[j-nsp] 6PE without family inet6 labeled-unicast

[Andrey Kostin]

Hello juniper-nsp,

I've accidentally encountered an interesting behavior and wondering if 
anyone already seen it before or may be it's documented. So pointing to 
the docs is appreciated.

The story:
We began to activate ipv6 for customers connected from cable network 
after cable provider eventually added ipv6 support. We receive prefixes 
from cable network via eBGP and then redistribute them inside our AS 
with iBGP. There are two PE connected to cable network and receiving 
same prefixes, so for traffic load-balancing we change next-hop to 
anycast loopback address shared by those two PE and use dedicated LSPs 
to that IP with "no-install" for real PE loopback addresses.
IPv6 wasn't deemed to use MPLS and existing plain iBGP sessions between 
IPv6 addresses with family inet6 unicast were supposed to be reused. 
However, the same export policy with term that changes next-hop for 
specific community is used for both family inet and inet6, so  it 
started to assign IPv4 next-hop to IPv6 prefixes implicitly.

Here is the example of one prefix.

## here PE receives prefix from eBGP neighbor:

uuuu at re1.agg01.LLL2> show route XXXX:XXXX:e1bc::/46

inet6.0: 52939 destinations, 105912 routes (52920 active, 1 holddown, 
24 hidden)
+ = Active Route, - = Last Active, * = Both

XXXX:XXXX:e1bc::/46*[BGP/170] 5d 13:16:26, MED 100, localpref 100
                       AS path: EEEE I, validation-state: unverified
                     > to XXXX:XXXX:ffff:f200:0:2:2:2 via ae2.202

## Now PE advertises it to iBGP neighbor with next-hop changed to plain 
IP:
uuuu at re1.agg01.LLL2> show route XXXX:XXXX:e1bc::/46 
advertising-protocol bgp XXXX:XXXX:1::1:140

inet6.0: 52907 destinations, 105843 routes (52883 active, 6 holddown, 
24 hidden)
   Prefix                  Nexthop              MED     Lclpref    AS 
path
* XXXX:XXXX:e1bc::/46     YYY.YYY.155.141      100     100        EEEE 
I

## Same output as above with details
{master}
uuuu at re1.agg01.LLL2> show route XXXX:XXXX:e1bc::/46 
advertising-protocol bgp XXXX:XXXX:1::1:140 detail  ## Session is 
between v6 addresses

inet6.0: 52902 destinations, 105836 routes (52881 active, 3 holddown, 
24 hidden)
* XXXX:XXXX:e1bc::/46 (3 entries, 1 announced)
  BGP group internal-v6 type Internal
      Nexthop: YYY.YYY.155.141                               ## v6 
prefix advertised with plain v4 next-hop
      Flags: Nexthop Change
      MED: 100
      Localpref: 100
      AS path: [IIII] EEEE I
      Communities: IIII:10102 no-export


## iBGP neighbor receives prefix with tooled next hop and uses 
established LSPs to forward traffic:
uuuu at re0.bdr01.LLL> show route XXXX:XXXX:e1bc::/46

inet6.0: 52955 destinations, 323835 routes (52877 active, 10 holddown, 
79 hidden)
+ = Active Route, - = Last Active, * = Both


XXXX:XXXX:e1bc::/46*[BGP/170] 5d 13:01:12, MED 100, localpref 100, from 
XXXX:XXXX:1::1:240
                       AS path: EEEE I, validation-state: unverified
                       to YYY.YYY.155.14 via ae1.0, label-switched-path 
BE-bdr01.LLL-vvvv-agg01.LLL2-1
                       to YYY.YYY.155.9 via ae12.0, label-switched-path 
BE-bdr01.LLL-vvvv-agg01.LLL2-2
                       to YYY.YYY.155.95 via ae4.0, label-switched-path 
BE-bdr01.LLL-vvvv-agg01.LLL-1
                       to YYY.YYY.155.9 via ae12.0, label-switched-path 
BE-bdr01.LLL-vvvv-agg01.LLL-2

uuuu at re0.bdr01.LLL> show route XXXX:XXXX:e1bc::/46 detail | match 
"Protocol|XXXX:XXXX|BE-"
XXXX:XXXX:e1bc::/46 (3 entries, 1 announced)
                 Source: XXXX:XXXX:1::1:240
                 Label-switched-path BE-bdr01.LLL-vvvv-agg01.LLL2-1
                 Label-switched-path BE-bdr01.LLL-vvvv-agg01.LLL2-2
                 Label-switched-path BE-bdr01.LLL-vvvv-agg01.LLL-1
                 Label-switched-path BE-bdr01.LLL-vvvv-agg01.LLL-2
                 Protocol next hop: ::ffff:YYY.YYY.155.141              
### Seems that IPv4 next hop has been converted to compatible form
                 Task: BGP_IIII.XXXX:XXXX:1::1:240
                 Source: XXXX:XXXX:1::7

## The policy assigning next-hop is the same for v4 and v6 sessions, 
only one term is shown:
uuuu at re1.agg01.LLL2> show configuration protocols bgp group internal-v4 
export
export [ deny-rfc3330 to-bgp ];

{master}
uuuu at re1.agg01.LLL2> show configuration protocols bgp group internal-v6 
export
export [ deny-rfc3330 to-bgp ];


uuuu at re1.agg01.LLL2> show configuration policy-options policy-statement 
to-bgp | display inheritance no-comments
term vvvv-vvvv {
     from {
         community vvvv-vvvv;
         tag 33;
     }
     then {
         next-hop YYY.YYY.155.141;
         accept;
     }
}


uuuu at re0.bdr01.LLL> show route forwarding-table destination 
XXXX:XXXX:e1bc::/46
Routing table: default.inet6
Internet6:
Destination        Type RtRef Next hop           Type Index    NhRef 
Netif
XXXX:XXXX:e1bc::/46 user     0                   indr  1049181    37
                                                  ulst  1050092     4
                               YYY.YYY.155.14     ucst     1775     1 
ae1.0
                               YYY.YYY.155.9     Push 486887     1859    
1 ae12.0
                               YYY.YYY.155.95     ucst     2380     1 
ae4.0
                               YYY.YYY.155.9     Push 486892     2555    
1 ae12.0

The result is that we have IPv6 traffic forwarded via MPLS without 6PE 
configured properly. ipv6-tunneling is configured under "protocols mpls" 
but no "family inet6 labeled-unicast explicit-null" under v4 iBGP 
session.
It works as far as we have v6 enabled on all MPLS links, so packets are 
not dropped because of implicit-null label.
Looks sketchy but it works. Has anybody seen/used it before?

-- 
Kind regards,

Andrey Kostin