JunOS IPv6 announcements over IPv4 BGP

Leo Bicknell bicknell at ufp.org
Fri Dec 21 20:04:13 UTC 2012

In a message written on Fri, Dec 21, 2012 at 11:45:24AM -0700, Pete Ashdown wrote:
> I've got a peer who wishes me to send my IPv6 announcements over IPv4 BGP. 
> I'm running around in circles with JTAC trying to find out how to do this
> in JunOS.  Does anyone have a snippet they can send me?

A believe you got the snippet, but I wanted to expand on why this
is a bad idea.  From a protocol perspective, BGP can create one
session over a particular transport (IPv4, or IPv6 typically) and
then exchange routes for multiple address families (IPv4 unicast,
IPv4 multicast, IPv6 unicast, IPv6 multicast, or even all sorts of
fun MPLS stuff).  From a network management perspective doing so
can complicate things immensely.

Today networks want to deploy IPv6 without impacting their IPv4
network.  Adding IPv6 AFI to an IPv4 transport session will tear
it down, impacting IPv4 customers.

Tomorrow, when IPv4 transport fails, IPv6 customers are also impacted
by the failure of the transport, even though there may be no IPv6
routing issues.  There is also a chance that IPv6 forwarding fails, but
the routing information lives on running the traffic into a black hole
since the routing information isn't sharing the failed transport.

In the future, IPv4 will be removed from the network.  If all of
the transport is IPv4, those sessions will have to be torn down and
new ones built with IPv6 transport before the IPv6 only network can
live on.

I believe the vast majority, approaching 100% of larger ISP's move
IPv4 routes over IPv4 transport, and IPv6 routes over IPv6 transport,
treating the two protocols as ships in the night.  It elminates all
three problems I've listed above at the grand expense of your router
having to open/track 2 TCP connections rather than one; a trivial
amount of overhead compared to the routes being exchanged.

Of course, there are people who like to be different, sometimes for good
reasons, often not... :)

       Leo Bicknell - bicknell at ufp.org - CCIE 3440
        PGP keys at http://www.ufp.org/~bicknell/
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