Layer 3 routing without routing protocols

[mahesh18]

                   Hi Everyone,

Need to know about layer 3 routing without using routing protocols.

Our Client has Network where they are doing Layer 3 routing with vlans without using routing protocols.

Never heard of this before.

Core switch runs routing protocol and it has Vlan configured which do the routing with all the distribution switches.

They have no VTP configured on distribution switches.VTP is turned off on distribution switches

Is there way where we can turn off VTP on cisco switches??

Users connect to distribution switches and they have different vlan configured for various groups on distribution switches

Connection to core is by vlan which is routing vlan and default gateway configured on distribution switches.

Need to know is this Network type layer 3 by  vlan??

Need to know more info how this type of network  works?

Any reference to reading material ???

Thanks

MAhesh

[Sandeep Choudhary]

HI Mahesh,

They must be using Layer 3 switch for the use of intervlan routing.

Layer 3 switches actually work at the Network layer.

While most switches operate at the Data layer (Layer 2) of the OSI, some incorporate features of a router and operate at the Network layer (Layer 3) as well. In fact, a Layer 3 switch is incredibly similar to a router.

When a router receives a packet, it looks at the Layer 3 source and destination addresses to determine the path the packet should take. A standard switch relies on the MAC addresses to determine the source and destination of a packet, which is Layer 2 (Data) networking.

The fundamental difference between a router and a Layer 3 switch is that Layer 3 switches have optimized hardware to pass data as fast as Layer 2 switches, yet they make decisions on how to transmit traffic at Layer 3, just like a router. Within the LAN environment, a Layer 3 switch is usually faster than a router because it is built on switching hardware. In fact, many of Cisco's Layer 3 switches are actually routers that operate faster because they are built on "switching" hardware with customized chips inside the box.

Layer 3 switch use Intervlan routing concept to communicate between vlans.

Hope this the answer of your question.

Regards

Please rate if it helps.

[mahesh18]

Hi Sandeep,

Thanks for reply.

Yes they are using Layer 3 switches.

Distribution is 4500 series and core is 6500.

So  they do not use IP routing protocols.

So you mean to say they are using intervlan routing ?

Thanks

MAhesh

[Reza Sharifi]

Hi Mahesh,

If the default gateway is on the 4500 (distribution devices) and the 4500s are connected to 6500 (core) than you need to have a routing protocol between the 4500s and the 6500s or use static routes. Usually if the SVIs are on the 4500, than you have /30 subnets connecting the 4500s to 6500s.  So, even though there is no routing protocol, I am sure there is static routes on both 4500s and the 6500s

HTH

[mahesh18]

Hi Reza,

Thanks for reply.

4500 have static route pointing to 6500 core

4500 config

interface Vlan21

desc ip routing

  ip address 10..x.x.x

ip route 0.0.0.0 0.0.0.0 10..x.x.x

where 10.x.x.x is IP  of 6500

4500 has data vlan and IP helper configured to point to DHCP servers.

Data Vlan on 4500

int vlan 22

des Data

ip address 10.x.x.x

ip helpder-address 10.x.x.x

6500 has also static routes pointing back to 4500.

So say users get ip address for data vlan from 4500.

Need to know users Gateway for vlan data is on 4500  or 6500 switch?

Thanks

Mahesh

[Reza Sharifi]

Hi Mahesh,

Need to know users Gateway for vlan data is on 4500  or 6500 switch?

Users gateway is on the first hop switch/router.  In this case it is on 4500.

HTH

Reza

[mahesh18]

Hi Reza,

Can you please explain how you conclude that Data Vlan has its gateway on 4500?

Also VTP is turned off on 4500 .

Thanks

MAhesh

[Reza Sharifi]

Hi Mahesh,

The way you can tell is by seeing that SVIs and the helper address for each vlan is configured on the 4500 (as your descriotion shows below). There should also be a helper address for vlan 21, just like vlan 22.

4500 config

interface Vlan21

desc ip routing

  ip address 10..x.x.x

4500 has data vlan and IP helper configured to point to DHCP servers.

Data Vlan on 4500

int vlan 22

des Data

ip address 10.x.x.x

ip helpder-address 10.x.x.x

so, basically the 4500s are the distro switches with SVIs (users default gateways) and the 6500s are the core switches.

VTP does not matter in this case

HTH

[mahesh18]

Hi Reza,

Yes ip helper address is configured for each vlan on 4500.

But for Vlan 21 which is for routing it has no ip helper configured.

So it works like this users on Data vlan gets the IP address via ip helper addss command.

Then it gets forwarded by default gateway configured on 4500 to 6500 core.

Then 6500 core has vlan Data configured which assigns IP address to user PCs right?

Also need to confirm this below

when we use SVI vlan as me know it is layer 3  and if we use ip helper address under it then we can say it has

users default gateway configured under it right?

Also i compare the data vlan with old design there it has no SVI vlan for data.

Thanks for help

Mahesh

[Reza Sharifi]

Hi Mahesh,

So it works like this users on Data vlan gets the IP address via ip helper addss command.

Then it gets forwarded by default gateway configured on 4500 to 6500 core.

It gets forwarded by default gateway configured on 4500 to users PCs, laptop, etc...

Then 6500 core has vlan Data configured which assigns IP address to user PCs right?

I thought, the end user devices are connected to the 4500, if this is the case than there is no need to for the 6500 to assign ip to anything.  Since the 4500 is doing layer-2 and layer-3 the helper ip address should be only configured on the 4500 SVI interfaces.

Also need to confirm this below

when we use SVI vlan as me know it is layer 3  and if we use ip helper address under it then we can say it has users default gateway configured under it right?

correct

If I am not underestimating your design correctly, than please provide a diagram showing how everything is connected.

Thanks,

Reza

[mahesh18]

Hi Reza,

6500 core connects to  infoblox to get the IP for users PC.

Users PC  do connect to 4500 directly.

Then 4500 has fibre connection to 6500

This is design i know.

Does it make sense now?

Thanks

MAhesh

[Reza Sharifi]

Hi Mahesh,

Ok, than I wrote in the previous post applies.

So, the DHCP server (infoblox) is connected to the 6500 directly.  In this case all you need is helper address on the SVIs on the 4500.  As long as the infoblox is reachable (you can ping it over the network) then that is all you need.  What vlan is the infoblox in?

HTH

[mahesh18]

Hi Reza,

So core has another vlan --vlanx

Vlan x config

ip helper-address x.x.x.x

Infoblox device connects to this vlan.

So it means that 4500  router passes request to host in vlan x  where host is the ip helper address x.x.x.x  right?

And this host answers the IP request for the user on 4500  right?

Thanks

MAhesh

[Reza Sharifi · Accepted solution]

Hi Mahesh,

That is correct.

Reza

[mahesh18]

Many thanks Reza again

Mahesh