Example for Configuring IS-IS Auto FRR

Networking Requirements

If a fault occurs on a network, IS-IS Auto FRR fast switches traffic to a backup link before the route convergence, which prevents traffic interruption.

In Figure 1:

IS-IS runs between four routers.
The four routers are all Level-1-2 routers.
If DeviceC or Link T fails, it is required that the traffic forwarded by DeviceA be rapidly switched to the backup link.

Figure 1 Configuring IS-IS Auto FRR

Device Name	Interface	IP Address
DeviceA	GE0/1/0	10.0.1.1/24
DeviceA	GE0/1/8	10.1.1.1/24
DeviceB	GE0/1/0	10.1.1.2/24
DeviceB	GE0/1/8	10.2.1.1/24
DeviceC	GE0/1/0	10.0.1.2/24
DeviceC	GE0/1/8	10.3.1.1/24
DeviceD	GE0/1/0	10.3.1.2/24
	GE0/1/8	10.2.1.2/24
	GE0/1/16	10.4.1.1/24

Configuration Roadmap

The configuration roadmap is as follows:

Enable basic IS-IS functions on each router.
Set a higher link cost (in compliance with the traffic protection inequality of IS-IS Auto FRR) on GE 0/1/8 of DeviceA, and ensure that Link T is preferentially selected.
Enable IS-IS Auto FRR on DeviceA that forwards the protected traffic.

Data Preparation

To complete the configuration, you need the following data:

IP addresses of interfaces on each router
NET of each router
Level of each router
Costs of interfaces on each router

Procedure

Configure IP addresses for interfaces. For configuration details, see Configuration Files in this section.

Configure basic IS-IS functions.

# Configure DeviceA.

[~DeviceA] isis 1
[*DeviceA-isis-1] is-level level-1-2
[*DeviceA-isis-1] network-entity 10.0000.0000.0001.00
[*DeviceA-isis-1] quit
[*DeviceA] interface gigabitethernet 0/1/0
[*DeviceA-GigabitEthernet0/1/0] isis enable 1
[*DeviceA-GigabitEthernet0/1/0] quit
[*DeviceA] interface gigabitethernet 0/1/8
[*DeviceA-GigabitEthernet0/1/8] isis enable 1
[*DeviceA-GigabitEthernet0/1/8] commit
[~DeviceA-GigabitEthernet0/1/8] quit

# Configure DeviceB.

[~DeviceB] isis 1
[*DeviceB-isis-1] is-level level-1-2
[*DeviceB-isis-1] network-entity 10.0000.0000.0002.00
[*DeviceB-isis-1] quit
[*DeviceB] interface gigabitethernet 0/1/0
[*DeviceB-GigabitEthernet0/1/0] isis enable 1
[*DeviceB-GigabitEthernet0/1/0] quit
[*DeviceB] interface gigabitethernet 0/1/8
[*DeviceB-GigabitEthernet0/1/8] isis enable 1
[*DeviceB-GigabitEthernet0/1/8] commit
[~DeviceB-GigabitEthernet0/1/8] quit

# Configure DeviceC.

[~DeviceC] isis 1
[*DeviceC-isis-1] is-level level-1-2
[*DeviceC-isis-1] network-entity 10.0000.0000.0003.00
[*DeviceC-isis-1] quit
[*DeviceC] interface gigabitethernet 0/1/0
[*DeviceC-GigabitEthernet0/1/0] isis enable 1
[*DeviceC-GigabitEthernet0/1/0] quit
[*DeviceC] interface gigabitethernet 0/1/8
[*DeviceC-GigabitEthernet0/1/8] isis enable 1
[*DeviceC-GigabitEthernet0/1/8] commit
[~DeviceC-GigabitEthernet0/1/8] quit

# Configure DeviceD.

[~DeviceD] isis 1
[*DeviceD-isis-1] is-level level-1-2
[*DeviceD-isis-1] network-entity 10.0000.0000.0004.00
[*DeviceD-isis-1] quit
[*DeviceD] interface gigabitethernet 0/1/0
[*DeviceD-GigabitEthernet0/1/0] isis enable 1
[*DeviceD-GigabitEthernet0/1/0] quit
[*DeviceD] interface gigabitethernet 0/1/8
[*DeviceD-GigabitEthernet0/1/8] isis enable 1
[*DeviceD-GigabitEthernet0/1/8] commit
[~DeviceD-GigabitEthernet0/1/8] quit

Set the cost of Gigabit Ethernet 0/1/8 on Device A to 30, and then check routing information.

# Configure the cost of GE 0/1/8 on DeviceA to 30.

[~DeviceA] interface gigabitethernet 0/1/8
[~DeviceA-GigabitEthernet0/1/8] isis cost 30
[*DeviceA-GigabitEthernet0/1/8] commit
[~DeviceA-GigabitEthernet0/1/8] quit

# Check information about the link from DeviceA to DeviceD. IS-IS preferentially selects link T to transmit traffic forwarded by DeviceA because link T has the smallest cost.

