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Beginner

ACI MP-BGP Route preference in Border leaf switches

Hi,

 

If the ACI fabric receives the same route (0.0.00.0) through two different border leafs using two different protocol eBGP and OSPF, how does the border leafs decide to take which path.

 

Link to any documentation would be really helpful

 

LEAF 107, 108 - EBGP -RECEIVING DEFAULT-ROUTE 0.0.0.0 from INTERNET

LEAF 105,106 - OSPF - RECEIVING DEFAULT-ROUTE 0.0.0.0 from other Data center

 

The Leaf 105 & 106 preferring the OSPF Route instead of  iBGP (MP-BGP) route. The leaf 105 &106 is preferring the locally originated OSPF route. How do we change this approach so that leaf 105 & 106 prefer the eBGP default-route. 

 


Thank you in advance

 

Regards,

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Collaborator

Hi @NAGA1 

Do you need the 0/0 prefix learned from the other DC (through OSPF)? It would be much easier to simply filter out (through import route control) or simply not advertise the default route through OSPF.

Alternatively, you can change the AD of OSPF routes to a higher value then iBGP. This is being done through VRF -> OSPF Timers policy -> create a new policy -> change the AD.

However, I think it will still be a better routing design to simply filter out the 0/0 route, unless some requirement to be there as a backup or something.

 

Stay safe,

Sergiu

 

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Hi, Thanks for the reply

 

Do you need the 0/0 prefix learned from the other DC (through OSPF)?  YES ( As a backup route)

 It would be much easier to simply filter out (through import route control) or simply not advertise the default route through OSPF. ( We want other DC OSPF default-route must be available in the entire fabric as a backup route so that  if local internet default-route unavailable then the fabric will pick the OSPF default-route.

 

 

Alternatively, you can change the AD of OSPF routes to a higher value then iBGP. This is being done through VRF -> OSPF Timers policy -> create a new policy -> change the AD. ( We changed the OSPF AD is 201 however it was not working)

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Hmm ok. Let me test that in the lab.

 

Sergiu

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Thanks.

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After you change the OSPF AD, run "show ip bgp 0.0.0/0 vrf [vrf]" from the CLI on the border leaf. What I suspect is that your locally injected route won the BGP path selection algorithm - likely weight, since locally injected routes have a weight of 32768 - which is why the border leaf continued to use the OSPF route despite the higher AD.
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