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Issue on router-on-a-stick topology + DHCP assignement + inter-vlan routing

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Hi folks,


I am running a router-on-a stick topology with 2 different vlans, each one for a subnet for separate data and voice traffic.

The router has 2 Fa0/0 subinterfaces, one for each vlan I want to make inter-communicate.

Also, this router has 2 dhcp pools configured, again one for data and the other one for the ip phones.

The uplink interface on the switch connecting hosts and ip phones is configured as a trunk.

From the router, I can see the two subnets:


MADrouter#sh ip route

Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP

D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area

N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2

E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP

i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area

* - candidate default, U - per-user static route, o - ODR

P - periodic downloaded static route


Gateway of last resort is not set is subnetted, 2 subnets

C is directly connected, FastEthernet0/0.1

C is directly connected, FastEthernet0/0.10



But the I cannot ping any host beyond the switch, and vice-versa.

Hosts are able to communicate between themselves and L2. Problem seems to be on the router.

Also, DHCP seems not to be working properly: I set up two excluded ip ranges and the hosts are taking ip´s from those ranges.


Router config:


ip dhcp excluded-address

ip dhcp excluded-address


ip dhcp pool VLAN_Datos



ip dhcp pool VLAN_VoIP



option 150 ip



interface FastEthernet0/0

description **Link a MADswitch**

no ip address

duplex auto

speed auto


interface FastEthernet0/0.1

encapsulation dot1Q 1 native

ip address


interface FastEthernet0/0.10

encapsulation dot1Q 10

ip address




What am I doing wrong?


PD: Find attached the .pkt lab I´m building with this topology.

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he's obviously got ip routing on because of his routing table.


has the dhcp service started? sometimes you need to do it




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I dont believe you need the helper address because your router is in the same subnet as the DHCP clients

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hello Popperlau,


did you create a truck port on the switch to route information between the switch and the router, also did you assigned the vlan's to the interfaces;



interface FastEthernet0/1

switchport access vlan 1

switchport mode access

switchport voice vlan 10

spanning-tree portfast


interface FastEthernet0/24


switchport trunk encapsulation dot1q

switchport mode trunk

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