ppp ip address assignment

What is PPP (Point-to-Point Protocol)? | How Does It Work?

PPP (Point-to-Point Protocol) is how computers talk and share data in networks. This protocol begins sessions by creating a secure link between ISPs and users. So this lets home users connect to the Internet.

What is the PPP Protocol in Networking, and What Exactly Does It Do?

The PPP protocol partners up with TCP/IP . Plus, it handles communication at the link layer between two PCs.

Specifically, it lets you connect to your service provider and set up the web link using a modem. Broadband connections such as PPPoE or PPPoA are used to accomplish this.

PPP has authentication and dynamic IP address assignment functions. It’s not just about transferring data; it does more. So, it doesn’t hand out IP addresses that ISPs gave to clients to all devices on the remote network.

Thus, users get an IP address when they connect to the ISP. As a result, the IP address they receive is valid until the PPP connection ends.

PPP History

William Simpson began developing PPP in the late 1980s. It became one of the most common protocols used for Internet access at that time. One of its most basic purposes was to provide Internet access to users.

Therefore, William designed PPP in detail to meet this need. And so it released its first version in 1990.

This protocol, accepted in the 1990s, became preferred by ISPs. As a result, they offered their users access to the Internet with PPP connections.

In the 2000s, users continued to use the PPP protocol. But it had to adapt to newer tech. In particular, when web speeds increase, technologies such as ADSL are developed. In this way, they have also created versions compatible with such connections.

As a result, it provides data transfer over various contact lines. It is flexible and suitable for a wide range of apps.

Today, people use the PPP in DSL and Fiber connection tech . People in modern times do it this way.

PPP Features

PPP is important because it is reliable, supports many protocols, has authentication, and helps detect errors. Also, these are its key features.

• Point-to-Point Connection

PPP works between two specific devices, ensuring a direct line of contact. In this case, it sends data securely and quickly. This is why they favor it, especially in telecom and web access.

• Multiple Protocol Support

It works in harmony with different protocols. Among them, it works compatible with TCP/IP, IPv6, and IPX/SPX. This makes it easy to integrate into various networks and systems.

• Authentication

They allow the users they want to access a particular network with confirmation. In this case, only approved persons have access to it.

• Error Detection and Correction

When two devices are far apart, they send information to each other, find mistakes, and fix them. They also send the data again and make sure they connect correctly.

It’s essential to make sure user data is sent securely over the net. That’s why PPP is significant for LAN connections like VPN , where it works professionally to keep things safe.

• Flexibility

It works well with things like Ethernet , modems , or serial connections. Also, this helps them connect easily to many devices.

• Session Management

Another of PPP’s active roles is session management. With this feature, it starts, ends, or resumes sessions.

• Internet Connections

For easy Web access, PPP is great for everyone. It works with cable, DSL, or dial-up connections.

What Are PPP Components?

This protocol has three main components. These:

• Frame Structure

It employs a framing method like HDLC. This wraps data securely and checks for errors.

Also, it uses LCP (Link Control Protocol) for setup. This helps set up, configure, and test the data link.

As a result, it sets up network protocols using NCP (Network Control Protocol).

How Does PPP Work?

You can learn how PPP works sequentially. So you can understand how it secures data transmission in the network.

Step 1: Physical Connection

During the initial connection phase, first create a physical link. This link connects the remote device to the server. Also, this link ensures seamless data transfer.

Step 2: Framing

In the second stage, PPP packages the data into frames while marking the beginning and end. It also includes ways to divide and arrange the data.

Step 3: Link Control Protocol (LCP)

The third step configures contact line details using the LCP protocol. Then, it starts the session and manages the data processing.

Step 4: Authentication

Step four checks if the user can access the server. It chooses an authentication method and sends it to the server. This allows the user to connect to the server.

Step 5: NCP (Network Control Protocol)

In the fifth step, NCP decides which network layer to use for data transfer. This protocol can choose TCP/IP, IPv6, or IPX/SPX.

Step 6: Data Transmission

The sixth step starts the link after setting up everything required. Also, it employs a framing way to achieve its objective during this process.

Step 7: Connection Termination

In the final stage, it wraps up the communication. However, if PPP ends the connection, it does so in this step.

