[LARTC] Best setup for redundant routers.

[Grant Taylor]

On 12/6/2007 11:40 AM, Shane McKinley wrote:
> Wouldn't the redundant VRRP cause an IP address conflict?

No.  Let me try to explain using pseudo IP addresses.  For the sake of 
discussion we will use the RFC test network of 192.0.2.0/24.  (All IPs 
below will be just the last octet in said subnet.)

Real routers A and B (RA and RB respectively) and virtual routers A and 
B (VA and VB respectively) will make up the routers of the network.

Have RA be primary for VA's IP and backup for VB's IP.  Then have RB be 
backup for VA's IP and primary for VB's IP.  So you would have four IPs 
in use (RA, RB, VA, and VB).  You would only have clients use VA and / 
or VB as their default gateway(s).

So, if you have the following IPs used:

VA = .254
VB = .253
RA = .252
RB = .251

Real router A would have it's ""management IP of .252 and participate 
(as the primary) in the VRRP virtual router A IP / MAC address of .254 
and (as the secondary) in the VRRP virtual router B IP / MAC address of 
.253.

Real router B would have it's ""management IP of .251 and participate 
(as the secondary) in the VRRP virtual router A IP / MAC address of .254 
and (as the primary) in the VRRP virtual router B IP / MAC address of .253.

As you can see there are four IP addresses used, two are what clients 
would use as potential default gateways and two are for management of 
the real routers.

With the two different IPs that you can hand out to clients, you could 
do some load balancing by having some clients use one virtual router and 
others use the other virtual router.

Heck, if you wanted to you could even add a third real router (RC) to be 
a tertiary router for virtual routers.

> If not, that would be sweet. I would have redundancy for my redundancy.

Start thinking about how sweet things can be....



Grant. . . .