Hi Harry,
> default, differences in route preference cause a JUNI to prefer an
> IGP route while ios prefer the bgp routs over IGP.
Let's make a clear distinction between preferring eBGP route versus iBGP
route. Talking CSCO here eBGP admin distance is as you say 20 while iBGP
as even the URL provided by yourself says it is 200.
So keeping in mind that usually hot potato routing is a desired
behaviour preferring EBGP learned path is highly recommended for a given
prefix.
If you say that JUNI is to prefer IGP route over BGP one I am sure you
must be referring to IBGP and not EBGP, but this is exactly the same in
both vendors.
> W/o this knob replacing a cisco with a juniper can result in
> previously advertised bgp routes no longer being advertised.
I can rest assure you that this was not the main intention of this knob :)
Cheers,
R.
I always thought that advertise-inactive was to make a juniper act
like a cisco with regard to BGP route announcements, when, by
default, differences in route preference cause a JUNI to prefer an
IGP route while ios prefer the bgp routs over IGP.
In junos, only the active route is readvertised/subject to export
policy. With advertise-inactive you can make a juniper router, whose
active route is an IGP route, advertise into BGP the "best bgp path",
which here is inactive due to the igp route being preferred.
W/o this knob replacing a cisco with a juniper can result in
previously advertised bgp routes no longer being advertised.
From:
http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094823.shtml
eBGP 20
. . .
OSPF 110
From:
http://www.juniper.net/techpubs/software/junos/junos64/swconfig64-routing/html/protocols-overview4.html
OSPF internal route 10
IS-IS Level 1 internal route 15 . . .
BGP 170
HTHS.
-----Original Message----- From: juniper-nsp-boun...@puck.nether.net
[mailto:juniper-nsp-boun...@puck.nether.net] On Behalf Of Keegan
Holley Sent: Wednesday, August 10, 2011 2:48 PM To:
rob...@raszuk.net Cc: juniper-nsp@puck.nether.net Subject: Re:
[j-nsp] load balancing in Route reflector scenario
2011/8/10 Robert Raszuk<rob...@raszuk.net>
Hi Keegan,
I think the advertise inactive knob turns that off, but I don't
know for
sure because I've never tried it. I know it's not supported on
cisco routers. The reason for it is the size of the BGP table.
So if the table is 400k routes and you have 5 different ISP's and
you advertise every route that would be 2M routes in the table.
Since BGP doesn't allow multiple version of the same route in the
routing table (separate from the BGP table where incoming routes
are stored) you would still only use the original 400K the other
1.8M routes would just go unused unless you manipulated them some
how.
Advertise inactive is not about what get's advertised - it is about
if the best path is advertised or not. And if is decided based on
the check if the BGP path to be advertised is inserted in the
RIB/FIB or not.
Oh I see. I have never used that command so thanks. Most of the
above example was what would happen if BGP advertised everything it
learned instead of just the best path or the path in the routing
table btw.
By default Junos and IOS-XR advertise only those best path in BGP
which actually are installed into forwarding. Advertising inactive
knob will overwrite it.
Wouldn't this lead to traffic being blackholed? If all the routes
for a given destination are inactive would this still cause BGP to
advertise a route for them?
IOS classic/XE (for historical reasons) advertises all best paths
from BGP table and to enforce it not to advertise what has not
been installed into RIB/FIB there is knob called "suppress
inactive".
Cheers, R.
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