I am Sourav Khanna. And welcome to networking services and applications part two. Today we’re going to be discussing network access services. And then we’re going to move on to other services and applications like DHCP, DNS, and Static IPs. As always, there’s a fair amount of ground to cover. So let’s go ahead and dive into this session. I will begin with network access services.
What is Network Interface Controller?
- Network interface controller
The first network access service that I’m going to discuss is actually a piece of hardware, the network interface controller or NIC, it can also be called the network interface card. The NIC is how a device connects to a network. The network interface controller works at two layers of the OSI model at layer two which is the data link layer.
It provides the functional means of network communication by determining which networking protocols will be used as in a NIC that will provide Ethernet communication or NIC that will provide Point to Point protocol.
It also provides the local network node address through its burned in physical media access control address at layer one of the physical layer, the network interface controller determines how the network data traffic will be converted a bit at a time into an electrical signal that can traverse the network media being used,i.e. it provides the connection to the network.
Most modern computers come with at least one built-in Ethernet NIC router and other network devices may use separate modules that can be inserted into the device to provide the proper network interface controller for the type of media they’re connecting to in the networking protocols that are being used.
What is Remote Authentication Dial-In User Service?
Another network access service is Radius Remote, an authentic dial-in user service. Radius is a remote access service that is used to authenticate remote users and grant them access to authorized network resources. It is a popular triple-A protocol that’s authentication, authorization, and accounting protocol.
It’s used to help ensure that only authenticated end users are using the network resources they are authorized to use. The accounting services of radius are very robust. The only drawback to radius is only the requesters the end-users password is encrypted.
Everything else gets sent in the clear terminal access controller access control system plus or TAC x plus terminal access controller access control system plus point what a mouthful, it sure is easier to say. TAC x plus is a remote access service that is used to authenticate remote devices and grant them access to authorized network resources.
It is also a popular triple-A protocol used to help ensure that only authenticated remote network devices are using the network resources that they are authorized to use. With TAC x plus the accounting, features are not as robust as those found in radius. But all network transmissions between devices are encrypted with TAC x plus, let’s move on to other services and applications.
What are Remote Access Services?
First up is our AAS Remote Access Services. Now, RS is not a protocol, but a roadmap. Rs is a description of the combination of software and hardware required for remote access connection. A client requests access from an RS server, which either grants or rejects that access.
Then we have web services, creating a means of cross-communication. Web Services provides the means for communication between software packages or disparate platforms. It’s usually achieved by translating the communication into an XML format, or Extensible Mark-up Language format.
It is becoming more popular as systems diverged. Last up is unified voice services. This is creating a better voice communication system. It’s a description of the combination of software and hardware required to integrate voice communication channels into a network as in Voice over IP.
That concludes this session on networking services and applications. Part Two. I began by talking about network access services. And I concluded with other services and applications.
What is DHCP? How does DHCP Host Configuration work?
Next, we’re going to be talking about static versus dynamic IP addresses. Then we’re going to move on to how DHCP works. And then we will conclude with the components and processes of DHCP. And with that, let’s go ahead and begin this session. And of course, we begin by talking about static versus dynamic IP addresses.
So how does a computer know what its IP configuration is? Well, more than likely a computer received its IP configuration from a Dynamic Host Configuration Protocol server. Not only did the server give the PC an IP address, but it also told the PC where the default gateway was, and more than likely how to find a DNS server.
The computer will receive its IP configuration in one of two ways. Either statically, which means manually set, or dynamically, which means through a service like DHCP static IP address assignment works fine for very small and stable networks, but quickly becomes unwieldy and error-prone as the network grows and more nodes come on to the network.
What is a Static IP Address?
So let’s talk a little bit more about static IP addresses. The administrator assigned An IP number and subnet mask to each host in the network, whether it be a PC, router, or some other piece of electronic equipment. Each network interface that is going to be available to connect to the network requires this information.
The administrator also assigns a default gateway location and DNS server location to each host in the network.
Now, these settings are required if access to outside networks is going to be allowed, that would be through the default gateway. And if human-friendly naming conventions are going to be allowed, that way, you can more easily find network resources, and that would be through a DNS server.
Now each time a change is made, as in a new default gateway is established, each IP configuration on each host must be updated. That’s why it becomes rather cumbersome and complicated as the network grows. Now with dynamic IP addressing the administrator configures.
What is DHCP and How it works?
DHCP server to handle the assignment process, which actually automates the process and eases management.
The DHCP server listens on a specific port for IP information requests. Once it receives a request, the DHCP server responds with the required information. Now let’s move on to how DHCP works. Here is the typical DHCP process. Upon boot up, a PC that is configured to request an IP configuration sends a DHCP discovery packet.
Now the discovery packet is sent to the broadcast address 255255255255 on UDP port 67. The DHCP server is listening to that port. It’s listening for that discovery packet. When the DHCP server receives the discovery packet, it responds with an offer packet, basically saying hey, I’m here to help.
Now the offer packet is sent back to the MAC address of the computer requesting help, and it’s sent on port 68. Once the computer receives that offer packet from the DHCP server, if it’s going to use that DHCP server, it returns a request packet. That means it’s requesting the proper IP configuration from that specific DHCP server.
