The Journey of a Network Engineer

Oct 27 2010   3:46AM GMT

From trunk ports to routed ports – part 2



Posted by: Sulaiman Syed
Tags:
access
Cisco
core
design
distribution
ip
network
routed
scheme
subnet
trunk
vlan

In this part, I would talk bout the migration from current network, to the proposed network.

Figure 1 shows a core layer with two distribution layer, the one on the left is current, and the one on the right is the proposed. Before explaining any further, take note that although user vlans were local (shouldn’t span to core and other distribution) they were spanning cause of some poor configuration.

Routed,Cisco,Ports

The core network will have ip address of 10.0.y.x/16 where y = 0 for core layer, and x = host number/id. The distribution layer follow the scheme of 10.0.y.x/16, where y = distribution switch location, x = host number/id. access switches will have same scheme as distribution just their x will start from 100.

The objective is to migrate to routed ports without loosing connectivity in management vlan and providing a good summary for routing table. This is possible by following the design on the right side of the figure. Change the subnet mask from /16 to /24 from distribution layer and lower. The routed ports will have IP address from the last subnet of the user vlans. The user vlan IP scheme follows as 10.y.x.z/24 where y is distribution switch location, x is vlan number, z is host id.  so for first distribution switch the following subnets were allocated for the routed ports. 10.1.255.255/31 and 10.1.255.252/31. second distribution switch used subnets 10.1.255.250/31 and 10.1.255.248/31.

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