Hi Nischal,
On Feb 19, 2009, at 3:56 PM, Nischal Sheth wrote:
Hi Acee,
Thanks for the response.
I have a related question about the intent of the RFC1583Compatibility
global parameter. When set to enabled, is the underlying objective to
emulate a RFC 1583 implementation (w.r.t. path selection among
ASBRs and
external LSAs) or is it "just" to allow compatible operation with
other
1583 routers in the network.
Offhand, I don't see much difference but I might be missing something.
IOW, does an implementation even need to
maintain multiple routes to an ASBR if RFC1583Compatibility is
enabled?
I went back to RFC 1583 and a path per area providing ASBR
reachability is still maintained. I believe an implementation could
maintain a single path but then you'd have to handle finding an
alternate path when an ASBR becomes unreachabile.
Thanks,
Acee
Thanks,
Nischal
Acee Lindem wrote:
Hi Nischal,
I think this certainly is ambiguous as to whether the route type
should be taken into consideration when determining the which ASBR
path is lowest cost. Your literal interpretation seems but
reasonable but I know of at least one implementation that would
consider the route type. Luckily, this confusion is eliminated if
RFC1583Compatiblity is disabled.
Thanks,
Acee
On Feb 16, 2009, at 9:49 PM, Nischal Sheth wrote:
I have a question about originating a type 4 summary
LSA when a router has an intra-area route (via area A) to
an ASBR as well as a lower cost inter-area route (via the
backbone) to the same ASBR through another ABR.
According to the sixth bullet in section 12.4.3 of RFC 2328:
Else, if the destination of this route is an AS boundary
router, a summary-LSA should be originated if and only
if the routing table entry describes the preferred path
to the AS boundary router (see Step 3 of Section 16.4).
If so, a Type 4 summary-LSA is originated for the
destination, with Link State ID equal to the AS boundary
router's Router ID and metric equal to the routing table
entry's cost. Note: these LSAs should not be generated
if Area A has been configured as a stub area.
According to section 16.4 item (3), the preferred route to
the ASBR would be the least cost route i.e. the inter-area
route, since RFC1583Compatibility is enabled.
Thus, as far as I can tell, we would generate a type 4
summary when processing the inter-area route entry and
advertise the summary into area A and not generate the
corresponding summary into the backbone. This would be
different than RFC 1583 behavior or RFC 2328 behavior
with RFC1583Compatibility disabled. In those two cases,
we would generate a type 4 summary into the backbone and
areas other than A when processing the intra-area route
entry, since the intra-area route would be the preferred
route.
Is this the correct interpretation of sections 12.4.3 and
16.4?
Thanks in advance for any responses.
-Nischal
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