PPP Advantages and Disadvantages

Let’s consider some of the pros and cons of this protocol:

• Reliable Communication: First, it authenticates users. Then, it fixes potential errors. As a result, it guarantees sending in a healthier way.
• Security : Provides strong encryption on commonly used network types such as VPN.
• Protocol Support: It facilitates the connection between systems by supporting many types of communication in complex networks.
• Flexibility : It works with Ethernet devices. Also, it works with modem devices.
• Error Detection : Its main job is to detect potential mistakes between the user and the remote server. This happens during the check process.

Disadvantages

• Connection : It helps one-on-one networks but doesn’t work for many links.
• Performance: There is a slight advantage when sending big files.
• Installation and Management : Setting it up can be more complex than other protocols.
• Cost : Installation costs may be higher than others. As a result, advanced devices and methods are required.

How do you make an Internet connection with PPP?

Setting up an Internet connection with PPP is easy. Home users can find these details right on their modem interfaces.

To access the web, you need a compatible modem. After setting it up, choose a method to confirm ISP information. Options include PPPoE and PPPoA for this stage.

Of course, remember that these protocols might vary depending on your Internet Service Provider.

After choosing the protocol provided to you, you need the username and password from your ISP for the Internet connection. Next, you need to enter the configuration interface of your modem or device. You will have access to the web after entering this information on your device.

In addition, check the DNS (Domain Name System) and IP address settings on your device. After that, check that DHCP can automatically distribute addresses to your local network.

After you have completed all these things, open a web browser on your PC and check your Internet connection. If everything works well, then you can make your current security settings.

As a recommendation, create a strong password for your modem’s admin accounts. This helps ensure better safety. Also, you can improve web security by regularly updating the software on your device.

What are PPPoE and PPPoA Concepts?

There are two types of communication protocols used according to the connection types. These;

• PPPoE (Point-to-Point Protocol over Ethernet)
• PPPoA (Point-to-Point Protocol over ATM)

They usually use these two methods in links, such as DSL (Digital Subscriber Line). Internet service providers also serve their clients in this way.

1. PPPoE (Point-to-Point Protocol over Ethernet)

The most widely used in Ethernet-based structures is PPPoE. In particular, they prefer DSL connection types. This form of connection offers flexibility and better network control.

The features of PPPoE:

• Authentication : Provides a username and password to connect users to the net. Thus, people have to enter the data they receive from their ISP.
• Encryption: These connections encrypt data and increase transfer privacy and security.
• Broad Area of Use: Provides connection support to home and workplaces. It also keeps devices such as DSL.
• Dynamic IP: Users usually get dynamic IP addresses with PPPoE. Thus, they get a new address each time they turn the modem on and off.

2. PPPoA (Point-to-Point Protocol over ATM)

Infrastructures that use ATM (Asynchronous Transfer Mode) technology support PPPoA. This is why DSL connections and specific fiber optic setups often choose it.

The features of PPPoA:

• Cellular Communication : PPPoA employs ATM technology, which breaks down and moves data in cells.
• Authentication : It helps verify users and provides a safe way.
• Connection Stability: Compared to the other type, it does a better job in DSL connection.
• Static IP: PPPoA usually uses a static IP address compared to PPPoE. In short, the address assigned by the ISP remains constant even if users reboot their device.

Differences Between PPPoE and PPPoA

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Difference between Serial Line Internet Protocol (SLIP) and Point-to-Point Protocol (PPP)

SLIP and PPP, which are the widely used serial connection techniques, help to connect the distant devices of the network. The fullform of SLIP is Session Layer Internetworking Protocol. SLIP being a primitive protocol put into use during the early connections to the Internet, when there was not much overhead. PPP is slightly more complex as the protocol, in addition to data encapsulation, has such functions as authentication, checksum, and protocol identification. In this article, we will see SLIP and PPP protocols in detail.  

What is SLIP? 

The SLIP is short for the Serial Line Internet Protocol and is actually a very rudimentary one that enables any IP packets to be sent over a serial port. It was conceived as a natural sequence to how the IP datagrams should be forwarded across a point-to-point serial link. As much as it is known and documented, SLIP is relatively simple and compact and therefore is well suited for use.

Features of SLIP

• Simple: SLIP is a simple protocol that does not include any error detection or correction mechanisms.
• Efficient: SLIP is an efficient protocol that does not include any unnecessary overhead, which makes it ideal for low-bandwidth connections.
• Supported by many operating systems: SLIP is supported by many operating systems, including Windows and Linux.
• Used for point-to-point connections: SLIP is used to establish a point-to-point connection between two network devices.

