4

I bought a new router yesterday, but I dont think that's relevant because on my previous router it happened too. The only difference now is that my first router wasn't dualband and this new one is. So that makes me think that might be the cause, but I also dont understand why it would list the device twice when I'm not using both wifi connections simultaneously.

What happens is two of my devices show up on the dhcp table twice. Its always the same two. My galaxy S5 phone and my Galaxy tablet. Something leads me to believe that there's something about galaxy devices that causes this to happen. But what?

Or it could be the routers because on my old router I had dd wrt and on my new router I have tomato.

But idk why. What makes them show up twice? This is what my dhcp table looks like.

    (Interface)    (MAC Address)    (IP Address)    (Name)  

    (br0)   (11:11:11:11:11:11)
    (10.12.1.8) (Tablet)            

    (br0)   (22:22:22:22:22:22)
    (10.12.1.24)    (Galaxy)                


    (eth1)  (22:22:22:22:22:22) 
    (Unknown)   (Unknown)   

    (eth2)  (11:11:11:11:11:11)
    (Unknown)   (Unknown)

Im guessing it has something to do with the interface. But I dont understand any of that. eth1 is ethernet. br0 is bridge. Idk what a bridge is but a quick google search says it connects a network to another network. How does a tablet become a bridge then when all it is is connected to my router which connects to my isp modem. Wouldnt that mean all of them were bridges since they all connect to my router and then my modem? Or only my router is a bridge since it connects my lan to a wan? So I dont understand that. I dont understand why wifi devices show up on ethernet either.

The MAC addresses dont really read 11 or 22 I just put those in. It does however say unknown for the ip and name. Which shouldnt happen since it shows up the first time. 

**/tmp/home/root$ arp -a**
Tablet (10.12.1.8) at 11:11:11:11:11:11 [ether] PERM on br0
Modem (1.1.1.1) at xx:xx:xx:xx:xx:xx [ether]  on vlan2
Galaxy (10.12.1.24) at 22:22:22:22:22:22 [ether] PERM on br0
ASUS (10.12.1.2) at xx:xx:xx:xx:xx:xx [ether] PERM on br0


**/tmp/home/root$ ifconfig**
br0        Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX
           inet addr:10.12.1.1  Bcast:10.12.1.255  Mask:255.255.255.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:278599 errors:0 dropped:0 overruns:0 frame:0
           TX packets:596937 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0 
           RX bytes:182443542 (173.9 MiB)  TX bytes:785616292 (749.2 MiB)

eth0       Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX  
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:728397 errors:0 dropped:0 overruns:0 frame:0
           TX packets:333202 errors:25 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000 
           RX bytes:800300423 (763.2 MiB)  TX bytes:261014853 (248.9 MiB)
           Interrupt:4 Base address:0x2000 

eth1       Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX  
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:65343 errors:0 dropped:0 overruns:0 frame:32840
           TX packets:181742 errors:10 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000 
           RX bytes:48388399 (46.1 MiB)  TX bytes:241940171 (230.7 MiB)
           Interrupt:3 Base address:0x1000 

eth2       Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX  
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:172063 errors:0 dropped:0 overruns:0 frame:4380
           TX packets:363352 errors:1435 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:1000 
           RX bytes:132062671 (125.9 MiB)  TX bytes:473613831 (451.6 MiB)

lo         Link encap:Local Loopback  
           inet addr:127.0.0.1  Mask:255.0.0.0
           inet6 addr: ::1/128 Scope:Host
           UP LOOPBACK RUNNING MULTICAST  MTU:16436  Metric:1
           RX packets:3185 errors:0 dropped:0 overruns:0 frame:0
           TX packets:3185 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0 
           RX bytes:261884 (255.7 KiB)  TX bytes:261884 (255.7 KiB)

vlan1      Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX  
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:41658 errors:0 dropped:0 overruns:0 frame:0
           TX packets:66122 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0 
           RX bytes:5658553 (5.3 MiB)  TX bytes:76240340 (72.7 MiB)

vlan2      Link encap:Ethernet  HWaddr XX:XX:XX:XX:XX:XX  
           inet addr:1.1.1.1  Bcast:1.1.1.1 Mask:255.255.255.0
           UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
           RX packets:686737 errors:0 dropped:0 overruns:0 frame:0
           TX packets:267105 errors:0 dropped:0 overruns:0 carrier:0
           collisions:0 txqueuelen:0 
           RX bytes:781530624 (745.3 MiB)  TX bytes:184812463 (176.2 MiB)




**/tmp/home/root$ ip addr show**
1: lo: <LOOPBACK,MULTICAST,UP,10000> mtu 16436 qdisc noqueue 
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 brd 127.255.255.255 scope host lo
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
4: eth2: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc pfifo_fast qlen 1000
    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
5: vlan1@eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc noqueue 
    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
6: vlan2@eth0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc noqueue 
    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
    inet 1.1.1.1/24 brd 98.167.198.255 scope global vlan2
7: br0: <BROADCAST,MULTICAST,UP,10000> mtu 1500 qdisc noqueue 
    link/ether XX:XX:XX:XX:XX:XX brd ff:ff:ff:ff:ff:ff
    inet 10.12.1.1/24 brd 10.12.1.255 scope global br0
8: imq0: <NOARP> mtu 1500 qdisc noop qlen 30
    link/void 
9: imq1: <NOARP> mtu 1500 qdisc noop qlen 30
    link/void
adam
  • 43

1 Answers1

3

Why did that fix it?

Because you are looking not at the list of DHCP clients, but to the list of devices, aka an ARP table.

An ARP table is the list of MAC addresses of devices connected to your router. Your router, like all routers, has no way of knowing whether a device is still present on any of its connections, unless of course these clients are active. In fact, many routers display the list of active clients, which does not include clients which are asleep/idle, or even disconnected.

All the router knows is that the IP address once allocated to a dead/asleep/idel client is now available for a new lease, because the dead/asleep/idle device did not renew the IP address lease at its expiration (typical expiration time is 1 hour). But it will keep in its ARP table memory of the formerly connected device so that, should it show up again (i.e., should it send the router the same MAC address), it will be allocated the same IP address, if available.

In other words, ARP tables have very long persistence times. Still your original table showed the MAC adress, not the IP address of your devices: this means they were once connected to the ethernet plug, but they are not anymore.

Now you can see why they have now disappeared: by plugging into the ethernet plugs two different devices, the router has become aware that your Tablet and Galaxy are not at the end of the cable line, since there are two new players. So the router updates the ARP table, and your two devices disappear, their place being taken by the newly-plugged devices, whatever they are.

Incidentally: there is no reason to delete all the MAC address, it is enough to delete the last 6 hexadecimal characters, because the first hexadecimal characters are unique to the producer (Samsung, Apple, Dell, HP, whatever), so they are sufficiently generic to prevent identification of your devices.

MariusMatutiae
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