gateway IP address
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From: mike7411 on 4 Jul 2006 16:03 Could someone refer me to a good explanation of how the gateway IP address is used in networking? I have a Cisco ATA186 analog telephone adapter, and it requires me to configure gateway IP address. It only has one RJ45 Ethernet port, so shouldn't it just be sending all the packets out of the port? Why would it need a gateway IP address?
From: thrill5 on 4 Jul 2006 17:28 Networking is all about encapsulation. Ethernet is Layer 2, IP is Layer 3. Layer 2 uses MAC address, and Layer 3 uses IP address. IP packets are encapsulated into Ethernet Frames. ARP is used to obtain the MAC address of a device on YOUR IP subnet. If you have two segments connected via a router, and you want to talk to a device on the other segment, you need to send the Ethernet frame to the router, so that it can pass it to the device on the other segment. You need to configure the default gateway (the routers IP address) so that you device can figure out the MAC address of the router. Example. Device A on Subnet 1, needs to talk to Device B on Subnet 2. Subnet 1 is connected to Subnet 2 via router R. Device A has a packet that it needs to Device B. It knows that the Device B is on a different subnet (IP address and subnet mask are used for this purpose), it knows that it needs to send the packet to the router (default gateway). When the packet leaves Device A, the source IP is itself, the source MAC is itself. The destination IP is Device B, the destination MAC is the router. The router gets the frame (because the destination MAC of the Ethernet frame is addressed to it), looks at the destination IP and determines where to send it, (in this case, a directly connected subnet.) When the frame leaves the router, the source IP is Device A, the source MAC is router, the destination IP is Device B, and destination MAC is Device B. This is a very simple example. For more information on the "Layers" (There are seven of them) Google "OSI Model" This will give you a more complete explanation of the workings of networking. Scott <mike7411(a)gmail.com> wrote in message news:1152043416.445618.84050(a)m79g2000cwm.googlegroups.com... > Could someone refer me to a good explanation of how the gateway IP > address is used in > networking? > > I have a Cisco ATA186 analog telephone adapter, and it requires me to > configure gateway IP address. It only has one RJ45 Ethernet port, so > shouldn't it just be sending all the packets out of the port? Why > would it need a gateway IP address? >
From: Chris Mason on 5 Jul 2006 05:25 A nice answer but I rather think not to the question as asked. I suspect that the true answer is that the logic used is in the device is general and hence applies to an IP node with multiple interfaces. Chris Mason thrill5 wrote: > Networking is all about encapsulation. Ethernet is Layer 2, IP is Layer 3. > Layer 2 uses MAC address, and Layer 3 uses IP address. IP packets are > encapsulated into Ethernet Frames. ARP is used to obtain the MAC address of > a device on YOUR IP subnet. If you have two segments connected via a > router, and you want to talk to a device on the other segment, you need to > send the Ethernet frame to the router, so that it can pass it to the device > on the other segment. You need to configure the default gateway (the > routers IP address) so that you device can figure out the MAC address of the > router. Example. > > Device A on Subnet 1, needs to talk to Device B on Subnet 2. Subnet 1 is > connected to Subnet 2 via router R. Device A has a packet that it needs to > Device B. It knows that the Device B is on a different subnet (IP address > and subnet mask are used for this purpose), it knows that it needs to send > the packet to the router (default gateway). When the packet leaves Device > A, the source IP is itself, the source MAC is itself. The destination IP is > Device B, the destination MAC is the router. The router gets the frame > (because the destination MAC of the Ethernet frame is addressed to it), > looks at the destination IP and determines where to send it, (in this case, > a directly connected subnet.) When the frame leaves the router, the source > IP is Device A, the source MAC is router, the destination IP is Device B, > and destination MAC is Device B. > > This is a very simple example. > > For more information on the "Layers" (There are seven of them) Google "OSI > Model" This will give you a more complete explanation of the workings of > networking. > > Scott > > > <mike7411(a)gmail.com> wrote in message > news:1152043416.445618.84050(a)m79g2000cwm.googlegroups.com... > > Could someone refer me to a good explanation of how the gateway IP > > address is used in > > networking? > > > > I have a Cisco ATA186 analog telephone adapter, and it requires me to > > configure gateway IP address. It only has one RJ45 Ethernet port, so > > shouldn't it just be sending all the packets out of the port? Why > > would it need a gateway IP address? > >
From: erik.freitag@pobox.com on 5 Jul 2006 07:09 mike7411(a)gmail.com wrote: > Could someone refer me to a good explanation of how the gateway IP > address is used in > networking? A good reference would be Comer's Internetworking with TCP/IP, Volume I, Principles, Protocols and Architecture. Relevant chapters would be Chapter 5 Mapping Internet Addresses To Physical Addresses (ARP), and the Routing chapters. > > I have a Cisco ATA186 analog telephone adapter, and it requires me to > configure gateway IP address. It only has one RJ45 Ethernet port, so > shouldn't it just be sending all the packets out of the port? Why > would it need a gateway IP address? The gateway IP tells the client (the ATA186 in this case) where to send packets that are not on the same subnet or subnets as directly attached interfaces. In this case, since there is only one interface there will likely be only one attached subnet. The gateway IP tells the client where to send packets that are not on that subnet. Since a router attached to a subnet can pretend to be any host not on the same subnet if proxy-arp is enabled, a gateway IP is not always necessary, even when the client has multiple interfaces. If you are always sending packets to the same subnet, neither a gateway IP nor proxy-arp is needed, although it sounds like your client still wants you to enter one. In any case, the gateway IP has nothing to do with the number of interfaces your device has.
From: sillymartin on 5 Jul 2006 07:20
mike7411(a)gmail.com schrieb: > Could someone refer me to a good explanation of how the gateway IP > address is used in > networking? > > I have a Cisco ATA186 analog telephone adapter, and it requires me to > configure gateway IP address. It only has one RJ45 Ethernet port, so > shouldn't it just be sending all the packets out of the port? Why > would it need a gateway IP address? yes it should send all packets out of this port, question is _where to_. here a shorter explanation: a device needs a gateway for ANY adress that is NOT in its own subnet. ipadress and netmask define which range the device considers as its own net. any interface needs to have a route for packets, whose destination is not the default gateway and not the local subnet.. imagine a room with one door. anypacket with destination _not in the room_ has to know where to get out. the door is the default gateway. of course you can have several doors to different destinations. and remember: your gateway has to be an adress in _your_ range, never in the destination net. (because you would't know how to get there , right :-) |