[chbot] DHCP questions

[Richard Jones]

Is the answer to ensure that there is exactly one DHCP server for the whole
network serving multiple wifi access points hopefully set for
non-overlapping channels and a single SSID?

Richard Jones

On Wed, Aug 17, 2022 at 2:33 PM Robin Gilks <gb7ipd at gmail.com> wrote:

> Hi Volker
>
> I'm up to speed on basic DHCP, I've been running my own server for over 20
> years including PXE booting of dumb clients, fixed MAC address mapping,
> blacklist and white list configurations.
>
> What I don't get is how to prevent a client that roams from one AP to
> another from losing its DHCP allocated address due to either not refreshing
> or starting from scratch on each roam.
>
> I feel it's something to do with VLANs and managed switches but I just
> don't know enough of the vocabulary to hold a conversation
>
>
> On Tue, Aug 16, 2022 at 5:28 PM Volker Kuhlmann <list57 at top.geek.nz>
> wrote:
>
>> Hi Robin,
>>
>> > Didn't have time last night to follow all the information about DHCP and
>> > network spanning etc. The conversation was getting outside my current
>> > knowledge base so if someone can point me at a couple of relevant
>> articles,
>> > so I can digest the basics and can then have a meaningful chat with our
>> > networking suppliers on how their product works, that would be great.
>>
>> Generic beginner rundowns on DHCP should be on the net, but I don't know
>> any off-hand. Ignore DHCP6 (DHCP for IPv6).
>>
>> The basics are simple enough though. DHCP is a protocol which endpoints
>> can use to obtain an IP address. It uses broadcasts, for obvious
>> reasons. The DHCP server grants a lease of an IP address which is valid
>> for a certain time, after which the client must request a new one.
>> Servers can be configured to allocate a static IP based on the MAC
>> address of the client.
>>
>> Things like your ATA basically always default to DHCP - least messing
>> around for the manufacturer. If they default to a fixed IP it's probably
>> printed on the label. The box's web interface may allow to configure
>> anything, factory reset should undo all that.
>>
>> It's easiest to start with DHCP. You can check with nmap -sP .../24
>> where the thing might be address-wise.
>>
>> There's a problem when the box's IP address is not on your computer's
>> network (with DHCP that doesn't happen). In that case alias another IP
>> address to your network interface (ip command, ifconf has been
>> deprecated for many years and may not be installed by default). Then run
>> nmap. You can alias a /16 if you need to. Pick any number for your own
>> interface but not the one the box has. 33..219 should be OK. Cake if
>> you collide...
>>
>> This holds for any network box, but things get a tad more complicated if
>> there is more than one RJ45 shaped hole in it.
>>
>> HTH
>>
>> Volker
>>
>> --
>> Volker Kuhlmann
>> http://volker.top.geek.nz/      Please do not CC list postings to me.
>>
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