ISP Wireless Modem WTF



  • Alright, this happened awhile ago, but something made me remember it tonight.

    Awhile ago I was running some services from a *nix box on my home network. I did this for months and everything was fine.

    Then came a day where I convinced my ISP to upgrade the lines going into my house. When they did this, they gave me a brand new modem. It was a modem and wireless router all-in-one. I didn't really like the idea of replacing my highly configurable router with their "noob friendly" one, but they insisted that I use this one.

    Here's the problem: It would always give out random local IPs. It doesn't matter if the device requested a certain IP, it would be given a random one. There was no way to configure the thing to give a set IP to a certain device or computer. Now, anyone with a brain knows this will cause a problem when you're forwarding ports. Everytime the modem/router got reset, my box would be given a new random IP, and the port forwards would break.

    Here's the WTF: In order to "save and apply" new port fowarding rules, the modem/router would need to restart itself....

    So, if I set up a port forwarding rule for the ip 192.168.0.111, the modem/router would restart and the device would then be given it's new random IP: 192.168.0.222, thus breaking the port fowarding rule.

    I complained, got them to give me another modem (which didn't include a router), and the problem was fixed.



  • Without seeming like I'm raining on your parade or anything, but why didn't you just fix all your local machines' IP addresses?



  •  From my post: "It doesn't matter if the device requested a certain IP"

     It doesn't matter if I fixed the IP on the device, the modem/router would give a random one.



  • @AlexSolonik said:

     From my post: "It doesn't matter if the device requested a certain IP"

     It doesn't matter if I fixed the IP on the device, the modem/router would give a random one.

    But that doesn't make sense. If you fix the IP on the device, there is no DHCP request, why would it reconfigure itself with another IP?


  • Discourse touched me in a no-no place

    @gremlin said:

    @AlexSolonik said:

     From my post: "It doesn't matter if the device requested a certain IP"

     It doesn't matter if I fixed the IP on the device, the modem/router would give a random one.

    But that doesn't make sense. If you fix the IP on the device, there is no DHCP request, why would it reconfigure itself with another IP?

    Are you implying that the router would refuse to talk to any IP address to which it hadn't handed out, but which was on the same subnet as it?



  • What I said was:There is no way to configure the router to give a specific IP to a specific device, and if you set up your device to use a certain local IP, it will not be given that IP.

    Using your logic there, If I tell my laptop to use "192.168.0.101" What happens when I join a network in which that IP already exists? My laptop is either going to re-configure itself, or if I tell it not to do that, it simply won't be allowed to join the network.

    Your device can't just say "This is my IP" and be stubborn about it. If another device tries to send that device data, they either use the IP the router assigned to that device, or the data won't be delivered.

     




  • @AlexSolonik said:

    if you set up your device to use a certain local IP, it will not be given that IP.

    of course, it will not be given any IP, since it will not ask for one, it will just use the one you told it to use. 

    @AlexSolonik said:


    Using your logic there, If I tell my laptop to use "192.168.0.101" What happens when I join a network in which that IP already exists? My laptop is either going to re-configure itself, or if I tell it not to do that, it simply won't be allowed to join the network.

    I'm not saying it's necessarily a good idea to fix the IP (especially if it is a portable device that will be used on other networks), I agree that router was a pile of shite that I would have gotten replaced too. If you choose an IP that is already in use by another device, of course there will be a conflict, and the way that is handled probably depends on the OS. But there is no reason why you can't do this, the router will not "refuse to let it join the network" if it doesn't use DHCP.

    @AlexSolonik said:

     

    Your device can't just say "This is my IP" and be stubborn about it.

     

    Of course it can, as long as it doesn't conflict with another device. DHCP is just a way to automatically assign IP addresses, no device is forced to use it if they don't want to.

    @AlexSolonik said:

     

    If another device tries to send that device data, they either use the IP the router assigned to that device, or the data won't be delivered.

    If there was no DHCP request, there is no "IP the router assigned to that device", there is just the IP that was fixed, and the device is identified by that IP. The router will find where that IP is connected using ARP whether is was configured with DHCP, or manually.


  • Discourse touched me in a no-no place

    @AlexSolonik said:

    Using your logic there, If I tell my laptop to use "192.168.0.101" What happens when I join a network in which that IP already exists? My laptop is either going to re-configure itself, or if I tell it not to do that, it simply won't be allowed to join the network.
    Well since the computer with services concerned would presumably be on the network prior, during and after a router reboot, this shouldn't be an issue, since your router shouldn't be handing out the address of that computer since it already exists on the network.



