[j-nsp] confederation bgp - path selection

[Dave Bell]

From:

https://www.juniper.net/documentation/en_US/junos12.3/topics/reference/general/routing-ptotocols-address-representation.html


"A confederation segment (sequence or set) has a path length of 0. "

On 12 June 2017 at 13:53, Aaron Gould <aaron1 at gvtc.com> wrote:

> 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
>
>
>
>
>
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