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Understanding VLANs when Sharing OSA Ports on System z



Document Author:

Linda Harrison


Document ID:

PRS3296


Doc. Organization:

Advanced Technical Sales


Document Revised:

08/05/2008


Product(s) covered:

Linux; zSeries; z/OS; z/VM







Abstract: This brief presentation attempts to explain the use of VLANs (802.1q) in a shared-OSA environment and how routing with VLANs occurs over a shared OSA. Some general concepts about VLANs are:
VLANs, or Virtual LANs, are a Layer 2 method of segmenting networks by assigning a VLAN Identifier (VLAN ID) to subnets of the network. In this way, what formerly looked like a shared medium (the network LAN segment), now looks like separate LAN segments, even though all the segments may terminate in the same shared adapter. In this paper, that shared adapter is the OSA port of the z platform. Therefore, separate VLANs should be configured in separate subnets. Layer 3 routing protocols (static, dynamic) route according to IP addresses and their subnets. Neither a routing table nor an IP stack takes a VLAN ID into consideration when building or acting upon entries in the routing tables. Therefore, the OSPF routing protocol does not know about VLANs and VLAN IDs. Network switches do make decisions based upon the Layer 2 concept of the VLAN ID. An OSA port primarily delivers a packet to a destination based upon its destination IP address or the PRIRouter and SECRouter definitions in an IP stack. However, once the OSA has selected a target based on the two criteria mentioned, it then subjects the delivery of the packet to an examination of a VLAN ID, if one has been provided.

OSA_VLAN_z.pdf



Classification:

Hardware; Software; Solutions

Category:

Planning and Design

Solution(s):

Business Integration



Platform(s):

IBM System z Family; Networking

S/W Pillar(s):

IBM System z Software

O/S:

z/OS

Keywords:

VLAN, VMAC, LAN, z/OS, Linux, z/VM, TRUNK, ACCESS, TAGGED


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