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From: Alex Zinin (azininNEXSI.COM)
Date: Mon Jul 23 2001 - 03:40:47 CDT
I saw some confusion in this thread. Let's clarify.
First off, a multi-access (broadcast or NBMA) network N1
with attached routers R1, R2,...Rz, where Rx is the DR
is topologically abstracted as a network-LSA, originated
by Rx, and including links to all R1...Rz, including Rx,
and type-2 links in the router LSAs originated by R1...Rz.
As far as the SPT calculation goes, Dijkstra _does_ see
the network-LSA as a vertex.
The next-hop calculation for a remote (non-directly connected
SPT-wise) vertex that is not connected to the calculating
router (the SPT root) via a transit network is indeed as
simple as inheriting next-hops from the parent nodes.
The second case can be explained as follows.
Rd is the calculating router and it does not really matter
which router is the DR. The abstracted topology representation
will be as follows:
So, when Rd calculates the next-hops to Ra, it can see that
Ra's parent is transit node, so what it does it examines the link
entries in Ra's router-LSA, finds those referring the netowrk-LSA
and uses the IP address in Link Data as the next-hop address in
the route (finding the outgoing interface is easy).
-- Alex Zinin
Sunday, July 22, 2001, 11:02:51 PM, Sina Mirtorabi wrote:
>> >> > >> > 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. >>
> I'm saying that R1 announce a link to DR ( link ID = DR IP address ) > which in fact represents N1 > if you like, in other words R1 announce a link to the network N1 ( again > represented by DR ) But my point was if N1 = 192.168.1.0 / 24 with DR ( > 192.168.1.1 ) then the IP subnet is meaning less for SPT and it consider > a link to 192.168.1.1 which is DR
>> >> > 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. >>
> see above I meant the IP subnet address, of corse N1 is represented by 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. >>
> I meant by " a link to all the attached routers" >>> it announce a link > back from DR to every attached router or if you like many link > ( with many = link to every attached ;-)
>> >> 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!? 登录免费雅虎电邮! http://mail.yahoo.com.cn >> >> <font color=#6666FF>无聊？郁闷？高兴？没理由？都来聊天吧！</font>—— >> 雅虎全新聊天室! http://cn.chat.yahoo.com/c/roomlist.html