Contents

Configuring IP forwarding basic settings························································ 1

About FIB table······························································································································· 1

Enabling last hop holding················································································································ 1

Enabling the FIB-based EXP setting for MPLS packets····································································· 2

Display and maintenance commands for FIB table············································································ 3

Configuring load sharing··················································································· 4

About load sharing·························································································································· 4

Configuring load sharing mode········································································································ 4

Enabling IPv4 bandwidth-based load sharing···················································································· 4

Configuring IP forwarding basic settings

About FIB table

A device uses the FIB table to make packet forwarding decisions.

A device selects optimal routes from the routing table, and puts them into the FIB table. Each FIB entry specifies the next hop IP address and output interface for packets destined for a specific subnet or host.

For more information about the routing table, see Layer 3—IP Routing Configuration Guide.

Use the display fib command to display the FIB table. The following example displays the entire FIB table.

<Sysname> display fib

Destination count: 4 FIB entry count: 4

Flag:

  U:Useable   G:Gateway   H:Host   B:Blackhole   D:Dynamic   S:Static

  R:Relay     F:FRR

Destination/Mask   Nexthop         Flag     OutInterface/Token       Label

10.2.0.0/16        10.2.1.1        U        GE1/0/1                  Null

10.2.1.1/32        127.0.0.1       UH       InLoop0                  Null

127.0.0.0/8        127.0.0.1       U        InLoop0                  Null

127.0.0.1/32       127.0.0.1       UH       InLoop0                  Null

A FIB entry includes the following items:

·     Destination—Destination IP address.

·     Mask—Network mask. The mask and the destination address identify the destination network. A logical AND operation between the destination address and the network mask yields the address of the destination network. For example, if the destination address is 192.168.1.40 and the mask 255.255.255.0, the address of the destination network is 192.168.1.0. A network mask includes a certain number of consecutive 1s. It can be expressed in dotted decimal format or by the number of the 1s.

·     Nexthop—IP address of the next hop.

·     Flag—Route flag.

·     OutInterface—Output interface.

·     Token—MPLS Label Switched Path index number.

·     Label—Inner label.

Enabling last hop holding

About this task

Last hop holding implements symmetric routing.

When the interface enabled with this feature receives the first IP packet of a forward flow, this feature implements the following operations:

·     Obtains the forward flow information and last hop information of the packet.

·     Based on the information, creates a fast forwarding entry for the reverse flow.

When packets of the reverse flow arrive at the device, the device forwards those packets based on the entry.

As is shown in Figure 1, when the external server sends a request to the internal server, the packet travels through ISP 1 to Interface A on the device. The last hop holding feature on the device ensures that the reply packet follows the same route as the request packet back to ISP 1. If last hop holding is disabled, the reply packet might be sent out of Interface B or Interface C to the external network.

Figure 1 Last hop holding application

Restrictions and guidelines

This feature is based on fast forwarding entries. If the MAC address of a last hop changes on an Ethernet link, this feature can function correctly only after the fast forwarding entry is updated for the MAC address.

This feature is not applicable to an MPLS network.

Procedure

1.     Enter system view.

system-view

2.     Enter interface view.

interface interface-type { interface-number | interface-number.subnumber }

3.     Enable last hop holding.

ip last-hop hold

By default, last hop holding is disabled.

Enabling the FIB-based EXP setting for MPLS packets

About this task

This feature modifies the EXP field value of MPLS packets based on the EXP value in the FIB entry that matches the packets. It must be used together with the apply mpls-exp command. For more information about the apply mpls-exp command, see routing policy commands in Layer 3—IP Routing Command Reference.

Procedure

1.     Enter system view.

system-view

2.     Enable the FIB-based EXP setting for MPLS packets.

ip forwarding apply mpls-exp enable

By default, the FIB-based EXP setting for MPLS packets is disabled.

Display and maintenance commands for FIB table

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Execute display commands in any view.

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Configuring load sharing

About load sharing

If a routing protocol finds multiple equal-cost best routes to the same destination, the device forwards packets over the equal-cost routes to implement load sharing.

Configuring load sharing mode

About this task

In the per-flow load sharing mode, the device forwards flows over equal-cost routes. Packets of one flow travel along the same routes. You can configure the device to identify a flow based on the following criteria: source IP address, destination IP address, source port number, destination port number, IP protocol number, and ingress port.

In the per-packet load sharing mode, the device forwards packets over equal-cost routes.

Procedure

1.     Enter system view.

system-view

2.     Configure load sharing.

In standalone mode:

ip load-sharing mode { per-flow [ dest-ip | dest-port | ip-pro | src-ip | src-port ] * | per-packet } global

In IRF mode:

ip load-sharing mode { per-flow [ dest-ip | dest-port | ip-pro | src-ip | src-port ] * | per-packet } { global | slot slot-number }

By default, the device performs per-flow load sharing.

Enabling IPv4 bandwidth-based load sharing

About this task

This feature load shares flow traffic among multiple output interfaces based on their load percentages. The device calculates the load percentage for each output interface in terms of the interface expected bandwidth.

Devices that run load sharing protocols, such as Locator/ID Separation Protocol (LISP), implement load sharing based on the ratios defined by these protocols.

Procedure

1.     Enter system view.

system-view

2.     Enable IPv4 bandwidth-based load sharing.

bandwidth-based-sharing

By default, the IPv4 bandwidth-based load sharing is disabled.

3.     (Optional.) Configure the expected bandwidth of the interface.

a.     Enter interface view.

interface interface-type interface-number

b.     Configure the expected bandwidth of the interface.

bandwidth bandwidth

By default, the expected bandwidth is the physical bandwidth of the interface.