NM-16ESW - adding a switch into a 3725 router slot - can i route traffic out of the switch ?

[SJ K]

Hi all,

I have added the above module (16 switch port) into my router.

 

R16#show ip int br
Interface                  IP-Address      OK? Method Status                Protocol
FastEthernet0/0            unassigned      YES unset  administratively down down
FastEthernet0/1            unassigned      YES unset  administratively down down
FastEthernet1/0            unassigned      YES unset  administratively down down
FastEthernet1/1            unassigned      YES unset  administratively down down
FastEthernet1/2            unassigned      YES unset  administratively down down
FastEthernet1/3            unassigned      YES unset  administratively down down
FastEthernet1/4            unassigned      YES unset  administratively down down
FastEthernet1/5            unassigned      YES unset  administratively down down
FastEthernet1/6            unassigned      YES unset  administratively down down
FastEthernet1/7            unassigned      YES unset  administratively down down
FastEthernet1/8            unassigned      YES unset  administratively down down
FastEthernet1/9            unassigned      YES unset  administratively down down
FastEthernet1/10           unassigned      YES unset  administratively down down
FastEthernet1/11           unassigned      YES unset  administratively down down
FastEthernet1/12           unassigned      YES unset  administratively down down
FastEthernet1/13           unassigned      YES unset  administratively down down
FastEthernet1/14           unassigned      YES unset  administratively down down
FastEthernet1/15           unassigned      YES unset  administratively down down
Vlan1                      unassigned      YES unset  up                    down

R16(config-if)#int fa1/0
R16(config-if)#ip address 192.168.10.1 255.255.255.0

% IP addresses may not be configured on L2 links.

R16(config-if)#

q1) Not being able to set IP to the interface as shown above, I would believe it is really a switch port.  Is there anyway I can see what kind of port a interface is or can be ? (switch port, routed port etc ?)   or whether is it a L2 or L3 switch ?

q2) in that case, since the switch is already inside the router, how do i route L3 traffic out of the switch ? 

Assuming fe0/1 on the router is the interface connected to external network.
and 2 workstations attached to the switch ports fe1/1 and and fe1/2, how can i set their gateway to point to fe0/1's IP ? Can fe0/1 to be connected to fe1/0 internally ?

Regards,
Noob

[Bilal Nawaz]

Q1 - Have you tried to issue "no switchport" command on the port you are trying to configure with IP address?

Q2 - you can create VLANs and vlan interfaces. Each port can be an access port in vlan X, and you also create an SVI for vlan X.

If you have two workstations on fa1/1 and fa1/2, you can put them in to a single broadcast domain (one VLAN) their default gateway will be the VLAN interface you create for that segment. Or you can create a vlan for each host if you had a reason to do so.

Then you route normally on the 3725.

Example:

Host 1 and host 2 are connected to fa1/1 and 1/2 respectively. They are in the same vlan, same subnet. Host 1 address is 10.0.0.11, host 2 address is 10.0.0.12

On router:

vlan X

interface range fa1/1 - 2

switchport

switchport mode access

switchport access vlan X

no shut

!

interface vlan X

ip address 10.0.0.1 255.255.255.0

no shut

So 10.0.0.1 will become the hosts default gateway, you need to set manually unless you have DHCP server to do so.

hth

Bilal

[SJ K]

Hi Bilal and Liam,

q1) I tried the no switchport command on the 16switch port module and it works. I can set an IP on the switch port.  But according to Liam, it is a L2 switch, how come we can assign no switchport command ?

q2) it is said that on a L2 switch only 1 SVI can be connected (for management purpose only) and L2 switch is not able to do routing. With the L2 switch module inserted into the router, will the SVI be able to do routing then ?

q3)Liam, you mention earlier fa0/0 is pointing to some network. is fa0/0 in the same router as the 16 switchport module ?

ip route 10.10.10.0 255.255.255.0 192.168.1.254 -- this command seems to be saying to access the 10.10.10.0 network, please go to the next hop IP 192.168.1.254 (but again, you are setting this next hop IP on the current router interface itself) - did i get anything wrong ?

Regards,
Noob

[Bilal Nawaz · Accepted solution]

Q1) Yes I thought you could do "no switchport" It has some limited function of a switch, but can be used for routed ports I believe.

Q2) Yes SVI's will be able to do routing. This is not like a Layer 2 switch, you can think of it as a multi-layer switch - L2 and L3 capabilities.

Q3) Liam is only trying to give you an idea of what needs to be done to ensure connectivity via a routed hop to another network. Though the route he put there doesn't make sense putting it on the 3725.

