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Groups > linux.debian.user > #190311

Re: Mixing and Matching DHCP and static IPs

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Le 26/12/2017 à 15:50, Dan Purgert a écrit :
> 
> Pascal Hambourg wrote:
>> Le 26/12/2017 à 12:33, Dan Purgert a écrit :
>>> [...]
>>> Sounds like perhaps the airstation is blocking client devices from
>>> talking to "bogus" network addresses.  This is generally a feature of
>>> consumer gear to stop you from trying to ask the internet for
>>> information about a RFC1918 address (as they are private / not routable
>>> on the internet).
>>
>> What do you mean by "ask the internet for information about a RFC1918
>> address" ? Sending an IP packet is not asking the internet for any
>> information.
> 
> No, but if you don't know how to get somewhere (e.g. 192.168.1.0/24 from
> 192.168.11.0/24), you "ask" your gateway for assistance in getting the
> packet to its intended destination.

The host does not really "ask" anything to the router ("gateway" is 
deprecated). It justs sends the packet to it. Also, from its routing 
table it knows how to get to the destination : through the router. What 
happens beyond the router is irrelevant to the host as long as the 
packet is forwarded to the destination in the end.

E.g. the following routing table :
default via 192.168.0.1 dev eth0  proto static
192.168.0.0/24 dev eth0  proto kernel  scope link  src 192.168.0.238

does not mean "I don't know how to route anything else than 
192.168.0.0/24". It means "192.168.0.0/24 is directly reachable, and all 
the rest is reachable through the router at 192.168.0.1.

> Now, since RFC1918 space is not routable on the internet, and consumer
> gear is meant to be "easy", some assumptions are made - such that "no,
> they'll never want to use this to talk to an upstream RFC1918 network,
> so we can safely block it and keep them from asking ISP gateways for
> networks that don't actually exist".

This assumption seems wrong. ISP networks use RFC1918 addresses, and 
such devices may be used on private networks

>> Maybe I missed something but I read no evidence in the OP's posts that
>> the netmask on the Airstation WAN side is actually /24. If for instance
>> the mask was set to /30 instead, 192.168.1.3 would be considered by the
>> Airstation as a broadcast address and would explain why it does not work.
> 
> That could also be possible, but I made the assumption that it was the
> "default(tm)" subnet from a generic residential gateway device.  Also,
> since he can apparently ssh into the rpi from whatever the firewall
> device is, it is not likely to be a broadcast address.

But the Air-station may be misled by a wrong DHCP netmask into believing 
that 192.168.1.3 is a broadcast address.

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Thread

Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-25 16:30 +0100
  Re: Mixing and Matching DHCP and static IPs Henning Follmann <hfollmann@itcfollmann.com> - 2017-12-25 17:00 +0100
    Re: Mixing and Matching DHCP and static IPs deloptes <deloptes@gmail.com> - 2017-12-25 18:10 +0100
      Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-26 01:50 +0100
      Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-26 02:00 +0100
        Re: Mixing and Matching DHCP and static IPs Gene Heskett <gheskett@shentel.net> - 2017-12-26 02:50 +0100
        Re: Mixing and Matching DHCP and static IPs deloptes <deloptes@gmail.com> - 2017-12-26 12:20 +0100
          Re: Mixing and Matching DHCP and static IPs Pascal Hambourg <pascal@plouf.fr.eu.org> - 2017-12-26 12:50 +0100
            Re: Mixing and Matching DHCP and static IPs deloptes <deloptes@gmail.com> - 2017-12-26 15:30 +0100
  Re: Mixing and Matching DHCP and static IPs Nemeth Gyorgy <friczy@freemail.hu> - 2017-12-25 18:30 +0100
  Re: Mixing and Matching DHCP and static IPs Pascal Hambourg <pascal@plouf.fr.eu.org> - 2017-12-26 02:40 +0100
  Re: Mixing and Matching DHCP and static IPs Dan Purgert <dan@djph.net> - 2017-12-26 12:50 +0100
    Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-26 13:10 +0100
      Re: Mixing and Matching DHCP and static IPs Dan Purgert <dan@djph.net> - 2017-12-26 15:50 +0100
        Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-26 16:30 +0100
    Re: Mixing and Matching DHCP and static IPs Pascal Hambourg <pascal@plouf.fr.eu.org> - 2017-12-26 13:10 +0100
      Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-26 15:00 +0100
        Re: Mixing and Matching DHCP and static IPs Pascal Hambourg <pascal@plouf.fr.eu.org> - 2017-12-26 15:50 +0100
          Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-26 16:10 +0100
            Re: Mixing and Matching DHCP and static IPs Pascal Hambourg <pascal@plouf.fr.eu.org> - 2017-12-26 16:40 +0100
              Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-27 16:10 +0100
                Re: Mixing and Matching DHCP and static IPs Pascal Hambourg <pascal@plouf.fr.eu.org> - 2017-12-27 18:20 +0100
                Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-28 13:10 +0100
                Re: Mixing and Matching DHCP and static IPs Pascal Hambourg <pascal@plouf.fr.eu.org> - 2017-12-28 15:40 +0100
                Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-28 17:00 +0100
        Re: Mixing and Matching DHCP and static IPs Dan Purgert <dan@djph.net> - 2017-12-26 16:20 +0100
          Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-26 16:30 +0100
      Re: Mixing and Matching DHCP and static IPs Dan Purgert <dan@djph.net> - 2017-12-26 16:10 +0100
        Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-26 16:20 +0100
        Re: Mixing and Matching DHCP and static IPs Pascal Hambourg <pascal@plouf.fr.eu.org> - 2017-12-26 16:50 +0100
  Re: Mixing and Matching DHCP and static IPs Michael Stone <mstone@debian.org> - 2017-12-26 17:00 +0100
    Re: Mixing and Matching DHCP and static IPs Pascal Hambourg <pascal@plouf.fr.eu.org> - 2017-12-26 17:10 +0100
      Re: Mixing and Matching DHCP and static IPs Michael Stone <mstone@debian.org> - 2017-12-26 17:30 +0100
        Re: Mixing and Matching DHCP and static IPs Pascal Hambourg <pascal@plouf.fr.eu.org> - 2017-12-26 17:30 +0100
      Re: Mixing and Matching DHCP and static IPs Mark Fletcher <mark27q1@gmail.com> - 2017-12-27 13:00 +0100

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