Jina

please if you reply do not cut the previous reply that we could understand
what we are talking about here is the initial mail and my reply

-------------------------------------
Umesh_MS wrote:

  Heloo..

  According to RFC 2328, section 16.1.1, there are two case for
  calculating next hop. The second case is for network. In that case I
  didn't get that how to calculate next hop and outgoing interface..
  can anybody explain this..(with the help of a figure)

  regards..

  Umesh

In the second case, the parent vertex is a network that
            directly connects the calculating router to the destination
            router. The list of next hops is then determined by
            examining the destination's router-LSA. For each link in
            the router-LSA that points back to the parent network, the
            link's Link Data field provides the IP address of a next hop
            router. The outgoing interface to use can then be derived
            from the next hop IP address (or it can be inherited from
            the parent network).

R1 R2 R3
| | |
---------------------------

imagine R1 is root and R2 is the DR further R2 is the parent of R3
if R2 was a router node and R1 didn't have a direct connection through a
transit network to R3 in this case R3 will just inherit the
outgoing interface and next hop from its parent ( R2 )
here R2 is a transit node so as stated we check if R3 announce a link back
to its parent ( R2 ) and the Link data field will give us
the next hop address
for outgoing interface it can be inherited from its parent ( R2 ) or found
directly since we have an common interface with the next
hop IP address

Sina
-----------------------------------------

now please see in line

Wu Jina wrote:

> Hello, Sina.
>
> I think it is not right. How to calculate the nexthop, these is a very
> clear description in RFC.
>
> About the second case, I think the the logice maybe like this:
>
> 1. If the parent is the router, then the algorithem will follow the
> the first case.
>

I guess you mean

If there is at least one intervening router in the current
            shortest path between the destination and the root, the
            destination simply inherits the set of next hops from the
            parent

we agree on that

>
> 2. If the parent is the network, then:
>
> a. Check if this network connect the root and current destination
> router directly, then OSPF calculate the next hop following the
> RFC.
>
> b. If this network don't connect the root and current destination
> router directly, then the nexthop of the destination router only
> inherit the parent network's nexthop.
>
> In your finger:
>
> R1 R2 R3
> | | |
> ---------------------------
> root DR Destination
>
> I convert the finger link this:
>
> -----------
> | R1 | root
> -----------
> |
> ----------------- N1
> | |
> --------- ----------
> | R2 | | R3 |
> --------- ----------
> DR DROTHER
>
> R1 is root, R2 is the DR, R3 is the CurrentRouter, but I think in SPF
> calculation, the parent of R3 is not R2, is N1, and DR/BDR is only used
> for send/receive packet, is not for SPF calculate.
>
> Thanks.

N1 is represented by DR, SPF sees only node and p2p adjacency so what do
you mean by "the parent of R3 is not R2, is N1 "
N1 is just an IP address that does not exist while we built SPT
also R1 does not have a direct adjacency to R3 but it announce a link type
2 ( transit ) to the DR and the DR announce a link to all the attached
routers.
so in the directed graph R1 should go through DR in order to reach R3 so
the parent of R3 is DR ( R2 )

Sina

>
>
> Jina.

• Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]