Lets take my example above, of two hosts on the 10.0.0.0/24 network

Host 1 = 10.0.0.11 - VLAN 10 - Default GW 10.0.0.1 - fa1/1

Host 2 = 10.0.0.12 - VLAN 10 - Default GW 10.0.0.1 - fa1/2

3725 = SVI VLAN 10 = 10.0.0.1

and assume 3725 is connected to another router point to point connection on Fa0/1

interface fa0/1

ip address 10.10.10.1 255.255.255.252

-----------------------------------------------------

The other routers interface connecting to fa0/1 has address of 10.10.10.2/30, behind this other router it has 172.16.0.0/24 network. We need a static route to route our host traffic to the 172 network via 10.10.10.2

So all we need to do is this

ip route 172.16.0.0 255.255.255.0 10.10.10.2

Finally we need to ensure that the "other router" has a route back to the 10.0.0.0/24 network via 10.10.10.1

Hope this helps

Bilal

[Liam Kenneally]

Hi Bilal, 

Was a late night for me when I wrote the previous post! I have revised what I said above. 

Kind Regards,

Liam

[SJ K]

Dear Bilai and Liam,

Thanks for replying. The forum should be having some issue as I did not receive any notification of your replies until today.

Yeap I tried it on GNS3 with the 16switch module and it really isn't a L2.  I can create multiple VLAN and SVIs. Also, I am using the SVI to do routing with the original routes already in the router (before the switch module is plugged in).

It's kinda a "wierd" add-on, as i am not sure if i am using the L3? switch to do routing or i am now using the router to do the routing.

Regards,
Noob

[Liam Kenneally · Accepted solution]

Hi KOE SIZE JIE, 

q1) I tried the no switchport command on the 16switch port module and it works. I can set an IP on the switch port.  But according to Liam, it is a L2 switch, how come we can assign no switchport command ?

As Bilal pointed out, I was mistaken you can issue the "no switchport" for a L3 routed port on that specific module. 

q2) it is said that on a L2 switch only 1 SVI can be connected (for management purpose only) and L2 switch is not able to do routing. With the L2 switch module inserted into the router, will the SVI be able to do routing then ?

I believe this goes back to what Bilal was saying about limited functionality on the EtherSwitch. I will have to play with one in GNS3 to give you a solid answer. 

But I think what it is trying to say is... You cannot use SVI's for inter-vlan routing. You can only have a single SVI for management purposes. 

q3)Liam, you mention earlier fa0/0 is pointing to some network. is fa0/0 in the same router as the 16 switchport module ?

ip route 10.10.10.0 255.255.255.0 192.168.1.254 -- this command seems to be saying to access the 10.10.10.0 network, please go to the next hop IP 192.168.1.254 (but again, you are setting this next hop IP on the current router interface itself) - did i get anything wrong ?

I have read back my post and this reads wrong. 

When i showed you the code snippet, 192.168.1.254 would be the interface on the next hop router. Not the router you are issuing the ip route command on. You would also need an IP address on the router interface directly connected to the next hop router. I.E 192.168.1.253

You will not then receive that error. Sorry about that, my sloppy config without a diagram!

HTHs,

Liam

[Liam Kenneally]

Hi KOE SIZE JIE, 

In regards to Q1 

The 16 port switch module you have configured inside your router is a layer 2 device. This means all 16 ports are switch ports. You cannot issue a "no switchport" on these to get routed ports. 

In Regards to Q2 

As per point one, these act as traditional layer 2 ports. so you would need to go under the interface and configure the port with your desired configuration. 

Example 

interface fa1/1

switchport mode access 

switchport access vlan 10 

no shut 

You will then need to create a layer 3 SVI (This is/would likely be your default gateway(DG) for your workstations 

To create a Switched Virtual Interface(SVI) 

interface vlan 10 

ip address 10.10.10.1 255.255.255.0 

no shut 

Lets say finally you have interface fa0/0 connecting to some network on 192.168.1.254. 

interface fa0/0 

ip add 192.168.1.253 255.255.255.0 

no shut 

Finally I would have put a static route to point the 10.10.10.0 network to the 192.168.1.254 device. 

ip route 10.10.10.0 255.255.255.0 192.168.1.254

Next hop router config

interface fa0/0

ip address 192.168.1.254

no shut 

You would also want a static route back to the other side 

ip route 0.0.0.0 0.0.0.0 192.168.1.253

Hope this helps. 

Liam