A very newbie question regarding modem and router IP address

supo

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Dec 2, 2016
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Hi all, I have very basic IP question since I'm no expert in networking and since I'm troubleshooting a big network issue at home I wanted to know something just to make sure.

If my modem/routers public IP (from my ISP) is let's say (made up by me now) 74.123.12.321

What should my own router (that is connected to ISP's modem/router) have as an IP address?

My ISP's modem/router is in bridge mode. My own router shows a different IP like let's say 74.123.11.345 meaning that it's not the same public IP but it's a different one. Is this how it is supposed to be? Two different IP addresses? My ISP only provides one IP that I know. Thanks in advance.
 

Grebuloner

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Yes, this is how it is supposed to be. Your home network (from the router) uses its own local IP settings so all the different devices can talk to each other, and the ISP's IP is for all the data coming to/from the outside world (you can look up Network Address Translation (NAT) to see how that data finds its way to the right devices once it arrives). Your modem/router does all the translation between your network and the rest of the world between the two address systems.

Your home address system is probably 192.168.x.x-style which is the most common default. There are three ranges of IP addresses (10.x.x.x, 172.16.x.x, 192.168.x.x) that are strictly reserved for private (LAN) network usage and don't work on the public internet. If you have something else, there's a setting in the router that should be fixed.
 

supo

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Dec 2, 2016
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Yes, this is how it is supposed to be. Your home network (from the router) uses its own local IP settings so all the different devices can talk to each other, and the ISP's IP is for all the data coming to/from the outside world (you can look up Network Address Translation (NAT) to see how that data finds its way to the right devices once it arrives). Your modem/router does all the translation between your network and the rest of the world between the two address systems.

Your home address system is probably 192.168.x.x-style which is the most common default. There are three ranges of IP addresses (10.x.x.x, 172.16.x.x, 192.168.x.x) that are strictly reserved for private (LAN) network usage and don't work on the public internet. If you have something else, there's a setting in the router that should be fixed.
Umm..if I take my modem/router out of bridge mode then my own router gets 192.168.x.x yes however when I enable bridge mode then I get something that is very similar to my Public IP adress from the ISP but not the exact same one. So this is wrong? In bridge mode, I should get 192.168.x.x instead?
What settings do I need fiddle with? I never had to do anything on my previous modem + my router as everything was automatic so to speak.
 

Grebuloner

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Don't use bridge mode. That is for using a separate router after the modem, but you have a combination modem/router device so you don't want that. With bridge mode on, you are essentially exposing your computer directly to the internet, which is A Very Bad Idea™ for the vast majority of home users.

Since turning it off gets you to the 192 system, there shouldn't be anything more that you need to do and you're good to go, but you can post your model and I can run through the manual to see if there are any other settings tweakable for convenience and safety.
 

supo

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Dec 2, 2016
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Don't use bridge mode. That is for using a separate router after the modem, but you have a combination modem/router device so you don't want that. With bridge mode on, you are essentially exposing your computer directly to the internet, which is A Very Bad Idea™ for the vast majority of home users.

Since turning it off gets you to the 192 system, there shouldn't be anything more that you need to do and you're good to go, but you can post your model and I can run through the manual to see if there are any other settings tweakable for convenience and safety.
As far as I know though, isn't it always advised to put your modem/router combo in bridge mode when you connect another router to it? So that there won't be any NAT issues etc.? I have a Sagemcom Fast 3890V3 modem/router (from my ISP) and a Netgear Nighthawk XR500 connected to it.
 

Machupo

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In that case, yes, you would want your ISP device to be in bridge mode and for your own router to be the primary device. In that implementation, your router's WAN IP would be of the 74.whatever series (unless you pay for a static IP, most ISPs are using DHCP to serve up an IP address for your connection, so that is why it is different), the LAN IP of your router should be one of the reserved address blocks (most I have used go to the 192.168.x.x block).

Can you describe your connection issues in a bit more detail?
 

