These are chat archives for Exa-Networks/exabgp

26th
Jan 2017
Vincent Bernat
@vincentbernat
Jan 26 2017 09:37
@thomas-mangin not related to ExaBGP, does encoding multiple next hops in a path attribute require a special capability?
or does it require the add-path capability?
RFC 7911 seems to say that's explicitely why add-path was made for
Vincent Bernat
@vincentbernat
Jan 26 2017 09:42
I was hoping this was more just to say "here are other paths, but they are not best paths for me, kthxbye"
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:39
30 seconds - digging not sure souddainly ..
You can not encode more than one next-hop per route, but you can send the same route multiple times with different next-hop
Vincent Bernat
@vincentbernat
Jan 26 2017 14:41
From my understanding, each one will replace the previous one
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:41
How this is handled by the router is a matter of configuration, it can decide to pick the best route, load-balance ...
Vincent Bernat
@vincentbernat
Jan 26 2017 14:41
without BGP add-path
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:42
I do not think so:
Vincent Bernat
@vincentbernat
Jan 26 2017 14:42
Each next-hop should be in a distinct BGP session then
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:42
By default the best path selection will occur and yes only one route will be programmed in the FIB
No, you should be able to send multiple from the same peer - but I never tried.
Vincent Bernat
@vincentbernat
Jan 26 2017 14:43
From the BGP receiver side, how will it be able to tell if it's a new route that should replace the previous one or if this is an alternative path ?
On juniper, I don't find such a configuration knob, I was surprised. In the documentation, they use BGP add-path, but you need pretty recent JunOS version for that
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:45
I would assume that if more than one route have the same med/localpref/etc. they will be load balanced and only if one is better it replace the previous one, but without a lab - I can not be sure
Vincent Bernat
@vincentbernat
Jan 26 2017 14:46
BIRD has BGP add-path support and if I don't enable it, it sends only one route
would iBGP and eBGP be different about that?
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:46
No, they would be the same
Oh .. hum .. let me check again ..
Vincent Bernat
@vincentbernat
Jan 26 2017 14:47
because Juniper emphasizes iBGP while the RFC says nothing about that
but maybe that's because with eBGP, you are likely to use direct link, while with iBGP, you can use route reflection
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:47
As I do not implement a FIB .. I never really had to ask myself the question
re-reading the RFC
Vincent Bernat
@vincentbernat
Jan 26 2017 14:48
don't bother too much, whatever the right answer is, I don't seem to be able to execute it on JunOS
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:49
I think iBGP or eBGP makes no difference.
"
The use of the ADD-PATH Capability is intended to address specific
needs related to, for example, eliminating route oscillations that
were induced by the MULTI_EXIT_DISC (MED) attribute
"
So clearly it is intended to work on both
what are you trying to achieve ?
Vincent Bernat
@vincentbernat
Jan 26 2017 14:50
I am announcing /32 and I was hoping to get anycast for free
But I use route reflectors (on QFX5100)
and they advertise only the selected active route
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:51
Yes, RR will perform Route Selection before re-advertising
Vincent Bernat
@vincentbernat
Jan 26 2017 14:51
so, I don't get load balancing
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:51
You will need to use add-path there … or use a BGP implementation which deals with it - BIRD does as it is used as RR by many IXes
Vincent Bernat
@vincentbernat
Jan 26 2017 14:52
yes, BIRD works fine with that, but I am directly using the ToR switches as RR
and I get support for additional families
notably BGP EVPN
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:53
Yes, that is a nice design for EVPN .. I can not tell you if JunOS can do it or not .. never had to look for that here
But if your code does EVPN it should do add-path - it is more recent.
Vincent Bernat
@vincentbernat
Jan 26 2017 14:53
I am using EVPN family only in route reflection
it supports add-path in rx mode
not in tx mode
but I just need to update to a more recent version
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:54
lovely .. ok - well - it looks like an upgrade is needed …. :-(
Vincent Bernat
@vincentbernat
Jan 26 2017 14:54
I am just surprised that getting ECMP routes is such a recent feature
Thomas Mangin
@thomas-mangin
Jan 26 2017 14:55
Yes it is ..
Using routers as LB is quite a recent development :smile:
Vincent Bernat
@vincentbernat
Jan 26 2017 15:07
I have already sold that to some clients, so I am a bit worried that I may not be able to execute it :)
Thomas Mangin
@thomas-mangin
Jan 26 2017 15:09
Ooops - to make your life more of a misery : releasing 3.4.19 :facepunch:
Vincent Bernat
@vincentbernat
Jan 26 2017 15:09
I think I missed 3.4.18 then
Thomas Mangin
@thomas-mangin
Jan 26 2017 15:09
Good luck on getting that done !
LOL - no worries
Vincent Bernat
@vincentbernat
Jan 26 2017 15:09
BTW, next Debian will get 3.4.17 since the full freeze is in a week
Thomas Mangin
@thomas-mangin
Jan 26 2017 15:10
It is ok. Just had a user on the ML noticing he needed github for the backport of the connect feature
So I released ...