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

[Liv_Liv]

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 route.

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

192.168.0.0/25 is subnetted, 2 subnets

C        192.168.0.0 is directly connected, FastEthernet0/0.1

C        192.168.0.128 is directly connected, FastEthernet0/0.10

MADrouter#

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, any of the hosts/phones are taking ip addresses automatically.

/// Router config ///

!

!

ip dhcp excluded-address 192.168.0.1 192.168.0.10

ip dhcp excluded-address 192.168.0.129 192.168.0.139

!

ip dhcp pool VLAN_Datos

network 192.168.0.0 255.255.255.128

default-router 192.168.0.1

ip dhcp pool VLAN_VoIP

network 192.168.0.128 255.255.255.128

default-router 192.168.0.129

option 150 ip 192.168.0.9

!

interface FastEthernet0/0

description **Link a MADswitch**

no ip address

duplex auto

speed auto

!

interface FastEthernet0/0.1

encapsulation dot1Q 1 native

ip address 192.168.0.1 255.255.255.128

!

interface FastEthernet0/0.10

encapsulation dot1Q 10

ip address 192.168.0.129 255.255.255.128

ip helper-address 192.168.0.1

!

/// Switch config ///

!

interface FastEthernet0/1

description **Link a MADrouter**

switchport mode trunk

!

interface FastEthernet0/10

description **PBX ASTERISK**

switchport mode access

!

!

interface FastEthernet0/22

description **PC 2**

switchport access vlan 2

switchport mode access

!

interface FastEthernet0/23

description **Puesto de RRHH #3**

switchport access vlan 2

switchport voice vlan 3

!

interface FastEthernet0/24

description **PC 1**

switchport access vlan 2

switchport mode access

!

!

interface Vlan2

description DATOS

ip address 192.168.0.1 255.255.255.128

ip helper-address 192.168.0.1

!

interface Vlan3

description VoIP

ip address 192.168.0.129 255.255.255.128

ip helper-address 192.168.0.1

!

What I am doing wrong? Thanks in advance.

[paul driver]

Hello

First of all, on the router you have specifed vlan 1 and 10 but on the switch you have vlan 2 & 3, and both have the same ip addresses!

interface FastEthernet0/0.1

encapsulation dot1Q 1 native

ip address 192.168.0.1 255.255.255.128

!

interface FastEthernet0/0.10

encapsulation dot1Q 10

ip address 192.168.0.129 255.255.255.128

Switch

the switch would only require to have one svi addrress  of either of these vlans and  make sure the L2 vlans are created on the switch.

lastly, try removing the ip helper addresses on the switch svi as  clients should be able to obtain dhcp from the related sub interface on  the router.

conf t

interface Vlan1

description DATOS

ip address 192.168.0.10 255.255.255.128

no interface Vlan2

no interface Vlan3

ip default-gateway 192.168.0.1

vlan2

exit

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[kcnajaf]

Hi Laura,

Modify the configuration as below

On Router

interface FastEthernet0/0.1

encapsulation dot1Q 1 native

ip address 192.168.0.1 255.255.255.128

!

interface FastEthernet0/0.10

encapsulation dot1Q 2

ip address 192.168.0.129 255.255.255.128

On Switch

interface Vlan1

description DATOS

ip address 192.168.0.x 255.255.255.128

!

interface Vlan2

description VoIP

ip address 192.168.0.x 255.255.255.128

!

interface FastEthernet0/22

description **PC 2**

switchport access vlan 1

switchport mode access

!

interface FastEthernet0/23

description **Puesto de RRHH #3**

switchport access vlan 1

switchport voice vlan 2

!

interface FastEthernet0/24

description **PC 1**

switchport access vlan 1

switchport mode access

In short you need to match the "encapsulation dot1Q X " X value on the router with same VLAN number on the switch end.

Hope that helps

Regards

Najaf

Please rate when applicable or helpful !!!

[paul driver]

Najaf

you have duplcate ip address assinment just like the OP has?

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[kcnajaf]

Thanks Paul for point this out. This is now corrected :-)

Regards

Najaf

Please rate when applicable or helpful !!!

[Richard Burts]

Najaf

You have correctly identified that the basic issue is a mismatch between the VLANs specified in the router config and the VLANs configured on the switch. Unfortunately in your suggestion you are giving 192.168.0.1 on both the router interface and switch interface and the same duplicate use of 192.168.0.129.

HTH

Rick

[kcnajaf]

Hi Rich,

Paul just pointed this out and i have corrected this now :-)

Thanks in advance.

