eBGP with two ISPs

RouterOS Forwarding Protocols
1

Hi..

can any one help, how can we configure ebgp with 2 diffrent isp. and auto fail over also.

Thanks in advance.

Ravish

2

Set up BGP peers to both isps
advertise your network
Set up routing filters for backup peer to prepend AS path.

3

Dear mrz,

thanks for the info,

i would like to know how do i assign ..path prepend.

can i have example ..pls

thanks

4

it is done by routing filters
for example prepend as three times
/routing filter
add chain= prefix=x.x.x.x/y set-bgp-prepend=3

5

dear sir,


i have many /24 blocks. i have two isp provider.

i want advertise some /24 blocks with isp1 and remaining with isp 2.

i have confiured bgp with two peers, bgp is established.

now how can advetise three /24 subnets with isp1 and 2 /24 subnets with isp 2.
and how to create route filter for backup failover.

Thanks
ravish

6

for example you have peer1 and peer2
and address blocks
x.x.1.0/24
x.x.2.0/24
x.x.3.0/24
x.x.4.0/24
x.x.5.0/24

/routing bgp peer
set peer1 out-filter=peer1-out
set peer2 out-filter=peer2-out

is you don't have corresponding route in routing table, disable sync

/routing bgp network
add network=x.x.1.0/24
add network=x.x.2.0/24
...
add network=x.x.5.0/24

/routing filter
add chain=peer1-out prefix=x.x.1.0/24 action=accept
add chain=peer1-out prefix=x.x.2.0/24 action=accept
add chain=peer1-out prefix=x.x.3.0/24 action=accept
add chain=peer1-out action=accept set-bgp-prepend=3

add chain=peer2-out prefix=x.x.4.0/24 action=accept
add chain=peer2-out prefix=x.x.5.0/24 action=accept
add chain=peer2-out action=accept set-bgp-prepend=3

BGP over two ISP with default route sending only
7

Dear mrz,

as u said its working, but there is some strange problem ia ma seeing,

i have advertised

xxx.xxx.1.0/24 --peer1
xxx.xxx.2.0/24 --peer1

xxx.xxx.3.0/24 --peer2
xxx.xxx.4.0/24 --peer2

both are advertising properly, but for testing i have stoped using peer2 ip blocks. but still the usage shows in peer2 connected ethernet interface. when put torch on the interface, src address are showing peer1 advertised list.

what could be the problem?

thanks
Ravish

8

Outbound traffic will still go out via peer 2 if that’s a better route. If you want to change this behaviour so peer 2 is only a backup look at changing the local preference on routes learned through one of the peers.