    Of course, since they've broken one part of the DHCP protocol, I'm sure it wouldn't be too much of a stretch to contemplate them breaking other parts of it.



  • @AlexSolonik said:

    Your device can't just say "This is my IP" and be stubborn about it. If another device tries to send that device data, they either use the IP the router assigned to that device, or the data won't be delivered.
    I don't get what your saying here. I've setup many routers and I never let the router decide the IPs for the devices. All the devices use static IPs and are stubborn about that - they'll never change. If they see someone else using there IP they'll say "another device on the network is using this IP", but thats all. 

    The routers also don't care what IP you use. They lookup the IP using the MAC address via ARP. 




  • @AlexSolonik said:

    What I said was:There is no way to configure the router to give a specific IP to a specific device, and if you set up your device to use a certain local IP, it will not be given that IP.

    Using your logic there, If I tell my laptop to use "192.168.0.101" What happens when I join a network in which that IP already exists? My laptop is either going to re-configure itself, or if I tell it not to do that, it simply won't be allowed to join the network.

    Hm. I think you are a little fuzzy on network concepts.

    If you have a static IP set, and your computer can't contact any other devices, it's not going to "reconfigure" itself-- it can't! You have a static IP set already. (Static IP and DHCP are mutually-exclusive.) If you set a static IP that matches the configuration of the rest of your network (i.e. the Gateway and Subnet mask are set correctly), you don't need to do anything else to have a working network connection. Your computer is just on the network at that static IP.

    If you set your laptop to 192.168.0.101 and that IP is already in use, yes you'll cause all kinds of chaos and most likely your device will be kicked offline. That's why you make sure you set your static IPs to IPs outside the DHCP pool. On my router, for example, the DHCP pool is only 192.168.0.100 - 192.168.0.199. That leaves a full 150 static IPs I can set that won't get clobbered by the router's DHCP.

    @AlexSolonik said:

    Your device can't just say "This is my IP" and be stubborn about it. If another device tries to send that device data, they either use the IP the router assigned to that device, or the data won't be delivered.

    Sure it can, why can't it? Hell, at the hospital I used to work at, everything had a static IP, even label printers and timeclocks. The DHCP pool was tiny, like 25 IP addresses, and only used for doctor's or administrator's laptops.

    Of course, in the real world the device stubbornly saying "this is my IP" won't get its IP assigned to anything else, either because you the administrator are smart enough to prevent it, or the router its plugged in to is smart enough to prevent it. Since your router is boneheaded, make sure you pick option 1.



  • Hmm,perhaps my network  concepts are fuzzy, but what I said remains:

    I could not set/fix an IP on a device. I included that as part of my original post, and if I had been able to do that , this wouldn't have been a WTF.



  • @AlexSolonik said:

    Hmm,perhaps my network  concepts are fuzzy, but what I said remains:

    I could not set/fix an IP on a device. I included that as part of my original post, and if I had been able to do that , this wouldn't have been a WTF.

    The part where you're losing us is:

    Why not?

    Setting the IP of a device is a function of the device itself, not the router. You're not suggesting that switching routers made the (for example) Xbox Live network settings panel disappear, are you?



  • I'm suggesting that my device would either use the assigned IP (assigned by DHCP), or it would not be allowed to communicate/join the network.



  • @AlexSolonik said:

    Hmm,perhaps my network  concepts are fuzzy, but what I said remains:

    I could not set/fix an IP on a device. I included that as part of my original post, and if I had been able to do that , this wouldn't have been a WTF.

     

    You still seem to be a little confused about some basic networking concepts. DHCP reservations (what it sounds like you're talking about) are different than static IPs (what everyone else is talking about). DHCP reservations (sometimes unfortunately called "static DHCP") are set on the DHCP server (eg. your router) so that the DHCP server always hands out the same IP address to a specified MAC address. Actual static IPs are set on the device. For example, in Windows, you can change your network settings to either use DHCP, so it asks for an address, or a static IP, where you can specify what IP address to use. I can't think of any devices I've ever worked on that couldn't have a statically assigned IP address. And as long as you specify an IP address in the proper subnet, with the correct subnet mask and gateway, and preferably outside of the DHCP pool, it should just work.

     Also, most ISP-provided modem/routers can be put into bridged mode. In bridged mode, the modem just acts like a modem, and you can use your own router to do the PPPoE (if it's DSL), and your own router gets the external IP address passed through to it.