Nicklebon

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Umm..if I take my modem/router out of bridge mode then my own router gets 192.168.x.x yes however when I enable bridge mode then I get something that is very similar to my Public IP adress from the ISP but not the exact same one. So this is wrong? In bridge mode, I should get 192.168.x.x instead?
What settings do I need fiddle with? I never had to do anything on my previous modem + my router as everything was automatic so to speak.
Yes this is the correct behaviour. The ISP router and your router have different MAC addresses that is why they will get different IPs. With the ISP device in bridge mode your router should get the public IP. If the ISP device is in router mode then your router will get a private IP. Any devices you plug into the LAN side of your router will get PATed using what ever address your router has. If the ISP device is in router mode it will also PAT your devices resulting in double PAT. Leave the ISP device in bridge mode and use your own router and plug all your devices into that. The only device that should plugged in ISP device is your router.
 

Grebuloner

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I misread your original post, my bad. Then yes, you want the combo unit in bridge mode and the only device connected to it should be your Netgear. Check the settings to make sure the wifi on the Sagemcom is turned off, too. It is odd that you get a second outside IP address (and that must be provided by the ISP), but if everything is working well, you access your router at a 192 address, and your computer reports its own IP address (you can run the command line and enter "ipconfig") as a 192 value, you're all good.
 

supo

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In that case, yes, you would want your ISP device to be in bridge mode and for your own router to be the primary device. In that implementation, your router's WAN IP would be of the 74.whatever series (unless you pay for a static IP, most ISPs are using DHCP to serve up an IP address for your connection, so that is why it is different), the LAN IP of your router should be one of the reserved address blocks (most I have used go to the 192.168.x.x block).

Can you describe your connection issues in a bit more detail?
What happens to me is that my Internet connection works perfectly for ~2 days then suddenly it slows down to a crawl and becomes unusable, can barely open a website etc.
To fix it temporarily what I do is I just unplug my ethernet cable from the back of the modem and plug it right back in then it works perfect again for ~2 days then the problem occurs again after.

Things I have tried: 3 different wireless routers (Asus ac86u, ac66u, Netgear XR500), changed ethernet cables with new ones, changed my modem/router with another one. I don't know what else to try I'm at a loss.

I have also an unmanaged switch connected to my router that's working perfectly since 2014. So switch is the only thing I didn't change yet but it's working without issues.

According to my ISP there are no issues with the modem/router combo either... My previous modem/router model worked perfectly for years without any issues...until they changed those to these new ones...

Edit: forgot to mention that I have also factory reset both several times just to make sure.
 
Last edited:

supo

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I misread your original post, my bad. Then yes, you want the combo unit in bridge mode and the only device connected to it should be your Netgear. Check the settings to make sure the wifi on the Sagemcom is turned off, too. It is odd that you get a second outside IP address (and that must be provided by the ISP), but if everything is working well, you access your router at a 192 address, and your computer reports its own IP address (you can run the command line and enter "ipconfig") as a 192 value, you're all good.
No worries. Yeah the Wifi is turned off automatically when I enable bridge mode. Yeah I enter my routers Web interface via 192.168.x.x without problem.
 

supo

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Yes this is the correct behaviour. The ISP router and your router have different MAC addresses that is why they will get different IPs. With the ISP device in bridge mode your router should get the public IP. If the ISP device is in router mode then your router will get a private IP. Any devices you plug into the LAN side of your router will get PATed using what ever address your router has. If the ISP device is in router mode it will also PAT your devices resulting in double PAT. Leave the ISP device in bridge mode and use your own router and plug all your devices into that. The only device that should plugged in ISP device is your router.
Ah yes. Yeah this is exactly what I do, modem/router in bridge mode, then only my wireless router connected to it, while everything else is connected to this router.
 

Machupo

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What happens to me is that my Internet connection works perfectly for ~2 days then suddenly it slows down to a crawl and becomes unusable, can barely open a website etc.
To fix it temporarily what I do is I just unplug my ethernet cable from the back of the modem and plug it right back in then it works perfect again for ~2 days then the problem occurs again after.

Things I have tried: 3 different wireless routers (Asus ac86u, ac66u, Netgear XR500), changed ethernet cables with new ones, changed my modem/router with another one. I don't know what else to try I'm at a loss.

I have also an unmanaged switch connected to my router that's working perfectly since 2014. So switch is the only thing I didn't change yet but it's working without issues.

According to my ISP there are no issues with the modem/router combo either... My previous modem/router model worked perfectly for years without any issues...until they changed those to these new ones...

Edit: forgot to mention that I have also factory reset both several times just to make sure.
Can you pull any logs from your router or your modem?

