Path: ...!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: The Natural Philosopher Newsgroups: comp.os.linux.misc Subject: Re: I never thought of this scenario Date: Mon, 8 Apr 2024 08:34:40 +0100 Organization: A little, after lunch Lines: 59 Message-ID: References: <07WdnchvLrr2GI_7nZ2dnZfqn_qdnZ2d@giganews.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Mon, 08 Apr 2024 07:34:41 +0200 (CEST) Injection-Info: dont-email.me; posting-host="539fd89de373294991652ff7019fc9c9"; logging-data="3544566"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX18ulneqGDZm+rMlZMrlEEj5cLj+hIcXx5g=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:KHdo8hhUfu0RHGFqnuztSFEvyg4= Content-Language: en-GB In-Reply-To: Bytes: 3689 On 07/04/2024 14:29, Robert Heller wrote: > At Sun, 7 Apr 2024 13:24:28 +0100 The Natural Philosopher wrote: > >> >> On 07/04/2024 12:37, Robert Heller wrote: >>>> My question is, if that had already been occupied by another piece of >>>> kit, would I have ended up with an IP address clash? >>> This would not happen. I believe that the DHCP server process does something >>> like an "arp" before it assigns leaases. >> >> I think it may in fact do a *ping*. In fact this led me to the >> realisation that none of my Raspberry PI PICO W widgets were responding >> to pings...another 2 hours of my life working out why...:-) >> >> "To prevent a newly allocated IP address conflicting with existing IP >> addresses, the DHCP server sends an ICMP Echo Request packet before >> sending a DHCP Offer message. This ICMP packet contains the IP address >> to be allocated in both the source and destination IP address fields. >> The server can allocate the IP address if it receives no ICMP Echo Reply >> packet within the detection period (no client is using this IP address). >> If the server receives an ICMP Echo Reply packet within the detection >> period, the DHCP server lists this IP address as a conflicting IP >> address (as it is in use by another client), and then waits for the next >> DHCP Discover message to start the IP address selection process again." >> >> https://support.huawei.com/enterprise/en/doc/EDOC1100126920/5cef90ad/how-a-dhcp-server-allocates-network-parameters-to-new-dhcp-clients >> >> >Also, anything with an "old" >>> (pre-reboot) lease would eventually ask for a lease renewal sooner or later >>> (eg when the lease runs out). It would ask for its existing IP address and the >>> router would likely grant that and create an entry int its lease table. >>> >> yes. >> >>> So, even if the router does not have any persistant lease data (eg saved >>> across reboots), the data would eventually be re-created is pretty shourt >>> order. I suspect the lease time for most od these little routersis fairly >>> should (an hour?), >> >> 24 hours... >> >>> so the problem you fear is a non-problem. >> >> It was a potential problem when my Pi Picos didnt respond to pings > > Which is not the *router's* problem, but a mis-configuration problem with the > Pi Picos... No argument there! >> > -- "In our post-modern world, climate science is not powerful because it is true: it is true because it is powerful." Lucas Bergkamp