Wireless router interfaces – help

[Wolfdale75]

Hi Guys,

I'm trying to set up a basic routing network in Cisco Packet Tracer. But I'm having some conceptual problems understanding what I need to do with the wireless router interfaces. I've asked on the Cisco forums and, while eager to help, they are mainly networking pros who don't seem able to speak at my very basic level. So I thought I would try asking here. May I ask the following:

What is the difference between the Router IP and the Internet IP on a wireless router? Can they be the same? Then a router also has a Default Gateway which apparently must be different from the Internet IP. I don't understand why all these interfaces are necessary. Can someone explain in simple terms what each interface does and how they interact with each other?

Thanks!

 

[kennyluu87]

Router IP and Default Gateway IP are usually the same thing. This IP address is what all internally connected computer and devices communicate to. This means that all the devices in your home are assigned an internal or private ip address. The main internal/private ip address is called the default gateway ip. This default gateway ip is what allows all the devices to communicate with one another in an internal/private network. The Internet IP is what allows you to communicate to the internet and access the world wide web. The Internet IP in the real world is what the ISP(internet service provider) gives you. Also note the internet ip is also called a public ip. For packet tracer you should be able to use the same ip address, but it's not recommended because when you are troubleshooting it will be confusing. The reason you need both Router IP and Internet IP is pretty much for your internal/private network to be able to access the internet/world wide web. I'm not sure if this is explanation helps.

 

[Nicklebon]

Ignore everything Kenny says above. This is very simple



A router has 2 or more interfaces. In your example one interface is on the inside network (router ip) and the other on the internet side (internet ip). The default gateway of the devices on the inside is the going to be the inside address of your router (router ip.) The default gateway of your router will be the IP of the nearest interface of the upstream router. The router below has 3 interfaces, two inside and one outside(internet).

 

[Wolfdale75]

Many thanks, guys, for trying to explain this to me. I appreciate that this probably seems like a simple question to you all. I think I understand it now. So the router IP/default gateway IP handle the internal traffic, and the Internet IP is the interface you use to get out of your own network. So you will have at least two router interfaces, but the router IP and default gateway IP are usually the same.

 

[Nicklebon]

Not exactly .... It is all relative. If you are configuring a device the default gateway is the IP of the next upstream router. In simplest terms the default gateway is where packets get sent to leave the network. Notice in my diagram the default gateway on each device points to the IP of the upstream device. The internet IP would just just be the external interface of the router you are configuring. Frankly, this is poor naming because it should not be assumed the interface connects to the Internet at all that said many devices would call it a WAN interface.

 

[IdiotInCharge]

Many thanks, guys, for trying to explain this to me. I appreciate that this probably seems like a simple question to you all. I think I understand it now. So the router IP/default gateway IP handle the internal traffic, and the Internet IP is the interface you use to get out of your own network. So you will have at least two router interfaces, but the router IP and default gateway IP are usually the same.

The IPv4 addressing scheme essentially predates the internet as we know it today.

On a TCP/IP network, every *'interface' has an IP address, whether that interface is physical like a port on a router or a PC network card / wireless modem.

So your basic router above has two interfaces: one for the internet, commonly labeled WAN on consumer / prosumer routers, and another for your local network, commonly labeled LAN. Note that WAN and LAN are conventions more than standards; the router's job is to route TCP/IP packets from one network to another.

To relate to Nicklebon's example above, the router has three interfaces: one that's used for the internet, one that's used for your wired network through your switch, and one that's used for your wireless network. Your two internal networks have default gateway addresses that are assigned to the router; not only must a device on one of these networks send packets to the gateway in order to reach addresses on the internet, but they must also send packets to the gateway to reach devices on the other internal network. That's the main distinction.

[*Note that switches are fundamentally layer 2 devices, meaning that they generally don't have 'interfaces' but instead have 'switch ports'. Layer 3 functionality on many modern switches allow them to host management pages and do various layer 3 flow control functions including access lists, firewalling, some routing, and so on, but these functions are not 'switch' functions. Switches switch (rather than route!) ethernet frames based on MAC addresses from interfaces.]

 

[scrappymouse]

A default gateway just tells the device you're on where to go next(next hop so to speak), in the case of devices on the your local(internal) network they go talk to your router IP, from there your router will determine where to send them next, your home router keeps track of all the devices connected to your wifi and physical interfaces on the router, so when say your want to transfer files from one computer(PC1) to another(PC2) on your home network, PC1 doesn't know how get to PC2, so he sends his request to the default gateway(your router ip), the router looks at that and says...yeah I know PC2 he's connected on my wifi, I'll send the request to PC2, and I'll he can respond to me and I'll forward it back to PC1. So for internal communication among your own network...you don't actually need an internet IP(or even an internet connection for that matter), But we all pay an ISP(Internet service provider) because we want to be on sites like hardforum . The ISP is what gives your router a "public internet IP" and also gives your router it's own default gateway. So now lets say PC1 wants to go to google.com, PC1 doesn't know how to get there...so it sends it its own default gateway(your router IP)(remember a default gateway...just says if you don't know go here), your router looks at Google.com and says...well Google.com is connected to me....I'm going to translate this(a process called NAT) to my internet IP, and send it along to my own gateway(The next router in the path(your ISP) and they can figure out how to get there. I'm simplifying some of the steps above for consumer gear. You can verify this on your own network, open up a command prompt when connected to your wifi, and do a traceroute to Google.com, the first IP you will see in the path will be your own router(192.168.x.x.) the next IP will belong to your ISP(you can confirm this by going to a site like whois and doing an ip lookup), from there your ISP will determine what to send next etc....

A consumer router is really 3 pieces of gear mashed into 1, an AP, a switch, and a router. In the professional world those get broken out into separate devices.