IP address allocation seems to be contrary to rules

[stevefowell]

Hi

I have the TalkTalk SAGEMCOM 5364 router and a Devolo 9791 Wi-Fi ac repeater set in repeater mode.

I am confused and surprised by the IP address allocation on the router.

My understanding is that the repeater has, for connecting to a router, a wifi antenna for 2.4GHz and another antenna for 5GHz. The 2.4GHz antenna has MAC address XX:XX:XX:XX:XX:X4 while the 5GHz antenna has MAC address XX:XX:XX:XX:XX:X5 (ie, only the last character is different). Although these two MAC addresses belong to the same device (the repeater) my understanding would be that, because they do have different MAC addresses, the router would assign different IP addresses to the 2.4GHz and 5GHz channels. But, looking at the device list in the router's admin panel, I can see that the 2.4GHz and 5GHz channels have the same IP address. How can this be? It seems to against the rules of IP address allocation.

Thanks for any explanations!

Steve

[KeithFrench]

Hi @stevefowell 

OK, one last attempt, other than that, if you don't believe either of us, Google it.

The manufacturer of your repeater is allocated a set of MAC addresses and it uses normally three contiguous ones from that range for each repeater it makes. Part of the repeater is a WiFi client and does use one of these MAC addresses. When it connects to the router it does get allocated an IP address. However, this IP address is not used for IP networking, other than to allow management of the repeater via a GUI, if the manufacturer even allows this. The other part of the repeater is a Wi-Fi Access Point & two of these MAC addresses are allocated within it to two BSSIDs, now they are no longer MAC addresses, but the BSSID does use the same format as those. 

A MAC address uniquely identifies the WiFi network adapter within a device. Now consider the repeater, a BSSID uniquely identifies an access point within an SSID. Assuming your repeater, as part of its setup cloned the router's WiFi information you have one SSID across both units. Within that SSID are four BSSIDs. These are allocated thus:-

1. Router 2.4GHz band.
2. Router 5GHz band.
3. Repeater 2.4GHz band.
4. Repeater 5GHz band.

If you check the router, it too has a group of contiguous MAC addresses, two of which are used as per the above for its BSSIDs.

BSSIDs do not have IP addresses associated with them. This is not breaking any rules as per your subject title, it is an IP networking fact. If you take nothing else away from this, please remember that.

The BSSID, in identifying an access point, is used in the initial connection event that takes place between a WiFi device such as a PC or phone etc, when they attempt to connect to either your router or repeater. That device is then allocated an IP address from the DHCP server (normally in the router but can be elsewhere on the subnet). When your device starts to be used after that, the router will store the combination of your device's IP address and its MAC address within its ARP cache. Note: I did not say BSSID, as that is not a MAC address & is not of any significance in your internet usage.

If you still do not believe me, download Wireshark & install it on a WiFi-connected device. Then read the documentation on how to take a trace with it using your WiFi NIC. Browse to a website, stop & save the trace & attach it to your reply. With anyone else, I would take the time to explain how to do this, but frankly, I can't be bothered in this case. Then when I see the trace I will take a screenshot from it to prove still further, that the BSSID, which you believe to be a MAC address, is not used during normal use.

When is a MAC address not a MAC address? When it is a BSSID!

[KeithFrench]

Both myself & @Gondola have tried to explain how the internet works. If you don't believe us then by all means please look up all of the RFC documentation & you will find that we are correct. 

Please be aware that we give our time freely to help people, but if you want to redefine the way that IP networking behaves, then try taking on Microsoft & Cisco Systems who are responsible for most of it anyway

.

[Gondola]

You obviously didn't understand my reply. Did I not make it basic enough?

Anyway, is the laptop communicating with the Internet via your Wi-Fi extenders? Yes / No?

[stevefowell]

Hi KeithFrench.
I agree that the extender needs an IP address principally to allow its management. You say that one IP address will have been allocated to it from the DHCP server within the router. You also say that the 2.4GHz & 5GHz bands of the router & repeater do not have MAC addresses.
However, all the documentation that I can find states that IP addresses are allocated in a on-to-one correspondence to MAC addresses. No MAC address, no IP address. And each MAC address is allocated a unique IP address. So I am still no further on in understanding how the Sagemcom router can allocate a single IP address to two distinct MAC addresses.
I think I will try contacting Sagemcom support.
Thanks for your responses.
Regards
Steve

[KeithFrench]

Your device connects via Wi-Fi to your repeater or router, there is no IP routing associated with this. The repeater is just extending the layer 2 subnet of the router to other parts of your property.