Once the DHCP server receives the request packet, it sends back an acknowledgement packet. Now, this acknowledgement packet contains all of the required IP configuration information.
Once the PC receives the acknowledgement packet, the PC changes its IP configuration to reflect the information that is received from the DHCP server. And that’s the typical DHCP process in a nutshell. Now let’s talk about components and the process of DHCP.
We’re going to begin by talking about the port’s use.
Now, I already mentioned this once, but I’m going to mention it again because you need to know this. The PC sends its discovery packet out on the broadcast address 255255255255 on port 67. That’s UDP port 67. When the DHCP server responds, it responds to the PC’s MAC address, Media Access Control address on UDP port 68.
That’s important. Remember the PC uses UDP port 67. The DHCP server responds on UDP port 68. Then there’s the address scope. The address scope is the IP address range that the administrator configures on the DHCP server. It is the range of addresses that the DHCP server can hand out to individual nodes. There are also what are called address reservations.
Now, these are administrator configured reserved IP addresses. The administrator reserves specific IP addresses to be handed out to specific MAC addresses. Now, these are used for devices that should always have the same IP address.
As in servers and routers. If you did do that there is the possibility that your default gateways IP address might change. Now the reason we use address reservation is this allows these addresses to be changed from a central location, instead of having to log in to each device and change the IP configuration separately.
Now part of the DHCP request process is what is called leases. The DHCP server hands out that IP configuration information for DHCP clients, but it sets a time limit for how long that IP configuration is good. This is called the lease.
So the parameters are only good for a specified amount of time. Now the administrator can configure how long the leases are, there are also options that the administrator can configure. The first one that’s pretty obvious is the default gateway location.
There’s also the DNS server address, and the administrator can configure more than one DNS server location. And administrator can also configure an option for the PC to synchronize with a time server. So the administrator can configure a time server address. There are many more additional options, but those are the big three that you should remember.
Now when a PC boots up, it does have a preferred IP address, that would be the IP address that it had the last time it booted up.
- Now he can request that same IP configuration from the DHCP server.
- Now the administrator can configure the DHCP server to either honour that preference or ignore it.
- Now under the right circumstances, a DHCP server isn’t required to reside on the local network segment.
Now as a general rule, broadcast transmissions cannot pass through a router. But if there’s not a DHCP server on the local network segment, the router can be configured to be a DHCP relay. When a DHCP relay, also called an IP helper receives a discovery packet from a node, it will forward that packet to the network segment on which the DHCP server resides.
This allows for there to be fewer configured DHCP servers in any given network, reducing the amount of maintenance that an administrator needs to perform. Now that concludes this session on DHCP in the network, we started with static versus dynamic IP addresses. And then we moved on to how DHCP works. And we concluded with the components and processes of DHCP.
What is DNS SERVER? | What is DNS?
Now we’re going to be talking about DNS servers, and DNS records, and we will conclude with a brief discussion on dynamic DNS. And with that, let’s go ahead and begin this session. We’re going to begin this session with a talk about DNS servers.
Now DNS is the process that maps human-friendly names as in www.google.com, to their appropriate IP addresses. Without DNS we would have to memorize all of the IP addresses that we wished to visit.
Now, DNS stands for Domain Name System, and it’s very structured in nature. If the local DNS server apparatus doesn’t contain the needed record, it sends the request up to the DNS chain until the positive response is received back.
Now, this positive response gets passed back down to the original requester. Now DNS does require that an FQDN fully qualified domain name is used in order for it to function properly known FQDN is www.google.com it’s that naming convention right there.
The www is the specific service that’s being requested. The Google portion is the local domain that contains the specific service. And the calm is top-level that contains the Google that contains the specific service that is an FQDN.
Now that we’ve got that covered, let’s talk about the different levels of DNS servers. First off, there can be a local DNS server. This is the server on the local network that contains the host’s file that map’s all of the FQ DNS to their specific IP addresses in the local subdomain, it may be present or it may not be present.
Then there are top-level domain servers, the TLD server.
Now, these are the servers that contain the records for the top-level domains, examples of top-level domains are .com, .org, .net, .edu, and so on and so forth. Now, each of these servers contains all of their information for their respective domains kind of what do I mean by kind.
Well, the TLD servers do delegate down to second level servers, their information, they do that to ease the load so that the TLD server is not overloaded. But the TLD server is the server that is responsible for maintaining the record.
Then there’s the root server. This is the server that contains all of the records for the TLD servers. So if you’re looking for a TLD, that is kind of unknown, you will actually go to the root server, which will then pass you on to the appropriate TLD. Then there are authoritative servers and non-authoritative servers. An authoritative DNS server is one that responds to a request.
And that authoritative server has been specifically configured to contain the requested information. An authoritative response comes from a DNS server that actually holds the original record. So an authoritative response comes from the name server that’s been specifically configured to contain that record, and then there are non-authoritative DNS servers.
Now a non-authoritative DNS server is one that responds to a request with DNS information that it received from another DNS server. A non-authoritative response is not a response from the official name server for the domain. Instead, it is a second or third-hand response that’s given back to the requester.
