Hi Craig,
Recently I asked in this list exactly the same question, how legit is
to not use "family inet6 labeled-unicast explicit-null" but just change
next-hop to IPv4 address for IPv6 BGP session. After some discussion I
was pointed out to RFC4798 that states
The 6PE routers MUST exchange the IPv6 prefixes over MP-BGP
sessions as per [RFC2545] running over IPv4. The MP-BGP Address
Family Identifier (AFI) used MUST be IPv6 (value 2). In doing
so,
the 6PE routers convey their IPv4 address as the BGP Next Hop for
the advertised IPv6 prefixes. The IPv4 address of the egress 6PE
router MUST be encoded as an IPv4-mapped IPv6 address in the BGP
Next Hop field. This encoding is consistent with the definition
of an IPv4-mapped IPv6 address in [RFC4291] as an "address type
used to represent the address of IPv4 nodes as IPv6 addresses".
This is not exactly how it works in our case, because next sentence
states that label MUST be provided for such prefixes:
In addition, the 6PE MUST bind a label to the IPv6 prefix as per
[RFC3107]. The Subsequence Address Family Identifier (SAFI) used
in MP-BGP MUST be the "label" SAFI (value 4) as defined in
[RFC3107].
For IPv6 BGP session AFI/SAFI is 2/1 instead of 2/4 as per RFC, however
it works.
Just for the record, possible AFI/SAFI combinations can be found here:
https://www.juniper.net/documentation/en_US/junos/topics/usage-guidelines/routing-enabling-multiprotocol-bgp.html
Following example makes me thinking that if IPv6 unicast session is
configured between mapped IPv4 addresses it may work without any
next-hop tooling and traffic will use MPLS tunnels if they exist:
https://www.juniper.net/documentation/en_US/junos/topics/example/bgp-ipv6.html
You are probably also aware that you have to run IPv6 in the core
because explicit-null label is not assigned in this case and you need
family inet6 on the ingress interface of egress PE. As long as this
condition met it works, no caveats or issues found so far.
craig washington писал 29.08.2018 10:55:
So my fix was leaving everything as is and just changing the next-hop
from self to the IPv4 address of the advertising PE under the v6
group
which is basically what would be happening anyway if I deleted the
groups and added everything to the v4 group.
My overall goal was to try to get IPv6 prefixes to use the same LSP's
as their IPv4 counterparts with as little trouble as possible. (not
adding new protocols or changing existing protocols if possible)
Simplest way I found was just changing the next hop. Everything
worked as expected when that was done.
I just didn't know if there was anything else anyone else was doing
of if anyone came across a similar situation.
--
Kind regards,
Andrey Kostin
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