02-12-2007 07:37 AM - edited 03-03-2019 03:42 PM
Hello,
Guys i have been reading about Local Preference. Wanted to clear my scenario. Input will be appreciated. Following is the
R1------------------------R2
| |
| |
| |
| |
R-3------------------------R-4
Sorry guys, LINES SHOULD BE SHOWING TO BE CONNECTED FROM R2 TO R4. Can't seem to create a straight line between R2 and R4
R-1 and R-2 both are running IBGP (Same AS).
R-3 and R-4 are running IBGP.
R-1 is connected to R-3 ( EBGP Connection)
R-2 is connected to R-4 ( EBGP connection).
Now the scenario is R-3 and R-4 both are sending the same set of Networks towards R1 and R2 respectively for eg (10.10.10.0/24). As the above connection is showing through EBGP.
What i want to acheive is What ever network R4 is sending towards R2. I want R-2 to access it going through R-1 and then to R-3. The networks coming from R-4 to R-2 i wanted to leave as it is with route-maps, just incase R-1 and R-2 connection goes down then R-2 has a way of knowing as to how to get to 10.10.10.0/24.
Let's say R-3 is sending 10.10.10.0/24 to R-1 and R-4 is sending 10.10.10.0/24 to R-2.
When i use Route-map on R-2, my local preference should be like this correct me if i am wrong
On R2#
route-map R1_to_R2_IN permit
match ip address R1_to_R2_IN
set local-preference 200 <---------------- This is correct or not
ip access-list standard R1_to_R2_IN
permit 10.10.10.0 0.0.0.255
route-map R2_to_R1_Out permit
match ip address R2_to_R1_Out
match ip address R2_to_R1_Out
permit 20.20.20.0 0.0.0.255
router bgp xxx
neigh x.x.x.x route-map R1_to_R2_IN
neigh x.x.x.x route-map R2_to_R1_Out
neigh x.x.x.x route-map R4_to_R2_IN
neigh x.x.x.x route-map R2_to_R4_Out
route-map R4_to_R2_IN permit
match ip address R4_to_R2_IN
ip access-list standard R4_to_R2_IN
permit 10.10.10.0 0.0.0.255
route-map R2_to_R4_Out permit
match ip address R2_to_R4_Out
ip access-list standard R2_to_R4_Out
permit 20.20.20.0 0.0.0.255
Solved! Go to Solution.
02-12-2007 09:28 AM
Got it. You can use distribute list to control routing updates. Apply the distribute list outbound in advertisements to R2 on R1 and vice versa. You would need a config similar to this one.
R1:
router bgp xxx
neighbor R2 distribute-list 10 out
access-list 10 permit 10.10.10.0 0.0.0.255
HTH
Sundar
02-12-2007 08:26 AM
As you may know, higher local preference is preferred. Hence, set the local preference to a higher value for Route(s) learnt from R3 on R1 and to a lower value on R2 for route(s) learnt from R4. Thus, all your IBGP/Internal routers would choose the path via R1-->R3 as the preferred path to get to 10.10.10.0/24. Local preference attribute is applicable only within an AS and therefore, you don't have to worry about filtering it on outbound updates to EBGP peers.
You need a configuration like the one noted below.
R1:
route-map from_R3 permit 10
match ip address 10
set local-preference 200
route-map from_R3 permit 20
access-list 10 permit 10.10.10.0 0.0.0.255
router bgp xxx
neighbor R3 route-map from_R3 in
R2:
route-map from_R4 permit 10
match ip address 10
set local-preference 150
route-map from_R4 permit 20
access-list 10 permit 10.10.10.0 0.0.0.255
router bgp xxx
neighbor R4 route-map from_R4 in
HTH
Sundar
02-12-2007 08:39 AM
Hello Sundar,
You have put the Local-preference 200 on Router # 1 so that 10.10.10.0/24 is prioritized from Router # 3
When i create a BGP neighbor on Router # 2 and Router # 1. Don't i have to define that 10.10.10.0/24 network is allowed to come in from Router 1 into Router 2 (IBGP connection) as mentioned in my notes above, and hosts on Router # 2 wants to access 10.10.10.0/24 then due to High local preference use the Router # 1.
Correct me if i am wrong
Regards,
Hassan
02-12-2007 08:53 AM
Hassan,
Unless, you are filtering any prefixes all routes should be advertised to all other BGP peers. I presume you don't want to filter anything you are learning from R1 and hence, there's no need to use route maps there. BGP table on R2 will have 2 paths for 10.10.10.0/24 and it will choose the one via R1 as the preferred path based on the higher local preference.
HTH
Sundar
02-12-2007 09:06 AM
Hello Sundar,
I do not want all routes to be advertised through R1 coming out of R2 and vice versa. That's why i am trying to control it through Route-maps.
Only those networks which R4 and R3 ( Same) are sending to R2 and R1 respectively. That's why i am putting a route-map on Router # 2 of networks which i wanted to learn from Router # 1 and saying if any hosts on Router # 2 wants to access this , then prefer this path. So in our example 10.10.10.0/24 i have put it in route-map in on Router # 2 coming from Router # 1 and have put a local-preference on it. So wouldn't this path will be prioritzed.
Thanks man...
Hassan
02-12-2007 09:28 AM
Got it. You can use distribute list to control routing updates. Apply the distribute list outbound in advertisements to R2 on R1 and vice versa. You would need a config similar to this one.
R1:
router bgp xxx
neighbor R2 distribute-list 10 out
access-list 10 permit 10.10.10.0 0.0.0.255
HTH
Sundar
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