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 1-1.
Figure 1-1 Cisco NX-OS Forwarding Architecture
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 topics:
Layer 3 Consistency Checker
In rare instances, an inconsistency can occur between the unicast RIB and the FIB on each module. Cisco NX-OS supports the Layer 3 consistency checker. This feature detects inconsistencies between the unicast IPv4 RIB and the FIB on each interface module. Inconsistencies include the following:
- Missing prefix
- Extra prefix
- Wrong next-hop address
- Incorrect Layer 2 rewrite string in the ARP or neighbor discovery (ND) cache
The Layer 3 consistency checker compares the FIB entries to the latest adjacency information from the Adjacency Manager (AM) and logs any inconsistencies. The consistency checker then compares the unicast RIB prefixes to the module FIB and logs any inconsistencies. See the “Triggering the Layer 3 Consistency Checker” section.
You can then manually clear any inconsistencies. See the “Clearing Forwarding Information in the FIB” section.
FIB Tables
The hardware provides two tables, a TCAM table and a Hash table. The TCAM table is shared between the longest prefix match (LPM) route and the /32 unicast route. The Hash table is shared between the /32 unicast entries and the multicast entries. Each table has approximately 8000 routes.
Virtualization Support
The Unicast RIB and FIB support Virtual Routing and Forwarding instances (VRFs). By default, Cisco NX-OS places you in the default VRF unless you specifically configure another VRF. For more information, see Chapter1, “Configuring Layer 3 Virtualization”
Licensing Requirements for the Unicast RIB and FIB
The following table shows the licensing requirements for this feature:
|
|
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 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 switch.
DETAILED STEPS
To display the FIB information on a switch, use the following commands in any mode:
|
|
switch# show ip fib adjacency
|
Displays the adjacency information for IPv4. |
show forwarding ipv4
adjacency
switch# show forwarding ipv4 adjacency
|
Displays the adjacency information for IPv4. |
switch# show ip fib interfaces
|
Displays the FIB interface information for IPv4. |
switch# show ip fib route
|
Displays the route table for IPv4. |
show forwarding ipv4
route
switch# show forwarding ipv4 route
|
Displays the route table for IPv4. |
This example shows the FIB contents on a switch:
switch# show ip fib route
IPv4 routes for table default/base
------------------+------------------+---------------------
Prefix | Next-hop | Interface
------------------+------------------+---------------------
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 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:
|
|
ip load-sharing address {
destination port destination |
source-destination [
port
source-destination ]} [
universal-id
seed ]
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:
|
|
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:
|
|
show ip route [
route-type |
interface
int-type number |
next-hop ]
|
Displays the unicast route table. The route-type argument can be a single route prefix, direct, static, or a dynamic route protocol. Use the ? command to see the supported interfaces. |
show ip adjacency [
prefix |
interface-type number [
summary ]|
non-best ] [
detail ] [
vrf
vrf-id ]
switch# show ip adjacency
|
Displays the adjacency table. The argument ranges are as follows:
- prefix —Any IPv4 prefix address.
- interface-type number —Use the ? command 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 ]
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 ? command to see the supported interfaces. |
This example displays the unicast route table:
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
Triggering the Layer 3 Consistency Checker
You can manually trigger the Layer 3 consistency checker.
To manually trigger the Layer 3 consistency checker, use the following commands in global configuration mode:
|
|
test [
ipv4 ] [
unicast] forwarding inconsistency [
vrf
vrf-name ] [
module {
slot |
all }]
switch(config)# test forwarding inconsistency
|
Starts a Layer 3 consistency check. The vrf-name can be any case-sensitive, alphanumeric string up to 32 characters. The slot range is from 1 to 10. |
To stop the Layer 3 consistency checker, use the following commands in global configuration mode:
|
|
test forwarding [
ipv4 ] [
unicast ]
inconsistency [
vrf
vrf-name ] [
module {
slot |
all }]
stop
switch(config)# test forwarding inconsistency stop
|
Stops a Layer 3 consistency check. The vrf-name can be any case-sensitive, alphanumeric string up to 64 characters. The slot range is from 1 to 10. |
To display the Layer 3 inconsistencies, use the following commands in any mode:
|
|
show forwarding [
ipv4 ]
inconsistency [
vrf
vrf-name ] [
module {
slot |
all }]
switch(config)# show forwarding inconsistency
|
Displays the results of a Layer 3 consistency check. The vrf-name can be any case-sensitive, alphanumeric string up to 32 characters. The slot range is from 1 to 10. |
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.
Caution
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:
|
|
clear forwarding {
ipv4 }
route {* |
prefix } [
vrf
vrf-name ] [
module {
slot |
all }]
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:
|
|
show routing memory estimate routes
num-routes
next-hops
num-nexthops
switch# show routing memory estimate routes 1000 next-hops 1
|
Displays the memory requirements for routs. 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.
Caution
The
* keyword is severely disruptive to routing.
To clear one or more entries in the unicast RIB, use the following commands in any mode:
|
|
clear ip
route {* | {
route |
prefix/length }[
next-hop
interface ]} [
vrf
vrf-name ]
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 ]
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:
|
|
show forwarding adjacency |
Displays the adjacency table on a module. |
show forwarding distribution { clients | fib-state } |
Displays the FIB distribution information. |
show forwarding interfaces module slot |
Displays the FIB information for a module. |
show forwarding ipv4 route |
Displays routes in the FIB. |
show hardware forwarding dynamic-allocation status |
Displays information about the TCAM allocation. |
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
|
|
Unicast RIB and FIB CLI commands |
Cisco Nexus 5000 Series Command Reference, Cisco NX-OS Releases 4.x, 5.x |
Feature History for Unicast RIB and FIB
Table 1-1 lists the release history for this feature.
Table 1-1 Feature History for Unicast RIB and FIB
|
|
|
Unicast RIB and FIB |
5.0(3)N1(1) |
This feature was introduced. |