GLBP how to do real load balancing ?

[adnane dakna]

Hi  ,

As I understand , GLBP work based in ARP request and give ARP response to host with @mac of Active virtual forwader  according to policy choosed (round roubin trip , host dependend ,.. ) , and host forward traffic to same router while the aging Time of arp host is not expired.

In the context of Having hosts in LAN working as servers  how Can a adjust arp timing to get real load balancing ?

[Jon Marshall]

If i understand what you are asking ie. you want real server load-balancing then you can't really as GLBP is not designed for this task. GLBP is an end host redundancy method with the additional benefit of being able to use multiple routers/switches to forward the traffic. The problem is -

1) if the clients are on the same vlan as the servers then GLBP doesn't come into it, ie the client simply arps out for the server IP

2) if the clients are on a different vlan then they do no arp for the server IP, they arp for their default-gateway so GLBP would not load-balance for the server IPs.

Basically load-balancing to servers is done by using multiple real IPs and mapping them to one VIP (virtual IP) and to do this you need either -

1) a dedicated load-balancer

2) if you have 6500 switches then you can use SLB (Server Load Balancing). If memory servers right this may be supported on 4900 switches as well. There are limitations with SLB.

You can of course use DNS round robin as well ie. have multiple IPs to the same DNS name and the DNS server hands them out in round robin fashion but the problem here is that the DNS server has no way of knowing if one of the servers has gone out of service so it will continue to hand out that IP.