BGP multihoming DUAL CE with single link to dual PE

[Halil.Zakaria]

Hello,

my question comes after reading the following cisco article:

http://www.cisco.com/c/en/us/support/docs/ip/border-gateway-protocol-bgp/13762-40.html

I have a question about this part:Load Sharing When Dual-Homed to One ISP Through Multiple Local Routers, please see the attached diagram

with respect to the path selection process, local preference comes before (preferring ebgp over ibgp routes)

given the output below, I don't understand why  R101 ignored the local preference for iBGP route and picked eBGP route

R101# show ip bgp

BGP table version is 5, local router ID is 192.168.12.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete

   Network          Next Hop            Metric LocPrf Weight Path
* i0.0.0.0          192.168.12.2                    100        0          10 i
*>                     10.10.13.3 0                                  0           10 i 

Thank you

[cofee]

Actually both routes have equal local preference which is 100 by default. All the route attributes are equal until they reach step 7 and router 101 is selecting an ebgp route over ibgp.

Below is BGP rib with default local preference:

R1#sh ip bgp

   Network          Next Hop            Metric LocPrf Weight Path
* i0.0.0.0          192.168.12.2             0    100      0 10 i
*>                  10.10.13.3               0                     0 10 I

Route selection changed once I configured higher local preference for routes learning from ibgp neighbor:

R1#sh ip bgp

   Network          Next Hop            Metric LocPrf Weight Path
*>i0.0.0.0          192.168.12.2             0    200      0 10 i
*                   10.10.13.3               0                       0 10 I

R1#sh route-map
route-map test, permit, sequence 10
  Match clauses:
  Set clauses:
    local-preference 200

R1#sh run | sec bgp
router bgp 11
 bgp log-neighbor-changes
 neighbor 10.10.13.3 remote-as 10
 neighbor 192.168.12.2 remote-as 11
 neighbor 192.168.12.2 route-map test in

[cofee · Accepted solution]

Adding "sh ip bgp 0.0.0.0" output showing that both routes have equal local preference by default. This output was taken before manipulating local preference:

R1#sh ip bgp 0.0.0.0
BGP routing table entry for 0.0.0.0/0, version 3
Paths: (2 available, best #2, table default)
  Advertised to update-groups:
     5
  10
    192.168.12.2 from 192.168.12.2 (192.168.12.2)
      Origin IGP, metric 0, localpref 100, valid, internal
  10
    10.10.13.3 from 10.10.13.3 (10.10.34.3)
      Origin IGP, metric 0, localpref 100, valid, external, best

[Halil.Zakaria]

Hello,

I've learnt the lesson : sh ip bgp doesn't show local preference for eBGP routes, subnet parameter needs to be indicated.

I thank you for all your appreciated efforts.