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NE40E-M2 V800R010C10SPC500 Feature Description - User Access 01

This is NE40E-M2 V800R010C10SPC500 Feature Description - User Access
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UNR Generation and Advertisement

UNR Generation and Advertisement

UNRs Used to Forward Network-to-User Traffic

When users with IP addresses access the BAS interface of a BRAS through a switch, no dynamic routing protocol can be used to forward the network-to-user traffic because the BAS interface has no IP address. In this situation, the BAS interface needs to generate UNRs and import them to a dynamic routing protocol so that other devices can learn them.

For example, 100 users dial up using PPPoE to go online from a BRAS's BAS interface, and the BRAS applies for IP addresses from a RADIUS server and then allocates the addresses to users. These IP addresses may belong to different network segments. Because the BAS interface does not have IP address, it cannot forward network-to-user traffic to each user.

In this case, the following two types of UNRs are generated on the BRAS:

  1. Network segment routes destined for the user network segment, with the BAS interface through which users access the BRAS as the next hop. Such routes are advertised to the devices connected to the BRAS to guide user traffic to the BRAS.
  2. Specific host routes destined for each user's IP address, with the BAS interface through which users access the BRAS as the next hop. When the traffic of the users who go online through the BRAS reaches the BRAS, the BRAS searches for specific host routes to forward the traffic to the users.

The BRAS can be configured to advertise address pool network segment routes or specific routes. Configuring the BRAS to advertise address pool network segment routes is recommended to reduce the number of routes and suppress route flapping when users go online and offline frequently.

UNR Classification and Generation

UNRs are classified as follows based on the generation mode:

  • User network segment routes generated based on the address pool configurations
  • Specific host routes generated after users go online
  • User network segment routes generated through the Framed-route attribute delivered by the RADIUS server
  • User network segment routes and specific host routes generated through the Framed-IP-Address and Framed-IP-Netmask attributes delivered by the RADIUS server

The following section describes how UNRs are generated and advertised based on the address pool configurations.

  1. Create an address pool, and configure a gateway address so that the main control board generates a user network segment route and a gateway route with a 32-bit mask.
  2. After users go online with obtained IP addresses, the BRAS generates a 32-bit host route for each user. The traffic destined for each host will be guided to the BRAS through the network segment route described in Step 1, and then the BRAS searches the routing table for a 32-bit host route to forward the traffic to the user.

UNRs can also be generated based on the attributes delivered by the RADIUS server.

Multiple Layer 3 users are attached to a PPPoE leased line user and connected to the BRAS through Layer 3 devices, such as routers. In most cases, each leased line user has a fixed IP address assigned by the BRAS from its local address pool or by the RADIUS server.

When the leased line user and the attached users belong to the same network segment and the leased line user's IP address is assigned by the RADIUS server, the RADIUS server delivers Framed-IP-Address and Framed-IP-Netmask attributes to the BRAS. The BRAS then generates network segment routes and specific host routes.

When the leased line user and the attached users belong to different network segments, the RADIUS server delivers the Framed-route attribute to the BRAS. The BRAS then generates UNRs.

UNR Advertisement

If a user needs to communicate with other network users, the BRAS needs to advertise the user's network segment route to a dynamic routing protocol, such as OSPF, IS-IS, or BGP

The advertisement of UNRs in the IPv4 local address pool, remote address pool, and IPv6 prefix pool is described as follows:

Table 4-2 IPv4 address pool types and route advertisement modes

IPv4 Address Pool Type

Address Pool Route Advertisement Mode

IPv4 local address pool (PPPoE or IPoE)

Recommended mode: Run the import-route unr command to import UNRs to a dynamic routing protocol. Then the network segment route rather than specific host routes is advertised.

Optional mode: Configure a static black-hole route and use a dynamic routing protocol to advertise it.

IPv4 remote address pool (DHCP relay address pool)

Recommended mode: Run the import-route unr command to import UNRs to a dynamic routing protocol. Then the network segment route rather than specific host routes is advertised.

Optional mode: Configure a static black-hole route and use a dynamic routing protocol to advertise it.

IPv4 NAT public address pool

  • Mode recommended if a NAT public address pool is configured by specifying start and end IP addresses:

    Recommended mode: Configure a static black-hole route and use a dynamic routing protocol to advertise it.

    If the import-route unr command is run, routes cannot be summarized automatically, and a large number of 32-bit host routes will be generated.

  • Mode recommended if the NAT public address pool is configured by specifying a network segment:

    Recommended mode: To advertise the network segment routes, run the import-route unr command to import them to the target routing protocol.

  • Another method:

    Import and advertise network segment routes of the public address pool directly through the target routing protocol.

Table 4-3 IPv6 address pool types and route advertisement modes

IPv6 Address Pool Type

Address Pool Route Advertisement Mode

IPv6 BAS local address pool (PPPoE or IPoE)

Recommended mode: Run the import-route unr command to import UNRs to a dynamic routing protocol. Then the network segment route with the specified IPv6 prefix rather than specific host routes is advertised.

Optional mode: Configure a static black-hole route and use a dynamic routing protocol to advertise it.

IPv6 BAS delegation address pool

Recommended mode: Run the import-route unr command to import UNRs to a dynamic routing protocol. Then the network segment route with the specified IPv6 prefix rather than specific host routes is advertised.

Optional mode: Configure a static black-hole route and use a dynamic routing protocol to advertise it.

IPv6 BAS remote address pool

Recommended mode: The address pool of this type contains specific routes, but no user network segment routes. You need to configure the BRAS to advertise specific routes and then run the import-route unr command.

Optional mode: Configure a static black-hole route and use a dynamic routing protocol to advertise it.

NOTE:

Route advertisement using the import-route unr command is easy to configure and requires no static black-hole route whose configuration is error-prone. To prevent incorrect routes from being advertised, apply a routing policy to UNR import.

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Updated: 2019-01-02

Document ID: EDOC1100058415

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