One reason that may force others down this track comes from exceeding the # of configurable BGP sessions on a box (think chassis switches). It does add a good bit of complexity in the initial roll-out but it's really not all that bad once you get used to it. The one piece that seems to make it a little easier is that you get a consolidated view on some devices, where the prefix counts are shown for both address families under the same "show ip bgp neighbor" display.
david. On Fri, Dec 21, 2012 at 3:04 PM, Leo Bicknell <bickn...@ufp.org> wrote: > 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 - bickn...@ufp.org - CCIE 3440 > PGP keys at http://www.ufp.org/~bicknell/
