[Xorp-hackers] BGP configuration

[Kristian Larsson]

On Fri, Oct 14, 2005 at 09:47:31PM -0700, Atanu Ghosh wrote:
>     Kristian> I have been labbing with BGP now for a while and I have a
>     Kristian> few thoughts about it...  You have to configure local-ip,
>     Kristian> this is something I like, it forces the user to pick a
>     Kristian> interface, be it a loopback for iBGP or a fixed interface
>     Kristian> for eBGP. But the next-hop? Why on earth do I need to set
>     Kristian> a next-hop? Alright if it's an option but it shouldn't be
>     Kristian> required or have I missed something?
> 
> For eBGP peerings we require the next-hop so we have annotated it as
> mandatory. We don't yet have a way of annotating a parameter as
> conditionally mandatory. Even worse at the moment if you configure an
> IPv6 only peering its still necessary to provide an IPv4 nexthop. This
> issue has come up a number of times recently and we have been trying to
> figure out how the condition should be specified. Your example is
> particularly interesting as it would require us to test the local as and
> the peer as for inequality before demanding a next-hop.
Why is it necessary for eBGP?
In my experience eBGP is seldom multihop and when
it is I have never had to specify the next-hop.
Can not such a value be calculated  from the
routing table?

And IPv6, it's a bit confusing that one could
actually specify both ipv4 and ipv6 next-hop 
addresses for one peer. Is it possible to have
"next-hop" receive both v4 and v6 addresses?

Last, isn't "local-ip-address" or "local-address"
more correct than "local-ip" as "ip" is a
protocol and we're talking about an ip address
here. It's just a minor ... ;)

>     Kristian> There's also a small annoying bug. Try doing: create
>     Kristian> protocols bgp set protocols bgp bgp-id 1.1.1.1 set
>     Kristian> protocols bgp local-as 112 commit (everthings fine) create
>     Kristian> protocols bgp peer <peer> commit (it will complain over
>     Kristian> missing arguments) now fill in the mising stuff, local-ip,
>     Kristian> next-hop and as. Try to commit, at least for me it won't
>     Kristian> work.  
> 
> It failed for me when the local-ip was an illegal value, which is very
> bad. It worked when the values were legal.
Strange, it does not for me. It complains on some
resolving error. I can't reproduce now as I lack a
computer to run XORP but I shall try as soon as I
get home.
> 
>     Kristian> I also would like to rename 'protocols bgp peer <peer>
>     Kristian> _as_' to 'peer-as' as it's not crystal clear as to what AS
>     Kristian> (local/peer) 'as' is actually referring to.
> 
> You may be right that peer-as would be clearer. We don't want to break
> existing configurations as soon as we have an aliasing story we can try
> and support both.
No offence here, but do you really think people
are using XORP in production and we need to honour
the old configuration?
Perhaps I am wrong but I still find XORP to be in
it's cradle and so making "drastic" changes like
this should be no problem.
It's better to do it now than later when people
actually start using it.

   Kristian.