From: Cielieska Nathan (ncielieska@gmail.com)
Date: Tue Jan 22 2008 - 13:41:48 ARST
And on that topic,
In the end, you just need an area to touch area 0.. ever time you
"overlay" a virtual-link from the backbone to an area, that router is
seen to have an interface in area 0.. therefore making it a part of
Area0.
What all this means is that you can virtual-link a virtual-link to
join area 0.
Another thing to keep in mind is that virtual-links "cover up" bad
network design. So i'm not sure there are "best practices" on
throwing in virtual-links, your options are usually very limited to
get them to work. Bottom line is every area needs to touch area 0.
As Shiran says, this task becomes relatively easy if you draw your
your areas on a piece of paper in a typical routing diagram fashion.
The virtual-link options usually jump out like a sore thumb. I would
read a strong document on the subject, diagram it out on paper... lab
it up and test.
Regards,
Nate
On Jan 22, 2008, at 1:34 AM, shiran guez wrote:
> you need to summerize the loopbacks on R1 also as the virtual
> link extend area 0 so If you draw this on paper you would see that R1
> is another area 0 point of connection to R3 so it also advertise
> to area 1
> and the area range command is advertising the summary to the other
> areas not
> to area 0 so there will be a leak from R1 to R3 of the specific
> routes.
>
> Draw the logical areas with the virtual link on paper and you will
> see what
> I mean.
>
> Just Rememeber *Virtual Link is area 0 logical link!
> *
> On Jan 22, 2008 5:19 AM, YourPal <dearprudence28@gmail.com> wrote:
>
>> Hi Experts,
>>
>> Can someone provide insight into this issue?
>>
>>
>> Thank you.
>>
>> BR,
>> Emil
>>
>>
>> On 1/19/08, YourPal <dearprudence28@gmail.com> wrote:
>>>
>>> Hi Group,
>>>
>>> I have the following OSPF area summarization issue:
>>>
>>> R4-----(area 0)-----R5-----(area 1)-----R3-----(area 1)-----
>>> R1-----(area
>>> 2)-----R2
>>>
>>> R4's lo0 (150.1.4.4/24) and R5's lo0 (150.1.5.5/24) are in area
>>> 0. The
>>> loopbacks are advertised as host route.
>>>
>>> R5 summarizes the two loopbacks using command "area 0 range
>>> 150.1.4.0
>>> 255.255.254.0". R3 correctly sees 150.1.4.0/23 and not the
>>> specifics.
>>>
>>> A virtual link is then built between R5 and R1 to connect area 2
>>> to the
>>> backbone. R1 also has the command "area 0 range 150.1.4.0
>>> 255.255.254.0
>> ".
>>>
>>> Now, R3 no longer sees the summary 150.1.4.0/23. Instead it sees the
>>> specific routes 150.1.4.4/32 and 150.1.5.5/32. Why is it so?
>>>
>>> In contrary, if I summarize area 1 routes on R5 and R1 using "area 1
>> range
>>> ..." command, R4 correctly sees the summary route. There's no
>>> "leakage"
>> of
>>> specific routes.
>>>
>>> The above issue is overcome by not using virtual link but
>>> building a GRE
>>> tunnel between R5 and R1 and including the tunnel interfaces in
>>> area 0.
>> The
>>> "area 0 range ..." command remains on R5 & R1.
>>>
>>> Appreciate if anyone can shed some light on the issue.
>>>
>>>
>>> Thank you.
>>>
>>> BR,
>>> Emil
>>
>> _____________________________________________________________________
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>
>
>
> --
> Shiran Guez
> MCSE CCNP NCE1
> http://cciep3.blogspot.com
> http://www.linkedin.com/in/cciep3
>
> ______________________________________________________________________
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