Multi vrf vs ASBR

Answered Question
Mar 21st, 2009

I was talking to another guy yesterday late in my team, we were talking about multi vrf's but he kept on mentioning ASBR and I did not understand. according to my understanding an asbr is associated with ospf and it's the router that connects to the outside world/network, when I asked him he just smiled and leave. Do you have any idea about the relation between the asbr and multi vrf ce.

Correct Answer by Giuseppe Larosa about 7 years 11 months ago

Hello Lawrence,

to be qualified as ASBR in OSPF terminology is just enough to redistribute connected


router ospf 10 vrf test

redistribute connected

network 10.0.0.2 0.0.0.0 area


this can be at the same time a multi VRF CE and an ASBR for VRF test


or if BGP is used as PE-CE and the BGP routes are redistributed into OSPF


router ospf 10 vrf test

red bgp 65000 subnets metric 50


Hope to help

Giuseppe









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Giuseppe Larosa Sat, 03/21/2009 - 13:38

Hello Lawrence,

an ASBR is a router that redistributes into OSPF.

A multi VRF CE is a device that has multiple VRFs.

A multi VRF CE can also be an ASBR the two concepts are compatible.


Hope to help

Giuseppe


mailaglady2 Sat, 03/21/2009 - 13:50

I still don't understand because I thought a CE is concentrating towards the customer LAN on one side and towards the pe on the other side? whilst ASBR is more like a gateway to the outside world on one side and on the other side is connected to the core network or the PE side?

Correct Answer
Giuseppe Larosa Sat, 03/21/2009 - 13:55

Hello Lawrence,

to be qualified as ASBR in OSPF terminology is just enough to redistribute connected


router ospf 10 vrf test

redistribute connected

network 10.0.0.2 0.0.0.0 area


this can be at the same time a multi VRF CE and an ASBR for VRF test


or if BGP is used as PE-CE and the BGP routes are redistributed into OSPF


router ospf 10 vrf test

red bgp 65000 subnets metric 50


Hope to help

Giuseppe









lamav Sat, 03/21/2009 - 14:02

Lawrence:


Your team member doesn't sound like he cares whether you understand what he's saying or not. Maybe his objective is to confuse you. You know, job security through obscurity. :-)


As Giuseppe said, having an ASBR on the edge of your OSPF domain that is running multiple VRF instances on a BGP connection to a service provider is very common.


The CE router will be BGP peering with the SP, running multiple VRFs in an MPLS VPN topology, and the routes it learns through MP-BGP can be redistributed into OSPF for the OSPF core to learn.


Those redistributed routes will be seen by the OSPF domain as O E2, by default.


Typical stuff, really...


HTH


Victor

Mohamed Sobair Sat, 03/21/2009 - 14:09


Hi,


In brief,


An ASBR terminology in OSPF is the router that redistribute different routing protocols into OSPF.


Although the ASBR is an OSPF trminology, but it does mean that a router actively act as a boundary router is an ASBR.


So , a Multi Vrf CE router is an ASBR.


The ASBR is also defined in "Inter AS architecture" where different Automnous systems are interconnected, the ASBR-PE router is the router that connects to another AS router.



HTH

Mohamed

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