Home Lab setup

dewey hafta

So I am beginning to setup my home lab for the CCNA so I can start following along with some of the 'hands on' labs in Todd Lammle's book. I have several switches and routers, but am starting on an 1841. I tried using VLSM and am running into a wall.

Right now I setup
Fa 0/0 192.168.1.1/29
and am trying to set
Fa 0/1 192.168.1.8/30

I get an error "Bad mask /29 for address 192.168.1.8"

I already ran no ip subnet-zero

Fa 0/1 will interface only with my 3550 switch, which is why I have it as /30.

Fa 0/0 will have my 1841 as DHCP and interface with my 2651XM.... after I figure out how to fix it from running through a loop at the boot frustrating.

Anyway, am I right to subnet Fa 0/1 to /30 since the only interface behind it will be the switch, so I will need one ip address for that? Or am I missing something else...

EDIT: When I show run I can see that what I was putting in for the interface ip and mask is correct see below

interface FastEthernet0/0
description test link 12/14/14
ip address 192.168.1.1 255.255.255.248
speed auto
full-duplex
!
interface FastEthernet0/1
ip address 192.168.1.6 255.255.255.252
shutdown
duplex auto
speed auto

Ltat42a

The reason you're getting the bad mask error, is because 192.168.1.8 is your network address. For that range, your valid IP's are 192.168.1.9 - 1.14. For the Fa0/1 address, it's generally not a good idea to assign a /30 address to an interface connected to a switch because with that mask, you only have 1 more available address to a device connected to the switch. The one scenario you could do that would be for an HSRP topology.

hth

clarson

as pointed out above, 192.168.1.8/30 is a network address. /30 subnet has 4 ip address per network. so, 0,4,8,12,16 are all network address. So, the first host ip address in that network is 192.168.1.9. The next host address is 192.168.1.10. and the broadcast address is 192.168.1.11.
As pointed out above also, having a network with just a router and a switch is unusal, but it is a lab where you get to do unusal things to see if they work. But, what you end up is with one useable port on the switch for that network. I guess it could be a trunk port that is the only port on a vlan. But, you won't be able to assign a svi to that vlan on the 3550 to do any intervlan routing. Using a /30 subnet with a switch is just to limiting (go ahead and use it and find out, that is what labbing is for). a /30 subnet only has 2 useable host ip addresses, so it is usually only used for point to point connections, such as between two routers.
And, in the edit portion, the 192.168.1.6 /30 address is a vlsm overlap with 192.168.1.1 /29 basically the router thinks they are connected to the same network, which will cause routing errors,
And, being your just starting out, it might be easier to start with something simple, like make all your networks /24 networks, until you learn more and gain more experience. you will learn vlsm, they just don't teach that on day one.

dewey hafta

Awesome, thanks, now I can see where I was making the mistake. I was able to fix it after reading through this.