1841 - Router On A Stick

[edenbridge]

Hi All,

I have a used 1841 router, which i have added a HWIC-4ESW module with 4 switch ports.
I understand from previous experience that defining router on a stick between a switch and router - you would create the relevant VLANs on the switch, create a trunk to the router, and on the router add sub interface for each vlan.

How would i accomplish this in a 1841 which is basically a switch & router....how do you define the router on a stick element, and create an internal trunk..?

Many thanks...

[Joseph W. Doherty]

I believe the answer depends on what interface you use.

If you use one of the 1841's routed interfaces, it's as you've already described.

If you use an switch module port, you configure a port as a trunk and use VLAN interface(s) on the router (this is much like how you would configure a L3 switch).

[edenbridge]

Thanks Joseph,

so in this scenario, with HWIC-4ESW install for access ports - would i create a trunk on say port 0/0/3 and physically jumper it to say FA0/1 (routed port) as VLAN tagged interface (trunk)

Wasn't sure with these units whether the "trunk" is actually internal or not..?

Cheers...

[Joseph W. Doherty]

Actually, it's been so long since I've touched an "old" small ISR with a switch module, the one thing I'm unsure about is whether you can configure one of the switch module ports as a trunk port.  It appears some of the other posters have confirmed you should be able to define multiple SVIs.

Assuming you can configure a module switch port as a trunk, you would do L3 via the SVIs defined.  You would only use a routed port, with subinterfaces, on a routed port, either one of the built-in port or on a routed port(s) module.

I.e. you wouldn't "loop" one of the router's switch module ports to one of the router's routed ports.

[Martin L]

Correct me If I wrong but those routers can have only 1 SVI up up state. so, not much inter-vlan routing you can do here. mostly, you should set up ROAS, then use those switching module ports for access (small office). 

Regards, ML
**Please Rate All Helpful Responses **

[andrew.butterworth]

That's certainly not the case with the C1841's I have in my lab.  I can create lots of VLANs and corresponding SVIs on the C1841.  Might be an IOS restriction with different software images maybe?

[Georg Pauwen]

I can configure SVIs on the 1841 as well, not sure why you couldn't...

1841#sh run
Building configuration...

Current configuration : 1476 bytes
!
version 12.4
no service timestamps log datetime msec
no service timestamps debug datetime msec
no service password-encryption
!
hostname 1841
!
no ip cef
no ipv6 cef
!
spanning-tree mode pvst
!
interface FastEthernet0/0
no ip address
duplex auto
speed auto
!
interface FastEthernet0/1
no ip address
duplex auto
speed auto
shutdown
!
interface FastEthernet0/0/0
switchport mode access
!
interface FastEthernet0/0/1
switchport mode access
!
interface FastEthernet0/0/2
switchport mode access
!
interface FastEthernet0/0/3
switchport mode access
!
interface FastEthernet0/1/0
switchport mode access
!
interface FastEthernet0/1/1
switchport mode access
!
interface FastEthernet0/1/2
switchport mode access
!
interface FastEthernet0/1/3
switchport mode access
!
interface Vlan1
no ip address
shutdown
!
interface Vlan10
mac-address 0001.4232.ba01
ip address 192.168.10.1 255.255.255.0
!
interface Vlan20
mac-address 0001.4232.ba02
ip address 192.168.20.1 255.255.255.0
!
interface Vlan30
mac-address 0001.4232.ba03
ip address 192.168.30.1 255.255.255.0
!
interface Vlan40
mac-address 0001.4232.ba04
ip address 192.168.40.1 255.255.255.0
!
interface Vlan50
mac-address 0001.4232.ba05
ip address 192.168.50.1 255.255.255.0
!
ip classless
!
ip flow-export version 9
!
line con 0
!
line aux 0
!
line vty 0 4
login
!
end