Step 7 - eBGP over iBGP ( 13 step seletion route BGP)

R2#show run | se router bgp

router bgp 2

 no synchronization

 neighbor 10.1.12.1 remote-as 1

 neighbor 10.1.23.3 remote-as 2

 neighbor 10.1.23.3 next-hop-self

 no auto-summary

R2#show ip bgp

BGP table version is 2, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

     Network              Next Hop            Metric LocPrf Weight Path

* > i8.8.8.0/24       10.1.23.3                0    100                         0 i

*                               10.1.12.1                0                                  0 1 i

Nhận xét: R2 học mạng 8.8.8.0/24 qua R3. Break step 4 (lowest length AS-Path)

                 1 - Weight: bằng nhau 0

2. Local prefer: bằng nhau 100

3. Perfer the path was locally..: bằng nhau
4. AS-path:  BREAK

• Giả sử bỏ qua step 4 xét về độ dài AS_PATH

R2#show run | se router bgp

router bgp 2

 bgp bestpath as-path ignore    //command  bỏ qua step 4 xét AS-PATH (bị ẩn trong IOS, hỗ trợ IOS 12.4)

R2#show ip bgp

BGP table version is 2, local router ID is 2.2.2.2

Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,

              r RIB-failure, S Stale

Origin codes: i - IGP, e - EGP, ? - incomplete

   Network                             Next Hop            Metric LocPrf Weight Path

* i8.8.8.0/24                        10.1.23.3                0    100                           0 i

*>                                         10.1.12.1                0                                  0 1 i

Nhận xét: R2 học mạng 8.8.8.0/24 qua R1 (eBgp) over R3 (iBGP)

1. Weight: bằng nhau

2. Local prefer: bằng nhau

3. Perfer the path was locally..: bằng nhau

4. AS-path: không xét.

5. Origin type : bằng nhau

6. Med: bằng nhau = 0

7. Prefer eBGP over iBGP:    BREAK. R2 học 8.8.8.0/24 qua R1 (eBGP) tốt hơn R3 (iBGP)