Subject: Intra-Area-Prefix LSA & duplicate prefixes

From: Ankur Sheth <[email-masked]>
Date: Thu, 8 May 2003 09:39:37 -0700

Say a router R1 has two Interfaces (both links to transit networks) and it
is fully adjacent with another router on interface I1 but has not
established any adjacency on I2.  Also let's assume that I2 has two global
IPv6 addresses 2001::1/64 and 2001::2a0:a5ff:fe12:615a/64.

Now when R1 is building an Intra-Area-Prefix LSA (which references it's own
Router LSA) does it include the prefix 3000::/64 twice?  Section 3.4.3.7 of
RFC 2740 pages 32-34 indicates that when a DR is building an
Intra-Area-Prefix LSA (referencing the Network LSA) it does checking for
duplicate prefixes, but does not say the same when you're building an
Intra-Area-Prefix LSA referencing your Router LSA?  Should the checking for
duplicate prefixes be done here as well?

thanks,
   Ankur

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From: Yasuhiro Ohara <[email-masked]>
Date: Fri, 9 May 2003 17:07:54 +0900

Hi.

I guess, we should. We should avoid the redundant prefix in originating
stub Intra-Prefix-LSA, as well as transit Intra-Prefix-LSA.
Originating the same prefix in a LSA is no more than just consuming
redundant bandwidth, though in this case OSPFv3 still works with having
duplicated prefixes unified during calculation of the LSA on receiving
routers.

Originating the same prefix in multiple LSAs (and how to avoid it) is
another issue. RFC 2740 does not specify the case, and I believe
most implementation will originate them as is (with having duplicated
prefixes included).

Assigning the same prefix to multiple link (i.e. duplicated) can be
considered configuration mistake. In this case hosts wishes to speak
to the prefix reaches different link, according to the place the host
exists.

Hope this helps.

regards,
yasu

From: Ankur Sheth <[email-masked]>
Subject: Intra-Area-Prefix LSA & duplicate prefixes
Date: Thu, 8 May 2003 09:39:37 -0700