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iBGP Scenario (03 ISPs)

jimmy20.bpl
Level 1
Level 1

Hello , 

We are working to extend iBGP connectivity. Since have to execute the changes in production environment. Requesting all your help to check & advice.

Current & Working Setup -   

We are having three /24 IP pools-

1) 10.10.1.0/24

2) 10.10.2.0/24  

3) 10.20.1.0/24

We are connected with two ISPs on two different routers (router-1 and router-2). We are advertising both IP pool#1 and 2 on ISP-1 and ISP-2 both.

Pool # 1 (10.10.1.0/24) is taking ISP-1 path and Pool#2 (10.10.2.0/24) is taking ISP-2 Path & in case of failure of either ISP traffic of respective ip pool has been shifted on other functional ISP. This is achieved  through AS path prepend & iBGP. 

Scenario is tested and working well.

Pool#3 is advertised on ISP-3 (third router), which is not connected or communicating to Routers 1 or 2. it's running standalone. 

Proposed Setup - 

Idea is to create iBGP between router -2 and router-3 , such that in case failure of ISP-1 & ISP-2 at same moment ..traffic of Pool#1 & pool#2 can take path for ISP-3. However for reverse case i.e In case of Failover of ISP-3 (router-3) failover of IP pool 10.20.1.0/24 traffic is not require.

Proposed network diagram is attached for more clarity.

We have prepared a configuration, please advice.

Router-A  (No Change Require at this Router)

router bgp 100
no bgp log-neighbor-changes
network 10.10.1.0 mask 255.255.255.0
network 10.10.2.0 mask 255.255.255.0
neighbor 172.16.1.1 remote-as 200
neighbor 172.16.1.1 next-hop-self
neighbor 172.16.1.1 soft-reconfiguration inbound
neighbor 172.16.1.1 route-map AS_PREP out
neighbor 172.16.1.1 filter-list 10 out

neighbor 10.10.1.3 remote-as 100
neighbor 10.10.1.3 next-hop-self
neighbor 10.10.1.3 soft-reconfiguration inbound
neighbor 10.10.1.3 prefix-list default out


ip prefix-list POOL1 seq 5 permit 10.10.2.0/24
ip prefix-list POOL2 seq 5 permit 10.10.1.0/24
ip prefix-list block seq 5 deny 0.0.0.0/0 ge 1
ip prefix-list default seq 5 permit 0.0.0.0/0

route-map AS_PREP permit 10
match ip address prefix-list POOL1
set as-path prepend 100 100 100 100 100

route-map AS_PREP permit 20

access-list 10 permit 10.10.1.0 0.0.0.255
access-list 20 permit 10.10.2.0 0.0.0.255

ip as-path access-list 1 permit ^200$
ip as-path access-list 10 permit ^$


+++++++++++++++++++++++++++

Router-B

router bgp 100
no bgp log-neighbor-changes
network 10.10.1.0 mask 255.255.255.0
network 10.10.2.0 mask 255.255.255.0
neighbor 10.10.1.2 remote-as 100
neighbor 10.10.1.2 version 4
neighbor 10.10.1.2 next-hop-self
neighbor 10.10.1.2 soft-reconfiguration inbound
neighbor 10.10.1.2 prefix-list default out


neighbor 172.16.1.5 remote-as 300
neighbor 172.16.1.5 next-hop-self
neighbor 172.16.1.5 soft-reconfiguration inbound
neighbor 172.16.1.5 route-map AS_PREP out
neighbor 172.16.1.5 filter-list 10 out


neighbor 10.50.1.2 remote-as 100
neighbor 10.50.1.2 version 4
neighbor 10.50.1.2 next-hop-self
neighbor 10.50.1.2 soft-reconfiguration inbound
neighbor 10.50.1.2 route-map AS_PREP out
neighbor 10.50.1.2 filter-list 10 out
neighbor 10.50.1.2 filter-list 20 out


!
ip as-path access-list 1 permit ^300$
ip as-path access-list 10 permit ^$


ip prefix-list POOL1 seq 5 permit 10.10.2.0/24
ip prefix-list POOL2 seq 5 permit 10.10.1.0/24
ip prefix-list block seq 5 deny 0.0.0.0/0 ge 1
ip prefix-list default seq 5 permit 0.0.0.0/0

route-map AS_PREP permit 10
match ip address prefix-list POOL2
set as-path prepend 100 100 100 100 100

route-map AS_PREP permit 20

access-list 10 permit 10.10.2.0 0.0.0.255
access-list 20 permit 10.10.1.0 0.0.0.255

++++++++++++++++++++++++

Router - C (New)


router bgp 100
no bgp log-neighbor-changes

network 10.20.1.0 mask 255.255.255.0
network 10.10.1.0 mask 255.255.255.0
network 10.10.2.0 mask 255.255.255.0

neighbor 172.19.1.1 remote-as 200
neighbor 172.19.1.1 next-hop-self
neighbor 172.19.1.1 soft-reconfiguration inbound
neighbor 172.16.1.1 route-map AS_PREP out
neighbor 172.16.1.1 filter-list 10 out


neighbor 10.50.1.1 remote-as 100
neighbor 10.50.1.1 next-hop-self
neighbor 10.50.1.1 soft-reconfiguration inbound


route-map AS_PREP permit 10
match ip address prefix-list POOL1
set as-path prepend 100 100 100 100 100

route-map AS_PREP permit 20
match ip address prefix-list POOL2
set as-path prepend 100 100 100 100 100


route-map AS_PREP permit 30


ip prefix-list POOL1 seq 5 permit 10.10.2.0/24
ip prefix-list POOL2 seq 5 permit 10.10.1.0/24
ip prefix-list POOL3 seq 5 permit 10.20.1.0/24


access-list 10 permit 10.20.1.0 0.0.0.255


ip as-path access-list 1 permit ^200$
ip as-path access-list 10 permit ^$

Rgds

 

4 Replies 4

jimmy20.bpl
Level 1
Level 1

please advice

Hello All, 

Waiting for suggestions..

This looks good to me but I have some questions on config. 

1) on router B why this command neighbor 10.50.1.2 filter-list 20 out. What you would like to achieve here you already have filter-list 10.

2) Router B must have have route for 10.10.1.0/24 from either any IGP like ospf, eigrp, static or directly connected. I hope you have that.

Hi Pawan, 

Thanks 

I feel, I have not added AS path prepand on Router-1 for third ISP. It should be there.