Hi Marko - thanks for the reply. I had read the Router LSA blog which got my mind racing and jumped straight into the lab without reading (or looking for) the Network LSA blog.
So I'm correct in the assumption that it takes the next-hop info from the neighbour table. This begs another question (more a statement). In an NSSA, in order to get to an external route, OSPF needs the info in 3 LSA's. It needs the LSA Type5 identifying the external route, it needs the LSA Type4 identifying the ASBR with the external routes and it then needs an LSA Type2 to identify the ABR from which the LSA Type4 was received. And then installs the route based on the next hop info of the ABR from the neighbour table? It's all falling together nicely!! Thanks, Neil -----Original Message----- From: Marko Milivojevic [mailto:[email protected]] Sent: 20 January 2011 01:14 To: O'Brien, Neil Cc: [email protected] Subject: Re: [OSL | CCIE_RS] OSPF LSA Type 1 & 2 Neil, Did you read blog articles on this subject I wrote some months ago? -- Marko Milivojevic - CCIE #18427 Senior Technical Instructor - IPexpert FREE CCIE training: http://bit.ly/vLecture Mailto: [email protected] Telephone: +1.810.326.1444 Web: http://www.ipexpert.com/ On Wed, Jan 19, 2011 at 15:18, O'Brien, Neil <[email protected]> wrote: > Hi Guys, > > > > I'm labbing up some OSPF LSA scenarios and I think I've confused > myself more than anything else but would appreciate some clarification. > > > > LSA Type 1 - Sent from all OSPF Routers in an Area, advertising the > links/networks it has. > > LSA Type 2 - Sent from DR to all OSPF routers telling everyone who's > in it's area. > > > > So within an LSA Type 1 packet, amongst everything else, there's the > Link State ID which appears to be the RID, there's the ADV Router > which appears to be the RID and then the types of networks it has > -stub, transit and their subnets. There's nothing that I can see that > says "This is the actual IP you can reach me at" > > > > In an LSA Type 2, it seems to just contain the RID's of all other OSPF > routers on the segment. > > > > The issues I seem to have is how does the SPF algorithm derive the > next hop for a network. The packet captures I've taken for LSA Types > 1 & 2 all deal in RID. > > > > Does it take it from the neighbour table which does contain actual > interface ip of its neighbour?? > > > > When I debug ospf spf, I see where it installs the route with the next > hop but I'm not sure where it actually gets the next hop info. > > > > Thanks in advance, > > Neil > > > > > > > > _______________________________________________ > For more information regarding industry leading CCIE Lab training, > please visit www.ipexpert.com > _______________________________________________ For more information regarding industry leading CCIE Lab training, please visit www.ipexpert.com
