[j-nsp] self-pointing route resolution: static vs. bgp ?

Alexandre Snarskii snar at snar.spb.ru
Thu Oct 22 13:30:00 EDT 2015


Imagine there is a directly connected network: 

A.B.C.40/29   *[Direct/0] 41w1d 00:10:40
                    > via xe-0/0/2.232

There is a good old trick: you can configure 'self-pointing'
host route with next-hop within this network: 

snar at router> show configuration routing-options static route A.B.C.43/32               
next-hop A.B.C.43;

it will be accepted, resolved and installed into routing table:

snar at router> show route A.B.C.43/32 detail 

A.B.C.43/32 (1 entry, 1 announced)
        State: <FlashAll>
        *Static Preference: 5
                Next hop type: Router, Next hop index: 1256
                Address: 0x21a45c90
                Next-hop reference count: 5
                Next hop: A.B.C.43 via xe-0/0/2.232, selected

(this trick was used before introduction vrf-table-label to install 
host routes in vrf's for customers who did not wanted to install CPE).

However, when such self-pointing route is received over iBGP 

snar at router> show route A.B.C.42/32 receive-protocol bgp ...

  A.B.C.42/32 (1 entry, 0 announced)
     Nexthop: A.B.C.42
     MED: 100
     Localpref: 20
     AS path: I

it becomes hidden with Unusable next-hop

snar at router> show route A.B.C.42/32 hidden detail 

A.B.C.42/32 (1 entry, 0 announced)
         BGP    Preference: 170/-21
                Next hop type: Unusable
                Address: 0x24e59bc
                Next-hop reference count: 3
                State: <Hidden Int Ext>
                Localpref: 15
                Indirect next hops: 1
                        Protocol next hop: A.B.C.42
                        Indirect next hop: 0 - INH Session ID: 0x0

and not installed into forwarding table. Well, Juniper documentation
clearly says[1] that it will not accept route pointing to device itself,
but it is not the case, Local address is .41:

A.B.C.41/32   *[Local/0] 44w0d 23:41:25
                      Local via xe-0/0/2.232

Question: are there any way to convince JunOS to resolve and install
such self-pointing route when received over iBGP ?  

12.3R5.7, MX80 if that matters.

Routes can be hidden for the following reasons:
The next hop address is the address of the local routing device.

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