Managing the Unicast RIB and FIB

This chapter describes how to manage routes in the unicast Routing Information Base (RIB) and the Forwarding Information Base (FIB) on the Cisco NX-OS switch.

This chapter includes the following sections:

Information About the Unicast RIB and FIB

The unicast RIB (IPv4 RIB) and FIB are part of the Cisco NX-OS forwarding architecture, as shown in Figure 13-1.

Figure 13-1 Cisco NX-OS Forwarding Architecture

 

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The unicast RIB maintains the routing table with directly connected routes, static routes, and routes learned from dynamic unicast routing protocols. The unicast RIB also collects adjacency information from sources such as the Address Resolution Protocol (ARP). The unicast RIB determines the best next hop for a given route and populates the unicast forwarding information base (FIBs) by using the services of the unicast FIB distribution module (FDM).

Each dynamic routing protocol must update the unicast RIB for any route that has timed out. The unicast RIB then deletes that route and recalculates the best next hop for that route (if an alternate path is available).

This section includes the following topic:

FIB Tables

The hardware provides two tables: a TCAM table and a hash table. The TCAM table is shared between longest prefix match (LPM) route /32 unicast route. The hash table is shared between the /32 unicast entries and the multicast entries. Each table has approximately 8000 routes.

If the LPM becomes 90% full, a warning messages appears. A message appears when there is sufficient space in the LPM and total usage is 70% or less. When the table is 100% full, the following message is displayed:

FIB_TCAM_RESOURCE_EXHAUSTION:FIB TCAM exhausted

Licensing Requirements for the Unicast RIB and FIB

The following table shows the licensing requirements for this feature:

 

Product
License Requirement

Cisco NX-OS

The unicast RIB and FIB require no license. Any feature not included in a license package is bundled with the Cisco NX-OS system images and is provided at no extra charge to you. For a complete explanation of the Cisco NX-OS licensing scheme, see the Cisco NX-OS Licensing Guide.

Managing the Unicast RIB and FIB

This section includes the following topics:

note.gif

Noteblank.gif If you are familiar with the Cisco IOS CLI, be aware that the Cisco NX-OS commands for this feature might differ from the Cisco IOS commands that you would use.

Displaying Module FIB Information

You can display the FIB information on a switchmodule.

DETAILED STEPS

To display the FIB information on a switchmodule, use the following commands in any mode:

 

Command
Purpose
show ip fib adjacency { ethernet | port-channel | vlan } slot
 
Example:
switch# show ip fib adjacency ethernet 2

Displays the adjacency information for FIB.

show forwarding { ipv4 adjacency { ethernet | port-channel | vlan } slot
 
Example:
switch# show forwarding ipv4 adjacency ethernet 2

Displays the adjacency information for IPv4.

show ip fib interfaces
 
Example:
switch# show ip fib interfaces

Displays the FIB interface information for IPv4.
show ip fib route adjacency { ethernet | port-channel | vlan } slot
 
Example:
switch# show ip fib route adjacency ethernet 2

Displays the route table for IPv4.
show forwarding ipv4 route adjacency { ethernet | port-channel | vlan } slot
 
Example:
switch# show forwarding ipv4 route adjacency ethernet 2

Displays the route table for IPv4.

 

This example shows how to display the FIB contents on a switch:

switch# show ip fib route
 
IPv4 routes for table default/base
 
------------------+------------------+---------------------
Prefix | Next-hop | Interface
------------------+------------------+---------------------
0.0.0.0/32 Drop Null0
255.255.255.255/32 Receive sup-eth1
 

Configuring Load Sharing in the Unicast FIB

Dynamic routing protocols, such as Open Shortest Path First (OSPF), support load balancing with equal-cost multipath (ECMP). The routing protocol determines its best routes based on the metrics configured for the protocol and installs up to the protocol-configured maximum paths in the unicast RIB. The unicast RIB compares the administrative distances of all routing protocol paths in the RIB and selects a best path set from all of the path sets installed by the routing protocols. The unicast RIB installs this best path set into the FIB for use by the forwarding plane.

The forwarding plane uses a load-sharing algorithm to select one of the installed paths in the FIB to use for a given data packet.

You can globally configure the following load-sharing settings:

  • load-share mode—Selects the best path based on the destination address and port or the source and the destination address and port.
  • Universal ID—Sets the random seed for the hash algorithm. You do not need to configure the Universal ID. Cisco NX-OS chooses the Universal ID if you do not configure it.
note.gif

Noteblank.gif Load sharing uses the same path for all packets in a given flow. A flow is defined by the load-sharing method that you configure. For example, if you configure source-destination load sharing, then all packets with the same source IP address and destination IP address pair follow the same path.

To configure the unicast FIB load-sharing algorithm, use the following command in global configuration mode:

 

Command
Purpose
ip load-sharing address { destination port destination | source-destination [ port source-destination ]} [ universal-id seed ]
 
Example:
switch(config)# ip load-sharing address source-destination

Configures the unicast FIB load-sharing algorithm for data traffic. The universal-id range is from 1 to 4294967295.

To display the unicast FIB load-sharing algorithm, use the following command in any mode:

 

Command
Purpose
show ip load-sharing
 
Example:
switch(config)# show ip load-sharing

Displays the unicast FIB load-sharing algorithm for data traffic.

