I always use aspath stuffing rather than MED for this kind of thing.
After localpref, the next level of choice for a bgp route is the AS path
length, with shorter winning.
Say you want prefix 1 to always prefer hv1 and prefix2 to prefer hv2. On
hv2, prepend your AS onto prefix 1 and on hv1, prepend your AS onto
prefix2. When the other end receives the routes, it will see that the AS
path length is longer to prefix1 from hv2, so it will always prefer hv1.
If hv1 dies, then it will only have the hv2 route and that will be used.
When hv1 starts advertising prefix 1 again, the traffic will flow back
to hv1.
It may seem a little gross, but it is simple and effective. MEDs are
much trickier and were designed for the case when you have two different
connections through an intervening AS between the source and destination AS.
jerry
On 3/7/17 11:16 AM, Thomas@PhaseHosting wrote:
Supp,
I want to send the med with eBGP to my hosts their routers so i can
influence where the network traffic enters my virtual envirement. I
have 3 hypervisors that run bird.
I can only controll the traffic from my virtual envirement to the
internet, because this runs on bird and ucarp. So through the
hypervisor where the ucarp interface is placed does my traffic leave.
this subnet is also distributed to the other hypervisors through iBGP.
These hypervisors have all an eBGP connection to my hosts addressing
the subnet. So hypervisor 1 isnt the single point of failure. But know
the best route (at my hosts to my subnet) is chosen on router age. So
in case the first hypervisor dies and the second takes over everything
works. but if the first hypervisor comes back alive the eBGP
connection from hypervisor 2 stays because of its age.
I want to send a med value on all the eBGp connections from the
hypervisors. So my hosts routes always first to hypervisor 1 and then
to 2 and so on.
so is this the right configuration to send a med value to my host with
the subnet as static route:
# your default gateway IP below here
protocol bgp eBGP {
import none;
export filter {
where proto = "static_packet";
bgp_med = 100;
};
local as 65000;
neighbor 10.80.x.x as 65530;
password "SECRET";
}
Op 3/7/2017 om 7:08 PM schreef Ondrej Zajicek:
On Tue, Mar 07, 2017 at 03:43:13PM +0100, Thomas@PhaseHosting wrote:
Supp,
thnqx for the reply,
The BGP i have figured out and i have confirmation from my host they
accept
customer-set MEDs. Only i couldn't get these working and i found 2
posts on
the internet with a different configuration and i don't know which
one is
the right one, "med metric 10;" or "default bgp_med 10;"
Am i right that MED is the only option to influence the eBGP and
manipulate
the prefered path? ( Values like AS are the same and others are not
accepted)
Hi
I do not understand if you are trying to manipulate your
hosts/routers (i.e.
outgoing direction) or neighbors routers (i.e. incoming direction).
Both could be influenced by bgp_med attribute (e.g. 'bgp_med = 100;' in
import or export filter) assuming your neighbors are from the same AS.
Option 'default bgp_med' is probably not what you want, that is used
only if
a route with MED is compared to a route without MED.
Option 'med metric' could be used if you want to compare bgp_med
attributes on routes received from different AS numbers. But it is a
true/false option, the MED still must be set in filters.
--
Soundhound Devops
"What could possibly go wrong?"
