Hello all,
Quick question about DHCP reservations: I have laptops with both wired and wireless NICs, is it okay to have the router assign the same IP to both interface? I am assuming it will let me do that. I will not, and do not ever, have both interfaces active at the same time. In order to make this post at least somewhat relevant to Fedora I am currently running three of them in my home office. I keep thinking that I am missing something, possibly obvious, as to why I shouldn't do this.
I have my new Netgear R6200v2 working perfectly and I don't want to do anything to piss it off.
Jim Lewis
On 02/02/2015 04:20 PM, Jim Lewis wrote:
Hello all,
Quick question about DHCP reservations: I have laptops with both wired and wireless NICs, is it okay to have the router assign the same IP to both interface? I am assuming it will let me do that. I will not, and do not ever, have both interfaces active at the same time. In order to make this post at least somewhat relevant to Fedora I am currently running three of them in my home office. I keep thinking that I am missing something, possibly obvious, as to why I shouldn't do this.
I have my new Netgear R6200v2 working perfectly and I don't want to do anything to piss it off.
What you are missing is how the lease is released. There is no, 'drop this lease' operation that can occur, say, when your system goes into suspend mode. Or you simply walk out of radio range.
You would have to set the lease time quite short and wait that time before connecting the other interface. You would have to turn off one interface, wait, then start the other.
Actually, with macPRIV we are moving in the other direction, to have frequent, different IP addresses for clients as your IP address is carried in all sorts of higher layers. And IPv6 further compounds this.
On 02.02.2015 22:20, Jim Lewis wrote:
Hello all,
Quick question about DHCP reservations: I have laptops with both wired and wireless NICs, is it okay to have the router assign the same IP to both interface? I am assuming it will let me do that. I will not, and do not ever, have both interfaces active at the same time. In order to make this post at least somewhat relevant to Fedora I am currently running three of them in my home office. I keep thinking that I am missing something, possibly obvious, as to why I shouldn't do this.
I have my new Netgear R6200v2 working perfectly and I don't want to do anything to piss it off.
Jim Lewis
You can promise whatever you want, but On DD-WRT, no matter what hostname and MAC Address are selected, if you try with the IP address already reserved, the following message pops up: "x.y.z.w" is already defined as a static lease"
On 02.02.2015 22:20, Jim Lewis wrote:
Hello all,
Quick question about DHCP reservations: I have laptops with both wired and wireless NICs, is it okay to have the router assign the same IP to both interface? I am assuming it will let me do that. I will not, and do not ever, have both interfaces active at the same time. In order to make this post at least somewhat relevant to Fedora I am currently running three of them in my home office. I keep thinking that I am missing something, possibly obvious, as to why I shouldn't do this.
I have my new Netgear R6200v2 working perfectly and I don't want to do anything to piss it off.
Jim Lewis
You can promise whatever you want, but On DD-WRT, no matter what hostname and MAC Address are selected, if you try with the IP address already reserved, the following message pops up: "x.y.z.w" is already defined as a static lease"
Ah, so my Netgear router is probably not going to allow the same IP. That is fine, I had a feeling that was going to be the case, and it's actually a good idea. This was more of a nice-to-have than a real problem.
When I decide to switch interfaces I always turn the current one off, wait about a minute, check ifconfig to make sure, and then start the other one. Have not ever had a problem with this, and Yes I use Network Manager :).
Jim Lewis
On Mon, 2015-02-02 at 11:20 -1000, Jim Lewis wrote:
Quick question about DHCP reservations: I have laptops with both wired and wireless NICs, is it okay to have the router assign the same IP to both interface?
I seem to recall being able to do that, with the DHCP server on my Fedora Core 4 installation (having two separate MAC matching clauses that applied the same IP). Other servers may try to prevent you doing that, as it can be problematic.
The client behaviour could be a bit wierd, especially if the client doesn't completely bring down the interface that previously had the same IP. On some clients, plugging in a cable doesn't disable or override the wireless. You'd have to manually do so.
