BGP-IPv4 local preference

LAB3: BGP – IPv4

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LAB 3: Diagram

Note: This Lab was developed on Cisco IOS Version15.2(4) M1 ADVENTERPRISEK9-M. 

LAB3: Configure BGP Local Preference Attributes

Task 1: Configure BGP Local Preference Attributes for Autonomous

• In the configuration mode of router configure BGP Local Preference Attributes by following command:

R2:

router bgp 65000

address-family ipv4

neighbor 11.0.1.1 route-map xyz in

exit

route-map xyz permit 10

set local-preference 5000

exit

(A policy is call on Router R2 that to reach 100 network via 11.0.1.1 through AS 65000 preference is set 5000.)

R1:

router bgp 65100

address-family ipv4

neighbor 22.0.1.2 route-map xyz out

exit

route-map xyz permit 10

set local-preference 10000

exit

(A policy is call on Router R1 that to reach 100 network via 22.0.1.2 through AS 65100 preference is set 10000.)

• Verify IPv4 BGP routes by following command:

R2#show ip bgp

BGP table version is 32, local router ID is 22.0.3.2

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

              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

              x best-external, a additional-path, c RIB-compressed,

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

RPKI validation codes: V valid, I invalid, N Not found

         Network          Next Hop       Metric LocPrf Weight   Path

 *>  11.0.1.0/24      11.0.1.1                  0   5000      0          65100 i

 *>  11.0.2.0/24      11.0.1.1                  0   5000      0          65100 i

 *>  11.0.3.0/24      11.0.1.1                  0   5000      0          65100 i

 *>  22.0.1.0/24      0.0.0.0                    0                 32768            i

 *>  22.0.2.0/24      0.0.0.0                    0                 32768            i

 *>  22.0.3.0/24      0.0.0.0                    0                 32768            i

 *>i 33.0.1.0/24      33.0.1.3                  0    100      0                     i

 *>i 33.0.2.0/24      33.0.1.3                  0    100      0                     i

 *>i 33.0.3.0/24      33.0.1.3                  0    100      0                     i

 *>i 44.0.1.0/24      44.0.1.4                  0    100      0           65200 i

 *>i 44.0.2.0/24      44.0.1.4                  0    100      0           65200 i

 *>i 44.0.3.0/24      44.0.1.4                  0    100      0           65200 i

 *>  100.0.0.0/24     11.0.1.1                       0   5000      0            65100 i

(Local Preference is by default 100 which is seen only on IBGP neighbor 

Local Preference is Local to an Autonomous. It is non-transitive parameter and is stripped of when routes are moving from one AS to another AS. 

R2 - Router R2 now selects 11.0.1.1 as best path because it can reach 100 network through As 65200 with Local Preference 5000, where as to reach 100 network via 44.0.1.4 through AS 65200 with Local Preference 100

Hence path is manipulated with help of Local Preference.

We as an Administrator changed the decision of Router R2 to reach 100.0.0.0 network via 44.0.1.4 to path via 11.0.1.1 as best path. Therefore it shows only one path in its BGP Table and is ironically known as Sukhiram.)

R3# show ip bgp

BGP table version is 25, local router ID is 33.0.3.3

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

              r RIB-failure, S Stale, m multipath, b backup-path, f RT-Filter,

              x best-external, a additional-path, c RIB-compressed,

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

RPKI validation codes: V valid, I invalid, N Not found

     Network          Next Hop            Metric LocPrf  Weight   Path

 *>i 11.0.1.0/24      11.0.1.1                 0       5000      0       65100 i

 *>i 11.0.2.0/24      11.0.1.1                 0       5000      0       65100 i

 *>i 11.0.3.0/24      11.0.1.1                 0       5000      0       65100 i

 *>i 22.0.1.0/24      22.0.1.2                 0       100        0                     i

 *>i 22.0.2.0/24      22.0.1.2                 0       100        0                     i

 *>i 22.0.3.0/24      22.0.1.2                 0       100        0                     i

 *>  33.0.1.0/24      0.0.0.0                   0                      32768            i

 *>  33.0.2.0/24      0.0.0.0                   0                      32768            i

 *>  33.0.3.0/24      0.0.0.0                   0                      32768            i

 *>  44.0.1.0/24      44.0.1.4                 0                       0         65200 i

 *>  44.0.2.0/24      44.0.1.4                 0                       0         65200 i

 *>  44.0.3.0/24      44.0.1.4                 0                       0         65200 i

 *>i 100.0.0.0/24     11.0.1.1                     0         5000         0           65100 i

 *                                   44.0.1.4                     0                            0           65200 i

(R3-As Local Preference is Local to an Autonomous and R3 belongs to same Autonomous, therefore Router R3 will also select best path as 11.0.1.1 but will show both the path in its BGP table and is ironically known as Dukhiram )