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TOPIC: router on a stick question

router on a stick question 10 years 8 months ago #13671

  • dph
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hiya's

quick question

Just playing around basically but I've setup a router for use with intervlan routing.

fa0/0 fa0/0.2 fa0/0.3 - all in different subnets

dot1q 2 and dot1q 3 configured on the 2 sub interfaces

on the switch (2950) fa0/12 is the trunk link. - switchport mode trunk

setup vlan 2 and vlan 3 and added fa0/2 to vlan 2 and fa0/3 to vlan 3

Now pc's in vlan 3 can ping pc's in vlan 2 and the other way around. However neither of them can ping the pc in vlan 1 which is hanging off fa0/1

Is this how its supposed to work? should I be able to ping devices in Vlan 1 with this kind of setup or not? If so where have I gone wrong. FYI I havn't setup a ip address for vlan 1 or gateway on the actual switch. But that shouldn't matter I'm guessing.

Thanks for any input.
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Re: router on a stick question 10 years 8 months ago #13673

  • d_jabsd
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Make sure vlan 1 is in the allowed vlan list on the switch:

switchport trunk allowed vlan 1-3

and make sure vlan 1 is the native vlan:

switchport trunk native vlan 1


then it should work as expected.
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Re: router on a stick question 10 years 8 months ago #13679

  • havohej
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fa0/0 fa0/0.2 fa0/0.3 - all in different subnets

dot1q 2 and dot1q 3 configured on the 2 sub interfaces

hey men, in the setup yuo describe you only have 2 subinterfaces in the router, who belongs to vlan 2 an 3, but what happens to the subif, of vlan 1??

if you dont have the subif of vlan 1, with the appropipate ip address you cant route the subnet that belongs to vlan 1, nor have connectivity to the other vlans from vlan 1.
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Re: router on a stick question 10 years 8 months ago #13686

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Make sure vlan 1 is in the allowed vlan list on the switch:

switchport trunk allowed vlan 1-3

and make sure vlan 1 is the native vlan:

switchport trunk native vlan 1


then it should work as expected.

Ta I'll give that go when I get home.

havohej, my understandiing of it is that because I'm using 802.1q then the management vlan, vlan 1 is not required to be on a sub interface. I think thats only required when using ISL.

So basically fa0/0 has ip address 192.168.1.1, and the two sub interfaces have 2.1 and 3.1 respectively. All vlans are using the 3 interfaces as their gateways etc etc.
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Re: router on a stick question 10 years 8 months ago #13698

  • havohej
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nO WAY, managemente vlan MUST have a subif, and athe appropiate ip address, Think the correct Setup looks like this:


interface fastethernet 0/0.1
description administrative
encapsulation dot1q 1 native
ip address 10.10.10.1 255.255.2555.0

interface fastethernet 0/0.2
encapstulation dot1q 2
ip address 20.20.20.1 255.255.255.0

interface fastethernte 0/0.3
encapsulation dot1q 3
ip address 30.30.30.1 255.255.255.0


So, int the switch you have switchport configured as belongs to vlan 1, 2 and 3, and the pcs in each vlan o each port, must point to the ip address of the subinterface of the router as the default gateway.

the same applies for isl.



Make sure vlan 1 is in the allowed vlan list on the switch:

switchport trunk allowed vlan 1-3

and make sure vlan 1 is the native vlan:

switchport trunk native vlan 1


then it should work as expected.

Ta I'll give that go when I get home.

havohej, my understandiing of it is that because I'm using 802.1q then the management vlan, vlan 1 is not required to be on a sub interface. I think thats only required when using ISL.

So basically fa0/0 has ip address 192.168.1.1, and the two sub interfaces have 2.1 and 3.1 respectively. All vlans are using the 3 interfaces as their gateways etc etc.
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Re: router on a stick question 10 years 8 months ago #13701

  • jwj
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On the subject of a router on a stick set-up, what would be the best way to set-up the interface? Assuming you have one ethernet interface for the LAN and one serial for the WAN, and you have a few class c address spaces. Would you use subinterfaces on the ethernet interface or secondary addresses? I'm curious about opinions for this type of design.
-Jeremy-
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