Unicast Reverse Path Forwarding configuration using CLI

This section provides CLI procedures for Unicast Reverse Path Forwarding configuration.

Enable urpf-mode Boot Flag

To configure Unicast Reverse Path Forwarding on a port or VLAN, you are required to enable the urpf-mode boot flag. If you try to configure uRPF on an interface, that is, enable or change the urpf operating mode with the urpf-mode boot flag disabled, a consistency check error message is displayed: Unicast Reverse Path Forwarding configuration is not supported when urpf-mode boot flag is disabled.

About this task

Use the following procedure to enable the urpf-mode boot flag. By default, urpf-mode is disabled.

Procedure

  1. Enter Global Configuration mode:

    enable

    configure terminal

  2. Enable the urpf-mode boot flag:

    boot config flags urpf-mode

  3. When you get the following prompt to reboot the switch, enter y to reboot.

    The new setting requires a reboot to take effect!

    The configuration will be saved and rebooted.

    Are you sure you want to re-boot the switch (y/n)?

    Note

    Note

    If you enter n, the following message is displayed: Warning: Please save the configuration and reboot the switch for this configuration to take effect.

  4. Check the status of the urpf-mode boot flag:

    show boot config flags

Example

Enable the urpf-mode boot flag:

Switch:1> enable
Switch:1# configure terminal
Switch:1(config)# boot config flags urpf-mode
The new setting requires a reboot to take effect!
The configuration will be saved and rebooted.
Are you sure you want to re-boot the switch (y/n)? y

View the status of the urpf-boot flag:

Note

Note

Flag support can vary across hardware models. 

Switch:1#show boot config flags
flags advanced-feature-bandwidth-reservation low
flags block-snmp false
flags debug-config false
flags debugmode false
flags dvr-leaf-mode false
flags enhancedsecure-mode false
flags factorydefaults false
flags flow-control-mode true
flags ftpd true
flags hsecure false
flags ipv6-egress-filter true
flags ipv6-mode false
flags logging true
flags macsec false
flags nni-mstp false
flags reboot true
flags spanning-tree-mode mstp
flags spbm-config-mode true
flags spbm-node-scaling true
flags sshd true
flags syslog-rfc5424-format true
flags telnetd true
flags tftpd true
flags trace-logging false
flags urpf-mode true
flags verify-config true
flags vrf-scaling true

Viewing unicast reverse path forwarding configuration on a port

About this task

Use the following procedure to view the status of the uRPF configuration on a port.

Before you begin

  • You must enable the urpf-mode boot flag.
    Note

    Note

    When you try to configure uRPF on an interface, that is, enable or change the urpf operating mode with the urpf-mode boot flag disabled, a consistency check error message is displayed: Unicast Reverse Path Forwarding configuration is not supported when urpf-mode boot flag is disabled.

  • You must log on to the GigabitEthernet Interface Configuration mode in CLI.

  • You must configure unicast reverse path forwarding on a port.

Procedure

  1. Enter GigabitEthernet Interface Configuration mode:

    enable

    configure terminal

    interface GigabitEthernet {slot/port[/sub-port][-slot/port[/sub-port]][,...]}

    Note

    Note

    If the platform supports channelization and the port is channelized, you must also specify the sub-port in the format slot/port/sub-port.

  2. Verify the configuration on the port:

    For IPv4, enter: show ip interface gigabitethernet

    For IPv6, enter: show ipv6 interface gigabitethernet

Example

Example for IPv4:
Switch:1> enable
Switch:1# configure terminal
Switch:1(config)# interface GigabitEthernet 1/10
Verify the configuration on the port:
Switch:1(config-if)# show ip interface gigabitethernet

=============================================================================================
                                         Brouter Port Ip
=============================================================================================
PORT VRF   IP_ADDRESS    NET_MASK      BROADCAST REASM   ADVERTISE DIRECT  RPC     RPCMODE
NUM  NAME                                        MAXSIZE WHEN_DOWN BCAST
---------------------------------------------------------------------------------------------
1/1  Glob~ 192.0.2.3     255.255.255.0 ones      1500    disable   disable disable exist-only
1/10 spbo~ 198.51.100.4  255.255.255.0 ones      1500    disable   disable disable exist-only


PORT  VRF
NUM   NAME
--------------------------------------------------------------------------------
1/1   GlobalRouter
1/10  spboip
Example for IPv6:
Switch:1> enable
Switch:1# configure terminal
Switch:1(config)# interface GigabitEthernet 4/16
Verify the configuration on the port:
Switch:1(config-if)#show ipv6 interface gigabitethernet

=============================================================================================================================
                                             Port Ipv6 Interface
=============================================================================================================================
IFINDX BROUTER PHYSICAL          ADMIN   OPER  TYPE  MTU  HOP REACHABLE   RETRANSMIT  MCAST    IPSEC    RPC      RPCMODE
INDX           ADDRESS           STATE   STATE            LMT TIME        TIME        STATUS
-----------------------------------------------------------------------------------------------------------------------------
192    4/16    e4:5d:52:3c:65:02 enable  down  ETHER 1500 2   30000       1000        disable  disable  disable  existonly

====================================================================================================
                               Port Ipv6 Address
====================================================================================================
IPV6 ADDRESS                            BROUTER      TYPE    ORIGIN    STATUS
----------------------------------------------------------------------------------------------------
2001:db8:0:0:0:0:0:ffff/64                   4/16          UNICAST MANUAL    INACCESSIBLE INF      INF
2001:db8:0:0:e65d:52ff:fe3c:6502/64          4/16          UNICAST LINKLAYER INACCESSIBLE INF      INF

1 out of 5 Total Num of Interface Entries displayed.
2 out of 10 Total Num of Address Entries displayed.

