ip route on layer 3 switch

[Robin Swan]

Will “ip route 0.0.0.0 0.0.0.0 10.1.1.1” route ALL network traffic on the layer 3 (edge) switch to the destination even if there are 2 different networks on the switch?

For instance, if the layer 3 (edge) switch would have an SVI of 10.200.x.x/29 for one network directly connected to it, and an uplink of 10.150.x.x/30 connecting to a different network of 10.200.x.x/24?

Thank you in advance.

Jay

[mmoulson1]

If you want to use 10.1.1.1 as a default route for the switch then it needs to be able to talk to 10.1.1.1.

Not sure what you mean by an uplink of 10.150.x.x/30?

[devils_advocate]

ip route 0.0.0.0 0.0.0.0 10.1.1.1 is called a 'Default Route'

Another name for it is a 'Gateway of last resort'.

Effectively, if the router does a lookup in its routing table and is unable to find a match, it will forward the packet to the next hop specified in the default route....assuming a default route is configured.

A Layer 3 switch will likely be doing the routing between your Vlans. Each VLAN maps to a subnet and these subnets will show up in the Routing table as 'Directly Connected'. If the router receives a packet which has a Destination IP address for a LAN subnet which is directly connected, it will just forward the packet directly to the host. It only uses the default route when it cannot find a match.

EDIT - I have just re-read your question again and I think I misunderstood your question!

I think it may be worth you drawing out the network so we can see it.

A router will store the subnet mask of any directly connected routes so having a subnet of 10.200.*.* /29 directly connected and also having a 10.200.*.* somewhere else in the network will not cause an issue as long as the subnets do not overlap.

[Robin Swan]

This is what I drew up yesterday.  The networks are different on the drawing than in the question, but it is the same question:

Thank you for your quick response.

[mmoulson1]

So in your example your common network is 192.168.250.x/29, so from the switch on the right of the diagram you would have 4 SVI's with your 192.168.40/50/60/70.x networks, then either a 5th SVI or a routed port for the 192.158.250.x.

Your default route would be via the 192.168.250.x address on the other side of the link.

Hope that makes sense?

[Robin Swan]

Actually in the drawing, 192.168.0.x/24 is the 10.1.1.0/24 network asked in the original question.  I made the drawing with bogus IP Addresses, but reflective of the network.

In the drawing, I put the Elster AMI IP Radio in a class A network simply to show that it is a totally different subnet than the sub-office.  The 192.168.0.x/24 (10.1.1.0/24) is the fiber transport network back to the Core network of which I have 59 tiny networks connected and expecting to triple in the next few years.  The Elser AMI IP Radio network (10.x.x.48/29) would be directly connected to the edge switch which is to bring All the networks back on the same fiber link through the IE3000 (default route 192.168.0.x/24). Right now, it is coming back with a direct connect through our ISP's Ciena transport switch and the SVI is defined on the fiber connected switch which is our hub near the core.  The 192.168.250.x/29 network connects to the access layer switch with the 4 SVI's.  2 of the addresses in the 192.168.250.x/29 network are on the  Motorola Canopy's exclusively for transport over the air (approximately a 21 mi distance).  Right now, the sub-office network comes back separately from the IP Radio and uses 1 MicroWave T1 throught a Serial port on a 3900 series router.  I want to get rid of the router and bring everything back on fiber using the IE3000 without changing the IP Address of the Elster AMI IP Radio and without having our ISP provision a separate port for the sub-office on their device for the transport on the fiber.  In other words, I want to bring back 2 totally separate networks on the same switch without changing IP Addresses.

I hope my explanation can be understood lol.

[mmoulson1]

I’ve read your post about 3 times but I can’t visualise it! LOL

If I understand your question yes you can bring back different networks, so you can have 10.x.x.x/29 and 192.168.0.x/24 and 192.168.250.x/29 all into the same layer 3 switch, as long as the switch has either an SVI or routed port configured on it.

What you need to consider is where you have ISP managed links where the ISP controls the routing. So if you add another subnet at the other end of a link, will the ISP pass traffic to it?

Hope that makes sense!

[Robin Swan]

Excellent (if the short answer is yet).

Yes, I do already have a "hub-spoke" setup on the fiber.  I'm migrating all the endpoints onto the fiber from the T1's and this is the last one I have to deal with for awhile.  It's just that at this one endpoint, there are 2 totally separate networks that have to come back to the "hub."  Presently, the IP Radio is connected directly to the Ciena Fiber switch (CSU/DSU), and the sub-office is connected to a MicroWave T1 through a 3900 series router.  The difference between the 2 networks is that the IP Radio will be connected directly to the IE3000, and the sub-office will be connected to the IE3000 through an access layer switch with a Motorola Wireless Canopy in between.

I know it's kind of hard to understand, but this is what I inherited and it is hard for me to transfer my knowledge to paper or voice.  That is why I'll never be a teacher :D.

Thank you to all who answered.