When you make a connection to the internet, your device was allocated a default gateway IP address (the router's IP address), when it was allocated its own IP address. All IP routing totally bypasses the repeater and goes directly to the internet via the router.

The only reason that the extender would have an IP address is to allow for managing its settings via its GUI. That one IP address will have been allocated to it from the DHCP server within your router.

Strictly speaking, the 2.4GHz & 5GHz bands of the router & repeater do not have MAC addresses, they are the BSSIDs (Basic Service Set ID) of each SSID (Basic Service Set ID - network name).

[Gondola]

The repeater is there to relay the wi-fi signal data from the laptop to the router. The router will see from the laptop's IP address that the packets of data originate from the laptop.

IP address(es) allocated by the router to the repeater are purely for management of the repeater.

[stevefowell]

Thanks KeithFrench and Gondola, however my query is at a more basic level than regarding TCP/IP layers and internet connectivity. I am just referring to what is happening on my local LAN when my repeater initially requests an IP address from the router using a DHCPDISCOVER request. My laptop only has one MAC address and can only connect on either the 2.4GHz frequency or the 5GHz frequency at any one time. It can have the same IP address no matter which frequency it is connected on because the MAC address is the same in either case. However my repeater has two MAC addresses, one for each frequency. So, because there should be a one-to-one correspondence between MAC address and IP address my repeater should have two IP addresses, corresponding to the two MAC addresses. I cannot understand how the router will know that the two repeater MAC addresses originate from the same physical device. How on earth does the router know this to allow it to allocate the same IP address to the two different MAC addresses?
Regards
Steve

[KeithFrench]

This can be a bit technical to explain, but here goes. The term Wi-Fi hub is purely a marketing term used by TalkTalk, it is a router actually. The repeater is a Wi-Fi Access Point.

An IP address is a "layer 3" address, whilst the MAC address is a "layer 2" address. Your source & destination layer 2 addresses are only significant within the home network or subnet. For example, a distant web server would not know your source MAC address when you visit that website.

It is impossible to route an IP packet based on MAC addresses, this is where IP addresses come into play, as they are routable. When an IP packet traverses the internet, it contains both a source & destination IP address. It is the only address type that is known, until an end-to-end connection is achieved. Then a further address comes into play, the source & destination TCP or UDP port numbers, which are "layer 4" addresses.

So your router & repeater both have MAC addresses and IP addresses to route to the management UI. The router allocates each device an IP address which is unique within your home network. If you want to then go to the https://microsoft.com website for example, your network card must be in possession of the following addresses:-

1. Its own IP address for the Source IP address of the IP packet.
2. Its own MAC address, which forms the source MAC address of the packet.
3. The IP address for the domain microsoft.com. This is is obtained via a DNS query. If the domain is successfully resolved to an IP address, the packet can be constructed. This is the destination IP address used within the packet.
4. The default gateway IP address. This is the IP address of the router, as it is the only device that will know how to get to an IP address out on the internet. It is allocated to your network card at the same time as the device is allocated its own IP address. This is all done via the DHCP protocol.
5. The MAC address of the default gateway. This is the destination MAC address used in the packet. It is only utilised within your home network. 

When the IP packet moves throughout the internet, both the source & destination MAC addresses will change.

There are other factors to consider, such as these MAC addresses are help in a cache & if not known ARP requests need to be sent. It is not always necessary to use DNS queries if the domain name such as microsoft.com is stored in another cache and hence its IP address is known already.

[Gondola]

Yes, the router, known as the Sagemcom 5364 Wi-Fi Hub, allocates an IP address.

The router hardware will have multiple MAC addresses allocated by the manufacturers of communication components.

The Internet doesn't care what the MAC address is of the radio components of the router. All it needs is the router IP address and the allocated IP address for the device as shown in the DHCP lookup.

[stevefowell]

Thanks for replying Gondola but I am none the wiser. I presume that you mean the router when you say wifi hub. But I thought IP addresses were assigned, by the router, to devices based on the device's MAC address. If a physical device (a repeater) has two MAC addresses shouldn't each MAC address be allocated a distinct IP address?  If this is not correct and the router allocates IP addresses to physical devices, irrespective of MAC addresses, how is the physical device identified to the router if not by MAC address?

Thanks

Steve

[Gondola]

Devices are assigned IP addresses by the Wi-Fi Hub. Not Wi-Fi channels.