Click the Exhibit button. Referring to the exhibit, you must advertise the 100.0.0.0/16 routes from AS1 to AS2, but R2 is not advertising any BGP routes to R5. Why is this happening in this scenario?
A.
The IBGP routes will not be advertised because you must use a policy to advertise IBGP routes.
B.
The IBGP routes are not active and EBGP will advertise only active routes.
C.
The IBGP routes will not be advertised because the AS path shows as incomplete.
D.
The IBGP routes are not active because the next hop is not reachable.
Guys, you are bit wrong. The question is "Why R2 is not advertising any BGP routes to R5?". The BGP routes are known but in this case they are inactive because of ISIS routes have pushed them out. Default BGP export policy behavior is advertising all the *active* BGP routes to eBGP neighbor.
I agree - I was immediately looking for the protocol designations and they sneakily took them out of the output.
I was thinking I stood for iBGP stupidly, but of course it's ISIS, thus, the BGP routes aren't active and cannot be redistributed to the neighbour.
As mentioned, by default, BGP advertises ALL active BGP routes without any policies.
I know this from first hand experience, if you have the full routing table, it's very easy to leak it without creating proper filters :)
https://www.juniper.net/documentation/en_US/junos/topics/concept/policy-routing-policies-actions-defaults.html
Default BGP Export Policy:
Readvertise all active BGP routes to all BGP speakers, while following protocol-specific rules that prohibit one IBGP speaker from readvertising routes learned from another IBGP speaker, unless it is functioning as a route reflector.
my 5 cents, I played with prefix 3.3.3.3/32, it was not advertised because ISIS won (low preference 18 vs 170)
ed@vMX-PE1# run show route table inet.0 terse 3.3.3.3/32
inet.0: 14 destinations, 17 routes (14 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
A V Destination P Prf Metric 1 Metric 2 Next hop AS path
* ? 3.3.3.3/32 I 18 10 >10.0.13.3
? B 170 100 0 3 I
unverified >10.0.13.3
[edit]
ed@vMX-PE1# run show route advertising-protocol bgp 2.2.2.2
inet.0: 14 destinations, 17 routes (14 active, 0 holddown, 0 hidden)
Prefix Nexthop MED Lclpref AS path
* 3.3.3.33/32 10.0.13.3 0 125 3 I
* 10.0.13.0/24 Self 125 I
[edit]
3.3.3.3/32 is advertised to peer now
ed@vMX-PE1# run show route advertising-protocol bgp 2.2.2.2
inet.0: 14 destinations, 17 routes (14 active, 0 holddown, 0 hidden)
Prefix Nexthop MED Lclpref AS path
* 3.3.3.3/32 10.0.13.3 0 125 3 I
* 3.3.3.33/32 10.0.13.3 0 125 3 I
* 10.0.13.0/24 Self 125 I
[edit]
ed@vMX-PE1# run show route table inet.0 terse 3.3.3.3/32
inet.0: 14 destinations, 17 routes (14 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
A V Destination P Prf Metric 1 Metric 2 Next hop AS path
* ? 3.3.3.3/32 B 170 100 0 3 I
unverified >10.0.13.3
? I 171 10 >10.0.13.3
[edit]
Team, I was wrong, sorry for that, I tested again, and the route is advertised from ibgp to eBGP if it is the best
ed@vMX-PE1# run show route advertising-protocol bgp 10.0.13.3
inet.0: 14 destinations, 18 routes (14 active, 0 holddown, 0 hidden)
Prefix Nexthop MED Lclpref AS path
* 10.0.24.0/24 Self I
[edit]
ed@vMX-PE1# run show route 10.0.24.0/24 terse
inet.0: 14 destinations, 18 routes (14 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both
A V Destination P Prf Metric 1 Metric 2 Next hop AS path
* ? 10.0.24.0/24 B 170 200 I
unverified >10.0.0.2
? S 250 >ipip.0
[edit]
without any policy, so correct answ. is "B"
ed@vMX-PE1# show protocols bgp group eBGP | display set
set protocols bgp group eBGP type external
set protocols bgp group eBGP family inet unicast rib-group inet0-to-test
set protocols bgp group eBGP peer-as 3
set protocols bgp group eBGP neighbor 10.0.13.3
[edit]
ed@vMX-PE1#
yes, should be A
https://www.juniper.net/documentation/en_US/junos/topics/reference/command-summary/show-route-terse.html
An asterisk (*) indicates this is the active route.
https://www.letsconfig.com/how-to-advertise-bgp-routes-in-juniper/
Routes advertisement will be completed in two steps. These are- 1. adding policy-statement, and 2. adding policy in bgp group.
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