Advantages of SLIP 

• Small coverage in which high volumes of information can be transmitted with a measure of economy over low-speed networks. 
• Ease of implementation; this is one of the major strengths of SLIP considering the fact that it is relatively easy to implement and use in a simple network. 

Disadvantages of SLIP 

• It also provides no evidence of authentication, error detection , or correction and is very slow. 
• This device supports only the fixed type of the IP addressing and can be applied only to the TCP/IP protocol .

What is PPP? 

Point-to-Point Protocol (PPP) is a more advanced and generalized protocol than that of SLIP, having some additional features such as authentication, error control , and the protocol of network layer independence. It is most sought-after for setting up end-to-end channels over the serial link joined in a range of networking settings. 

Features of PPP

• Authentication: PPP includes authentication mechanisms such as Password Authentication Protocol ( PAP ) and Challenge Handshake Authentication Protocol ( CHAP ) to ensure secure communication.
• Error detection and correction: PPP uses error detection and correction mechanisms such as CRCs and acknowledgments to ensure the integrity of the transmitted data.
• Network layer protocol independence: PPP is independent of the network layer protocol being used, making it compatible with various network protocols.
• Multilink support: PPP supports multilink connections, which allow multiple physical connections to be combined to increase the data transmission rate.

Advantages of PPP 

• Sustains communications with protection methods such as authentication. 
• Dynamic IP addresses can be provided with ease and with high capacity, flexibility, and easy configuration. 
• Facilitates error control, making it possible for the receiver to detect errors and get assistance to correct them, hence reliable data transmission. 

Disadvantages of PPP 

• Hierarchy is richer and therefore has more overhead than SLIP, which can be a nuisance in low bandwidth networks. 
• Slightly slower than other types of data because of the additional functionalities that it supports, such as authentication and error checking.

Similarities between SLIP and PPP

• Both are used to establish a point-to-point connection between two network devices.
• Both are widely used in various communication systems and have been standardized by international organizations.
• Both are used for transmitting data over serial connections.
• Both can be used with a variety of networking hardware, including modems and serial cables.

SLIP and PPP are both protocols used for communication over serial connections, but they differ in several key aspects, including authentication, network layer protocols, error detection and correction, frame size, flexibility, and compatibility. While SLIP is a simpler and more lightweight protocol, PPP is more modern and offers more features, such as authentication and support for multiple network layer protocols.

Frequently Asked Questions on SLIP and PPP – FAQ’s 

Why is ppp preferred over slip in modern networks.

PPP is favored since it comes with such aspects as authentication, error detection, and dynamic IP addressing, which are significant in safe and efficient communication in networks today. 

Can SLIP and PPP be used interchangeably?

Both are capable of setting up a point-to-point connection but are not always mutually substitutive. SLIP is ideal for basic plain vanilla applications, which have low utilization and a low data rate, while PPP is applicable in a case of authentication and error detection, as well as other higher features. 

Does PPP support encryption?

PPP does not contain functionality for encryption, but it contains the mechanisms for the authentication. In the case of encryption, it can be adopted in conjunction with such protocols as the IPsec. 

Is SLIP still in use today?

SLIP has faded away from the scene but yet can be observed in some applications that need extremely low overhead for transferring data.

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What is the p-t-p (or remote IP) address in PPPoE connections?

In Linux when I connect to PPPoE via the pon command, the plog command shows two IP addresses:

• local IP address (which is my internet public IP)
• remote IP address (which I don't know what is it?)

All my question is about what is this "remote IP address"?

When I run the ifconfig ppp0 command it shows "local IP address" and "remote IP address" as "inet addr" and "P-t-P" respectively.

When I traceroute to some IP, the first hop is this "remote IPaddress", and when I traceroute from some other IP to my inet IP, there is no sign of this "remote IP address".

PPPoE refers to Point-to-Point Protocol over Ethernet. The "P-t-P" you are seeing is specifically "Point-to-Point".

What this effectively means is a method of tunnelling an internet connection over an ethernet network, most likely through your local exchange. This works by you being given a local IP address for your modem and then the address for the remote machine that you need to use as a gateway for your internet connection.

