04-Layer 3—IP Services Configuration Guide

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06-IP forwarding basics configuration
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06-IP forwarding basics configuration 62.25 KB

Contents

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

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

Saving the IP forwarding entries to a file··························································································· 2

Forwarding ARP and MLD packets received from VXLAN tunnels in hardware  2

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

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

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

Specifying a shift value for load sharing algorithm result··································································· 4

Enabling local-first 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: 8 FIB entry count: 8

 

Flag:

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

  R:Relay     F:FRR

 

Destination/Mask   Nexthop         Flag     OutInterface/Token       Label

0.0.0.0/32         127.0.0.1       UH       InLoop0                  Null

127.0.0.0/8        127.0.0.1       U        InLoop0                  Null

127.0.0.0/32       127.0.0.1       UH       InLoop0                  Null

127.0.0.1/32       127.0.0.1       UH       InLoop0                  Null

127.255.255.255/32 127.0.0.1       UH       InLoop0                  Null

224.0.0.0/4        0.0.0.0         UB       NULL0                    Null

224.0.0.0/24       0.0.0.0         UB       NULL0                    Null

255.255.255.255/32 127.0.0.1       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.

Saving the IP forwarding entries to a file

Restrictions and guidelines

The feature automatically creates the file if you specify a nonexistent file. If the file already exists, this feature overwrites the file content.

This feature triggers one-time saving of the IP forwarding entries.

To automatically save the IP forwarding entries periodically, configure a schedule for the device to automatically run the ip forwarding-table save command. For information about scheduling a task, see Fundamentals Configuration Guide.

Procedure

To save the IP forwarding entries to a file, execute the following command in any view:

ip forwarding-table save filename filename

Forwarding ARP and MLD packets received from VXLAN tunnels in hardware

About this task

The device might receive a large number of ARP and MLD packets from VXLAN tunnels when it acts as a VTEP in a distributed EVPN gateway network. By default, these packets are delivered to the CPU for processing. ARP rate limiting does not take effect on ARP packets received from VXLAN tunnels because they are encapsulated in VXLAN. When the number of VXLAN-encapsulated ARP or MLD packets exceeds the processing threshold of the CPU, the CPU starts to drop arriving protocol packets. Then, service failure might occur on the network. For example, service anomaly might occur on some VTEP-attached downstream devices or endpoints, because of their failure to receive ARP or MLD packets.

To resolve this issue, enable the device to forward ARP and MLD packets received from VXLAN tunnels in hardware without delivering them to the CPU.

Restrictions and guidelines

Traffic forwarding issues might occur if you use this command together with either of the following commands:

·     flooding disable all all-direction

·     flooding disable broadcast all-direction

To make sure the device can forward traffic correctly, perform the following steps before you enable this feature:

1.     Check the configuration for the flooding disable all all-direction and flooding disable broadcast all-direction commands.

2.     If either command exists, do the following:

a.     Execute the undo flooding disable command to enable flooding on the device.

b.     Execute the flooding disable all command to disable the device from flooding any types of traffic received from ACs to VXLAN tunnel interfaces of the VSI.

c.     Configure port isolation for the ACs to confine their flooding traffic.

To ensure access to slient devices, such as dumb terminals, you must also execute the undo mac-address static source-check enable command to disable the static source check feature. If you cannot identify whether silient devices exist, disable static source check as a best practice.

Procedure

1.     Enter system view.

system-view

2.     Enable hardware forwarding of ARP and MLD packets received from VXLAN tunnels.

forwarding vxlan-packet inner-protocol { ipv4 | ipv6 } *

By default, the device processes ARP and MLD packets received from VXLAN tunnels in its CPU.

Display and maintenance commands for FIB table

Execute display commands in any view.

 

Task

Command

Display FIB entries.

display fib [ vpn-instance vpn-instance-name ] [ ip-address [ mask | mask-length ] ]

 


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.

By default, the device uses the following criteria to identify a flow for per-flow load sharing: source and destination IP addresses, source and destination port numbers, source and destination MAC addresses, and ingress port.

Specifying a shift value for load sharing algorithm result

About this task

when traffic is not load shared equally, you can use the shift keyword to adjust the load sharing algorithm result.

Procedure

1.     Enter system view.

system-view

2.     Specify a shift value for the load sharing algorithm result.

ip load-sharing mode per-flow algorithm algorithm-number [ shift shift-number ] { global | slot slot-number }

By default, the device uses the shift value 0 for the load sharing algorithm result.

Enabling local-first load sharing

About this task

Local-first load sharing distributes traffic preferentially across the output interfaces on the receiving IRF member device if output interfaces for multiple equal-cost routes are on different members. This feature enhances packets forwarding efficiency.

Procedure

1.     Enter system view.

system-view

2.     Enable local-first load sharing.

ip load-sharing local-first enable

By default, local-first load sharing is enabled.