Cisco Trunking vlan tagging

Ronnie Wong

The DHCP server on your SOHO router is serving DHCP out the physical ports of the router. So if plug one of those ports into a vlan 10 port on your 3750 port, it should also get DHCP too.

Victor Rosa-Serrano

Let me go back a little, When the cisco switch was in their original state, I just plug a cable from fa 4/0/1 to the soho and everything was working at that point. Then I created the vlans and they were working, then I created the trunk port and is there when I got hiccups, but it work, So When I move fa 4/0/1 from default settings to access mode is when everithing started. Mean time my trunk port is 4/0/24 is connected to the soho router. Vlan 10 is allowed in the trunk port. My question then is, Previously Vlan 1 was getting an IP address, Now it doesn't, How do I assign a static IP to the trunk link, I think that's my issue. The switch doesn't have a valid IP.

Ronnie Wong

@Victor-Rosa-Serrano,

You don't assign an ip to a trunk link, as far as I know. You can assign an IP to the entire switch by using interface vlan 1.

You can change a physical switchport to a routed port and assign an IP address there by using the no switchport command. I've never tried this on a trunk port.

Let me ask what you're trying to accomplish. This might help me to figure out why this isn't working.

Victor Rosa-Serrano

Thanks for your time. I'm practicing and creating a home lab environment. Where I can see the cables connected to what devices and so on. How can I test if indeed my trunk link is working? Because I ping the vlan and its reply is, not reachable. Regular network, 192.168.1.1/24 Router, the trunk needs to have some sore of ID right? If the vlan is 192.168.2.1/24, Who's the gate way, the Vlan ip right? My network looks like this, PC-Cisco Switch Fa 10&11. FA24 is the trunk to the soho router

WU-TANG

@Ronnie, I don't see a model number, but do random routers understand 802.1q? Can a trunk talk to any port on a given router and just be understood?

Victor Rosa-Serrano

Is a Ubee Soho router.

Victor Rosa-Serrano

What is an Inbound access list? I run sh ip int fa4/0/24 (my trunk link) line is up, protocol is up, Inbound access list is not set.

Ronnie Wong

@WU-TANG,

Most managed switches today support 802.1q. It used to be where they would support ISL and 802.1q.

The trunk link is a single link that carries traffic from multiple vlans across it. Whereas, if it's not a trunk, it can only carry the traffic of a single vlan across it.

The trunk itself doesn't send data. We can configure it to allow for all, some, or one vlan to traverse it.

You only tend to create trunks on switches rather than routers. ON a router you're creating subinterfaces (multiple logical interfaces to interact with vlans that communicate over a single physical link.

Victor Rosa-Serrano

So I created a trunk to pass traffic from vlan 10,20 and 50. But for some reason I can't pass that traffic to the gateway.

Ronnie Wong

@Victor-Rosa-Serrano,

So on a switch you can creat a virtual interface called interface vlan 1 and assign an ip address to it.

SW1(config)#interface vlan 16
SW1(config-if)#ip address 192.168.16.1 255.255.255.0
SW1(config-if)#no shutdown

If I have a switchport in vlan 16 and a host is attached to the device on that port. You can assign a static ip address to it e.g. 192.168.16.100 255.255.255.0 default gateway: 192.168.16.1

you should be able to ping 192.168.16.1 sucessfully.

Ronnie Wong

@Victor-Rosa-Serrano,

The problem that you'll have is that you'll need a separate gateway for vlans 10, 20 and 50. You will not share a gateway for 10, 20 and 50.

Then you'll have to configure reachability with a port going to each gateway or you can configure a trunk...and have that trunk connect to a ROUTER that will allow you to configure subinterfaces on that port as your gateways.

Victor Rosa-Serrano

So I create the trunk, So I need to create the sub interfaces in the router then, That may be the part that I'm missing. Now what you mentioned earlier make sense that my soho may not support multiple scopes. I'll try again with a manage Sophos firewall and will update.

Victor Rosa-Serrano

Victor Rosa-Serrano

So I have a workstation in vlan 10 but no dhcp. But the trunk should allow that traffic to my home router. Everything seems ok in that side righ?

Ronnie Wong

@Victor-Rosa-Serrano,

Plug your SOHO router that is serving dhcp into fa4/0/10, fa4/0/11, fa4/0/12, fa4/0/20

If your router will not allow you to create scopes for vlan 10 and vlan 20. Then it will only serve one vlan.

Victor Rosa-Serrano

I did What you said and instead I have an image from a sophos router. It worked, But Now I would like to know, How to add the remain vlans to work, like vlan20. Should I create a relay agent for dhcp? Thanks

Ronnie Wong

@Victor-Rosa-Serrano,

Does your DHCP router support multiple scopes? if not, you will need to put a DHCP in each VLAN.

Victor Rosa-Serrano

No it doesn't but I could place a dchp server. In the real world they don't place relay agents? How will that be configure. If My dhcp is in vlan 10 I know I could create a relay agent to comunicate with it. Thanks for all your help Mr Ronnie

Ronnie Wong

@Victor-Rosa-Serrano,

You will find dhcp-relays in the real world to allow you to send the DHCP Broadcast beyond the Broadcast Domain.
I'm sure that within our Cisco courses you'll see how to configure a DHCP relay agent.

I've never tried to do this the way you're describing.

You'll need a need either a router between the vlans or setup SVIs, then configure the dhcp relay agent correctly.