And lease expiry time wasn't an issue, that would only apply if I was hoping for a dynamically supplied IP to be re-supplied. My configuration was fixed IPs doled out by the DHCP server. So if your MAC matched, you were assigned that IP, as long as something else didn't prevent it.
Robert Moskowitz:
What you are missing is how the lease is released. There is no, 'drop this lease' operation that can occur, say, when your system goes into suspend mode. Or you simply walk out of radio range.
While I agree that "losing signal" has no way to gracefully log out, I would have thought that going into suspend ought to log off the network on the way out.
On 02/03/2015 02:01 AM, Tim wrote:
Robert Moskowitz:
What you are missing is how the lease is released. There is no, 'drop this lease' operation that can occur, say, when your system goes into suspend mode. Or you simply walk out of radio range.
While I agree that "losing signal" has no way to gracefully log out, I would have thought that going into suspend ought to log off the network on the way out.
I have checked my DHCP report from another machine and it shows me still assigned the address.
On 03.02.2015 08:01, Tim wrote:
On Mon, 2015-02-02 at 11:20 -1000, Jim Lewis wrote:
Quick question about DHCP reservations: I have laptops with both wired and wireless NICs, is it okay to have the router assign the same IP to both interface?
I seem to recall being able to do that, with the DHCP server on my Fedora Core 4 installation (having two separate MAC matching clauses that applied the same IP). Other servers may try to prevent you doing that, as it can be problematic.
The client behaviour could be a bit wierd, especially if the client doesn't completely bring down the interface that previously had the same IP. On some clients, plugging in a cable doesn't disable or override the wireless. You'd have to manually do so.
And lease expiry time wasn't an issue, that would only apply if I was hoping for a dynamically supplied IP to be re-supplied. My configuration was fixed IPs doled out by the DHCP server. So if your MAC matched, you were assigned that IP, as long as something else didn't prevent it.
The combination of the same IP address on two different network interfaces is prohibited for obvious reasons. At least via the WebUI. But no one defends leave one network interface on the router DHCP static leas, and make local static profile with the same IP with other network interface, making sure that both interfaces are not simultaneously in operation. However if someone decides to do the same on the LAN, there goes a trouble. Also not to be excluded, in the absence of a morning dose of caffeine, the one that set the same address at the two interfaces can confuse imself. All in all it's just a call to the circus.
Jim Lewis wrote:
Quick question about DHCP reservations: I have laptops with both wired and wireless NICs, is it okay to have the router assign the same IP to both interface?
I wrote:
I seem to recall being able to do that, with the DHCP server on my Fedora Core 4 installation (having two separate MAC matching clauses that applied the same IP). Other servers may try to prevent you doing that, as it can be problematic.
Just following up, since I wasn't clear. My comment was along the same lines as the original poster, trying to see what would happen if I assigned the same IP to wireless or wired network interfaces on my laptop, where only one of them would be active at any one time.
The reason I tried, was that it was annoying having changing addresses, one way or another. Whether that was the IP address, or the named address attached to the current IP.
For instance, my hostname might be wired.example.com or wireless.example.com, because the IP changed. Either change brought about their own set of nuisances.
And, no, the common Fedora approach of associating your desired machine hostname against 127.0.0.1 is not a sensible alternative, either.
Having multiple interfaces is a nuisance, and the best I could come up with was having to use the GUI to manually disconnect one device or the other, not letting any automatic system attempt it.
A whole slew of other problems came about should both interfaces be up and active at the same time.
On Wednesday 04 February 2015 00:55:29 Tim wrote:
Jim Lewis wrote:
Quick question about DHCP reservations: I have laptops with both wired and wireless NICs, is it okay to have the router assign the same IP to both interface?
I wrote:
I seem to recall being able to do that, with the DHCP server on my Fedora Core 4 installation (having two separate MAC matching clauses that applied the same IP). Other servers may try to prevent you doing that, as it can be problematic.
Just following up, since I wasn't clear. My comment was along the same lines as the original poster, trying to see what would happen if I assigned the same IP to wireless or wired network interfaces on my laptop, where only one of them would be active at any one time.