  • @AlexSolonik said:

    I'm suggesting that my device would either use the assigned IP (assigned by DHCP), or it would not be allowed to communicate/join the network.

    And... this is the router's fault, and not yours for setting a bad IP/Subnet/Gateway?

    Sorry, I'm not trying to pick on you, just trying to figure out what the issue is. I've no doubt the router is a piece of crap, but I don't buy for a moment that it won't route manually-assigned IPs.


  • Discourse touched me in a no-no place

    @AlexSolonik said:

    I'm suggesting that my device would either use the assigned IP (assigned by DHCP), or it would not be allowed to communicate/join the network.
    Given the sparse information thus far provided, the router was not the problem in this instance.



  • @blakeyrat said:

    Sorry, I'm not trying to pick on you, just trying to figure out what the issue is.

     

     

    Get off the forum! Your kind aren't welcome here!



  • @PeriSoft said:

    @blakeyrat said:

    Sorry, I'm not trying to pick on you, just trying to figure out what the issue is.

     

     

    Get off the forum! Your kind aren't welcome here!

    yeah, I guess if people here had to make me feel like a 'tard about dispHtmlElementCollection, then it's my duty to make other newcomers feel like a 'tard about whatever their issue is.



  • It's not necessarily a requirement to feel like a 'tard. As long as they realise the WTF forums are full of programmers with psychic or
    telekinetic powers.



  • @b_redeker said:

    Filed under: when googling for dispHtmlElementCollection, your blog came up second :)

    That's because it's still completely undocumented. :) Other than this site, and my blog, that is.

    Getting a few emails and comments from other people who were equally confused as I was after seeing dispHtmlElementCollection in the debugger has made me feel a whole lot better about the whole thing. I'd still prefer it were documented, but at least I'm not alone in thinking it's goofy that it's not documented.



  • @AlexSolonik said:

    I'm suggesting that my device would either use
    the assigned IP (assigned by DHCP), or it would not be allowed to
    communicate/join the network.

    Thats the part I don't get. If you set your PC to 'Use the following IP' instead of 'Obtain an IP automatically', your router is not going to try and throw you off the network and say "No, that's not the IP I want you to have, your not talking". It cant do that. Just set the subnet and gateway and you'll be able to talk anyway. 



  • @Mole said:

    Thats the part I don't get. If you set your PC to 'Use the following IP' instead of 'Obtain an IP automatically', your router is not going to try and throw you off the network and say "No, that's not the IP I want you to have, your not talking". It cant do that. Just set the subnet and gateway and you'll be able to talk anyway. 


    Actually, it's perfectly possible to have a router so brain-dead that it accepts connections only from nodes in its DHCP IP range, or worse, only from MAC addresses in its "I DHCP'd to this one" list.

    And as we all know, if something's THAT stupid, it surely exists somewhere.



  •  Or better yet.. put your fancy router that you already have and loved so much BEHIND the router given to you by the ISP and forward ALL ports to it. Then use your own fancy router however you like.



  •  Having seen my share of crappy routers, I can completely sympathize. I once had an ISP that insisted I use their router/modem device. It would not permit any static DHCP addresses to be configured. It was addresses as 192.168.0.1/24 period, you could not change it. And it would assign DHCP addresses from .2 through .255 in apparently random order, whether they were in use or not.

     So you have no choice but to use dynamic IP addresses and had no way to keep a machine on the same IP. On the bright side, it didn't support port forwarding, so I didn't have the OPs problem. I finally quarrantined it behind a Linux box that made things sane.

     



  • @AlexSolonik said:

    I'm suggesting that my device would either use the assigned IP (assigned by DHCP), or it would not be allowed to communicate/join the network.

    Sorry. I am willing to accept, that the modem has totally broken DHCP server, but I am not willing to accept that even a clinically insane modem would not talk to device with statically assigned IP in correct subnet.

    The thing is, that there are two subsystems -- the router and the DHCP server. And they don't talk to each other. DHCP simply assigns addresses in correct range and router routes anything in that range. If you turn off the DHCP server and assign the IP addresses (from the same set) in another way, the router won't know the difference.



  • Guys, we need to speak clearly to help him:

     lern2IP



  •  PROTIP: think twice before posting on a website whose main theme is : "le'ts mock the failures of others and feel superior about it".

