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londonesx
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BGP blue routes

Tue Jul 12, 2022 4:41 pm

BGP should add only the best routes to the routing table ???

I assembled a simple stand (tested on different versions of 6.x)
A ring of 4 routers connected in series between neighbors.(see attach eBGP_test1-4.png )


BGP was raised on routers and the 1 loopback (10.230.255.x) address was announced
On different routers of this network there is a different number of inactive (blue routes).


I thought that bgp will choose only the best and will not add the rest.
Or If adds all possible paths to the table. then all routers should have the same number of routes.
(see attach Routes01.PNG )


Trying to make filters:
prepend
weight
MED
doesn't really affect the picture.



the only thing i found out
the smallest ID router has the fewest blue routes.
(see attach Routes2-RouterID.PNG )
(config files attached))

The question is, I don’t understand something, or does BGP on Mikrotik have hidden mechanisms for calculating which route to add in blue and which to discard.

I want to have only black routes on all routers (30 routers in a fell mesh topology in the future)
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mrz
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Re: BGP blue routes

Tue Jul 12, 2022 6:36 pm

There can be only one best BGP route.
 
londonesx
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Re: BGP blue routes

Tue Jul 12, 2022 7:02 pm

There can be only one best BGP route.
Do I understand you correctly that there should not be blue routes from BGP?

I attached the configurations of the routers, did I make a mistake somewhere when setting up the BGP?
 
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mrz
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Re: BGP blue routes

Tue Jul 12, 2022 7:16 pm

"Blue" route is not the best route there can be a lot of inactive routes but only one best (Active) to the destination.
 
londonesx
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Re: BGP blue routes

Tue Jul 12, 2022 7:31 pm

"Blue" route is not the best route there can be a lot of inactive routes but only one best (Active) to the destination.
Why is the number of blue routes on routers different?
 
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chechito
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Re: BGP blue routes

Tue Jul 12, 2022 10:31 pm

 
londonesx
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Re: BGP blue routes

Wed Jul 13, 2022 9:41 am

I read it, maybe I missed something, correct me.
So far, I think that the problem is in the BGP.
BGP sends extra routes to RIB.

Reading the description of BGP
https://wiki.mikrotik.com/wiki/Manual:B ... _Algorithm

Of the many routes, the bgp must choose the winner
According to my symmetrical scheme without filters
differences only in AS-PATH And ROUTER ID
And victory must happen at step 5
But it turns out that the router is checked earlier and simply does not reach point 5
 
londonesx
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Re: BGP blue routes

Wed Jul 20, 2022 12:37 pm

I repeated the scheme on cisco in the simulator

10.0.0.0/8 is variably subnetted, 8 subnets, 2 masks
C 10.80.1.0/24 is directly connected, Ethernet1/1
L 10.80.1.1/32 is directly connected, Ethernet1/1
C 10.80.2.0/24 is directly connected, Ethernet1/0
L 10.80.2.1/32 is directly connected, Ethernet1/0
C 10.230.255.81/32 is directly connected, Loopback1

B 10.230.255.82/32 [20/0] via 10.80.2.2, 00:07:42
B 10.230.255.84/32 [20/0] via 10.80.1.2, 00:05:17
B 10.230.255.85/32 [20/0] via 10.80.1.2, 00:03:54

There are no extra routes.
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