Cisco Router and only two Ethernet ports

[stompin]

Ok pretty new to this but it would seem an awful lot of cisco routers only have 1 or 2 ethernet ports. I need to plug a firewall into a router which then needs to route between 2 networks - in effect 3 ethernet ports are required. How do we do this and how do we connect routers to routers and routers to switches?

Thanks

 

[ChrisAC]

Does the firewall need to route between the networks or the router? If you need three ethernet ports then buy a router with expansion slots and buy ethernet cards.

Router to router - cross over cable.

Router to switch - straight through cable.

Chris.

**********************
Chris A.C, CCNA, CCSA
**********************

 

[stompin]

The router needs to route between two subnets. So when you connect router to router or switch this needs an ethernet cable (straight or Xover)from the routers ethernet port into the other routers/switches ethernet ports?

This is what I need...

DSL Rtr--->FW--->Router--->two subnets

So go get an ethernet card for expansion?

 

[ChrisAC]

Basically, yes! Of course it all depends on if your router is modular or fixed.

Chris.

**********************
Chris A.C, CCNA, CCSA
**********************

 

[stompin]

Good man - cheer's for the advice.

 

[robbieguy2003]

If your router isnt modular and you have a cisco switch you could .1q the connections back to it although i would advise against this.

I wish someone would just call me Sir, without adding 'Your making a scene'.

Rob

 

[JayNEC]

You could assign a subinterface to the same ethernet port and have it route then. Two separate subnets assigned to the same physical port.
"Router on a stick" or "one armed routing" is what it's known as.

 

[stompin]

Yer talking about a "sub interface" is that known as a secondary ip address. If both subnets are reachable through one port off the router and the second subnet is through a L2 switch how does that work?

Eg.

RT--->SW(subnet1)---->SW(subnet2)

router(config-if)# ip address [subnet2][mask] secondary

 

[fynx]

I don't think that will work for your installation... a secondary IP address on an interface or an address on a subinterface will only route traffice on two different IP subnets which exist on the same L2 VLAN. If you have two subnets and two vlans you will either have to use the 802.1q trunking option or use another physical interface.

good luck,

If everything is coming your way then you're in the wrong lane.

 

[JayNEC]

The original post made no mention of VLAN's...

 

[stompin]

ya not wrong... jayNEC can you elaborate on your post about "Two separate subnets assigned to the same physical port" cus I'm thinking thats what I need. Having two separate networks through only one eth port - secondary addressing, but still how does the routing work?

 

[JayNEC]

interface FastEthernet0/0
ip address 10.10.247.2 255.255.255.0
interface FastEthernet0/0.1
ip address 10.1.1.1 255.255.255.0

Devices on the 10.10.247.x network will use 10.10.247.2 for their gateway.
Devices on the 10.1.1.x network will use 10.1.1.1 for their gateway.
The router will loop packets back out the same interface to the other subnet. Hence the "router on a stick" - in and back out on the same cable.
I've done this for lab environments and testing, but for real production routing of traffic it could be a bottleneck.