     Also there is no central authority on Ethernet networks that says who can and can't connect to it. If you want to take the IP of another host and wreak havoc, you can. It's the basis of a class of attacks called ARP poisoning. DHCP is a facility invented long after Ethernet.



  • TRWTF is that you lot can't believe that an ISP would send out a crappy non-router. As it is, though, I've seen them in action. One generation of BT Homehub did this, If I recall correctly, and I've certainly seen it other places as well.

    Basically, ISP-supplied network-box-thingies are usually a firewall as well as a router and DHCP server (and modem). It's not massively unusual to find that traffic to all addresses on the network is blocked except to addresses that have been assigned by the router. Every now and again, you get a router that does that, and also does not permit static IP assignment - it is, indeed, a stupid WTF in the firmware, and it breaks manual port-forwarding when it happens.



  • Hm?  What would the upstream network gear have anything to do with client settings?  The network could be plugged into a gallon of milk and the client computer can still set a static IP.



  • You can set any IP address you like, and for all I know, the router part of the box will try and direct traffic to it. The firewall part, though, will block that traffic unless the router assigned the IP address. It's not at all uncommon for all traffic to all ports on all internal addresses to be blocked by default, with the only way to unblock it to have your address assigned by DHCP or statically by the router. It's a lot rarer to also be unable to assign static IPs from the router, but not unheard of.



  • @davedavenotdavemaybedave said:

    You can set any IP address you like, and for all I know, the router part of the box will try and direct traffic to it. The firewall part, though, will block that traffic unless the router assigned the IP address. It's not at all uncommon for all traffic to all ports on all internal addresses to be blocked by default, with the only way to unblock it to have your address assigned by DHCP or statically by the router. It's a lot rarer to also be unable to assign static IPs from the router, but not unheard of.

    I'm not going to say you're wrong, but I will say that I've worked with tons of networking equipment over the years and I've never seen anything like this.

    You're basically saying that you've come across a router that, for all intents and purposes, refused to route to anything not using DHCP? Again, I'm not sure I buy it...


  • Discourse touched me in a no-no place

    @blakeyrat said:

    You're basically saying that you've come across a router that, for all intents and purposes, refused to route to anything not using DHCP? Again, I'm not sure I buy it...
    Consider a home-unit that has a firewall bundled in with it. Default is to block all outgoing traffic.



    Anyone getting a DHCP IP address gets a hole punched into that firewall to allow traffic out from that IP.



    No provision is made to allow for static IP addresses on this unit or to manually fiddle with the firewall in any way. Those with static IP's are free to do what they want within the network, but they're not going to get very far if they want to get off it.



    Well that's how I'd put together a brain-dead cable-modem anyway.



  • @PJH said:

    @blakeyrat said:
    You're basically saying that you've come across a router that, for all intents and purposes, refused to route to anything not using DHCP? Again, I'm not sure I buy it...
    Consider a home-unit that has a firewall bundled in with it. Default is to block all outgoing traffic.



    Anyone getting a DHCP IP address gets a hole punched into that firewall to allow traffic out from that IP.



    No provision is made to allow for static IP addresses on this unit or to manually fiddle with the firewall in any way. Those with static IP's are free to do what they want within the network, but they're not going to get very far if they want to get off it.



    Well that's how I'd put together a brain-dead cable-modem anyway.

    I agree that you could set up a modem that way, what I'm saying is that I don't believe anybody has.



  • @blakeyrat said:

    @davedavenotdavemaybedave said:
    You can set any IP address you like, and for all I know, the router part of the box will try and direct traffic to it. The firewall part, though, will block that traffic unless the router assigned the IP address. It's not at all uncommon for all traffic to all ports on all internal addresses to be blocked by default, with the only way to unblock it to have your address assigned by DHCP or statically by the router. It's a lot rarer to also be unable to assign static IPs from the router, but not unheard of.

    I'm not going to say you're wrong, but I will say that I've worked with tons of networking equipment over the years and I've never seen anything like this.

    You're basically saying that you've come across a router that, for all intents and purposes, refused to route to anything not using DHCP? Again, I'm not sure I buy it...

    Allow me to demonstrate: http://www.google.co.uk/search?q=fucking+linksys

    This is not something that happens on proper kit, but the lower down the evolutionary scale the end-users are expected to be, the more locked-down the 'plug it into the wall, job done' installation process gets. Bear in mind that for 99.99% of the target market, this will never be an issue.


Log in to reply
 

Looks like your connection to What the Daily WTF? was lost, please wait while we try to reconnect.