Viewing unicast reverse path forwarding configuration on a VLAN

About this task

Use the following procedure to view the status of the uRPF configuration on a VLAN.

Before you begin

  • You must enable the urpf-mode boot flag.
    Note

    Note

    When you try to configure uRPF on an interface, that is, enable or change the urpf operating mode with the urpf-mode boot flag disabled, a consistency check error message is displayed: Unicast Reverse Path Forwarding configuration is not supported when urpf-mode boot flag is disabled.

  • You must log on to the VLAN Interface Configuration mode in CLI.
    Important

    Important

    You must assign a valid IP address to the selected port.

  • You must configure unicast reverse path forwarding on a VLAN.

Procedure

  1. Enter VLAN Interface Configuration mode:

    enable

    configure terminal

    interface vlan <1–4059>

  2. Verify the configuration on the VLAN:

    For IPv4, enter: show interfaces vlan ip

    For IPv6, enter: show ipv6 interface vlan

Example

Example for IPv4:
Switch:1> enable
Switch:1# configure terminal
Switch:1(config)# interface vlan 2
Verify the configuration on the VLAN:
Switch:1(config-if)# show interfaces vlan ip


==============================================================================================================
                                                   Vlan Ip
==============================================================================================================
VLAN VRF    IP            NET              BCASTADDR REASM   ADVERTISE DIRECTED  RPC     RPCMODE     RMON
ID   NAME   ADDRESS       MASK             FORMAT    MAXSIZE WHEN_DOWN BROADCAST
--------------------------------------------------------------------------------------------------------------
1050 Globa~ 192.0.2.9     255.255.255.0    ones      1500    disable   disable   disable exist-only  disable
1102 Globa~ 198.51.100.1  255.255.255.0    ones      1500    disable   disable   disable exist-only  disable
1133 iir3   192.0.2.10    255.255.255.0    ones      1500    disable   disable   disable exist-only  disable
1500 spboip 192.0.2.11    255.255.255.0    ones      1500    disable   disable   disable exist-only  disable
1590 spboip 198.51.100.2  255.255.255.0    ones      1500    disable   disable   disable exist-only  disable
4057 Globa~ 192.0.2.12    255.255.255.0    ones      1500    disable   disable   disable exist-only  disable


All 16 out of 16 Total Num of Vlan Ip Entries displayed


VLAN VRF
ID   NAME
--------------------------------------------------------------------------------
1050 GlobalRouter
1102 GlobalRouter
1133 iir3
1500 spboip
1590 spboip
4057 GlobalRouter

All 16 out of 16 Total Num of Vlan Ip Entries displayed
Example for IPv6:
Switch:1> enable
Switch:1# configure terminal
Switch:1(config)# interface vlan 2
Verify the configuration on the VLAN:
Switch:1(config-if)# show ipv6 interface vlan

=============================================================================================================================
                                             Vlan Ipv6 Interface
=============================================================================================================================
IFINDX VLAN PHYSICAL          ADMIN   OPER  TYPE  MTU  HOP REACHABLE   RETRANSMIT  MCAST    IPSEC    RPC      RPCMODE
INDX        ADDRESS           STATE   STATE            LMT TIME        TIME        STATUS
-----------------------------------------------------------------------------------------------------------------------------
3170   1122 2c:f4:c5:dc:b4:89 enable  up    ETHER 1500 64  30000       1000        disable  disable  disable  existonly
3174   1126 2c:f4:c5:dc:b4:8b enable  up    ETHER 1500 64  30000       1000        disable  disable  disable  existonly
3185   1137 2c:f4:c5:dc:b4:90 enable  up    ETHER 1500 64  30000       1000        disable  disable  disable  existonly

================================================================================
                               Vlan Ipv6 Address
================================================================================
IPV6 ADDRESS                            VLAN-ID      TYPE    ORIGIN    STATUS
--------------------------------------------------------------------------------
2001:db8:0:0:0:0:0:1                      V-1122       UNICAST MANUAL    PREFERRED
2001:db8:0:0:2ef4:c5ff:fedc:b489          V-1122       UNICAST LINKLAYER PREFERRED
2001:db8:0:0:0:0:0:1                      V-1126       UNICAST MANUAL    PREFERRED
2001:db8:0:0:2ef4:c5ff:fedc:b48b          V-1126       UNICAST LINKLAYER PREFERRED
2001:db8:0:0:0:0:0:1                      V-1137       UNICAST MANUAL    PREFERRED
2001:db8:0:0:2ef4:c5ff:fedc:b490          V-1137       UNICAST LINKLAYER PREFERRED

3 out of 4 Total Num of Interface Entries displayed.
6 out of 7 Total Num of Address Entries displayed.
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