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Issue with Router on a stick Configuration

Shruti3482
Level 1
Level 1

I have connected a modem on switch port 23 and below config is the config on router subinterface and switch port.

This is not working. I can't ping the next hop x.x.x.97. This was working when modem was connected directly to the router.

Any suggestions?

ROUTER

interface GigabitEthernet0/0.110
encapsulation dot1Q 110
vrf forwarding IWAN-PUBLIC
ip address x.x.x.108 255.255.255.240

 

SWITCH

interface FastEthernet0/23
switchport access vlan 110
switchport mode access

14 Replies 14

Mark Malone
VIP Alumni
VIP Alumni

Hi

Is the modem is the front facing device with the WAN IP address to get out to the internet ?

It should be connected to the router not the switch , why are you connecting it to the switch ?

 

the modem wold have to understand how to route back if its connected somewhere else , but if its a modem for the internet it should be connected to the router

 

good example of RnS

http://www.firewall.cx/cisco-technical-knowledgebase/cisco-routers/336-cisco-router-8021q-router-stick.html

Yes modem is a front facing device with WAN IP. There is no free port on the router. Hence, router on a stick.

 

Router is a CISCO1921/K9 with Gi0/0 connected to switch and Gi0/1 connect to Primary Internet link. The modem in question is secondary connection.

 

 

Pawan Raut
Level 4
Level 4

Make sure the router port connected to switch is trunk and allowed that vlan 110

Yes. Router is connected  on Gi0/1 of switch and 110 vlan is allowed on it.

 

SW-10#sh int trunk

Port Mode Encapsulation Status Native vlan
Fa0/24 on 802.1q trunking 4
Gi0/1 on 802.1q trunking 2
Gi0/2 on 802.1q trunking 4

Port Vlans allowed on trunk
Fa0/24 1-4094
Gi0/1 1-4094
Gi0/2 1-4094

Port Vlans allowed and active in management domain
Fa0/24 1-2,4,52-57,110
Gi0/1 1-2,4,52-57,110
Gi0/2 1-2,4,52-57,110

Port Vlans in spanning tree forwarding state and not pruned
Fa0/24 1-2,4,52-57,110
Gi0/1 1-2,4,52-57,110
Gi0/2 1-2,4,52-57,110

When you did connect the modem to router port for test then what is the configuration you do on router interface

Below is the config on router which was working. After moving modem to switch, I created a subinterface with 110 vlan, created L2 vlan 110 on switch and configured switch port connected to modem as access port for vlan 110.

 

interface GigabitEthernet0/1

vrf forwarding IWAN-PUBLIC
ip address x.x.x.108 255.255.255.240
duplex auto
speed auto

 

ip route vrf IWAN-PUBLIC 0.0.0.0 0.0.0.0 x.x.x.97

Hello,

 

it gets really confusing now to figure out what you have connected to what. Post a schematic drawing of your topology so we can see which devices are connected to which devices.

 

A switch is a layer 2 device, you cannot use that as a substitue for a router...

Router gi0/0 - connected to switch on Gi0/1

Switch Fa0/23 - connected to Modem.

 

Config on router --

 

interface GigabitEthernet0/0

Description - SW1
no ip address
load-interval 30
duplex full
speed 1000
end

 

interface GigabitEthernet0/0.2
description Data VLAN
encapsulation dot1Q 2 native
ip address y.y.y.2 255.255.255.0
ip access-group wormkiller in
ip access-group wormkiller out
ip directed-broadcast
ip wccp 61 redirect in
ip pim dr-priority 200
ip pim sparse-dense-mode
end

 

interface GigabitEthernet0/0.110
description Modem
encapsulation dot1Q 110
vrf forwarding IWAN-PUBLIC
ip address x.x.x.108 255.255.255.240
no cdp enable
end

 

ip route vrf IWAN-PUBLIC 0.0.0.0 0.0.0.0 x.x.x.97

 

Config on Switch ---------------------------------------------------------

 

interface FastEthernet0/23
description Modem
switchport access vlan 110
switchport mode access
end


interface GigabitEthernet0/1
description RTR01
switchport trunk native vlan 2
switchport mode trunk
mls qos trust cos

 

 

 

 

I tested modem by connecting it on Router Gi0/1 with below config and I was able to ping the next hop - x.x.x.97

 

interface GigabitEthernet0/1
description Modem
vrf forwarding IWAN-PUBLIC
ip address x.x.x.108 255.255.255.240
duplex auto
speed auto

 

ip route vrf IWAN-PUBLIC 0.0.0.0 0.0.0.0 x.x.x.97

 

Hope this clears the confusion.

Hello,

 

post the full running configs (sh run) of both the router and the switch...

