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New Member

BGP Routing Method

I am looking for some advice on routing into my network

I have 2 routers to the same MPLS provider, using eBGP - this links to my other sites roughly 20 (small number of routes advertised by each)

I have a switch connected to both routers and behind the switch the rest of the local network (running OSPF)

My current thinking is to have the routers and switch talking with iBGP

I then need to redistribute the iBGP into OSPF

I have used the bgp redistribute-internal command on the switch

I have some concerns about this command and was hoping someone might put my mind at rest as to whether this will work

Or is there a better way of doing things?

I'd like to be able to

- control outbound traffic, so that some subnets are routed via one router and the rest the other way (hence the iBGP)

- i'd also like the routers to advetise routes to the provider, so to get to a specific subnet use a specific router, would MED do this?

Thanks in advance

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2 ACCEPTED SOLUTIONS

Accepted Solutions
New Member

BGP Routing Method

Hi Simon

If there is only one switch between both the routers and an OSPF domain behind the switch, then I don't see a need of redistrubuting BGP to OSPF.  Let OSPF neighbors reach the switch using a default route (using default information originate) and then switch decide which WAN router the traffic shoud be forwarded based on the local preference.  If not, then your idea of redistributing with a combination of acl and route-map is fine.

For incoming traffic, you need to contact your service provider and mutually agree to use MED as it is an optional, non-transitive attribute.  Your service provide may rewrite it. 

Also, do the branches have two links to MPLS cloud or just one?  If two, then you can apply the same concept there as well for load sharing among WAN links. 

Cisco Employee

this is a test from amy

this is a test from amy

6 REPLIES
Silver

BGP Routing Method

I would use iBGP between the routers and the switch. You can use local preference to influence traffic outbound and communities or MED to influence traffic inbound.

Be careful when redistributing from BGP to OSPF. Bad things can happen if the provider accidentally leaks routes so only redistribute those routes in that you are expecting.

Also consider traffic flows, do you use HSRP and so on to try to avoid asymmetrical traffic flows.

Daniel Dib
CCIE #37149

Daniel Dib CCIE #37149 Please rate helpful posts.
New Member

BGP Routing Method

Daniel thanks for the reply

BGP to OSPF is my concern

I am assuming that I should configure a route-map matching an access-list inbound on the BGP switch

Then I should be able to redistribute into OSPF using bgp redistribute-internal, with the routes matched by the route map.

By default I would drop any leaked routes from the provider

New Member

BGP Routing Method

Hi Simon

If there is only one switch between both the routers and an OSPF domain behind the switch, then I don't see a need of redistrubuting BGP to OSPF.  Let OSPF neighbors reach the switch using a default route (using default information originate) and then switch decide which WAN router the traffic shoud be forwarded based on the local preference.  If not, then your idea of redistributing with a combination of acl and route-map is fine.

For incoming traffic, you need to contact your service provider and mutually agree to use MED as it is an optional, non-transitive attribute.  Your service provide may rewrite it. 

Also, do the branches have two links to MPLS cloud or just one?  If two, then you can apply the same concept there as well for load sharing among WAN links. 

BGP Routing Method

Hello, Simon.

Could you please clarify your design:

  • why do you need to redistribute OSPF into BGP, why not to distribute some summary (or even default gateway) only from hub site?
  • what load balancing are you looking for - inbound or outbound traffic (on spoke or on hub)?

If you want to load-balance inbound traffic, you could advertise summary via both links, but longer match via the link you want to be preferred.

I would also say that design for spokes and hub should be different: hub may advertise summary and should accept routes from spokes, spokes should accept summary and advertise only local subnets (that are not frequently changed).

Cisco Employee

this is a test from amy

this is a test from amy

New Member

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