[~DeviceA] display isis route verbose 10.4.1.1
                                                                                
                         Route information for ISIS(1)                          
                         -----------------------------                          
                                                                                
                        ISIS(1) Level-1 Forwarding Table                        
                        --------------------------------    
   
IPV4 Dest  : 10.4.1.0/24        Int. Cost : 30            Ext. Cost : NULL  
Admin Tag  : -                  Src Count : 2             Flags     : A/-/L/-  
Priority   : -                  
NextHop    :                    Interface :               ExitIndex :     
    10.0.1.2                         GE0/1/0                   0x00000010 
     Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, S-IGP Shortcut,
                                 U-Up/Down Bit Set  
     Protect Type: L-Link Protect, N-Node Protect
                                                                                
                                                                                
                        ISIS(1) Level-2 Forwarding Table                        
                        --------------------------------  
 
IPV4 Dest  : 10.4.1.0/24        Int. Cost : 30            Ext. Cost : NULL  
Admin Tag  : -                  Src Count : 2             Flags     : -/-/-/-/-  
Priority   : -                  
NextHop    :                    Interface :               ExitIndex :     
                                      -                    
     Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, S-IGP Shortcut,
                                 U-Up/Down Bit Set 
     Protect Type: L-Link Protect, N-Node Protect

Enable IS-IS Auto FRR.

# Enable IS-IS Auto FRR on DeviceA.

[~DeviceA] isis
[~DeviceA-isis-1] frr
[*DeviceA-isis-1-frr] loop-free-alternate
[*DeviceA-isis-1-frr] commit
[~DeviceA-isis-1-frr] quit
[~DeviceA-isis-1] quit

Verify the configuration.

# Check information about the link from DeviceA to DeviceD. The command output shows that IS-IS generates a backup link because IS-IS Auto FRR is enabled.

[~DeviceA] display isis route verbose 10.4.1.1
                                                                                
                         Route information for ISIS(1)                          
                         ----------------------------- 
                       ISIS(1) Level-1 Forwarding Table                        
                        --------------------------------      
                  
IPV4 Dest  : 10.4.1.0/24        Int. Cost : 30            Ext. Cost : NULL  
Admin Tag  : -                  Src Count : 2             Flags     : A/-/L/-  
Priority   : -                  
NextHop    :                    Interface :               ExitIndex :     
    10.0.1.2                         GE0/1/0                   0x00000010 
    (B)10.1.1.2                      GE0/1/0                   0x0000000f(N)
     Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, S-IGP Shortcut,
                                 U-Up/Down Bit Set  
     Protect Type: L-Link Protect, N-Node Protect  
                                                                                
                                                                                
                        ISIS(1) Level-2 Forwarding Table                        
                        --------------------------------    
                    
IPV4 Dest  : 10.4.1.0/24        Int. Cost : 30            Ext. Cost : NULL  
Admin Tag  : -                  Src Count : 2             Flags     : -/-/-/-/-  
Priority   : -                  
NextHop    :                    Interface :               ExitIndex :     
                                      -                    
     Flags: D-Direct, A-Added to URT, L-Advertised in LSPs, S-IGP Shortcut,
                                 U-Up/Down Bit Set 
     Protect Type: L-Link Protect, N-Node Protect

Configuration Files

DeviceA configuration file

#
sysname DeviceA
#
isis 1
 network-entity 10.0000.0000.0001.00
 frr
  loop-free-alternate level-1
  loop-free-alternate level-2
#
interface gigabitethernet 0/1/0
 undo shutdown
 ip address 10.0.1.1 255.255.255.0
 isis enable 1
#
interface gigabitethernet 0/1/8
 undo shutdown
 ip address 10.1.1.1 255.255.255.0
 isis enable 1
 isis cost 30
#
return

DeviceB configuration file

#
 sysname DeviceB
#
isis 1
 network-entity 10.0000.0000.0002.00
#
interface gigabitethernet 0/1/0
 undo shutdown
 ip address 10.1.1.2 255.255.255.0
 isis enable 1
#
interface gigabitethernet 0/1/8
 undo shutdown
 ip address 10.2.1.1 255.255.255.0
 isis enable 1
#
return

DeviceC configuration file

#
sysname DeviceC
#
isis 1
 network-entity 10.0000.0000.0003.00
#
interface gigabitethernet 0/1/0
 undo shutdown
 ip address 10.0.1.2 255.255.255.0
 isis enable 1
#
interface gigabitethernet 0/1/8
 undo shutdown
 ip address 10.3.1.1 255.255.255.0
 isis enable 1
#
return

DeviceD configuration file

#
sysname DeviceD
#
isis 1
 network-entity 10.0000.0000.0004.00
#
interface gigabitethernet 0/1/0
 undo shutdown
 ip address 10.3.1.2 255.255.255.0
 isis enable 1
#
interface gigabitethernet 0/1/8
 undo shutdown
 ip address 10.2.1.2 255.255.255.0
 isis enable 1
#
interface gigabitethernet 0/1/16
 undo shutdown
 ip address 10.4.1.1 255.255.255.0
 isis enable 1
#
return