Stub vs. Total Stub in OSPF

Answered Question
May 6th, 2009
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If you ever had a need to have a stub network, would there ever be a need to not just go total stub? I can't see a reason why I would want to opt for stub vs. total stub, unless I just wanted to see what routes I was being handed from my neighbor.


Thanks,

John

Correct Answer by Edison Ortiz about 7 years 11 months ago

If you have multiple ABRs in the stub area and both ABRs are sending the same summary LSAs but one ABR has a best cost towards that LSA, you may want that route information in the stub area so the path towards the destination can be more efficient.


The decision to use stub vs totally-stubby is often done based on customer requirements or network requirements but knowing summary specifics subnets instead of just a default out of the area can be really helpful in terms of traffic engineering.


__


Edison.

Correct Answer by Giuseppe Larosa about 7 years 11 months ago

Hello John,

OSPF totally stub is a Cisco extension to RFC2328 so it cannot be used in a multivendor environment (or at least only if all ABR are Cisco routers).


When this feature was introduced redistributing from BGP to OSPF was a viable solution so filtering all external routes could be enough to minimize the LSDB of routers inside the stub area.


In a MPLS environment you need the details of /32 loopbacks or remote PE nodes to correctly setup LSPs so in an MPLS scenario it is likely that a stub area is to be preferred.

Area filter-list command allows to use a prefix-list so it is possible to let only /32 routes to enter an area.

This allows for scalability.


Hope to help

Giuseppe


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Correct Answer
Giuseppe Larosa Wed, 05/06/2009 - 11:30
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Hello John,

OSPF totally stub is a Cisco extension to RFC2328 so it cannot be used in a multivendor environment (or at least only if all ABR are Cisco routers).


When this feature was introduced redistributing from BGP to OSPF was a viable solution so filtering all external routes could be enough to minimize the LSDB of routers inside the stub area.


In a MPLS environment you need the details of /32 loopbacks or remote PE nodes to correctly setup LSPs so in an MPLS scenario it is likely that a stub area is to be preferred.

Area filter-list command allows to use a prefix-list so it is possible to let only /32 routes to enter an area.

This allows for scalability.


Hope to help

Giuseppe


John Blakley Wed, 05/06/2009 - 11:34
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So the total stub concept is Cisco proprietary? That's good to know :)


Thanks!

John

Correct Answer
Edison Ortiz Wed, 05/06/2009 - 11:36
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If you have multiple ABRs in the stub area and both ABRs are sending the same summary LSAs but one ABR has a best cost towards that LSA, you may want that route information in the stub area so the path towards the destination can be more efficient.


The decision to use stub vs totally-stubby is often done based on customer requirements or network requirements but knowing summary specifics subnets instead of just a default out of the area can be really helpful in terms of traffic engineering.


__


Edison.

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