Vlsm

I'm trying to configure a router in packet tracer using the following commmand:

HQ(config)# interface FastEthernet 0/0
HQ(config-if)# ip address 192.168.158.0 255.255.255.128

However, I get the error:

Bad mask /25 for address 192.168.158.0

But I can't see what is wrong, as I'm certain that my calculations are correct. I have an exam tomorrow, and I need to have understood this, and I thought I did, but this has just made me a little worried, lol

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Comments

Megadeth4168

Your IP is wrong..

Instead of 192.168.158.0 you need 192.168.158.1 ( which is the first valid host for the 192.168.158.0 subnetwork).

Good luck on your exam!

wellscov

Thank you so much - that's a massive help

Megadeth4168

wellscov wrote: »

Thank you so much - that's a massive help

I ended up doing the same exact thing... It took me a good few minutes of looking at it to realize that I was trying to use the reserved subnet address.

I think you probably already know this, but just in case I'll break this down even further.

You have 192.168.158.0 /25

The valid hosts are 192.168.158.1 through 192.168.158.126
192.168.158.127 is reserved for broad cast

192.168.158.128 is the next subnet so that address is reserved.
Valid hosts on 192.168.158.128 /25 network are 192.168.158.129 - 192.168.158.254

I hope this helps!

wellscov

Yeah, I understand it now - it's annoyingly simple once you look at it like that, lol