Previous posts covered about using Traffic-Engineering bgp-igp vs Mpls Forwarding. Though technically both of them does the same job, there is a huge difference and may short-comings in using bgp-igp

Below is the topology



We have a core-area and R5 router just gets loopback of R4 through BGP via R1 and R5. The policy on R1 is written such that it matches Protocol IGP ospf and a specific Route-Filter for R4 Loopback. Lets look at the policy and bgp peering


Lets look at R1 routing table and also the advertised routes to R5


Lets have a quick look on R5 and see the peering to R4


Now lets introduce the knob – te bgp-igp


As we can see no R4 loopback being set to R5 and this becomes a disaster if your policy is based on IGP match criteria. Using this knob will over-write the inet.3 and put all ldp/rsvp routes in inet.0 which have more Preference/AD than OSPF.

Let see the result in R5 and wrap up



Play with Caution, Its always better to use mpls-forwarding so that both your tables are in-tact and forwarding will be via MPLS for IGP



Rakesh M