You sure it is time repeatable (or is it traffic-volume repeatable)?
 

supo

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Can you pull any logs from your router or your modem?

You sure it is time repeatable (or is it traffic-volume repeatable)?
Okay so here is some logs from my modem:


2020-02-02 00:29:14​
Warning
DHCPC​
WAN DHCP client (1) stopped
2020-02-02 00:23:03​
Info
SYS​
TR-069 connectivity to (acs.get.no) has failed
2020-02-01 23:09:37​
Info
SYS​
TR-069 connectivity to (acs.get.no) has failed
2020-02-01 22:06:15​
Info
SYS​
TR-069 connectivity to (acs.get.no) has failed
2020-02-01 21:20:22​
Info
SYS​
TR-069 connectivity to (acs.get.no) has failed
2020-02-01 20:16:59​
Info
SYS​
TR-069 connectivity to (acs.get.no) has failed

So here is another thing I found out. On my Asus ac86u the problem occurs always in ~2-3 but on my Netgear XR500 it happens in ~1 day, and no I don't believe it's because of the traffic volume. And also I have disconnected my router and wanted to use only my modem/router combo now and it seems like the connection works in general much much better than when I have a external router connected. So my conclusion is no matter which external router I use there is a conflict going on between the modem/router and the external router. I guess I need to do something more with the settings of the modem/router other than putting it in bridge mode but I don't know what else should I change. I want to use my own external router as I always have, I don't want to use the crappy router functionality of the modem/router from my ISP...
 

rekd0514

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Why not request a modem only from your ISP instead of the combo device? Or just buy your own and stop renting one.
 

Machupo

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many routers have mac cloning capability, have you tried setting it the same as your modem wan port?

have you reset both modem and router to default factory config?

if those logs are from your modem, it seems like you have some line issues, do the logs show similar reports when you are plugged directly into your modem (e.g. not bridge mode)? can you get into the administrative menu and see your channel signal strengths?
 

supo

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many routers have mac cloning capability, have you tried setting it the same as your modem wan port?

have you reset both modem and router to default factory config?

if those logs are from your modem, it seems like you have some line issues, do the logs show similar reports when you are plugged directly into your modem (e.g. not bridge mode)? can you get into the administrative menu and see your channel signal strengths?
What does MAC cloning do exactly? Yeah I have factory reset both several times and started from scratch etc. I don't think I have a line issue though since if I use only my ISP modem/router alone everything works perfect, but when I use any external router then connection becomes bad after a while like 1-3 days but not right away though. And forgot to mention that when the issue occurs it affects both wired and wireless connection.
 

Nicklebon

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Just to make sure I have an accurate description of the problem.

With ISP device in bridge mode everything works well for some time. After some time internet activity gets VERY slow but things do work just extremely slowly. Yes or No?

Once thing the problem occurs to fix it you just unplug your router from the ISP device and then plug it back in. Yes?

Assuming all of those are yes:

1. Exactly what is the ISP device?
2. Is your router plugged directly into the ISP device with no switches or cross connects in between. Just a simple short CAT 5E or better patch cable going from WAN port of your router to LAN port of the ISP device? Is the cable a cross over cable? I ask this because a lot devices especially from ISPs come with shitty cross over cables, shitty cables in general because they are cheap, and they are the devil.

If traffic is flowing it sounds like a speed/duplex mismatch or even a clocking issue. I'm pretty sure you another thread on here about this and you said that you were not specifying the connection speed anywhere. This is true yes?
 

supo

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Just to make sure I have an accurate description of the problem.

With ISP device in bridge mode everything works well for some time. After some time internet activity gets VERY slow but things do work just extremely slowly. Yes or No?

Once thing the problem occurs to fix it you just unplug your router from the ISP device and then plug it back in. Yes?

Assuming all of those are yes:

1. Exactly what is the ISP device?
2. Is your router plugged directly into the ISP device with no switches or cross connects in between. Just a simple short CAT 5E or better patch cable going from WAN port of your router to LAN port of the ISP device? Is the cable a cross over cable? I ask this because a lot devices especially from ISPs come with shitty cross over cables, shitty cables in general because they are cheap, and they are the devil.

