BGP with few subnets

[Andrey Avdeev]

Hi team!

I have a question: Now i have my own AS with /22 mask and here is example configuration (with other IPs):

R1:

router bgp 100
bgp log-neighbor-changes
network 150.0.0.0 mask 255.255.252.0 - this pool for ISP
network 150.0.0.0 mask 255.255.255.0 - this pool for DDOS recovery GRE tunnel
neighbor 10.0.0.2 remote-as 100 - iBGP
neighbor 30.0.0.2 remote-as 200 - eBGP
neighbor 30.0.0.2 route-map ISP1_IN in
neighbor 30.0.0.2 route-map ISP1_OUT out

route-map ISP1_IN permit 10
match ip address prefix-list ISP1_IN
set local-preference 300

route-map ISP1_OUT permit 10
match ip address prefix-list ISP1_OUT
set community 100:200

ip prefix-list ISP1_IN seq 5 permit 0.0.0.0/0
ip prefix-list ISP1_OUT seq 5 permit 150.0.0.0/22

R2:

router bgp 100
bgp log-neighbor-changes
network 150.0.0.0 mask 255.255.252.0 
network 150.0.0.0 mask 255.255.255.0 
neighbor 10.0.0.2 remote-as 100
neighbor 30.0.0.2 remote-as 200 
neighbor 30.0.0.2 route-map ISP2_IN in
neighbor 30.0.0.2 route-map ISP2_OUT out

route-map ISP2_IN permit 10
match ip address prefix-list ISP2_IN

route-map ISP2_OUT permit 10
match ip address prefix-list ISP2_OUT
set as-path prepend 100 100

ip prefix-list ISP2_IN seq 5 permit 0.0.0.0/0
ip prefix-list ISP2_OUT seq 5 permit 150.0.0.0/22

Question: what can you say about this configuration? i mean is it normal solution for this situation?

Moreover, when i make "set community (for example) 100:200" at R1  in route-map ISP1_OUT and delete "set as-path prepend 100 100" from R2  route-map ISP2_OUT - > this community makes the  ISP2 more prefer but any IPs from network  150.0.0.0 makes unreachable. Question" why and how?

[paul driver]

Hello

when i make "set community (for example) 100:200" at R1  in route-map ISP1_OUT and delete "set as-path prepend 100 100" from R2  route-map ISP2_OUT - > this community makes the  ISP2 more prefer

Not sure i understand here , prefer for what ?- As-prepending would affect incoming traffic towards your 150.x.x.x/22 network.so when you remove the pre-prepending, which by the way is a higher path attribute (PA) than community PA in the bgp path selection process

Then the route path selection would be down to what/how the ISP's are advertising your network based on whatever (if any) PA they receive for your 150x.x.x/22 

but any IPs from network  150.0.0.0 makes unreachable. Question" why and how?

You saying from within your network (150.0.0./22) you cannot access anything off site-  I see you are using LP to prefer ISP1  as your egress path - How is this being propagated to your Lan and does this just happen when you remove the pre-pending?

res
Paul

[Andrey Avdeev]

HI Paul,

Issue solved!

Thank you for response!