Bad mask/24

[spivy66]

to all, for some reason i cant change the ip address for eth0/1 from 207.209.115.48 to 172.17.0.3.I get this error

router(config-if)#ip address 172.17.0.3 255.255.255.0
Bad mask /24 for address 172.17.0.3

This is my config

no ip subnet-zero
ip dhcp excluded-address 172.28.2.99
!
ip dhcp pool Replication-->DR
network 172.28.2.96 255.255.255.224
domain-name ***
dns-server 167.206.67.112
default-router 172.28.2.97
lease 100
!
ip dhcp pool Replication
lease infinite
!
!
!
!
interface Ethernet0/0
description Internet 207 MASK
ip address 207.209.115.48 255.255.255.0
ip broadcast-address 207.209.115.255
full-duplex
no cdp enable
!
interface Ethernet0/1
description Replication
ip address 172.28.2.97 255.255.255.224
full-duplex

 

[ak8899]

Hi

Have you tried "ip classless" ?

regards
Alain


regards,
Alain

 

[spivy66]

I'm kind of a newbie at cisco, so no i have not.Can you explain?

thank you

 

[chipk]

no ip subnet zero" is your problem.

172.17.0.0 is the zero network for a 255.255.255.0 mask. You need to ensure that your equipment supports subnet zero - it probably does.

 

[lgarner]

router(config)# ip classless

Classful addressing implies a subnet mask based on the class of address: A, B, or C. An address beginning with 172 is a class B and has a default mask of 255.255.0.0.

Classless addressing ditches the default masks and allows you to specify whatever you want. That's the standard way of handling addresses these days, I think.

I should point out that I've always used "ip classless" and have never seen your problem even when subnetting a 10. address with /30, so I don't know if that is your problem.

 

[castlesmadeofsand]

I thought ip subnet zero only came into effect when you subnet the subnet (vlsm).

Jimi

 

[chipk]

172 is a class B, so 255.255.255.0 is a VLSM, even though it is the default for class C.

 

[spivy66]

Thank you all for your input , in anycase i change the ip address to 172.17.1.1/24 so i dont have the issue ,now my problem is setting the gateway.. here my config

Gateway of last resort is 172.17.1.1 to network 0.0.0.0

172.17.0.0/24 is subnetted, 1 subnets
C 172.17.1.0 is directly connected, Ethernet0/0
172.28.0.0/27 is subnetted, 1 subnets
C 172.28.2.96 is directly connected, Ethernet0/1
S* 0.0.0.0/0 [1/0] via 172.17.1.1

now both theses networks can see each other but i can't get on on the net. I also created a route on my fire wall 172.28.2.96/27 to 172.17.1.3

any ideas what i'm doing wrong.. I had this working on before when this router was setup on a different mask, I just cant rember what I did.

thanks again

 

[spivy66]

nevermind i'm an (_|_) I forgot my dns..

 

[castlesmadeofsand]

Well, a class b with a c mask is simply subnetted, not vlsm. Vlsm is a subnet that is further subnetted, where the subnet zero and subnet 255 come in. Later.
Jimi

 

[chipk]

Yeah, bad terminology on my part, but subnet zero does not only come into play with vlsm, it comes into play with any subnetting. It's why you had to always do:

2^n - 2 = # of networks

The -2 is because so you wouldn't count the 0 and 255 subnet, "subnet zero" and "the all ones subnet".

http://www.cisco.com/en/US/tech/tk648/tk361/technologies_tech_note09186a0080093f18.shtml

 

[UnaBomber]

Vlsm is a subnet that is further subnetted, where the subnet zero and subnet 255 come in.

Is it?

I know its semantics, but isnt VLSM a term used when talking within the scope of routing?

IE you can variably subnet your class address across your domain using certain routing protocols which support it. The idea being that classes no longer have any relevance, and instead we use CIDR techniques with VLSM and summaries addresses

UnaBomber
ccnp mcse2k

 

[chipk]

UnaBomber - I'd say you're probably right. I've only ever seen Microsoft use that terminology when describing VLSM - "a subnet that is further subnetted". I'd have to read the RFC to really be sure what the verdict is on this. It may just be that different vendors use the term differently.

 

[castlesmadeofsand]

Cisco says it!!!

 

[chipk]

Really, castelmadeofsand, I'm not just trying to be disagreeable, but can you point to a web site with a quote? I was just being honest when I said I never saw Cisco define VLSM that way. Many people tend to use "VLSM" and "subnetting" interchangeably.

 

[castlesmadeofsand]

You are correct about the vlsm, and I apologize for sounding arguementative. Did I spell that correctly? Anyway, Cisco academy does not exactly define it that way, but they say "sometimes referred to as 'subnetting a subnet' ", which actually I think is true. The command
router(config)#ip subnet-zero
will fix that problem. Sorry for the mix up. Here, in CCNP 1 Advanced Routing, version 3.0, Cisco Academy...

"Variable-Length Subnet Mask (VLSM) allows an organization to use more than one subnet mask within the same network address space. Implementing VLSM is often referred to as subnetting a subnet and it can be used to maximize addressing efficiency."

Thanks.

Jimi

 

[UnaBomber]

"Variable-Length Subnet Mask (VLSM) allows an organization to use more than one subnet mask within the same network address space. Implementing VLSM is often referred to as subnetting a subnet and it can be used to maximize addressing efficiency."

Within a Classless domain, there is no such thing as subneting a subnet. It doesnt make any sense, unless you are changing the sense of the word subnet.

10.1.1.0/24 is a subnet
10.1.1..0/25 is a subnet

They are both subnets, however they have different masks, implying the amount of ip address available within the subnet are less.

Now if you are using the term subnet to mean segment, then you could 'subnet a subnet' but the two terms are not interchangeable

UnaBomber
ccnp mcse2k

 

[chipk]

Glad we got that cleared up because I was racking my brain trying to figure out the difference. No worries, caslemadeofsand, I didn't think you were arguing.

 

[castlesmadeofsand]

I guess it's all a matter of context. When you tahe 10.0.0.1/24 and another address within the same network address space could be 10.0.0.129/28 is taking 10.0.0.0/24 and further subnetting it. I understand what you are saying, that each is actually a subnet. Period. How can you take one thing that's called a subnet and further segment it, and call the result a subnet? But you take a subnet and further segment, or create yet a smaller subnet within the first one. This is why I thought the all 1's and subnet zero came in. The word subnet has always actually confused me. For my CCNA, though, I went thru the Cisco Academy classes. They can be confusing. Thanks.

Jimi (actually, just a fan---real name is Tim)