 

 

Displaying Routing and Adjacency Information

You can display the routing and adjacency information.

To display the routing and adjacency information, use the following commands in any mode:

 

Command
Purpose
show ip route [ route-type | interface int-type number | next-hop ]
 
Example:
switch# show ip route

Displays the unicast route table. The route-type argument can be a single route prefix, direct, static, or a dynamic route protocol. Use the ? keyword to see the supported interfaces.
show ip adjacency [ prefix | interface-type number [ summary ]| non-best ] [ detail ] [ vrf vrf-id ]
 
Example:
switch# show ip adjacency

Displays the adjacency table. The argument ranges are as follows:

  • prefix —Any IPv4 prefix address.
  • interface-type number —Use the ? keyword to see the supported interfaces.
  • vrf-id —Any case-sensitive, alphanumeric string up to 32 characters.
show ip routing [ route-type | interface int-type number | next-hop | recursive-next-hop | summary | updated { since | until } time ]
 
Example:
switch# show routing summary

Displays the unicast route table. The route-type argument can be a single route prefix, direct, static, or a dynamic route protocol. Use the ? keyword to see the supported interfaces.

This example shows how to display the unicast route table:

switch# show ip route
IP Route Table for VRF "default"
'*' denotes best ucast next-hop
'**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
 
192.168.0.2/24, ubest/mbest: 1/0, attached
*via 192.168.0.32, Eth1/5, [0/0], 22:34:09, direct
192.168.0.32/32, ubest/mbest: 1/0, attached
*via 192.168.0.32, Eth1/5, [0/0], 22:34:09, local
 

This example shows the adjacency information:

switch# show ip adjacency
 
IP Adjacency Table for VRF default
Total number of entries: 2
Address Age MAC Address Pref Source Interface Best
10.1.1.1 02:20:54 00e0.b06a.71eb 50 arp mgmt0 Yes
10.1.1.253 00:06:27 0014.5e0b.81d1 50 arp mgmt0 Yes
 

Clearing Forwarding Information in the FIB

You can clear one or more entries in the FIB. Clearing a FIB entry does not affect the unicast RIB.

caut.gif
Caution blank.gif The clear forwarding command disrupts forwarding on the switch.

To clear an entry in the FIB, including a Layer 3 inconsistency, use the following command in any mode:

 

Command
Purpose
clear forwarding { ip | ipv4 } route {* | prefix } [ vrf vrf-name ] [ module { slot | all }]
 
Example:
switch(config)# clear forwarding ipv4 route *

Clears one or more entries from the FIB. The route options are as follows:

  • *—All routes.
  • prefix —Any IP prefix.

The vrf-name can be any case-sensitive, alphanumeric string up to 32 characters. The slot range is from 1 to 10.

Estimating Memory Requirements for Routes

You can estimate the memory that a number of routes and next-hop addresses will use.

To estimate the memory requirements for routes, use the following command in any mode:

 

Command
Purpose
show routing memory estimate routes num-routes next-hops num-nexthops
 
Example:
switch# show routing memory estimate routes 1000 next-hops 1

Displays the memory requirements for routes. The num-routes range is from 1000 to 1000000. The num-nexthops range is from 1 to 16.

Clearing Routes in the Unicast RIB

You can clear one or more routes from the unicast RIB.

caut.gif
Caution blank.gif The * keyword is severely disruptive to routing.

To clear one or more entries in the unicast RIB, use the following commands in any mode:

 

Command
Purpose
clear ip | ipv4 route {* | { route | prefix/length }[ next-hop interface ]} [ vrf vrf-name ]
 
Example:
switch(config)# clear ip route 10.2.2.2

Clears one or more routes from both the unicast RIB and all the module FIBs. The route options are as follows:

  • *—All routes.
  • route —An individual IP route.
  • prefix/length —Any IP prefix.
  • next-hop —The next-hop address
  • interface —The interface to reach the next-hop address.

The vrf-name can be any case-sensitive, alphanumeric string up to 32 characters.

clear routing [ multicast | unicast ] [ ip | ipv4 ] {* | { route | prefix/length }[ next-hop interface ]} [ vrf vrf-name ]
 
Example:
switch(config)# clear routing ip 10.2.2.2

Clears one or more routes from the unicast RIB. The route options are as follows:

  • *—All routes.
  • route —An individual IP route.
  • prefix/length —Any IP prefix.
  • next-hop —The next-hop address
  • interface —The interface to reach the next-hop address.

The vrf-name can be any case-sensitive, alphanumeric string up to 32 characters.

Verifying the Unicast RIB and FIB Configuration

To display the unicast RIB and FIB configuration information, perform one of the following tasks:

 

Command
Purpose

show forwarding adjacency

Displays the adjacency table on a module.

show forwarding distribution { clients | fib-state }

Displays the FIB distribution information.

show forwarding interfaces

Displays the FIB information for a interface.

show forwarding { ip | ipv4 } route

Displays routes in the FIB.

show ip adjacency

Displays the adjacency table.

show ip route

Displays IPv4 routes from the unicast RIB.

show routing

Displays routes from the unicast RIB.

Additional References

For additional information related to managing unicast RIB and FIB, see the following sections:

Related Documents

Related Topic
Document Title

Unicast RIB and FIB CLI commands

Cisco Nexus 6000 Series Command Reference, Cisco NX-OS Releases 7.x