As per that Wikipedia article:

By using PPPoE, users can virtually "dial" from one machine to another over an Ethernet network, establish a point to point connection between them and then securely transport data packets over the connection.

The machine you are "dialling" (the remote IP) is going to be the gateway for your internet service provider.

The reason it always shows up in an outbound connection is because it has to in order for you to have a valid internet connection. I suspect that the reason it does not show up on an incoming tracert may be because it is not actually your machine that is getting the connection. You may well have a disposable "local" IP address that is not seen outside of your local telephone exchange.

• and what is the difference between my p-t-p server and the inet ip server? i think both are doing the same. –  sia Commented Aug 26, 2012 at 20:33
• The only difference is in how the connection is set up and handled by your local telephone exchange or internet service provider, the actual job happening is the same. –  Mokubai ♦ Commented Aug 26, 2012 at 22:01

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Configuring PPP negotiation

PPP negotiation includes the following parameters:

Negotiation timeout time.

IP address negotiation.

IP segment match.

DNS server IP address negotiation.

ACCM negotiation.

ACFC negotiation.

PFC negotiation.

Configuring the PPP negotiation timeout time

The device starts the PPP negotiation timeout timer after sending a packet. If no response is received before the timer expires, the device sends the packet again.

If two ends of a PPP link vary greatly in the LCP negotiation packet processing rate, configure the LCP negotiation delay timer on the end with a higher processing rate. The LCP negotiation delay timer prevents frequent LCP negotiation packet retransmissions. After the physical layer comes up, PPP starts LCP negotiation when the delay timer expires. If PPP receives LCP negotiation packets before the delay timer expires, it starts LCP negotiation immediately.

To configure the PPP negotiation timeout time:

Configuring IP address negotiation

To configure the device as the client:

Configure the server to assign an IP address to a client by using the following methods:

Method 1: Specify an IP address for the client on the server interface.

Method 2: Specify a PPP or DHCP address pool on the server interface.

Method 3: Associate a PPP or DHCP address pool with an ISP domain.

For clients requiring no authentication, you can use either method 1 or method 2, but not both.

For clients requiring authentication, you can use one or more of the three methods, but cannot use method 1 and method 2 at the same time. When multiple methods are configured, method 3 takes precedence over method 1 or method 2.

PPP supports IP address assignment from a PPP or DHCP address pool. If you use a pool name that identifies both a PPP address pool and a DHCP address pool, the system uses the PPP address pool.

To configure the device as the server (Method 1):

To configure the device as the server (Method 2: Specify a PPP address pool):

To configure the device as the server (Method 2: Specify a DHCP address pool):

To configure the device as the server (Method 3: Associate a PPP address pool with an ISP domain):

To configure the device as the server (Method 3: Associate a DHCP address pool with an ISP domain):

Enabling IP segment match

This feature enables the local interface to check whether its IP address and the IP address of the remote interface are in the same network segment. If they are not, IPCP negotiation fails.

To enable IP segment match:

Configuring DNS server IP address negotiation

Configure DNS server settings depending on the role of your device in PPP negotiation.

Configuring the local end as the client

During PPP negotiation, the server will assign a DNS server IP address only for a client configured with the ppp ipcp dns request command. For some special devices to forcibly assign DNS server IP addresses to clients that do not initiate requests, configure the ppp ipcp dns admit-any command on these devices.

To configure the local end as the client:

Configuring the local end as the server

Configuring ACCM negotiation

PPP uses the escape mechanism on asynchronous links to avoid treating payload characters as control characters. The escape mechanism converts all one-byte asynchronous control characters into two-byte characters. This mechanism increases the size of asynchronous control characters and reduces the payload size.

The ACCM configuration option provides a method to negotiate with the peer of the local control characters, which must be converted on asynchronous links. The ACCM field contains 32 bits numbered 1 to 32 from left to right. Each bit corresponds to an asynchronous control character numbered the same. If the value of a bit is 0, the system does not convert the corresponding asynchronous control character. If the value of a bit is 1, the system converts the corresponding asynchronous control character by prefacing it with a backslash (\). For example, if the value of the bit numbered 19 is 0, the asynchronous control character numbered 19 (DC3, Control-S) will be sent without being converted.

ACCM negotiation is implemented at the LCP negotiation stage. After ACCM negotiation is completed, the peer converts asynchronous control characters according to the Async Control Character Mappings when sending packets.

