The documentation set for this product strives to use bias-free language. For the purposes of this documentation set, bias-free is defined as language that does not imply discrimination based on age, disability, gender, racial identity, ethnic identity, sexual orientation, socioeconomic status, and intersectionality. Exceptions may be present in the documentation due to language that is hardcoded in the user interfaces of the product software, language used based on RFP documentation, or language that is used by a referenced third-party product. Learn more about how Cisco is using Inclusive Language.
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 device.
The unicast RIB (IPv4 RIB and IPv6 RIB) and FIB are part of the Cisco NX-OS forwarding architecture, as shown in Figure 14-1.
Figure 14-1 Cisco NX-OS Forwarding Architecture
The unicast RIB exists on the active supervisor. It 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 bases (FIBs) on the modules 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:
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 on the supervisor module and the FIB on each interface module. Inconsistencies include the following:
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.
The following table shows the licensing requirements for this feature:
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.
To display the FIB information on a module, use the following commands in any mode:
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 Routing Information Base (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 Forwarding Information Base (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.
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:
To display the unicast FIB load-sharing algorithm, use the following command in any mode:
|
|
---|---|
|
Displays the unicast FIB load-sharing algorithm for data traffic. |
To display the route that the unicast RIB and FIB use for a particular source address and destination address, use the following command in any mode:
This example shows how to display the route selected for a source/destination pair:
You can display the routing and adjacency information.
To display the routing and adjacency information, use the following commands in any mode:
This example shows how to display the unicast route table:
switch#
show ip route
IP Route Table for Context "default"
'*' denotes best ucast next-hop '**' denotes best mcast next-hop
'[x/y]' denotes [preference/metric]
0.0.0.0/0, 1 ucast next-hops, 0 mcast next-hops
*via 10.1.1.1, mgmt0, [1/0], 5d21h, static
0.0.0.0/32, 1 ucast next-hops, 0 mcast next-hops
*via Null0, [220/0], 1w6d, local, discard
10.1.0.0/22, 1 ucast next-hops, 0 mcast next-hops, attached
*via 10.1.1.55, mgmt0, [0/0], 5d21h, direct
10.1.0.0/32, 1 ucast next-hops, 0 mcast next-hops, attached
*via 10.1.0.0, Null0, [0/0], 5d21h, local
10.1.1.1/32, 1 ucast next-hops, 0 mcast next-hops, attached
*via 10.1.1.1, mgmt0, [2/0], 5d16h, am
10.1.1.55/32, 1 ucast next-hops, 0 mcast next-hops, attached
*via 10.1.1.55, mgmt0, [0/0], 5d21h, local
10.1.1.253/32, 1 ucast next-hops, 0 mcast next-hops, attached
*via 10.1.1.253, mgmt0, [2/0], 5d20h, am
10.1.3.255/32, 1 ucast next-hops, 0 mcast next-hops, attached
*via 10.1.3.255, mgmt0, [0/0], 5d21h, local
255.255.255.255/32, 1 ucast next-hops, 0 mcast next-hops
*via Eth Inband Port, [0/0], 1w6d, local
This example shows how to display the adjacency information:
switch#
show ip adjacency
IP Adjacency Table for context 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
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:
To stop the Layer 3 consistency checker, use the following commands in global configuration mode:
To display the Layer 3 inconsistencies, use the following commands in any mode:
You can clear one or more entries in the FIB. Clearing a FIB entry does not affect the unicast RIB.
To clear an entry in the FIB, including a Layer 3 inconsistency, use the following command in any mode:
You can configure the maximum number of routes allowed in the routing table.
4. maximum routes max-routes [ threshold [ reinstall threshold ] | warning-only]
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:
You can clear one or more routes from the unicast RIB.
To clear one or more entries in the unicast RIB, use the following commands in any mode:
To display the unicast RIB and FIB information, perform one the following tasks:
|
|
---|---|
For additional information related to managing unicast RIB and FIB, see the following sections:
|
|
---|---|
Cisco Nexus 9000 Series NX-OS System Management Configuration Guide |