Re: OSPF Problem

I answered my own question -- The sham-link CAN be in area 0 but does not
HAVE to be .... so there is a major difference between a sham-link and a
virtual-link aside from what they are used for in practice. The sham-link
is extending the area it is part of across the SP domain.

On Tue, Jul 5, 2011 at 12:11 PM, Joe Astorino <joeastorino1982_at_gmail.com>wrote:

> A virtual-link is an extension of area 0 to solve a few specific problems
> -- bridging together multiple area 0 backbones or bridging area 0 together
> with an area not directly connected to area 0
>
> A sham-link is sort of like a virtual-link through an MPLS service provider
> and is there to solve a different problem -- When you run OSPF as a CE/PE
> routing protocol the LSAs you receive on your CE will be either inter-area
> type 3 LSAs or external type 5 LSAs depending on configuration of the OSPF
> domain ID. The rules of OSPF dictate that intra-area routes are always
> preferred over inter-area and external routes. Thus if you have a backup
> "back door" link between your sites, but you want traffic to flow over the
> MPLS by default you have a problem. The Sham-Link fixes that specific
> problem by allowing your CE to see the inter site routes as intra area LSAs
> instead of inter-area or external LSAs.
>
> If I remember correctly, the sham-link does not HAVE to be in area 0
> though....it can be a member of any area you tell it to be. I believe you
> are just extending that area across the service provider cloud, but I MIGHT
> be wrong on that. I would have to double check. Perhaps somebody else can
> elaborate on that point.
>
>
>
>
> On Tue, Jul 5, 2011 at 11:17 AM, Routing Freak <routingfreak_at_gmail.com>wrote:
>
>> Hey mates,
>> I have a little confusion. What is the difference between Sham link and
>> Virtual Link?
>>
>> I know that Virtual Link is to extend ur backbone
>> Sham link is used as a false link between two PE's . Is it extending ur
>> Area to other area and fool them that they r in the same area??
>>
>> Because Sham link mainly used as a virtual cable which sends Intra area
>> LSA's ( which is the Type 1 LSA's) to other PE .
>>
>> What does exactly the difference betwen Virtual links and Sham links
>>
>>
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>
>
> --
> Regards,
>
> Joe Astorino
> CCIE #24347
> Blog: http://astorinonetworks.com
>
> "He not busy being born is busy dying" - Dylan
>
>

-- 
Regards,
Joe Astorino
CCIE #24347
Blog: http://astorinonetworks.com
"He not busy being born is busy dying" - Dylan
Blogs and organic groups at http://www.ccie.net