3 ms·

Title should really have said "with a managed switch".

AnIdiotOnTheNet 5y ago
It is actually possible to do it without a managed switch (and therefore vlans). You just assign a separate subnet between your router and modem than what you use internally and put both router addresses on the same interface.
- tw04 5y ago
  With a single port? How exactly are you planning on preventing one of your end-hosts from pulling the external IP by accident anytime the modem or pi gets rebooted? Are you going to make every host on the LAN a static IP? Ignoring the security implications.
  - tmottabr 5y ago
    if your connection require authentication, like pppoe, you can just disable the dhcp on the modem and use statis addresses between the modem and the pi. then the actual connection will be established by the pi via pppoe and the only DHCP would be the pi when it is up. As for the security implications, i agree.. It surely is a crappy design for the network but it can be done..
  - AnIdiotOnTheNet 5y ago
    > How exactly are you planning on preventing one of your end-hosts from pulling the external IP by accident anytime the modem or pi gets rebooted? Depends on the modem, but since many of them are also routers you just set them up to do single-nat to a static IP corresponding to the "WAN" address of your pi and otherwise not act as a DHCP server at all. Otherwise you could also get a static IP from your ISP so nothing ever changes. > Are you going to make every host on the LAN a static IP? No, they get DHCP addresses from the pi. > Ignoring the security implications. I said it was possible, not that it was a good idea.
    - tw04 5y ago
      >Depends on the modem, but since many of them are also routers you just set them up to do single-nat to a static IP corresponding to the "WAN" address of your pi and otherwise not act as a DHCP server at all. Otherwise you could also get a static IP from your ISP so nothing ever changes. If your modem is doing NAT there's literally no reason for this setup. And it would cause even more issues because you'd have two DHCP servers on the same subnet offering up more than one IP. Even if you set the LAN side of the modem to disable DHCP and only offer a static address, you've still got both the "public" NAT address and "private" in the arp table of all of your hosts. You will absolutely run into issues. >No, they get DHCP addresses from the pi. If you have the modem spitting out DHCP addresses and the PI spitting out DHCP addresses you cannot force your end hosts to grab them from one or the other, they get whichever responds first.
      - AnIdiotOnTheNet 5y ago
        > If your modem is doing NAT there's literally no reason for this setup. Unless you wanted more options than your crappy router/modem gives you. > And it would cause even more issues because you'd have two DHCP servers on the same subnet offering up more than one IP. No, I specifically said the modem would have to not act as a DHCP server at all, just turn it off. > Even if you set the LAN side of the modem to disable DHCP and only offer a static address, you've still got both the "public" NAT address and "private" in the arp table of all of your hosts. Incorrect on two counts. 1) ARP tables only store address translations for your subnet precisely because all addresses not on your subnet must be reached through a gateway. 2) there are only two addresses in the modem<->pi subnet because the pi is performing NAT/PAT for your "LAN" subnet. > You will absolutely run into issues. Maybe, it has been a while since I've done anything this silly, but as I recall from doing stuff like this in a lab I had no issues shoving as many subnets as I wanted to on the same network without VLANs. > If you have the modem spitting out DHCP addresses and the PI spitting out DHCP addresses [...] You don't. You disable DHCP on the modem.

It is actually possible to do it without a managed switch (and therefore vlans). You just assign a separate subnet between your router and modem than what you use internally and put both router addresses on the same interface.

tw04 5y ago
With a single port? How exactly are you planning on preventing one of your end-hosts from pulling the external IP by accident anytime the modem or pi gets rebooted? Are you going to make every host on the LAN a static IP? Ignoring the security implications.
- tmottabr 5y ago
  if your connection require authentication, like pppoe, you can just disable the dhcp on the modem and use statis addresses between the modem and the pi. then the actual connection will be established by the pi via pppoe and the only DHCP would be the pi when it is up. As for the security implications, i agree.. It surely is a crappy design for the network but it can be done..
- AnIdiotOnTheNet 5y ago
  > How exactly are you planning on preventing one of your end-hosts from pulling the external IP by accident anytime the modem or pi gets rebooted? Depends on the modem, but since many of them are also routers you just set them up to do single-nat to a static IP corresponding to the "WAN" address of your pi and otherwise not act as a DHCP server at all. Otherwise you could also get a static IP from your ISP so nothing ever changes. > Are you going to make every host on the LAN a static IP? No, they get DHCP addresses from the pi. > Ignoring the security implications. I said it was possible, not that it was a good idea.
  - tw04 5y ago
    >Depends on the modem, but since many of them are also routers you just set them up to do single-nat to a static IP corresponding to the "WAN" address of your pi and otherwise not act as a DHCP server at all. Otherwise you could also get a static IP from your ISP so nothing ever changes. If your modem is doing NAT there's literally no reason for this setup. And it would cause even more issues because you'd have two DHCP servers on the same subnet offering up more than one IP. Even if you set the LAN side of the modem to disable DHCP and only offer a static address, you've still got both the "public" NAT address and "private" in the arp table of all of your hosts. You will absolutely run into issues. >No, they get DHCP addresses from the pi. If you have the modem spitting out DHCP addresses and the PI spitting out DHCP addresses you cannot force your end hosts to grab them from one or the other, they get whichever responds first.
    - AnIdiotOnTheNet 5y ago
      > If your modem is doing NAT there's literally no reason for this setup. Unless you wanted more options than your crappy router/modem gives you. > And it would cause even more issues because you'd have two DHCP servers on the same subnet offering up more than one IP. No, I specifically said the modem would have to not act as a DHCP server at all, just turn it off. > Even if you set the LAN side of the modem to disable DHCP and only offer a static address, you've still got both the "public" NAT address and "private" in the arp table of all of your hosts. Incorrect on two counts. 1) ARP tables only store address translations for your subnet precisely because all addresses not on your subnet must be reached through a gateway. 2) there are only two addresses in the modem<->pi subnet because the pi is performing NAT/PAT for your "LAN" subnet. > You will absolutely run into issues. Maybe, it has been a while since I've done anything this silly, but as I recall from doing stuff like this in a lab I had no issues shoving as many subnets as I wanted to on the same network without VLANs. > If you have the modem spitting out DHCP addresses and the PI spitting out DHCP addresses [...] You don't. You disable DHCP on the modem.