The reason I tried, was that it was annoying having changing addresses, one way or another. Whether that was the IP address, or the named address attached to the current IP.
For instance, my hostname might be wired.example.com or wireless.example.com, because the IP changed. Either change brought about their own set of nuisances.
And, no, the common Fedora approach of associating your desired machine hostname against 127.0.0.1 is not a sensible alternative, either.
Having multiple interfaces is a nuisance, and the best I could come up with was having to use the GUI to manually disconnect one device or the other, not letting any automatic system attempt it.
A whole slew of other problems came about should both interfaces be up and active at the same time.
Surely "hot-swapping" IP addresses between interfaces wont work very well, since forgetting DHCP its ARP that will cause a problem. Each previously communicating host will have a MAC address logged in its ARP table for the offending IP address. If the IP address changes MAC addresses, the ARP entries on all other hosts must time-out in order to be renewed via an ARP broadcast.
On both a dd-wrt and a recent asus router I have successfully got the older bonding module to bring up wireless and wired in a active/passive mode (wired is active if there). Both interfaces would have the same IP and mac address and I can unplug the wired and immediately have it switch over to wireless with no obvious drops. I can also switch back to a wired connection with no drops (usually done in the middle of a big data transfer to speed it up). This is outside of network manager, and was a major pain to get it working consistently after a reboot, but I believe it now works consistently on reboots. I believe the bonding module does force arps when it switches interfaces.
On Tue, Feb 3, 2015 at 8:37 AM, Andrew R Paterson andy.paterson@ntlworld.com wrote:
On Wednesday 04 February 2015 00:55:29 Tim wrote:
Jim Lewis wrote:
Quick question about DHCP reservations: I have laptops with both wired and wireless NICs, is it okay to have the router assign the same IP to both interface?
I wrote:
I seem to recall being able to do that, with the DHCP server on my Fedora Core 4 installation (having two separate MAC matching clauses that applied the same IP). Other servers may try to prevent you doing that, as it can be problematic.
Just following up, since I wasn't clear. My comment was along the same lines as the original poster, trying to see what would happen if I assigned the same IP to wireless or wired network interfaces on my laptop, where only one of them would be active at any one time.
The reason I tried, was that it was annoying having changing addresses, one way or another. Whether that was the IP address, or the named address attached to the current IP.
For instance, my hostname might be wired.example.com or wireless.example.com, because the IP changed. Either change brought about their own set of nuisances.
And, no, the common Fedora approach of associating your desired machine hostname against 127.0.0.1 is not a sensible alternative, either.
Having multiple interfaces is a nuisance, and the best I could come up with was having to use the GUI to manually disconnect one device or the other, not letting any automatic system attempt it.
A whole slew of other problems came about should both interfaces be up and active at the same time.
Surely "hot-swapping" IP addresses between interfaces wont work very well, since forgetting DHCP its ARP that will cause a problem. Each previously communicating host will have a MAC address logged in its ARP table for the offending IP address. If the IP address changes MAC addresses, the ARP entries on all other hosts must time-out in order to be renewed via an ARP broadcast.
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On 03.02.2015 16:20, Roger Heflin wrote:
On both a dd-wrt and a recent asus router I have successfully got the older bonding module to bring up wireless and wired in a active/passive mode (wired is active if there). Both interfaces would have the same IP and mac address and I can unplug the wired and immediately have it switch over to wireless with no obvious drops. I can also switch back to a wired connection with no drops (usually done in the middle of a big data transfer to speed it up). This is outside of network manager, and was a major pain to get it working consistently after a reboot, but I believe it now works consistently on reboots. I believe the bonding module does force arps when it switches interfaces.
root@DD-WRT:~# grep -i bond /lib/modules/3.2.66/modules.* ; echo $? 1
Where the bonding module should be? :)
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Andy Paterson -
Jim Lewis -
poma -
Robert Moskowitz -
Roger Heflin -
Tim