Re: Secondary IP address

[Acee Lindem <[e-mail]>]

Hi Krishna,

Krishna Rao wrote:
> Hi,
>       Secondary IP address usage in OSPF is little shaddy.

Paraphrasing Mark Twain, "The rumors of the lack of OSPF
support for secondary addresses are greatly exaggerated."

OSPFv2 runs a subnet and makes no distinction as to whether or
not the subnet is primary or secondary. There is at least one
heavily deployed implementation that doesn't support OSPF on
secondary addresses.

 From section 1.2 of RFC 2328:

         Network
             In this memo, an IP network/subnet/supernet.  It is possible
             for one physical network to be assigned multiple IP
             network/subnet numbers.  We consider these to be separate
             networks.  Point-to-point physical networks are an exception
             - they are considered a single network no matter how many
             (if any at all) IP network/subnet numbers are assigned to
             them.

         Interface
             The connection between a router and one of its attached
             networks.  An interface has state information associated
             with it, which is obtained from the underlying lower level
             protocols and the routing protocol itself.  An interface to
             a network has associated with it a single IP address and
             mask (unless the network is an unnumbered point-to-point
             network).  An interface is sometimes also referred to as a
             link.

> Should
> we allow secondary address to be advertised in point-to-point and
> point-to-multipoint?

 From the above, it seems the answer should be yes for P2MP and no
for P2P. However, in our implementation we do allow OSPF
to be configured on multiple subnets on a P2P interface. This
allows the P2P interface to be an intra-area link in more than one
area.

>
> Regards,
> Krishna
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--
Acee