Thanks in advance,

I have 3 routers A,B,C connectied in Triangle ,ebgp running between A->C and A->B.Router A on top have BGP peer with AS 34846(ISP 1) and B,C have bgp peer with AS 3356(ISP2) ,All user are connected through router B and C.

I made the chage below on router B to preffer AS 34846 towards ISP1 for prefix 43.252 4.0/22, but it still Preferring path AS 3356 ISP2. All 3 routers gets 0/0 route from my both ISP.

I would like traffic for prefix 43.252.4.0/22 in and out through ISP1 which is peer on router A.

Bit correction with previous config on router B

neigh 95.50.116.53 route-map AS out

Config for router A

router bgp 34846

no synchronization

bgp log-neighbor-changes

network 43.252.12.0 mask 255.255.255.0

network 43.252.4.0 mask 255.255.252.0

neighbor 89.200.130.48 remote-as 4589

neighbor 89.200.130.48 route-map LOCAL_PREF in

neighbor 43.252.0.5 remote-as 10753 <---------peer with router B

neighbor 43.252.0.9 remote-as 10753 <----------peer with router C

maximum-paths 2

no auto-summary

!

ip classless

ip route 43.252.12.0 255.255.255.0 Null0

ip route 43.252.4.0 255.255.255.0 Null0

no ip http server

!

!

ip access-list standard NETOUT

permit 43.252.4.0 0.0.3.255

permit 43.252.12.0 0.0.0.255

!

route-map LOCAL_PREF permit 10

match ip address name NETOUT

set local-preference 200

!

route-map LOCAL_PREF permit 20

!

regards,

Hi,

So you only get default routes but would like to influence traffic for 43.252.4.0/22 specifically through ISP1?

If you do not own 43.252.4.0/22 yourself and this is an internet prefix then the cleanest approach would be to get 43.252.4.0/22 announced by ISP1, as then the longest match would sort out all your issues.

In case this is not possible, you could use a static route in router A towards ISP1 and insert insert it into BGP. Remove all network statements in router B and C with respect to 43.252.4.0/22 and make sure you do not announce the prefix to the internet.

Currently router B prefers the locally inserted prefix because of the weight 32768 set per default. Removing all network statements in router B would remove this issue.

In case you own 43.252.4.0/22 then use your IGP to internally route to the proper destination and use AS path prepending towards your ISPs to influence the return path.

Hope this helps! Please rate all posts.

Regards, Martin

I have also posted the same on the other forum but the issue is confusing as you seem to be saying your accepting the prefix form a peer and you want to local preference it and then equally in the same config your originating the prefix by adding the null0 static route and BGP network statement.

What are you doing advertising it or accepting it in ?

Hi,

I am accepting this from B on router A , so I have removed from the config.

no network 43.252.4.0 mask 255.255.252.0

no ip route 43.252.4.0 255.255.252.0 null0

now prefix 43.252.4.0/22 is coming from router B on A.I like this to go through Isp1 on router A and isp2 on router B as 2nd prefer path.

Also there is ebgp between router A and B.

Please advice.

regards,

Hi

to add more ,43.252.4.0/22 is advertised on router B in BGP , because I have users on this subnet connect by swith which connect to router B.if I remove network command under BGP then it will stop advertising to ISP2 as well on router B , will not I lose internet connection ?.

If your are the owner of that subnet and originating then yes. You will need the network statement and null0 setup.

If you own all three routers you need to setup iBGP between them all so influence the selection within the AS.

HI,

thanks for all but I am still not able to make it work,

I have redone the config as below.

Only i want to do is prefix 43.252.4.0/22 which is connected on router B and C will prefer ISP2 for in/out traffic and ISP1 as backup.I own these 3 routers and prefix 43 and also own 2 diffrent local AS 10753 on router B&C and AS 34846 on router A, and this cant be changed.

Please advice.

Config for router A

router bgp 34846

no synchronization

bgp log-neighbor-changes

neighbor 89.200.130.48 remote-as 4589 <--------ISP2

neighbor 43.252.0.5 remote-as 10753 <---------peer with router B

neighbor 43.252.0.9 remote-as 10753 <----------peer with router C

maximum-paths 2

no auto-summary

---------------------------------------------------------------

RouterB config

router bgp 10753

no synchronization

bgp log-neighbor-changes

network 43.252.4.0 mask 255.255.252.0

neighbor 43.252.0.6 remote-as 34846 <------PEER WITH ROUTERA

neighbor 95.50.116.53 remote-as 3356 <----ISP1

maximum-paths 3

default-metric 100

no auto-summary

IP ROUTE 143.252.4.0 255.255.252.0 NULL0

------------------------------------------

ROUTER C CONFIG

router bgp 10753

no synchronization

bgp log-neighbor-changes

network 43.252.4.0 mask 255.255.252.0

neighbor 43.252.0.10 remote-as 34846 <-----PEER WITH ROUTER A

neighbor 95.50.116.100 remote-as 3356 <---ISP1

maximum-paths 3

default-metric 100

no auto-summary

IP ROUTE 143.252.4.0 255.255.252.0 NULL0

I assume the ip route 143.x.x.x should be 43.x.x.x

I still recommend iBGP between the two B and C routers for attributes to be shared between them.

You will have to as prepend on B and C to your ISP to depref that route (43.x.x.x) and you will have to setup a local preference on B and C taking the internet route or default if your not full routing from A so the return path is from A as you dont prepend that peer and outbound is through A as you set an LP on B & C through A.

A should advertise the prefix it receives (43.x.x.x) from B and C normally as long as your upstream ISP is not prefix list preventing it.

I would also recomend setting soft reconfig on peers for ease of filter changes and peer resets.

hi,

143 is 43,upstream isp2 is recieving 43 prefix with path 34846 10753 .

I am also reciving 0/0 on router A from ISP2 and Router B&C from isp1 and router A.

I can set ibgp between B&C but not with A.

I thought Lcocal_Pref to work you do need ibgp but I am running ebgp between A to B and A to C.

What about changing Weight on B and C for prefix 43.

Regards,

Local preference is non transative so it stays within an AS but iBGP needs to be setup between B&C. I dont see that in your config. Router A may see BGP from B&C but B&C dont have a neighbor statement to each other with their AS set as the remote AS.

Agree, I will set the ibgp between B&C.But really I am worried about A and B cos C will be comming off when A start working properly.but I still wont be able to put ibgp between A&B due to 2 diff local AS.

Regards,