Hello


@Shruti3482 wrote:

Yes modem is a front facing device with WAN IP. There is no free port on the router. Hence, router on a stick.

 

Router is a CISCO1921/K9 with Gi0/0 connected to switch and Gi0/1 connect to Primary Internet link. The modem in question is secondary connection.



Why are you making gig0/0 on the router a subinterface for vlan 110, does it need to be, Can you not just have its a normal routed port and have the two ports on the switch interconnecting the router and the modem access port vlan 1.

 

If the router gig0/0 needs to be in a subinterface for vlan110, then make the port on the switch connecting to the router a trunk port and the port connecting to the modem an access port in vlan 110, but dont forget in a vrf you need to ping the vrf table

ping vrf WAN-PUBLIC x.x.x.97

 

 


Please rate and mark as an accepted solution if you have found any of the information provided useful.
This then could assist others on these forums to find a valuable answer and broadens the community’s global network.

Kind Regards
Paul

Hi Paul, I am creating sub-interface because there is no free port on router.

And yes I am pinging using vrf.

See below .. Hope this helps in understanding the scenario -

 

Router gi0/0 - connected to switch on Gi0/1

Switch Fa0/23 - connected to Modem.

 

Config on router --

 

interface GigabitEthernet0/0

Description - SW1
no ip address
load-interval 30
duplex full
speed 1000
end

 

interface GigabitEthernet0/0.2
description Data VLAN
encapsulation dot1Q 2 native
ip address y.y.y.2 255.255.255.0
ip access-group wormkiller in
ip access-group wormkiller out
ip directed-broadcast
ip wccp 61 redirect in
ip pim dr-priority 200
ip pim sparse-dense-mode
end

 

interface GigabitEthernet0/0.110
description Modem
encapsulation dot1Q 110
vrf forwarding IWAN-PUBLIC
ip address x.x.x.108 255.255.255.240
no cdp enable
end

 

ip route vrf IWAN-PUBLIC 0.0.0.0 0.0.0.0 x.x.x.97

 

Config on Switch ---------------------------------------------------------

 

interface FastEthernet0/23
description Modem
switchport access vlan 110
switchport mode access
end


interface GigabitEthernet0/1
description RTR01
switchport trunk native vlan 2
switchport mode trunk
mls qos trust cos

 

 

 

 

I tested modem by connecting it on Router Gi0/1 with below config and I was able to ping the next hop - x.x.x.97

 

interface GigabitEthernet0/1
description Modem
vrf forwarding IWAN-PUBLIC
ip address x.x.x.108 255.255.255.240
duplex auto
speed auto

 

ip route vrf IWAN-PUBLIC 0.0.0.0 0.0.0.0 x.x.x.97

Hello,

 

post a schematic drawing of your topology. You cannot connect the modem to a switch and the router to the switch as well. What brand/model are the router and the switch ? 

I believe the connections cannot be like this 

 

Modem ----------- switch--------- router

 

as the ISP is going to give a single IP space

 

https://www.quora.com/Can-I-connect-the-modem-to-the-switch-then-to-the-router

 

But yes, network diagram would be of great help.

Please do not hesitate to click the STAR button if you are satisfied with my answer.

See below .. Hope this helps in understanding the scenario -

 

Router gi0/0 - connected to switch on Gi0/1

Switch Fa0/23 - connected to Modem.

 

Config on router --

 

interface GigabitEthernet0/0

Description - SW1
no ip address
load-interval 30
duplex full
speed 1000
end

 

interface GigabitEthernet0/0.2
description Data VLAN
encapsulation dot1Q 2 native
ip address y.y.y.2 255.255.255.0
ip access-group wormkiller in
ip access-group wormkiller out
ip directed-broadcast
ip wccp 61 redirect in
ip pim dr-priority 200
ip pim sparse-dense-mode
end

 

interface GigabitEthernet0/0.110
description Modem
encapsulation dot1Q 110
vrf forwarding IWAN-PUBLIC
ip address x.x.x.108 255.255.255.240
no cdp enable
end

 

ip route vrf IWAN-PUBLIC 0.0.0.0 0.0.0.0 x.x.x.97

 

Config on Switch ---------------------------------------------------------

 

interface FastEthernet0/23
description Modem
switchport access vlan 110
switchport mode access
end


interface GigabitEthernet0/1
description RTR01
switchport trunk native vlan 2
switchport mode trunk
mls qos trust cos

 

 

 

 

I tested modem by connecting it on Router with below config and I was able to ping the next hop - x.x.x.97

 

interface GigabitEthernet0/1
description Modem
vrf forwarding IWAN-PUBLIC
ip address x.x.x.108 255.255.255.240
duplex auto
speed auto

 

ip route vrf IWAN-PUBLIC 0.0.0.0 0.0.0.0 x.x.x.97

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