IPv6 eBGP next_hop

[Mathias Wolkert]

On 10/14/11 15:38 , Ondrej Zajicek wrote:
> On Thu, Oct 13, 2011 at 01:03:52PM +0200, Mathias Wolkert wrote:
>> Hi
>> 
>> I need to alter the next_hop for IPv6 prefixes advertised over
>> IPv6 eBGP.
>> 
>> I'm using a filter that says "bgp_next_hop = x:x:0:1c::1 ;". And
>> it is seen in the birdc6 with: show route all <filtername> as
>> 
>> BGP.next_hop: x:x:0:1c::1
>> 
>> but on the line I see:
>> 
>> Next hop: x:x:0:1c::2 (16)		#The GUA of the router Next hop:
>> fe80::230:48ff:feba:6b17 (16)	#The LL of the router
>> 
>> which also is what I see on the receiving cisco.
>> 
>> Has this behavior changed? i believe I had this working in
>> bird-1.2.5
> 
> I don't think so.
> 
> See 'missing lladdr' option, it is probably related to your
> problem. You probably need to set it to 'ignore'.

So you believe it will send only GUA if I set lladdr to ignore?

> 
>> I'm now running bird-1.3.5 on Debian Lenny.
> 
>> 
>> What I'm really looking for is a way to only send a manually set 
>> globally unique address and no link-local.
>> 
>> When I read the bird docs, it seems odd that this is referred to
>> as a "improper bgp update".
>> 
>> My interpretation of rfc2545 section 3 is that link-local is
>> optional.
> 
> 
> I don't think so:
> 
> The link-local address shall be included in the Next Hop field if
> and only if the BGP speaker shares a common subnet with the entity 
> identified by the global IPv6 address carried in the Network
> Address of Next Hop field and the peer the route is being
> advertised to ...
> 
> That does not sound as optional - if the condition (common subnet) 
> is satisfied, link-local address should be used, otherwise it 
> shouldn't.

Well, I think this is confusing... today when I read it, I agree with you.

> 
> But in some cases it is inevitable, esp. on route servers.
> 
> 
>> My general feeling is that what was simple in IPv4, is not
>> thought through in IPv6.
> 
> I agree, this issue with link-local address in BGP updates is a bit
> ugly.
> 

Thanks for the empathy. :)

/Tias