
the router, you risk an IP address conflict and can end up with
colliding packets

Can you explain the relationship between packet collision (physical
layer) and IP address conflict (network layer) ?

In article , Pascal Hambourg
wrote:

How does setting a static IP on a linux Android mobile device prevent the
linux router from assigning that IP address to another device?

It doesn't

From dhcpd.conf manpage :
================================================== ======================
IP ADDRESS CONFLICT PREVENTION
The DHCP server checks IP addresses to see if they are in use before
allocating them to clients. It does this by sending an ICMP Echo request
message to the IP address being allocated. If no ICMP Echo reply is
received within a second, the address is assumed to be free.
================================================== ======================

Of course this works only if the device with the static address is
online and replies to ICMP echo (aka ping) requests.

it only works if the dhcp server does that. not all do. most do not.

On 6/9/19 3:14 AM, Carlos E.R. wrote:
snip

While your post is interesting, why write now, after the thread died two
years ago? :-)



My newsserver had a hiccup and I ended up downloading some ancient
articles (back to 2014).. I didn't notice until I had already posted.

On 11/06/2019 09.07, Johann Beretta wrote:
On 6/9/19 3:14 AM, Carlos E.R. wrote:
snip

While your post is interesting, why write now, after the thread died two
years ago? :-)



My newsserver had a hiccup and I ended up downloading some ancient
articles (back to 2014).. I didn't notice until I had already posted.

Happens to us all now and then :-)

--
Cheers, Carlos.