In most cases, when we send a DNS request, we get a non-authoritative response back. Now let’s move on to the various DNS record types. The first record that we’re going to talk about is the record. Now the record maps hostnames are FQ DNS to their respective ipv4 addresses.
Closely associated with the record is the record or quadruple a record this maps that FQDN to its respective ipv6 address. Then there’s the C name record. Now, this maps a canonical name or alias to a hostname.
What that means is that you can have edcc.edu be the same as EDC dot o r g without having to maintain two sites, the EDC c dot o r g can be the canonical name for EDC c.edu. This works in part because the pointer records the PTR record. It’s a pointer record that points out to DNS that there is a canonical name. And finally, we have the MS record.
Now, this record maps to the email server that is specified for a specific domain. It is the record that determines how email travels from sender to recipient. And now let’s move on to dynamic DNS. Now dynamic DNS or DNS permits lightweight immediate updates to a local DNS database.
This is very useful when the FQDN or hostname remains the same, but the IP address is able to change on a regular basis. Dynamic DNS is implemented as an additional service to DNS and it’s implemented through DD ns updating.
Now, this is a method of updating traditional names. Without the intervention of an administrator, there’s no manual editing or inputting of the configuration files required. A DNS provider supplies software that will monitor the IP address of the reference system.
Once the IP address changes, the software sends an update to the proper DNS server. DNS is useful when access is needed to a domain whose IP address is being supplied dynamically by an ISP or internet service provider.
That way the IP address can change but people can still get to the service that they’re looking for. Now, that concludes this session on the introduction to the DNS service. We talked about DNS servers, we moved on to DNS records. And then we concluded with a very brief discussion about dynamic DNS.
What is Network Address Translation? How does Network Address Translation work?
Now, we’re going to be talking about the purpose of network address translation. And then we’re going to discuss how network address translation works. And with that, let’s go ahead and begin this discussion. Of course, we’re going to begin by talking about the purpose of network address translation.
Network address translation or Nat solves a very serious problem of how to route non-routable IP addresses. As a partial effort to conserve the ipv4 address space, the private ipv4 addressing spaces were developed, these address spaces were removed from the public ipv4 address space and made non-routable across public ipv4 networks.
And this led to the problem being non-routable preventing that private ipv4 address from communicating with remote public networks. NAT very simply solves this problem.
A router with Nat enabled will translate a private IP address into a routable public IP address. When the response returns to the router, it passes the response back to the device that requested it. So now that we’ve covered the purpose, let’s talk about how network address translation works.
First off, we get to talk about the fact that there are two categories of Nat. First up is static Nat. With static Nat, each private IP address is assigned to a specific routable public IP address this relationship is kept and maintained by the NAT-enabled router. When a device needs access outside of the local network.
The router translates the local IP address to the assigned public IP address. And when the response comes back, the router will translate the public IP address back into a local one. Static Nat is not flexible in leads to some scalability issues.
An individual routable IP address must be kept for every device that requires access outside of the local network. So as the network grows, you need to increase the number of public IP addresses that are under your control. That gets kind of expensive and kind of complicated. They developed dynamic Nat to resolve some of that issues.
With dynamic Nat, the NAT-enabled router dynamically assigns a routable IP address to devices from a pool of available IP addresses. When a device needs access outside of the local network. The router performs the NAT function only the public IP address comes from a reusable pool of public IP addresses.
That private IP address is assigned the public IP address from the pool and once outside accesses stop the routable IP address goes back into the pool to be reused.
As initially designed dynamic Nat was more flexible than static Nat, but it still led to some scalability issues. As more network traffic required access to outside networks. The pool of available public IP addresses needs to increase or outside Access cannot be achieved.
But thankfully, there is a solution to this. And that solution is called port address translation, or in Cisco terms, that would be net with Pat.
Pat is a type of dynamic Nat that was developed to increase the scalability of network address translation. When a local network device requires access to a public network, the net-enabled router dynamically assigns the public IP address to the device.
With the addition of dynamically assigning a port number to the end of the public IP address. The router tracks the IP address’s important numbers to ensure that network traffic is routed to and from the proper devices. Pat still requires a pool of public IP addresses.
But the pool may only contain one public IP address, or it may contain several for a large private network. This is the preferred method of implementing network address translation for two reasons.
First off, there are fewer public IP addresses that are required. And it makes it easier for an administrator to maintain.
Now let’s talk about Nat’s terminology, specifically about the types of addresses. And we begin with the inside a local address, which is a private IP address on the local network. It is the private IP address assigned to a specific device. Then there’s the inside global address a public address referencing an inside device.
The inside global address is the public IP address assigned to the inside device by the NAT-enabled router allowing access outside of the network. Then there’s the outside global address, which is a public IP address referencing an outside device. It is the public IP address assigned to a device outside of the local network.
Then there’s the outside local address, which is the private IP address assigned to an outside device. This is the private IP address assigned to the outside device by the NAT-enabled router on the interior of the local network so that the inside device can communicate correctly with the outside device.
Now that concludes this session on introducing network address translation. We talked about the purpose of network address translation. And then we talked about how network address translation works.