[j-nsp] confederation bgp - path selection

[Aaron Gould]

I'm working through a Confederation Lab for JNCIP-SP study

 

Why is r3 choosing that the prefix with the longer AS PATH is better ?

 

I thought shortest AS Path was typically more attractive

 

JNCIP book...
https://www.juniper.net/assets/us/en/local/pdf/study-guide/study-guide-jncip
.pdf 

 

on page 444 of 708  ...the topology is just one page prior...

 

4th bullet...

 

- Configure r1 and r2 to redistribute a 192.168.100/24 static route into
IBGP and ensure that all other routers forward through r1 when its IBGP
session is up.   ( i haven't done any tweaks on attributes yet to make r1
more attractive because i wanted to first understand why r2's path is
preferred from r3's perspective even though it has longer AS PATH )

 

i wonder if this has something to do with it - "Inactive reason: Not Best in
its group - Router ID"

 

[edit]

r3 at lab-mx104:r3# run show route receive-protocol bgp 10.0.6.1 192.168.100.0

 

inet.0: 38 destinations, 41 routes (38 active, 0 holddown, 0 hidden)

  Prefix                  Nexthop              MED     Lclpref    AS path

  192.168.100.0/24        10.0.6.1                     100        I

 

[edit]

r3 at lab-mx104:r3# run show route receive-protocol bgp 10.0.2.6 192.168.100.0

 

inet.0: 38 destinations, 41 routes (38 active, 0 holddown, 0 hidden)

  Prefix                  Nexthop              MED     Lclpref    AS path

* 192.168.100.0/24        10.0.6.2                     100        (65001) I

 

[edit]

r3 at lab-mx104:r3# run show route protocol bgp 192.168.100.0

 

inet.0: 38 destinations, 41 routes (38 active, 0 holddown, 0 hidden)

+ = Active Route, - = Last Active, * = Both

 

192.168.100.0/24   *[BGP/170] 00:51:05, localpref 100, from 10.0.2.6

                      AS path: (65001) I, validation-state: unverified

                    > to 10.0.4.2 via lt-0/1/0.32

                    [BGP/170] 00:50:56, localpref 100, from 10.0.6.1

                      AS path: I, validation-state: unverified

                    > to 10.0.4.14 via lt-0/1/0.31

 

[edit]

r3 at lab-mx104:r3# run show route protocol bgp 192.168.100.0 detail

 

inet.0: 38 destinations, 41 routes (38 active, 0 holddown, 0 hidden)

192.168.100.0/24 (2 entries, 1 announced)

        *BGP    Preference: 170/-101

                Next hop type: Indirect

                Address: 0x2bd4e80

                Next-hop reference count: 6

                Source: 10.0.2.6

                Next hop type: Router, Next hop index: 874

                Next hop: 10.0.4.2 via lt-0/1/0.32, selected

                Session Id: 0x158

                Protocol next hop: 10.0.6.2

                Indirect next hop: 0x2c68110 1048622 INH Session ID: 0x201

                State: <Active Int Ext>

                Local AS: 65000 Peer AS: 65001

                Age: 51:08      Metric2: 1

                Validation State: unverified

                Task: BGP_65001.10.0.2.6+50172

                Announcement bits (3): 2-KRT 4-BGP_RT_Background 5-Resolve
tree 2

                AS path: (65001) I

                Accepted

                Localpref: 100

                Router ID: 10.0.3.4

         BGP    Preference: 170/-101

                Next hop type: Indirect

                Address: 0x2bd4844

                Next-hop reference count: 4

                Source: 10.0.6.1

                Next hop type: Router, Next hop index: 1099

                Next hop: 10.0.4.14 via lt-0/1/0.31, selected

                Session Id: 0x152

                Protocol next hop: 10.0.6.1

                Indirect next hop: 0x2c68000 1048575 INH Session ID: 0x1fc

                State: <NotBest Int Ext>

                Inactive reason: Not Best in its group - Router ID

                Local AS: 65000 Peer AS: 65000

                Age: 50:59      Metric2: 1

                Validation State: unverified

                Task: BGP_65000.10.0.6.1+179

                AS path: I

                Accepted

                Localpref: 100

                Router ID: 10.0.6.1

 

 

- Aaron Gould