By default, the ACCM field takes the value of 0x000A0000. To increase the payload size on low-rate links, set the ACCM field to 0x0 so the system does not convert asynchronous control characters.

To configure ACCM negotiation:

Configuring ACFC negotiation

PPP can compress the address and control fields of PPP packets to increase the payload size.

ACFC negotiation notifies the peer that the local end can receive packets carrying compressed address and control fields.

ACFC negotiation is implemented at the LCP negotiation stage. After the ACFC negotiation succeeds, PPP does not include the address and control fields in non-LCP packets. To ensure successful LCP negotiation, PPP does not apply the compression to LCP packets.

As a best practice, use the ACFC configuration option on low-speed links.

To configure the local end to send ACFC requests:

To configure the local end to reject ACFC requests received from the peer:

Configuring PFC negotiation

PPP can compress the protocol field of PPP packets from 2 bytes to 1 byte to increase the payload size.

PFC negotiation notifies the peer that the local end can receive packets with a single-byte protocol field.

PFC negotiation is implemented at the LCP negotiation stage. After PFC negotiation is completed, the device compresses the protocol field of sent non-LCP packets. If the first eight bits of the protocol field are all zeros, the device does not add those bits into the packet. To ensure successful LCP negotiation, PPP does not apply the compression to LCP packets.

As a best practice, use this configuration option on low-speed links.

To configure the local end to send PFC requests:

To configure the local end to reject PFC requests received from the peer:

© Copyright 2017 Hewlett Packard Enterprise Development LP

Explanation of the IP address assignment using PPP.

The IP address for the PPP network interface is assigned using the following modes:

• Static IP The IP address is configured manually in the Net_Config_PPP.h file. However, it is possible to change the IP address at runtime . The static configuration specifies also a primary and optional secondary DNS server.
• Automatic IP This mode is mostly used. The IP address for the PPP client is obtained from the Dial-up server . The Dial-up server specifies also a primary and optional secondary DNS server. In order to use this mode, the option "Obtain Client IP address automatically" must be enabled in the system configuration. When this option is enabled the Local IP address configuration settings are ignored.

General configuration guidelines for flexible IP address assignment

Flexible IP addressing for IPoE/PPPoE v4 and v6 hosts is by default disabled. In other words, the subscriber hosts are instantiated in the BNG with ability to forward traffic only if their assigned IP addresses belong to one of the configured subnets/prefixes that are associated with the subscriber-interfaces. IPv4 and IPv6 cases are be examined separately:

By default, IPoE and PPPoE subscriber host creation fails in the following two cases:

The subscriber-interface does not have an IPv4 address configured, and therefore it is be operationally down. This configuration is also known as unnumbered subscriber-interface.

The subscriber-interface does have an IPv4 address configured but the IPv4 address assigned to the subscriber host itself is outside of the subscriber-interface configured subnets. In such case, the host is instantiated, but the forwarding is disabled.

Subscriber host instantiation and forwarding can be explicitly enabled for both cases above with flexible IP addressing functionality.

For case 1, this can be achieved by borrowing an IP address for the subscriber-interface from any interface that is operationally up within the routing context. This functionality can be enabled with the configure service ies | vprn < service-id > subscriber-interface < ip-int-name > unnumbered < ip-int-name | ip-address > command.

To enable forwarding for the subscribers whose IP address falls outside of the configured subnet under the subscriber-interface (case 2), the configure service ies | vprn <s service-id > subscriber-interface < ip-int-name > allow-unmatching-subnets command must be entered.

The above commands ( unnumbered and allow-unmatching-subnets ) are mutually exclusive. In addition, the unnumbered command can be configured only if the subscriber interface does not have an IP address already configured. Otherwise the execution of this command fails.

In both of these cases the host is installed in the routing table as /32.

For IPv6 there is a single command that enables flexible IP addressing for both cases:

IPv6 prefixes are not configured under the sub-if > ipv6 node

IPv6 prefixes are configured but the actual address or prefix assigned to the subscriber (by DHCP, LUDB or RADIUS) is outside any prefix that is configured under the sub-if > ipv6 hierarchy.

This single command is configure service ies | vprn < service-id > subscriber-interface < ip-int-name > ipv6 allow-unmatching-prefixes .

