Junos OS

Hi,

I have  a BGP session there I receive a route with mask /16 

I want to leake only the first /24 from the /16 to another routing instance.

I know that I can use a static route with next-hop <another routing-instance>, but I would like to avoid this.

Is it possible with RIB leaking?

Configuration example?

Thank Niklas

Hi,

I believe it would be possible to leak the routes if there's an active route for the /24 in the primary routing-table.

Example:

set routing-instances TEST protocols bgp family inet unicast rib-group BGP
set routing-options rib-groups BGP import-rib [ TEST.inet.0 TEST1.inet.0 ]
set routing-options rib-groups BGP import-policy IMPORT-RIB
set policy-options policy-statement IMPORT-RIB term BGP from route-filter x.x.x.0/24 exact
set policy-options policy-statement IMPORT-RIB term BGP then accept
set policy-options policy-statement IMPORT-RIB then reject

If there's no /24 active route in the primary routing-table, a static route for the /24 may need to be added.

However, adding a static discard route to then leak in rib-groups would result in traffic blackhole.  So the /24 static route would require a valid next-hop.

set routing-instances TEST routing-options static route x.x.x.0/24 next-hop z.z.z.z
set routing-instances TEST routing-options static rib-group STATIC
set routing-options rib-groups STATIC import-rib [ TEST.inet.0 TEST1.inet.0 ]
set routing-options rib-groups STATIC import-policy IMPORT-RIB 

Cheers,

Ashvin

Hi,

Is the static route I'm trying to avoid.

If the /16 is removed from bgp the route leaking prefix should also disappear.

//Niklas

Hi, 

Maybe you could use a generate route.

Cheers,

Ashvin

Hi,

Unfortunately, the generated route would not work as well as we are trying to generate a more specific route.

"A generated route becomes active when it has one or more contributing routes. A contributing route is an active route that is a more specific match for the generated destination. For example, for the destination 128.100.0.0/16, routes to 128.100.192.0/19 and 128.100.67.0/24 are contributing routes, but routes to 128.0.0.0./8, 128.0.0.0/16, and 128.100.0.0/16 are not."

Is it not possible to receive the /24 route from the BGP neighbor?

Cheers,

Ashvin

unfortunately not

//Niklas

Hi,

Although it does not seem very neat, I believe you could do this by adding static route for the /24 with a next-hop resolve, the next-hop being a route part of the /16. Example:

set routing-options static route 172.17.0.0/24 next-hop 172.17.255.254 resolve

Test Result:

root@PE1# run show route table TEST.inet.0 172.17.0.0/16 

TEST.inet.0: 19 destinations, 23 routes (19 active, 0 holddown, 1 hidden)
+ = Active Route, - = Last Active, * = Both

172.17.0.0/16      *[BGP/170] 00:20:40, localpref 100
                      AS path: 65001 I, validation-state: unverified
                    > to 10.2.2.2 via ge-0/0/5.0
172.17.0.0/24      *[Static/5] 00:18:07, metric2 0
                    > to 10.2.2.2 via ge-0/0/5.0

[edit]
root@PE1# run show route table TEST1.inet.0 172.17.0.0      

TEST1.inet.0: 5 destinations, 5 routes (5 active, 0 holddown, 0 hidden)
+ = Active Route, - = Last Active, * = Both

172.17.0.0/24      *[Static/5] 00:00:24, metric2 0
                    > to 10.2.2.2 via ge-0/0/5.0

When /16 is not present:

root@PE1# run show route table TEST.inet.0 172.17.0.0/16    

TEST.inet.0: 18 destinations, 22 routes (17 active, 0 holddown, 2 hidden)

[edit]
root@PE1# run show route table TEST1.inet.0 172.17.0.0/16   

TEST1.inet.0: 5 destinations, 5 routes (4 active, 0 holddown, 1 hidden)

[edit]
root@PE1# run show route table TEST1.inet.0 172.17.0.0/16 hidden 

TEST1.inet.0: 5 destinations, 5 routes (4 active, 0 holddown, 1 hidden)
+ = Active Route, - = Last Active, * = Both

172.17.0.0/24       [Static/5] 00:00:19
                      Unusable

[edit]
root@PE1# run show route table TEST.inet.0 172.17.0.0/16 hidden     

TEST.inet.0: 18 destinations, 22 routes (17 active, 0 holddown, 2 hidden)
+ = Active Route, - = Last Active, * = Both

172.17.0.0/24       [Static/5] 00:23:49
                      Unusable

Cheers,

Ashvin