Subject: why Virtual IP addresses and not Virtual IP subnets

From: Yaron Presente <[email-masked]>
Date: Thu, 28 Jun 2001 14:43:43 +0300

Hi all,
As far as I could understand from the RFC, when a backup VRRP router
serves as a Master for a virtual router, it actually has to implement a
'virtual' IP
interface/s for the address/es associated with this virtual router, so
that it can route
packets sent by hosts from within this subnet to their default gateway
address. However,
I couldn't figure out how this router could tell what is the subnet mask
(/24, /28,
etc.) that the address/es which it backs up belong to.
In other words, I think that the term IP interface in a router should
refer to an IP & mask
couple and not just to an IP address.
Any clarifications would be appreciated,
Thanks,
Yaron
==============================================
Yaron Presente
Optical Access (http://www.opticalaccess.com/)
E-mail:  [email-masked]
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From: Peter Hunt <[email-masked]>
Date: Thu, 28 Jun 2001 09:31:34 -0700

> However, I couldn't figure out how this router could tell what is the
> subnet mask (/24, /28, etc.) that the address/es which it backs up
> belong to.

The router backing up the virtual address has its own "real" address
configured in that subnet. When the master fails, the backup VRRP
router installs the virtual address as an additional address in that
subnet. So it doesn't need to know the mask length of the network as
part of VRRP; it already knows it because it has its own address
configured in that subnet.

	Peter.