To summarize, the following scenarios are possible:

An IPv4 address under the subscriber-interface is configured

By default, hosts outside of the sub-intf subnet are instantiated but they are in a non-forwarding-state. Traffic is dropped.

allow-unmatching-subnets is configured. This command is allowed only if subscriber-interface has also configured its own IPv4 address(es). In this case the IP address for IPCP negotiation is one of the sub-intf addresses. Hosts outside of the sub-intf subnets are instantiated and forwarded.

The unnumbered < ip-address | ip-int-name > command is not allowed in this scenario.

An IPv4 address under the subscriber-interface is not configured

By default, the subscriber-interface is operationally down. Subscribers cannot be instantiated.

The allow-unmatching-subnets command has no effect because a subscriber-interface does not have an IPv4 address configured and is therefore operationally down. No subscribers can be instantiated.

The unnumbered < ip-address | ip-int-name > command is the only viable option in this case. The subscriber-interface borrows an IPv4 address from another interface that is operationally UP and consequently this allows subscribers to be instantiated. This command is mutually exclusive with allow-unmatching-subnets . In addition, this command can only be configured if the subscriber interface itself does not have explicitly configured an IPv4 address.

Like the PPPoE case above.

IPoEv6 and PPPoEv6

The allow-unmatching-prefixes command is independent of any IPv4 command related to flexible IP address assignment ( unnumbered or allow-unmatching-subnets ). This command can always be enabled, regardless of the v6 prefixes configured under the sub-if > ipv6 hierarchy. Any subscriber, regardless of the subscriber interface prefix configuration is instantiated and forwarded.

PPPoE server IP address assignment through the local DHCP server configuration example

Network requirements.

As shown in Figure 6 , configure the PPPoE server as a DHCP server to assign an IP address to the host.

Figure 6: Network diagram

Configuration procedure

# Configure Virtual-Template 10 to use PAP for authentication and use a DHCP address pool for IP address assignment, and configure an IP address for Virtual-Template 10.

# Enable the PPPoE server on GigabitEthernet 1/0/1, and bind the interface to Virtual-Template 10.

# Enable DHCP.

# Configure DHCP address pool pool1 .

# Create a PPPoE user.

Verifying the configuration

# Log in to the router by using username user1 and password pass1 .

# Display information about IP addresses assigned by the DHCP server.

The output shows that the router has assigned an IP address to the host.

© Copyright 2017 Hewlett Packard Enterprise Development LP

• Previous : Determining Requirements for Your Configuration Type
• Next : Routing Considerations

Determining IP Addressing for Your PPP Link

To enable communications over the PPP link, the machine at one end of the link must know the host name and IP address of the peer host on the other end of the link. The PPP configurations often require a particular addressing scheme. This section explains the addressing schemes and where each should be used.

Specifying IP Addresses

On each endpoint machine, you specify addressing information in these places:

/etc/asppp.cf configuration file

/etc/inet/hosts file

NIS+, NIS, or DNS databases, if applicable

When you edit the local machine's asppp.cf file, you must provide the host names and, in certain cases, the IP addresses for each endpoint machine to be on the link. For example, you must type either the IP addresses or host names for each endpoint as arguments in the ifconfig section in the configuration file:

See "Editing the Configuration File" for information regarding the format of /etc/asppp.cf .

Additionally, to enable communications, you must add the IP address and host name of the remote endpoints to the hosts database on the local endpoint by editing /etc/inet/hosts . This process is explained in "Configuring Network Clients" .

Types of Addressing Schemes

You have a choice of several addressing schemes for PPP, depending on your configuration type. Before you edit the asppp.cf file and hosts database, you must decide on the appropriate addressing scheme for your configuration. These schemes include:

Using the same IP addresses for the PPP endpoints as is assigned to their primary network interface in their local /etc/inet/hosts files

Assigning a unique IP address for each PPP endpoint

Assigning a new network number for the network created by the PPP link

Using the Same IP Address as the Primary Network Interface

This addressing scheme is appropriate for point-to-point links only. In this scheme, you specify the addresses of the primary network interface for each endpoint. (See Chapter 2, Network Services Overview for more information about the primary network interface.) These endpoints might be:

Two standalone machines communicating over the PPP link (if they have existing IP addresses)

Two network endpoints communicating over the PPP link

Remote host connecting to a network dial-in server through a point-to-point link

Dial-in server connecting to remote hosts through a dynamically allocated point-to-point link

When you edit the /etc/inet/hosts file on a local endpoint, supply the IP address of its primary network interface and host name and the IP address of the peer host on the other end of the link.