If traffic is flowing it sounds like a speed/duplex mismatch or even a clocking issue. I'm pretty sure you another thread on here about this and you said that you were not specifying the connection speed anywhere. This is true yes?
Yes to both questions. As I said after 1-3 days internet becomes extremely slow/unstable, it happens to both wired and wireless connection so it means the whole connection is going haywire somehow. Yes, to fix the connection temporarily for 1-3 days again, it's enough to unplug the ethernet cable from the back of the modem (the one that goes to the wan port of the router) and plug it right back in, then magically everything works good again.. And also if I only use the ISP device without any extra router attached to it then connection never goes bad (had it on for 2 weeks without issues).

1. The ISP device is a Sagemcom Fast 3890V3 modem/router combo.
2. Yes my router is directly connected to the ISP device with nothing in between. ISP device ---> wireless router ---> every other device. All my cables are CAT 6-7 cables. After I noticed I'm getting this issue I changed all my cables with new ones just to rule out bad cable possibility.

Yeah traffic is still flowing however I also noticed that suddenly the wan led on my routers shut off and come back quickly meaning the connection also completely dies momentarily. I have tried 3 different routers with the same behavior attached to the ISP device. Yeah I had another thread but I wanted to ask a new question about IP's so that's why I created a new one. I contacted my ISP again and explained everything to them and even they said they really don't have a clue why this is happening as the ISP device should work good in bridge mode and that's it. They could not find anything wrong on their side, also sadly they don't provide a modem only device to their customers anymore..
 

Nicklebon

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FWIW I did a search and I see someone on another forum reporting DHCP issues on the WAN port with this same Sage 3890v3+ an Asus 88u very simliar to yours. There are also numerous post that would seem to indicate this Sage device has a general issues with wan disconnects. I'm guessing getting your own bridge is not an option? Just grasping at a staw but, have you tried a different port on the Sage? It looks like it has 4 lan ports.
 

Dead Parrot

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Any chance your ISP is using the combo device to run a 2nd WiFi AP for 'customer only' public wifi access? Both Cox and AT&T are known to do this and limit end user ability to not offer the wifi AP. That might explain why it shows up with a public IP(so the customer AP can function) while providing a 2nd public IP to your device. Even if 'your' part of the combo wifi is off, doesn't mean the ISP part is off.

If the failure after 1~3 days is repeatable, check the IP lease times the modem gets from the ISP. Might have an issue with lease renewal. As bridge mode is a non-standard setup for most folks, it probably doesn't get as much testing for new firmware rollouts.
 

supo

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FWIW I did a search and I see someone on another forum reporting DHCP issues on the WAN port with this same Sage 3890v3+ an Asus 88u very simliar to yours. There are also numerous post that would seem to indicate this Sage device has a general issues with wan disconnects. I'm guessing getting your own bridge is not an option? Just grasping at a staw but, have you tried a different port on the Sage? It looks like it has 4 lan ports.
Yeah I have also seen some posts on the net about issues with this particular device.. Yes I have tried all the lan ports 1-4 and its all the same.

Any chance your ISP is using the combo device to run a 2nd WiFi AP for 'customer only' public wifi access? Both Cox and AT&T are known to do this and limit end user ability to not offer the wifi AP. That might explain why it shows up with a public IP(so the customer AP can function) while providing a 2nd public IP to your device. Even if 'your' part of the combo wifi is off, doesn't mean the ISP part is off.

If the failure after 1~3 days is repeatable, check the IP lease times the modem gets from the ISP. Might have an issue with lease renewal. As bridge mode is a non-standard setup for most folks, it probably doesn't get as much testing for new firmware rollouts.
As far as I know no my ISP doesn't use a secondary WiFi Ap. And when it comes to Dhcp I have also been suspecting this about renewal times but the connection can go bad even when I still have time left on the leasing time so I ruled out that it's a Dhcp renewal issue. All in all I think this ISP device is just bad and doesn't want to work with any other external router. Don't have an option to change ISP as well because we are locked to them and their awful new device in my area :(
 

Nicklebon

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Don't have an option to change ISP as well because we are locked to them and their awful new device in my area :(
Are you able to use your own bridge device? I'm guessing you're outside the US but, docsis bridges are generally available and not very expensive.
 

Mac2

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Is there any way you can copy the settings from current modem and replace both ISP owned devices with other off the shelf units?
 
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