IBM PureFlex System and IBM Flex System Products and Technology

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VLAGs are also useful in multi-layer environments for both uplink and downlink redundancy to

any regular LAG-capable device as shown in Figure 6-6.

Figure 6-6 VLAG with multiple layers

6.4.5 Virtual Router Redundancy Protocol

If you are integrating the Enterprise Chassis into a Layer 3 network with different subnets,

routing, and routing protocols, some Layer 3 techniques can be used. These techniques

provide high availability service to clients. Traditionally, in multi-subnet IP networks, servers

use IP default gateways to communicate with each other. In a redundant network, in case of a

router failure, certain protocols need to be used to keep network availability. One of them is

Virtual Router Redundancy Protocol (VRRP).

VRRP enables redundant router configurations within a LAN, providing alternative router

paths for a host to eliminate single point of failure within a network. Each participating routing

device with VRRP function is configured with the same virtual router IPv4 address and ID

number. One of the routing devices is elected as the master router and controls the shared

virtual router IPv4 address. If the master fails, one of the backup routing devices takes control

of the virtual router IPv4 address and actively processes traffic addressed to it.

Currently, switch modules use VRRP version 2, which supports only IPv4 protocol. VRRP

version 3 is defined in RFC 5798. VRRPv3 introduces support for IPv6 in addition to IPv4. But

implementation for IPv6 is still not stable, so current switch operating systems do not support

IPv6 for VRRP.

The IBM Flex System Fabric EN4093 10 Gb Scalable Switch and IBM Flex System EN2092 1

Gb Ethernet Scalable Switch for Enterprise Chassis both offer the VRRP function.

LACP-capable

Switch

LACP-capable

Server

VLAG 2

VLAG

Peers

VLAG

Peers

VLAG 1

VLAG

Peers

VLAG 3 VLAG 4

ISLISL

ISL

LACP-capable

Routers

VLAG 5 VLAG 6

Layer 2/3 Border

Layer 2/3 Region

with multiple levels

Servers