""Jenny McLeod"" wrote in message
news:200210280429.EAA24675@;groupstudy.com...
> The Long and Winding Road wrote:
> [snipped]
> > > area 0 range 172.16.1.0 255.255.255.0 area not working on ABR
> > either
> > >
> >
> > CL: well, area 0 range is an illegal command. you may be able
> > to enter it,
> > but it does nothing. the area range command is design to
> > summarize non
> > backbone routes into the backbone. if you think aout it, there
> > is probably
> > not a real good reaso for backbone routes to be summarized
> >
> >
> JMcL: Since when??
> I use the area 0 range blah blah command (without the "area" at the end,
if
> that was supposed to be part of the command above), and it certainly
doesn't
> do nothing. As far as I've seen, it works in exactly the same way as area
> anything else range blah blah.
All right, Miss Smarty Pants. I don't know what IOS versions you use / have
been using, but I have been through this song and dance with OSPF area 0
summarization, or lack thereof for a while now. I have yet to see it work.
Seriously, Jen, you know I respect your wisdom and value your advice. I am
absolutely certain that I have never successfuly summarized area 0 routes
over a couple of years of lab rat living. The following is from my current
study pod, and the IOS version is 12.1.5T10.
First, router 1 configurations. There are a number of loopbacks,containing
the route addresses in question.
router ospf 123
log-adjacency-changes
area 0 range 100.100.0.0 255.255.240.0
redistribute rip subnets route-map rip2ospf
network 99.99.99.1 0.0.0.0 area 51
network 100.100.0.1 0.0.0.0 area 0
network 100.100.1.1 0.0.0.0 area 0
network 100.100.2.1 0.0.0.0 area 0
network 100.100.3.1 0.0.0.0 area 0
network 100.100.4.1 0.0.0.0 area 0
network 100.100.5.1 0.0.0.0 area 0
network 100.100.6.1 0.0.0.0 area 0
network 100.100.7.1 0.0.0.0 area 0
network 160.160.255.0 0.0.0.255 area 0
note the summary in the R1 routing table:
Gateway of last resort is not set
100.0.0.0/8 is variably subnetted, 9 subnets, 2 masks
O 100.100.0.0/20 is a summary, 00:11:57, Null0
now observe router 2's table:
100.0.0.0/24 is subnetted, 8 subnets
O 100.100.0.0 [110/26] via 160.160.255.1, 00:12:53, TokenRing0
O 100.100.1.0 [110/26] via 160.160.255.1, 00:12:53, TokenRing0
O 100.100.2.0 [110/26] via 160.160.255.1, 00:12:53, TokenRing0
O 100.100.3.0 [110/26] via 160.160.255.1, 00:12:53, TokenRing0
O 100.100.4.0 [110/26] via 160.160.255.1, 00:12:53, TokenRing0
O 100.100.5.0 [110/26] via 160.160.255.1, 00:12:53, TokenRing0
O 100.100.6.0 [110/26] via 160.160.255.1, 00:12:54, TokenRing0
O 100.100.7.0 [110/26] via 160.160.255.1, 00:12:54, TokenRing0
99.0.0.0/32 is subnetted, 1 subnets
This has remained constant through several reconfigurations and several ospf
process resets.
It also remain true even if on R1 I use a more generic network 100.100.0.0
0.0.255.255 area 0 command.
So........
I stand by my statement that even though you may be able to enter the
commands, the fact is that you cannot summarize area 0 routes on a cisco
router, at least not that I've been able to figure out.. My position is
further supported by the Cisco documentation, which states "The area range
command is used only with area border routers (ABRs). It is used to
consolidate or summarize routes for an area. The result is that a single
summary route is advertised to other areas by the ABR. Routing information
is condensed at area boundaries."
http://www.cisco.com/univercd/cc/td/doc/product/software/ios121/121cgcr/ip_r
/iprprt2/1rdospf.htm#xtocid4
watch the wrap
Of course, I am ready to learn something new, if you've got a trick I have
yet to learn.
> Why not summarise backbone routes for the same reasons as summarising
> non-backbone routes - reduce routing tables, database sizes, route change
> propagations etc?
In regards to the wisdom of summarizing backbone routes in an OSPF network,
while I was pondering your response, I went through a few ideas, and I see
where it "might" be advantageous.. I still believe that generally speaking,
one would want all backbone routes to be visible throughout the backbone to
allow for uninterrupted routing should one or more backbone routers fail.
This assuming a redundant backbone design.
I can't located specifics in the RFC, but I "suspect" that Mr. Moy is of
similar mind.
with all respects
Chuck
--
>
> JMcL
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=56430&t=56136
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