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Unable to add Loopback interface

Answered Question
Nov 13th, 2011
User Badges:

Hi all,


i am trying to add loopback interface 0  and asisgn it IP address here is issue


2620Router(config-if)#  ip address 172.16.0.0 255.55.0.0

Bad mask 0xFF370000 for address 172.16.0.0


How can i fix this?


Thanks

Mahesh

Correct Answer by cadet alain about 5 years 9 months ago

Hi,


your IP didn't work because:

1) it was not a host IP address but a network or subnet IP

AND

2) your mask was incorrect: 255.55.0.0 it should have been 255.255.0.0 because in a mask you must have contiguous bits

which is not the case in 55( 00110111) and the message was giving you your wrong mask in hex representation

0xFF370000 is 255.55.0.0 in dotted decimal.

Provided point 1 was corrected you could have put any valid mask  for a subnet in which the IP was included like a /24 for example. But it's best practice and in some cases mandatory like in MPLS VPNs to give loopbacks a /32 mask.


Regards.


Alain

Correct Answer by Reza Sharifi about 5 years 9 months ago

Hi Mahesh,

172.16.0.0/16 is a network/subnet You need to assign a host address to the interface

try this:

interface Loopback0

ip address 172.16.1.1 255.255.255.255


HTH

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Correct Answer
Reza Sharifi Sun, 11/13/2011 - 12:24
User Badges:
  • Super Bronze, 10000 points or more
  • Cisco Designated VIP,

    2017 LAN

Hi Mahesh,

172.16.0.0/16 is a network/subnet You need to assign a host address to the interface

try this:

interface Loopback0

ip address 172.16.1.1 255.255.255.255


HTH

mahesh18 Sun, 11/13/2011 - 12:48
User Badges:

Hi Reza,


that worked can you please  explain me why my IP  does not work and urs worked?


thanks


mahesh

Correct Answer
cadet alain Sun, 11/13/2011 - 13:04
User Badges:
  • Purple, 4500 points or more

Hi,


your IP didn't work because:

1) it was not a host IP address but a network or subnet IP

AND

2) your mask was incorrect: 255.55.0.0 it should have been 255.255.0.0 because in a mask you must have contiguous bits

which is not the case in 55( 00110111) and the message was giving you your wrong mask in hex representation

0xFF370000 is 255.55.0.0 in dotted decimal.

Provided point 1 was corrected you could have put any valid mask  for a subnet in which the IP was included like a /24 for example. But it's best practice and in some cases mandatory like in MPLS VPNs to give loopbacks a /32 mask.


Regards.


Alain

mahesh18 Sun, 11/13/2011 - 14:27
User Badges:

Hi,


Many thanks again Reza and alain.


regards

mahesh

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