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New Member

What is the lowest prefix possible and the lowest IP@

1) The lowest prefix possible is /8 ? Or we can go further down ?

For instance could we summarize:

8.0.0.0/8

9.0.0.0/8

into

8.0.0.0/7

2) The lowest IP address that we could assign to a host is 0.0.0.1 ?

  • LAN Switching and Routing
5 REPLIES
Hall of Fame Super Bronze

Re: What is the lowest prefix possible and the lowest IP@

1) Technically, you can go as low as 8.0.0.0/1 which provides a host range from 0.0.0.1 to 127.255.255.255.254

2) That's a good question. While the summarization allows you to include such host, you are unable to enter such IP in Windows or Cisco IOS

Rack1R1(config)#int f0/1

Rack1R1(config-if)#ip add 0.0.0.1 255.255.255.0

Not a valid host address - 0.0.0.1

Rack1R1(config-if)#ip add 0.0.0.2 255.255.255.0

Not a valid host address - 0.0.0.2

Rack1R1(config-if)#ip add 1.0.0.1 255.255.255.0

HTH,

__

Edison

New Member

Re: What is the lowest prefix possible and the lowest IP@

Thanks Edison.

Do you have any idea then what is the range 0.0.0.1 to 0.255.255.254 used for, as long as we are not allowed to assign any of those IP addresses to any host nor to any router interface ?

Hall of Fame Super Bronze

Re: What is the lowest prefix possible and the lowest IP@

Do you have any idea then what is the range 0.0.0.1 to 0.255.255.254 used for

AFAIK, it isn't used for anything at the moment.

It just happens that range will be included in you were to summarize 8.0.0.0/1

HTH,

__

Edison.

New Member

Re: What is the lowest prefix possible and the lowest IP@

Hate to disagree with a fellow CCIE, but an 8.0.0.0/1 would be invalid. a /1 would seem to indicate that the first bit only (the 128 bit) would be the network address. RFC specifies that a network address cannot be all 0's or 1's, that is why 127.x.x.x/8 is not valid and no 0.x.x.x/8 or less is not valid.

I have not tried this, but I would guess that a /7 to summarize 8.0.0.0 and 9.0.0.0 (0000 1000 and 0000 1001 summarized to 0000 100) would be valid.

Hall of Fame Super Bronze

Re: What is the lowest prefix possible and the lowest IP@

Hate to disagree with a fellow CCIE, but an 8.0.0.0/1 would be invalid. a /1 would seem to indicate that the first bit only (the 128 bit) would be the network address.

It's not invalid. The router will interpret this summary as 0.0.0.0 128.0.0.0

Rack1R1(config)#router bgp 1

Rack1R1(config-router)#aggre

Rack1R1(config-router)#aggregate-address 8.0.0.0 128.0.0.0

Rack1R1(config-router)#do show run | be router bgp 1

router bgp 1

no synchronization

bgp log-neighbor-changes

aggregate-address 0.0.0.0 128.0.0.0

While /7 will just include the two major subnets of 8.0.0.0 and 9.0.0.0 - the OP wanted to know if he could use a lower value on the prefix.

I didn't say all 0s will be a network address, please read the entire thread.

__

Edison.

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