Distribution / Core switch connections

mzinz

I'm revamping pieces of our production network.

Currently, we have no real core. Our servers connect to 2 switches, and these 2 switches connect to a 3800 series router. Right now, the router is doing all inter-vlan routing.

Traffic is low, so things are OK for right now, but should this router go down, we're dead.

I'm considering getting a couple 3560's to use at the core.

As we know, it is not advised to have VLANs run all the way to the core, so I will likely have them terminate at our existing switches, and setup layer 3 connections between the existing switches and the new 3560's. Our existing router would hook directly into the 3560's as well.

Here's my question: When Cisco says that they recommend layer 3 links between distribution and core switches, do they recommend setting up arbitrary /30 IP connections, or should all distribution/core links fall in the same subnet?

I intend on having the 3560s do as little packet inspection as possible (no vlans, no acl, routing protocols??).

Any advice would be great

networker050184

If all you have are two switches and a router I don't really see the need for adding more equipment. Over complicating things isn't always the best plan. If the existing switches are L3 switches then you can just go with a collapsed core design. I think that would make a lot more sense in your situation.

On the L3 uplinks, I always use a /31 and run OSPF/EIGRP to avoid static routes.

mzinz

networker050184 wrote: »

If all you have are two switches and a router I don't really see the need for adding more equipment. Over complicating things isn't always the best plan. If the existing switches are L3 switches then you can just go with a collapsed core design. I think that would make a lot more sense in your situation.

On the L3 uplinks, I always use a /31 and run OSPF/EIGRP to avoid static routes.

For simplicities sake I made our network sound smaller than it is, although it is still fairly small

We currently are using 3 switches, each of them is almost totally full. The biggest problem is that the router is currently doing all of the inter-vlan routing, so every packet switching vlan/subnet has to travel through our entire network.

We are growing, so we will need more hardware anyway, and the three switches we have now are all ExtremeNetworks... I know they make decent gear, but having some Cisco hardware in a true core seems like it will be the easiest to maintain and open up a lot more options for scalability.

As for the L3 links - do you mean /30? The routing protocols definitely make sense... I'm assuming only core/distribution switches participate?

ColbyG

/31s are valid:

CORE(config-if)#ip add 192.168.2.1 255.255.255.254
% Warning: use /31 mask on non point-to-point interface cautiously

interface GigabitEthernet0/11
 no switchport
 ip address 192.168.2.1 255.255.255.254

Networker43980439034094309430943 showed me this a couple months ago.

mzinz

ColbyNA wrote: »

/31s are valid:

CORE(config-if)#ip add 192.168.2.1 255.255.255.254
% Warning: use /31 mask on non point-to-point interface cautiously

interface GigabitEthernet0/11
 no switchport
 ip address 192.168.2.1 255.255.255.254

Networker43980439034094309430943 showed me this a couple months ago.

Weird. What do you assign to the other end of the link?

ColbyG

The other side of that one would be .0, probably not the best IP to use in real life, lol.

APA

for a point to point topology the /31 is recommended........ Run a routing protocol across the uplinks from dist to core as networker said......

mzinz

ColbyNA wrote: »

The other side of that one would be .0, probably not the best IP to use in real life, lol.

Hehe, yeah. After I wrote that I had sorta a "oh, duh" moment. I think /31 just caught me off guard since I've never used one in real life.

I'll lab it tonight just for kicks.

Thanks again!

CSCOnoob

We're using some links /31. When I first saw this, I was like WTF?