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I am trying to implement BGP session. I was given this table.

When I try to configure loopbacks the first loopback works in the proper way

R1(config)#interface loopback 0
R1(config-if)#ip
*Mar  1 00:45:15.839: %LINEPROTO-5-UPDOWN: Line protocol on Interface Loopback0, changed state to up
R1(config-if)#ip address 1.1.1.1 255.255.255.255

But when i try to configure loopback 1 that's the error I get

> R1(config)#interface loopback 1
> R1(config-if)#ip address 192.168.11.0 255.255.255.0
> Bad mask /24 for address 192.168.11.0

I don't know if i understand it in the proper way. Or maybe the table is wrong.

1 Answer 1

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You can't have an IP address where the host part is all zeros (=network address) or all ones (=directed broadcast address). If you use any other address from 192.168.11.1/24 to 192.168.11.254/24 it'll work.

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  • 1
    With a /32 mask Commented Dec 11, 2018 at 11:14
  • @BenjaminDale, or with a /31 address`
    – Ron Maupin
    Commented Dec 11, 2018 at 13:20
  • /31? interesting - what is the application? Commented Dec 12, 2018 at 0:09
  • @BenjaminDale /31 is used for numbered point-to-point links - essentially like /30 but with only half the address consumption.
    – Zac67
    Commented Dec 12, 2018 at 7:19
  • Sorry - I get what a /31 is - just wondering the application of putting a non /32 mask on a loopback interface would be? Commented Dec 13, 2018 at 0:54

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