Hi Manoj,
I agree that is not unclear. I've modified section 3.8.2 in the RFC
2740 update.
***************
*** 2698,2713 ****
In IPv6, the calculation of the next hop's IPv6 address (which
will
be a link-local address) proceeds along the same lines as the IPv4
! next hop calculation (see Section 16.1.1 of [OSPFV2]). The only
! difference is in calculating the next hop IPv6 address for a router
! (call it Router X) which shares a link with the calculating router.
! In this case the calculating router assigns the next hop IPv6
address
! to be the link-local interface address contained in Router X's
Link-
! LSA (see Appendix A.4.9) for the link. This procedure is necessary
! for some link types, for example NBMA, where the two routers
need not
! be neighbors and might not be exchanging OSPF Hello packets. For
! other link types, the next hop address may be determined via the
IPv6
! source address in the neighbor's Hello packet.
3.8.3. Calculating the inter-area routes
--- 2698,2724 ----
In IPv6, the calculation of the next hop's IPv6 address (which
will
be a link-local address) proceeds along the same lines as the IPv4
! next hop calculation (see Section 16.1.1 of [OSPFV2]). However,
! there are some differences. When calculating the next hop IPv6
! address for a router (call it Router X) which shares a link with
the
! calculating router, the calculating router assigns the next hop
IPv6
! address to be the link-local interface address contained in Router
! X's Link- LSA (see Appendix A.4.9) for the link. This procedure is
! necessary for some link types, for example NBMA, where the two
! routers need not be neighbors and might not be exchanging OSPF
Hello
! packets. For other link types, the next hop address may be
! determined via the IPv6 source address in the neighbor's Hello
! packet.
!
! Additionally, when calculating routes for the area's intra-area-
! prefix-LSAs, the parent vertex can be either a router-LSA or
network-
! LSA. This is in contrast to the second stage of the OSPFv2 intra-
! area SPF (Section 16.1 in [OSPFV2]) where the parent vertex is
always
! a router-LSA. In the case where the intra-area-prefix-LSA's
! referenced LSA is a directly connected network-LSA, the prefixes
are
! also considered to be directly connected. In this case, the
next-hop
! is solely the outgoing link and no IPv6 next hop address is
selected.
3.8.3. Calculating the inter-area routes
Thanks,
Acee
On Apr 26, 2007, at 9:47 PM, Goyal, Manoj wrote:
Hi,
I have a doubt in the determination of the next hop
for the adjacent router's prefixes on a Broadcast link.
R2 (DR, pfx: n2)
|L2
| L3
R1-------------------R3 (pfx: n3)
The router R1 is the calculating router and R2 is the DR.
R2 has prefix n2 on the link and R3 has n3 and the link local
address are L2 and L3 respectively.
Here the DR R2 generates the Intra-Area-Prefix(IAP) Lsa
for the network with prefixes n2 and n3 in that.
While calculating the routing table, R1 goes through the
IAP lsa of R2 and calculates the next hop for both
n2 and n3 as L2 only.
This will cause wrong forwarding
from R1 to R2 for the packets destined to n3.
In the draft, there does not seem to be a mention of
this situation.
In this case, to calculate the right next hop, the R1
has to look at the Link-Lsa of R3 and see that
the prefix n3 appears in it, then install the route
n3 with next-hop as Link-Local address from this Link Lsa.
Is there something I am missing here?
Though the purpose 2 of the link-lsa indirectly explains it.
Thanks,
Manoj
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