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New Member

OSPF- BGP Influencing routes over 2 carriers

Headquarters will have 2 routers and links (one from each carrier). CE to PE will be running BGP, while internally they will be running iBGP (OSPF) between L3 switch and CE. Remote sites will be configured similar. We want to send non-critical traffic over one carrier, while critical traffic over the other carrier. We want return traffic over the same source link while maintaining redundancy.

What is the best way to influence the routes so they select a particular path for both egress and ingress?

New Member

Re: OSPF- BGP Influencing routes over 2 carriers

deterministic advertisement of summary routes per egress path (now in english)

Use ospf summary routes to give the carrier running non-critical traffic a less specific route prefix of your internal networks. the more specific routes will be perferred over the "other carrier" for the critical traffic.

I.E. send over the "non-critical carrier" and over the "critical carrier".

You can do this all in using

area x range command on the ABR's.


New Member

Re: OSPF- BGP Influencing routes over 2 carriers

thank you joe. what would you suggest for non-company routes (internet) over the non-critical traffic carrier? The challenge is the return internet traffic from remote, want to insure it routes back through non-critical carrier to remote. FYI: all internet traffic routes through HQ.

Re: OSPF- BGP Influencing routes over 2 carriers

Hello Daniel,

To influence ingress traffic the best would be seting MED or preepending AS on the routes sent to the CEs.

To influence egress traffic you can use local-preference or Weight(this is only used inside 1 router, not transmitted between routers).

Give us more details on your configs and we'll be glad to help.

Anyway check:

for many examples and setups.

HTH a bit,


New Member

Re: OSPF- BGP Influencing routes over 2 carriers

Hi Daniel, to influence return traffic, you may want to perform MED, AS path prepend or weight when you advertise your prefixes to your 2 different providers.

Hope this will be useful.



New Member

Re: OSPF- BGP Influencing routes over 2 carriers

I have attached a simple schematic of the network. In this example I am looking at the same host accessing "critical and non-critical traffic" simultaneously. The destination AS and prefix would be the same at the remote end. I know that CEF by default enables destination based sessions, which should have the return traffc follow the same path as the initiated session but I dont know that it can be guaranteed. Hope this clarifies my question.

New Member

Re: OSPF- BGP Influencing routes over 2 carriers

Hi Daniel,

For returned traffic:

- create a tunnel interface btw HQWAN1 and InternetRtr;

- Configure static routes for Host's networks on InternetRtr, with the next-hop of the tunnel interface;

ip route Net-of-Host tunnel x

- Configure lower ospf metric on HQSWAN2 than on HQSWAN1, when redistributing BGP to OSPF.

- you may add tunnel interfaces to OSPF and make them as a passive-interface.

Hote it helps.



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