Subject: [OSPF] Question: Intra-area Prefix Lsa

From: "Vivek Dubey" <[email-masked]>
Date: 20 Jun 2006 13:18:34 -0000

Hi,
Queries tagged by <vivek> for (3) cases listed below.

1) Case1: Transit Link
----------------------
Draft quote
"Each IPv6 address prefix that has been configured on Link L is added to the link-LSA by specifying values for PrefixLength, PrefixOptions, and Address Prefix fields"

So prefix can be:
a) Global Ipv6 address (LA bit) i.e global ipv6 address associated 
   with the link (RFC 4293 ipAddressTable)
b) Global Ipv6 Prefix i.e global ipv6 prefix associated with the link 
   (RFC 4293 ipAddressPrefixTable)
c) Further (a) can be part of (b) or independent (RFC 4293 
   ipAddressPrefix)

Further while DR builds an intra-area-prefix lsa associated with the network LSA

Draft quote
"the list of prefixes in the link-LSA is copied into the intra-area-prefix-LSA that is being built.  Prefixes having the NU-bit and/or LA-bit set in their Options field SHOULD NOT be copied, nor should link-local addresses be copied"

<vivek1> Since DR does not use prefixes having NU/LA bit set while 
         originating intra-area-prefix lsa, why should they be made 
         part of link lsa originated for the transit link

<vivek2> If global ipv6 address associated with the link, is not part 
         of global ipv6 address prefix of the link, how would that be 
         reachable in the Ospf domain, as DR does not advertise such 
         prefixes (LA bit set), in the intra-area-prefix LSA

2) Case2: P2P link
-------------------
The link prefixes can be:
a) Global Ipv6 address (LA bit) i.e global ipv6 address associated
   with the link (RFC 4293 ipAddressTable)
b) Global Ipv6 Prefix i.e global ipv6 prefix associated with the link 
  (RFC 4293 ipAddressPrefixTable)
c) The entry (a) part of prefix (b) above (RFC 4293 ipAddressPrefix)
d) The entry (a) NOT part of prefix (b) above (RFC 4293 
   ipAddressPrefix being NULL)

<vivek3> Should intra-area prefix Lsa associated with the router 
         include separate entry for:
	 a) Global Ipv6 address (LA bit)
	 b) Global Ipv6 Prefix i.e global ipv6 prefix associated with 
            the link

<vivek4> If (c) above is TRUE, should (a) be included separately or 
         just (b) would do?

3) Case3: Stub Link
--------------------
The link prefixes can be:
a) Global Ipv6 address (LA bit) i.e global ipv6 address associated 
   with the link (RFC 4293 ipAddressTable)
b) Global Ipv6 Prefix i.e global ipv6 prefix associated with the link 
   (RFC 4293 ipAddressPrefixTable)
c) The entry (a) part of prefix (b) above (RFC 4293 ipAddressPrefix)
d) The entry (a) NOT part of prefix (b) above (RFC 4293 
   ipAddressPrefix being NULL)

<vivek5> Should intra-area prefix Lsa associated with the router 
         include separate entry for:
	 a) Global Ipv6 address (LA bit)
	 b) Global Ipv6 Prefix i.e global ipv6 prefix associated with 
            the link

<vivek6> In (c) above is TRUE, should (a) be included separately or 
         just (b) would do?

Thanks
Vivek

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---

From: Acee Lindem <[email-masked]>
Date: Tue, 20 Jun 2006 10:21:17 -0400

Hi Vivek,

>Queries tagged by <vivek> for (3) cases listed below.
The link-LSA has always included a complete set of prefixes for the 
link. In the case where
the multi-access network has only one connected router, the prefixes 
will be advertised
in the intra-area-prefix LSA associated with the router and will be more 
useful.

Note that for all link types other than broadcast and NBMA, the prefixes 
in the link LSA
are NOT used and the link-LSA could, in fact, be limited to the 
link-local address. Maybe,
I should document this as an option. I've been somewhat hesitant to 
provide additional
capabilities in the respin since the purpose is mainly to correct and 
clarify what is currently
in RFC 2740.

IMHO, we should have deprecated MOSPF which would have gotten rid of the 
NU and
MC bits. However, there was some opposition to this - perhaps, we will 
be able to do
it in the future.

>         prefixes (LA bit set), in the intra-area-prefix LSA
A router that has a virtual link is responsible for advertising at least 
one address with
the LA-bit set in the intra-area-prefix-LSA corresponding to the router. 
If it is necessary
for this address to be the interface address of a multi-access link, it 
would be advertised
there. For the other cases where the draft dictates that the LA-bit is 
set, the DR isn't
applicable (loopback and Point-to-Multipoint interfaces).

>2) Case2: P2P link
For P2P links, the global IPv6 address with the LA-bit set should only 
be advertised if
it necessary to provide an endpoint for a virtual link. In this case, 
both the global prefix
and the local address (i.e., /128) should be advertised.

>3) Case3: Stub Link
Same as P2P links.

Thanks,
Acee

>Thanks
>Vivek
>
>
>  
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