Troubleshooting Layer 3 Or Layer 4 Load Balancing Example; Verifying Parallel Links In The Routing Table - Cisco CRS-1 - Carrier Routing System Router Troubleshooting Manual

Configuration Examples for Troubleshooting Load Balancing

Troubleshooting Layer 3 or Layer 4 Load Balancing Example

Table 13-1
Two routers, Router A and Router B, connect back to back over three serial Gigabit Ethernet interfaces.
Table 13-1
Router A
interface GigabitEthernet0/6/5/5
ipv4 address 10.12.48.1 255.255.255.0
!
interface GigabitEthernet0/6/5/6
ipv4 address 10.12.44.1 255.255.255.0
!
interface GigabitEthernet0/6/5/7
ipv4 address 10.12.40.1 255.255.255.0
router ospf 200
!
area 0
!
interface GigabitEthernet0/6/5/5
interface GigabitEthernet0/6/5/6
interface GigabitEthernet0/6/5/7
cost 10
The bold text identifies those configurations that affect load balancing.

Verifying Parallel Links in the Routing Table

Troubleshooting of load balancing starts with the routing table, as described in the following sections:
•
•
•
Checking the IGP Routing Table
This section shows how Router B selects one or more paths to reach Router A's loopback interface,
10.1.2.1.
By default, Open Shortest Path First (OSPF) supports four equal-cost paths to a destination. In this
scenario, Router B is configured with maximum-paths equal to one, so it chooses only one path from the
possible equal-cost paths. Use the show route command to view the current path to Router A:
RP/0/RP0/CPU0:RouterB# show route 10.1.2.1
Fri Sep 19 11:02:00.732 PST DST
Routing entry for 10.1.2.1/32
Known via "ospf 200", distance 110, metric 2, type intra area
Installed Sep 19 06:49:40.555 for 04:12:20
Routing Descriptor Blocks
No advertising protos.
Cisco IOS XR Troubleshooting Guide for the Cisco CRS-1 Router
13-240
shows the sample configuration that this section uses to describe the troubleshooting process.
Sample Configuration
Checking the IGP Routing Table
Checking the Maximum Paths
Checking the Route Metric
10.12.48.1, from 10.1.2.1, via GigabitEthernet0/6/5/5
Route metric is 2
Chapter 13 Troubleshooting Load Balancing
Router B
interface GigabitEthernet0/6/5/5
ipv4 address 10.12.48.2 255.255.255.0
!
interface GigabitEthernet0/6/5/6
ipv4 address 10.12.44.2 255.255.255.0
!
interface GigabitEthernet0/6/5/7
ipv4 address 10.12.40.2 255.255.255.0
router ospf 200
maximum-paths 1
area 0
!
interface GigabitEthernet0/6/5/5
interface GigabitEthernet0/6/5/6
interface GigabitEthernet0/6/5/7
cost 10
OL-21483-02