--- Sina Mirtorabi <sinaCISCO.COM> µÄÕýÎÄ£º> 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 "

From the rfc, spf sees only the router-lsa and
network-lsa,which router-lsa represents the links of
router and network-lsa represents the links of
network.

> N1 is just an IP address that does not exist while
> we built SPT

N1 is represents by the network-lsa,which is generated
by the DR.

> 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.

DR announce a network lsa, whick includes many links
of network, not a link.

Regards,
zhang

> 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.

_________________________________________________________
Do You Yahoo!? µÇ¼Ãâ·ÑÑÅ»¢µçÓÊ! http://mail.yahoo.com.cn

<font color=#6666FF>ÎÞÁÄ£¿ÓôÃÆ£¿¸ßÐË£¿Ã»ÀíÓÉ£¿¶¼À´ÁÄÌì°É£¡</font>¡ª¡ª
ÑÅ»¢È«ÐÂÁÄÌìÊÒ! http://cn.chat.yahoo.com/c/roomlist.html

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