Why IBGP route is preferred over EBGP?

[AlexSimen96450]

Hi,

I have a simple topology like this:

CE < --- eigrp---> PE1 <---iBGP---> PE2 <---eBGP---> ISP

Initially PE1 router recieved default from CE via EIGRP

Then default route was redistributed into bgp and pass via iBGP to PE2 router

After that I added new eBGP link between PE2 and ISP and now PE2 recieve default route via booth - ISP via eBGp and PE1 via iBGP

But PE2 still prefer iBGP path over eBGP.

Why?

RP/0/RSP0/CPU0:PE2#sh bgp vrf internet 0.0.0.0/0
BGP routing table entry for 0.0.0.0/0, Route Distinguisher: 1.2.3.4:0
Paths: (2 available, best #1)
Path #1: Received by speaker 0
Not advertised to any peer
Local, (received & used)
1.1.1.1 (metric 6) from 11.1.1.1 (1.1.1.1)
Received Label 25294
Origin incomplete, metric 3072, localpref 100, valid, internal, best, group-best, import-candidate, imported
Received Path ID 0, Local Path ID 1, version 244347
Extended community: COST:128:129:3072 EIGRP route-info:0x2:65002 EIGRP AD:264:512 EIGRP RHB:255:1:2560 EIGRP LM:0x0:1:1500 EIGRP AR:65001:10.20.30.1 EIGRP PM:9:0 RT:1.2.3.4:0
Source AFI: VPNv4 Unicast, Source VRF: internet, Source Route Distinguisher: 1.2.3.4:0
Path #2: Received by speaker 0
Not advertised to any peer
65001 65002 65003
10.10.10.1 from 10.10.10.1 (10.10.10.1)
Origin IGP, localpref 100, valid, external, group-best
Received Path ID 0, Local Path ID 0, version 0
Extended community: RT:1.2.3.4:0

[Giuseppe Larosa]

Hello @AlexSimen96450 ,

in MP BGP address family Vpnv4 on in a vrf context the i MP BGP advertisements are considered comparable with true eBGP advertisements coming from a CE in vrf.

The eBGP advertisement has an AS path made of three entries "65001 65002 65003" so I suppose this is the reason why the route coming from the other PE is preferred

You can set a local-preference like 150 in af vrf internet for neighbor 10.10.10.1 to change this choice.

address-family ipv4 vrf internet

neighbor 10.10.10.1 local-preference 150

Hope to help

Giuseppe

[AlexSimen96450]

Giuseppe Larosa, I believe you're right.
Could you tell me where can I read in more details about path selection in MP BGP?

I've changed local preference for the default route but nothing changed.

RP/0/RSP0/CPU0:PE2#sh bgp vrf internet
Network Next Hop Metric LocPrf Weight Path
*>i0.0.0.0/0 1.1.1.1 3072 100 0 ?
* 10.10.10.1 200 0 65001 65002 65003 i

[Martin L]

you changed local preference? to what value? note that 100 is default value of LP, so you would have to change it to higher value. (higher is better)

Regards, ML
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