Router on a stick

[skk391]

Hi all,

Just doing some revision for my ICDN2 exam, I have got to the 'router on a stick' section & I have a question relating to config and theory.

ROAS is for routing between two VLans?
So say I have a host in vlan 20 ip address 192.168.0.20
& host in Vlan 30 with ip address 10.0.0.10

I can set up ROAS so that the two hosts can communication with each other.

But say the two hosts have ip address in the same address classes/subnet

i.e host A ip address 10.0.0.10 in Vlan 10 (subinterface fa 0/1.10 on router )
Host B ip address 10.0.0.20 in Vlan 20(subinterface fa 0/1.20 )

When I try to configure sub-interface .20 on the router I cannot assigned the ip address to the sub- interface it gives me a error that the ip address overlaps with one already configured for int fa 0/1.10.

So does this means that it two hosts have ip address in the same subnet but different vlans that you cannot use ROAS?

Thanks

 

[lerdalt]

Post your config for us to look at quick.

 

[lerdalt]

The short quick answer that I'd come up with though is that you can not have 2 interfaces on the same router in the same subnet regardless of vlans or sub-interfaces.

Of course I want to caveat that by stating as far as the CCNA is concerned you can't do that.....there are ways, but don't want to get you confused for the exam.

 

[Belushi]

As the router stated you are overlapping your IP addresses. The rule of thumb is that you do not assign the same subnet to two different vlans which is what you appear to have done here. I'm not 100% certain because you are only posting IP addresses and not subnet masks as well.

Think about it logically, a router which the same network on two different interfaces would definitely cause a problem. The router would not know which interface to route traffic too because the networks are the same. There are ways around this by usign things like NAT and VRF light within the router but I would not reccomend this and that is certainly not the point of your router on a stick exercise.

 

[cisconooblet]

For the CCNA each vlan requires a different subnet. For each subnet on each vlan to communicate with each other they must be routed through a layer 3 device. A router must have an interface in each vlan with the respective ip/subnet or an interface must be trunked and subinterfaces created with the respective ip/subnets.

 

[burtsbees]

A vlan is a separate subnet, so two vlans cannot overlap with eachother. The overlapping takes place in the mask. VLSM and/or subnetting will take care of that, putting each into their own subnet.

/

tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!

 

[burtsbees]

The only way to do that is

router(config)#no ip routing

turning the router into a layer 2 device.

/

tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!

 

[burtsbees]

Shave and a haircut...two bits!

/

tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!

 

[skk391]

Thanks Guys, good answers

 

[burtsbees]

eetha-itha-itha-itha-That's All, Folks!

/



tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!