Hi Zhibo,
On 10/13/22, 2:26 AM, "Lsr on behalf of Huzhibo" <[email protected] on
behalf of [email protected]> wrote:
Hi LSR:
LSInfinity
The metric value indicating that the destination described by an
LSA is unreachable. Used in summary-LSAs and AS-external-LSAs
I want to clarify the meaning of unreachable in LSifinity,
Assume that a node advertise specific route of 1.1.1.1/32, and an aggregate
route 1.1.0.0/16 is configured.
This node should premature aging of the 1.1.1.1/32 LSA.
If this node using LSInfinity metric instead of prematuring aging, route
1.1.1.1/32 is still reachable.
Therefore, the "unreachable" described by LSifinity is not really
unreachable.
If your OSPF implementation includes unreachable LSAs in the summary cost
computation, it is indeed broken.
Thanks,
Acee
Thanks
Zhibo hu
> -----Original Message-----
> From: Lsr [mailto:[email protected]] On Behalf Of Peter Psenak
> Sent: Wednesday, October 5, 2022 5:32 PM
> To: [email protected]
> Subject: [Lsr] RFC 8362 and LSInfinity
>
> Hi Folks,
>
> metric of LSInfinity (0xFFFFFF) has been defined in RFC2328:
>
> LSInfinity
> The metric value indicating that the destination described by an
> LSA is unreachable. Used in summary-LSAs and AS-external-LSAs
> as
> an alternative to premature aging (see Section 14.1). It is
> defined to be the 24-bit binary value of all ones: 0xffffff.
>
> RFC5340 inherited it from RFC2328:
>
> Appendix B. Architectural Constants
>
> Architectural constants for the OSPF protocol are defined in
> Appendix
> B of [OSPFV2]. The only difference for OSPF for IPv6 is that
> DefaultDestination is encoded as a prefix with length 0 (see
> Appendix A.4.1).
>
> Both RFC2328 and RFC5340 used 16 bits metric for intra-area prefix
> reachability, so the LSInfinity was not applicable for intra-area
prefixes.
>
> RFC8362 defines 24-bit metric for all prefix reachability TLVs -
> Intra-Area-Prefix TLV, Inter-Area-Prefix TLV, External-Prefix TLV.
> Although it is silent about the LSInfinity as such, it is assumed that
such
> metric means unreachability for Inter-Area-Prefix TLV and External-Prefix
> TLV. Given that Intra-Area-Prefix TLV now has 24 bits metric as well, it
> would make sense to define the LSInfinity as unreachable for
> Intra-Area-Prefix TLV as well.
>
> Would anyone object such a clarification in RFC8362?
>
> thanks,
> Peter
>
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