Redistribution

Unanswered Question
Jul 31st, 2009

Need some assistance in configuration & clarification.

Remote Offices connects to DataCenter via MPLS using service-provider and running BGP as routing Protocol.

On our LAN we run OSPF, MPLS Router connects LAN with Service Provider.

Goal is Branch office to acccess services hosted on DataCenter and communicate with other branches for Voice.

My Question for DataCenter:

1. Do I need to run a mutual redistribution of OSPF and BGP.

2. Do I need to use passive interface.

3. Do I need to use redistributed connected.

4. can i have single host advertise under ospf process which connects to my core.

5. I need to filter networks to be seen on Branch Offices? I dont know how.

I have this problem too.
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Giuseppe Larosa Sat, 08/01/2009 - 05:41

Hello Saquib,

my answers follow

1)

mutual redistribution is not needed

MPLS router can use network commands under router bgp process to advertise DataCenter and other central site IP subnets.

In BGP network command works for IP subnets in ip routing table not only for connected interfaces like it happens for OSPF or other IGP.

BGP routes representing remote sites can be redistributed from BGP into OSPF.

key parameter the subnets you can use a route-map to specify what routes if present to inject in the OSPF domain

router ospf 10

red bgp your.ASN route-map select1 subnets

route-map select1 permit 10

the route-map can use ip prefix-list to describe expected routes

So I suggest redist in one way BGP to OSPF.

2)

in OSPF the network ... area command + passive-interface is to be preferred over redistribute connected.

The second method introduces unnecessary external OSPF routes

3) not recommended see above

4) not clear if you mean a single BGP/OSPF router acting as ASBR yes this is possible but two devices would be better for fault tolerance and redundancy

5) no the service provider in the MPLS L3 VPN service propagates the routes that you advertise at MPLS router at main site to remote branch routers.

Also remote branch routes are seen on main site.

Actually with an any-to-any connectivity model remote sites can communicate directly without going via the central site.

This can be decided by service provider.

Other connectivity models like central site are possible depending on your needs.

Hope to help

Giuseppe

saquib.nawazz Sat, 08/01/2009 - 12:02

Giuseppe thanks.

Do confirm if I understood correctly

You stated

**MPLS router can use network commands under router bgp process to advertise DataCenter and other central site IP subnets**

router bgp 109

network 10.10.0.0 [ what about subnet mask ]

How to restribute OSPF External routes into BGP

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