Creating a Unique IP Address and Host Name

In this method, you assign a unique host name and IP address to the PPP network interface. (You might want to call the interface hostname-ppp .) Use this addressing scheme for:

Endpoint machines on a network used as a multipoint dial-in server.

Machines on a virtual network.

Remote host that uses a dedicated IP address for communicating with a dial-in server over a dynamically allocated PPP link. (Note that this is not a requirement for the dynamic link configuration.)

Machine that is also configured as a router for a physical network, such as Ethernet or Token Ring.

Machine in a standalone-to-standalone configuration that does not have an existing IP address. (The PPP interface becomes the primary network interface.)

You must specify the unique address and host name for the PPP network interface in the asppp.cf configuration file.

To create the new host name and IP address, add it to the /etc/inet/hosts file on the endpoint machines, as described in " hosts Database" .

Assigning a Network Number to the PPP Link

You create a new network number for the PPP configuration when it involves:

Virtual networks of computers communicating through PPP multipoint links (required)

A multipoint dial-in server and its remote hosts (required)

The PPP link between two networks, particularly when one or both of the network endpoint machines are also routers for a physical network (optional)

(See Chapter 5, Planning Your TCP/IP Network for information on network numbers.)

The PPP link becomes a virtual network , since it does not involve any physical network media. You need to type its network number in the networks database on all endpoint machines, along with the network numbers of the networks being linked.

The following sample shows an /etc/inet/networks file for an internetwork with PPP.

Example 22-1 /etc/inet/networks File for an Internetwork With PPP

In the sample file, kalahari and negev are two local area networks, and nubian-ppp is the name of the PPP link.

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Address Pool for L2TP Network Server IP Address Allocation

With an address pool , you configure an address or address range. When you define an address pool for a client, the L2TP network server ( LNS ) allocates IP addresses for clients from an address pool. If you do not want to use an address pool, you can specify an IP address by means of the framed-ip-address statement at the [edit access profile profile-name client client-name ppp] hierarchy level. For information about specifying an IP address, see Point-to-Point Protocol (PPP) .

When an address pool is modified or deleted, all the sessions using that pool are deleted.

To define an address or a range of addresses, include the address-pool statement at the [edit access] hierarchy level:

pool-name is the name assigned to the address pool.

To configure an address, include the address statement at the [edit access address-pool pool-name ] hierarchy level:

address-or-prefix is one address or a prefix value.

When you specify an address range, it cannot exceed 65,535 IP addresses.

To configure the address range, include the address-range statement at the [edit access address-pool pool-name ] hierarchy level:

low lower-limit —The lower limit of an address range.

high upper-limit —The upper limit of an address range.

The address pools for user access and Network Address Translation (NAT) can overlap. When you configure an address pool at the [edit access address-pool pool-name ] hierarchy level, you can also configure an address pool at the [edit services nat pool pool-name ] hierarchy level.

Related Documentation

• Point-to-Point Protocol (PPP)
• Layer 2 Tunneling Protocol (L2TP)
• Address-Assignment Pools for Subscriber Management

PPP MultiLink

Lesson Contents

Sometimes we see a network design where we have more than one serial link between two routers. Perhaps a single serial link doesn’t provide enough bandwidth or you want some extra redundancy. Each interface on a router requires a different IP address, so with two serial links you might end up with a design that looks like this:

Above we see that the first link uses the 192.168.12.0/24 subnet, the second link uses 192.168.21.0/24.When we use two subnets between two routers and when you configure a routing protocol like OSPF or EIGRP, it will form two neighbor adjacencies:

When the metric on both links is the same, our routing protocol will use load balancing so both links will be used. By default, Cisco IOS will load balance based on the destination. For example, if 2.2.2.2 would be behind R2 then R1 might use Serial 0/0/0 for all traffic destined to 2.2.2.2. Another destination might use the Serial 0/1/0 interface.