Regards

Najaf

[Liv_Liv]

Thank you all for your valuable responses.

Based on your comments I made modifications on both the router and switch. I fixed the VLAN IDs mismatch and configured the default gw on the switch. Also removed the unnecessary ip helper command on the vlans. Now the DHCP assignment is working perfectly on all hosts and also on the phone !!For clarification, this is the resultant config:

//Router//

!

ip dhcp excluded-address 192.168.0.1 192.168.0.10

ip dhcp excluded-address 192.168.0.129 192.168.0.139

!

ip dhcp pool VLAN_Datos

network 192.168.0.0 255.255.255.128

default-router 192.168.0.1

ip dhcp pool VLAN_VoIP

network 192.168.0.128 255.255.255.128

default-router 192.168.0.129

option 150 ip 192.168.0.9

!

!

interface FastEthernet0/0

description **Link a MADswitch**

no ip address

duplex auto

speed auto

!

!

interface FastEthernet0/0.2

description **matches Vlan2 for Data**

encapsulation dot1Q 2

ip address 192.168.0.1 255.255.255.128

!

interface FastEthernet0/0.3

description **matches Vlan3 for Voice**

encapsulation dot1Q 3

ip address 192.168.0.129 255.255.255.128

ip helper-address 192.168.0.1

!

//Switch//

!

hostname MADswitch

!

!

spanning-tree mode pvst

!

interface FastEthernet0/1

description **Link a MADrouter**

switchport mode trunk

!

!

interface FastEthernet0/10

description **PBX ASTERISK**

switchport mode access

!

!

interface FastEthernet0/22

description **PC 2**

switchport access vlan 2

switchport mode access

!

!

interface FastEthernet0/23

description **Puesto de RRHH #3**

switchport access vlan 2

switchport voice vlan 3

!

interface FastEthernet0/24

description **PC 1**

switchport access vlan 2

switchport mode access

!

!

interface Vlan2

description DATOS

ip address 192.168.0.1 255.255.255.128

!

interface Vlan3

description VoIP

ip address 192.168.0.129 255.255.255.128

!

ip default-gateway 192.168.0.1

!

Now I have a second issue I wasn´t aware of.I have an asterisk server from which my phone is trying to register. This Asterisk server has a static ip address of 192.168.0.9 and mask 255.255.255.128 + gw 192.168.0.1

The thing is that this server isn´t reachable from any point of the network (router-switch or any of the hosts inside the LAN). I believe I should place it under some vlan? But I´m not sure, because if I do that I believe the ip automatic assigment will be overriden and I need it to be under an static IP.

!

interface FastEthernet0/10

description **PBX ASTERISK**

switchport mode access

!

Any suggestion?again, thank you very much ALL.

[Richard Burts]

Laura

With this configuration your asterisk server is in vlan 1. And you do not have any addressing or routing configured for vlan 1 that I can tell. If you put FastEthernet0/10 into vlan 2 it should work just fine. And the static addressing would not be an issue because you have configured excluded addresses that include 192.168.0.9.

I will point out that your config has the same issue that we found in the original suggestion from Najaf. Your vlan interfaces on the switch are using the same IP addresses as the router. The easy thing would be to make them 1 larger than what is configured now.

HTH

Rick

[paul driver · Accepted solution]

Hello Larua,

Your switch config is still not correct? You dont require two svi interfaces on a L2 switch.

As stated in my first posting, remove the svi on the L2 switch and add just one interface:

conf t

interface Vlan1

description DATOS

ip address 192.168.0.x 255.255.255.128

no interface Vlan2

no interface Vlan3

ip default-gateway 192.168.0.1

vlan2

exit

Then all DATOSaccess ports

switchport access vlan 1

Then all VOICE access ports

switchport access vlan 2

this should also resolve your server connection issue?

res

Paul

Please don't forget to rate any posts that have been helpful.

Thanks.

[Liv_Liv]

Thank you all,

I put the PBX port under data vlan as per Richard advise and re-write vlan config as  pdriver suggested. Now I have one data vlan (modified ip to avoid  duplication with the router interfaces) and another "empty" voice vlan.  This is now working and I have both end-to-end network connectivity.

Once again thank you very much for your great help !!

[Richard Burts]

Laura

I am glad that our suggestions helped you to find solutions for these issues. Thank you for using the rating system to rate responses and to mark this question as answered. It makes the forum more useful when people can read about problems and can know that a solution was found. Your markings have contributed to this process.

HTH

Rick