Re: [OSPF] Unnumbered PtoP router LSA question.

[Acee Lindem <acee at redback.com>]

Hi Joakim,
While it certainly isn't described very well, the intent is that the  
second router link is omitted for unnumbered links. If you look at  
the example for RT3's backbone area router LSA on page 134, you'll  
note the omission.

 ; RT3's router-LSA for the backbone

        LS age = 0                     ;always true on origination
        Options = (E-bit)              ;
        LS type = 1                    ;indicates router-LSA
        Link State ID = 192.1.1.3      ;RT3's router ID
        Advertising Router = 192.1.1.3 ;RT3's router ID
        bit E = 0                      ;not an AS boundary router
        bit B = 1                      ;area border router
        #links = 1
               Link ID = 18.10.0.6     ;Neighbor's Router ID
               Link Data = 0.0.0.3     ;MIB-II ifIndex of P-P link
               Type = 1                ;connects to router
               # TOS metrics = 0
               metric = 8

I'll keep this in my list of RFC 2328 inaccuracies.

Thanks,
Acee


On Jan 6, 2009, at 11:18 AM, Joakim Tjernlund wrote:

> In RFC 2328, Chap 12.4.1.1, reads:
>             12.4.1.1.  Describing point-to-point interfaces
>
>                 For point-to-point interfaces, one or more link
>                 descriptions are added to the router-LSA as follows:
>
>                 o   If the neighboring router is fully adjacent, add a
>                     Type 1 link (point-to-point). The Link ID  
> should be
>                     set to the Router ID of the neighboring router.  
> For
>                     numbered point-to-point networks, the Link Data
>                     should specify the IP interface address. For
>                     unnumbered point-to-point networks, the Link Data
>                     field should specify the interface's MIB-II [Ref8]
>                     ifIndex value. The cost should be set to the  
> output
>                     cost of the point-to-point interface.
>
>                 o   In addition, as long as the state of the interface
>                     is "Point-to-Point" (and regardless of the
>                     neighboring router state), a Type 3 link (stub
>                     network) should be added. There are two forms that
>                     this stub link can take:
>
>                     Option 1
>                         Assuming that the neighboring router's IP
>                         address is known, set the Link ID of the  
> Type 3
>                         link to the neighbor's IP address, the Link  
> Data
>                         to the mask 0xffffffff (indicating a host
>                         route), and the cost to the interface's
>                         configured output cost.[15]
>
>                     Option 2
>                         If a subnet has been assigned to the point-to-
>                         point link, set the Link ID of the Type 3 link
>                         to the subnet's IP address, the Link Data  
> to the
>                         subnet's mask, and the cost to the interface's
>                         configured output cost.[16]
>
> I have a hard time figuring out what to do with Option 1 and Option  
> 2 for unnumbered
> PtoP interfaces. I don't think either of them applies to an  
> unnumbered link so
> I wonder if one should omit both Options?
> However 12.4.1.1 starts with:
>    For point-to-point interfaces, one or more link
>    descriptions are added to the router-LSA as follows
>
> which could be read as there must always be one or more items and  
> as the first
> item needs to have a fully adjacent router you could end up with  
> zero items in the LSA for
> a PtoP interface.
> So what should one do?
>
>      Jocke
>
>
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