Hi Alex,
Multi-Area interface disambiguation is required to support the OSPF MIB as
specified in RFC 4750. The table indexing doesn’t include the area. For example:
-- OSPF Interface Table
ospfIfTable OBJECT-TYPE
SYNTAX SEQUENCE OF OspfIfEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The OSPF Interface Table describes the interfaces
from the viewpoint of OSPF.
It augments the ipAddrTable with OSPF specific information."
REFERENCE
"OSPF Version 2, Appendix C.3 Router interface
parameters"
::= { ospf 7 }
ospfIfEntry OBJECT-TYPE
SYNTAX OspfIfEntry
MAX-ACCESS not-accessible
STATUS current
DESCRIPTION
"The OSPF interface entry describes one interface
from the viewpoint of OSPF.
Information in this table is persistent and when this object
is written the entity SHOULD save the change to non-volatile
storage."
INDEX { ospfIfIpAddress, ospfAddressLessIf }
::= { ospfIfTable 1 }
Note that if you really want to support this optimally, you could use a
separate subnet pre-area and have adjacencies on secondary addresses. My
Redback/Ericsson implementation allowed for this.
Thanks,
Acee
From: Lsr <[email protected]> on behalf of Alexander Okonnikov
<[email protected]>
Date: Monday, November 30, 2020 at 5:27 AM
To: "Peter Psenak (ppsenak)" <[email protected]>
Cc: "[email protected]" <[email protected]>
Subject: Re: [Lsr] Link Data value for Multi-area links
Hi Peter,
30 нояб. 2020 г., в 12:56, Peter Psenak
<[email protected]<mailto:[email protected]>> написал(а):
Hi Alex,
On 27/11/2020 13:49, Alexander Okonnikov wrote:
Hi Peter,
Which kind of ambiguity is meant? In case of numbered point-to-point each link
has its own unique IP address, so there is no ambiguity.
Per my understanding this problem has appeared due to follow reasons:
1) In old versions of the draft (up to -05) it was proposed that multi-area
links are treated as unnumbered. ifIndex to be encoded in Link Data field,
irrespectively whether interface has its own IP address (numbered) or borrow it
(unnumbered);
2) From -06 to -08 multi-area links are still treated as unnumbered, but if
interface is numbered, then IP address of the neighbor (rather than local one)
to be encoded into Link Data, in order to make the link look like unnumbered;
3) In version -09 of the draft and in RFC 5185 itself there is no more mentions
that multi-area link to be treated as unnumbered. Rather, another approach is
used - if router's interface is numbered, then link is also numbered; if
router's interface is unnumbered, then link is unnumbered. The rule that
specifies omitting corresponding type 3 link is added. Mention of 'unnumbered'
link is also removed from section 3 in RFC 5185. >
Hence, in version -09 with removing unnumbered nature of multi-area links Link
Data for numbered links had to be changed from Neighbor's IP address to own IP
address, as it is specified in RFC 2328. From perspective of other routers this
link can be treated as numbered or unnumbered, depending on configuration of
neighbor's corresponding interface.
you are free to advertise the link as unnumbered. RFC5185 is not mandating to
send IP address really.
The same valid for numbered ones. I.e. I'm free to advertise the link as
numbered. This is straightforward when the link is numbered indeed. And if we
would prefer to have deal with unnumbered interfaces, we would not need RFC
5185 (section 1.2).
One question - how neighboring router will perform next-hop calculation (in
case it needs to do so)? If neighbor is configured with numbered interface, it
will treat Link Data as IP next hop, which will be its own IP interface address.
Another question - how router will be able to match Link TLV (RFC 3630) to
corresponding Link in Router LSA? For example, we want to calculate RSVP-TE LSP
based on IGP metric (RFC 3785) and thus router needs to match IGP link to TE
link.
I don't believe you are going to do any traffic engineering over a multi-area
adjacency. MADJ is there to address the OSPF route preference rules that may
lead to sub-optimal routing. MADJ link is not advertised for TE purposes.
Why not? We need multi-area configuration and at the same time we need ability
to build intra-area RSVP-TE LSPs within each of areas. And what about
calculating IP next hop? Which compatibility is meant in section 3?
thanks,
Peter
Thank you.
Thank you.
27 нояб. 2020 г., в 14:50, Peter Psenak
<[email protected]<mailto:[email protected]>> написал(а):
Alexander,
On 26/11/2020 17:58, Alexander Okonnikov wrote:
Hi WG,
RFC 5185 says that Neighbor's IP address to be encoded into Link Data field.
Per RFC 2328 router's own IP address to be encoded into Link Data. What is the
reason to advertise neighbor's IP address for multi-area links and not local IP
address? It seems like bug. Could someone comment on this?
Advertising a neighbor address/ifindex helps to eliminate ambiguity in case of
parallel point-to-point adjacencies. It's not perfect, but that's how it was
specified. So it's not a bug.
thanks,
Peter
Thanks in advance.
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