What if we add more serial links? For each serial link, we will have to configure another subnet and we will get another neighbor adjacency. It will work but we can make things much easier…

Multilink PPP allows us to combine multiple physical serial links into a single logical link . We will only need a single subnet for the logical multilink interface and if you use OSPF or EIGRP, only a single neighbor adjacency is required:

MLPPP also does load balancing on layer two. This is pretty efficient, when it receives some data like an IP packet that has to be forwarded over the multilink interface, it will fragment the IP packet in two pieces and forwards it on the multilink interface. The receiving router takes the fragments and reassembles them into the original IP packet:

By using PPP multilink, we simplify our configuration on layer three since there will be only one logical interface to work with.

Configuration

Let’s see how we configure PPP multilink. I will use the following topology:

First, don’t forget to specify a clock rate. I will check which of my routers has the DCE end of the cable:

R2 is the DCE and you can see a clock rate was configured. Let’s enable PPP encapsulation on all serial interfaces on R1:

And we do the same thing on R2:

Now we can create the multilink interface on both routers:

You can pick whatever multilink interface number you like, just make sure that it’s the same on both ends. This is where we configure the IP address.

On the physical serial interfaces, we have to configure to which multilink interface they belong with the ppp multilink group command. Let’s start with R1:

And let’s do the same thing on R2:

That takes care of the PPP multilink configuration.

To see the PPP multilink interface in action, let’s configure OSPF on both routers:

That completes our configuration.

Verification

Let’s verify our work step-by-step. First, let me quickly show you multilink interface in the running configuration:

We only created the multilink 1 interface and configured an IP address but you can see that Cisco IOS automatically added the ppp multilink and ppp multilink group commands.

Let’s continue, I want to make sure that the physical interfaces are up and running:

The interfaces are up/up which tells us that the clock rate is configured correctly and that PPP encapsulation is configured on both ends. Let’s take a look at the multilink interface:

The multilink interface is up too, it also shows me the IP address. Let’s take a closer look at the PPP details of the multilink interface:

The output above tells me that the multilink interface is up and has bundled Serial 0/0/0 and Serial 0/1/0 to the multilink interface. One more command to verify the PPP multilink interface, let’s look at its IP settings:

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Forum Replies

Hello Vianney

Take a look at this lesson on PPP Multilink. It describes the configuration and various principles that you need to keep in mind. Take a look, and if you have any questions or concerns, let us know.

https://networklessons.com/cisco/ccna-routing-switching-icnd2-200-105/ppp-multilink

I hope this has been helpful!

Hi Vianney,

From what I know, PPP multilink is reliable and shouldn’t impact your latency/bandwidth. It’s also used in VoIP scenarios where they recommend to enable interleaving. When you do this, the smaller (delay sensitive) packets are not multilink encapsulated.

If you want a definitive answer, it would be best just to test this. Lab it up on some real hardware, then see how it compares against two regular PPP links.

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Point-to-Point (PPP) Protocol Field Assignments

Registries included below

PPP DLL Protocol Numbers

Ppp link control protocol (lcp) and internet protocol control protocol (ipcp) codes, ppp lcp configuration option types, ppp tncp configuration option types, ppp ecp configuration option types, ppp ccp configuration option types, ppp sdcp configuration options, ppp authentication algorithms, ppp lcp fcs-alternatives, ppp multilink endpoint discriminator class, ppp lcp callback operation fields, ppp atcp configuration option types, ppp osinlcp configuration option types, ppp banyan vines configuration option types, ppp bridging configuration option types, ppp bridging mac types, ppp bridging spanning tree, ipx compression protocol values (value 3), ipx routing protocol options (value 4), nbfcp configuration options - name-projection 'added' field (value 1), nbfcp configuration options - peer-information (value 2), ppp eap request/response types, ppp vendor specific oui options, ppp ipcp configuration option types, ppp ipv6cp configuration options, ip-compression-protocol types, ipv6-compression-protocol types, ip header compression configuration option suboption types, rohc configuration option suboption identifier values, ppp over ethernet versions.

PPP (IPXCP) Configuration Options

NetBIOS Frames Control Protocol (NBFCP) Configuration Options

Contact Information

• Configuration
• View page source

[ip-pool] 

Configuration of ippool module.

gw-ip-address=x.x.x.x

Specifies single IP address to be used as local address of ppp interfaces.

Range format should be x.x.x.x/mask or x.x.x.x-y Specifies range of local address of ppp interfaces.

tunnel=range

Specifies range of remote address of ppp interfaces, format is same as above.

x.x.x.x/mask,pool_name | x.x.x.x-y,pool_name

Also specifies range of remote address of ppp interfaces.