Re: How the prefixes configured on point-to-point link are handle d in OSPFv3

Nic Neate <Nic.Neate@DATACONNECTION.COM> Fri, 13 August 2004 10:23 UTC

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Date: Fri, 13 Aug 2004 11:12:54 +0100
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From: Nic Neate <Nic.Neate@DATACONNECTION.COM>
Subject: Re: How the prefixes configured on point-to-point link are handle d in OSPFv3
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Prasanna,

In the case of point-to-point links, I think the text you have quoted is
just saying that the IPv6 prefixes configured on an interface are advertised
in the Intra-area-prefix-LSA in preference to interface addresses.  The
interface addresses are only advertised when there are no prefixes
configured.

Hence in your example, RTA will advertise the prefixes configured on serial
1 if there are any, and if not will advertise the site-local and global
interface addresses.  RTA does not know what prefix configuration is on RTB
- the purpose of the Intra-area-prefix-LSA is for him to discover that.

Hope this helps.

Nic


---------
Nic Neate
Network Protocols Group
Data Connection Ltd (DCL)
Tel:   +44 20 8366 1177
Fax:   +44 20 8363 1039
Email: nic.neate@dataconnection.com
Web:   http://www.dataconnection.com


-----Original Message-----
From: prasanna [mailto:KSPrasanna@HUAWEI.COM]
Sent: Friday, August 13, 2004 9:44 AM
To: OSPF@PEACH.EASE.LSOFT.COM
Subject: How the prefixes configured on point-to-point link are handled in
OSPFv3


Hi
What does the following sentence (section 3.4.3.7) in the RFC 2740 mean?

Router RTX examines its list of interfaces to the area. If the
      interface is in state Down, its prefixes are not included. If the
      interface has been reported in RTX's router-LSA as a Type 2 link
      description (link to transit network), its prefixes are not
      included (they will be included in the intra-area-prefix-LSA for
      the link instead). If the interface type is Point-to-MultiPoint,
      or the interface is in state Loopback, or the interface connects
      to a point-to-point link which has not been assigned a prefix,
      then the site-local and global scope IPv6 addresses associated
      with the interface (if any) are copied into the intra-area-
      prefix-LSA, setting the LA-bit in the PrefixOptions field, and
      setting the PrefixLength to 128 and the Metric to 0.  Otherwise,
      the list of site-local and global prefixes configured in RTX for
      the link are copied into the intra-area-prefix-LSA by specifying
      the PrefixLength, PrefixOptions, and Address Prefix fields. The
      Metric field for each of these prefixes is set to the interface's
      output cost.

Considering the following example

RTA<serial 1>-------------------<serial1>RTB

Does it mean that RTA will advertise the prefix configured on serial 1 with
LA bit set, iff there is no prefix configured on the serial1 of RTB?

Thanx and regards
Prasanna

Re: How the prefixes configured on point-to-point… Nic Neate