BGP Prepend not working (CCR with RouterOS 6.5)

RouterOS Forwarding Protocols
1

CCR 1036
RouterOS 6.5

BGP Prepend Filter is not having any affect. I’ve confirmed this with both upstream providers (Cogent and TWTelecom). When I have a filter setup they are not seeing any prepend on their end and the traffic is still the same when a prepend is set or not, so I’m not able to depriortize a particular network on provider

add network=38.121.0.0/20 synchronize=no
add network=38.121.16.0/20 synchronize=no

/routing bgp peer
add in-filter=cogent-in name=“cogent” out-filter=cogent-out remote-address=38.104.232.97 remote-as=174 ttl=default
add in-filter=tw-in multihop=yes name=twtelecom out-filter=tw-out remote-address=64.128.204.49 remote-as=4323 ttl=default

/routing filter
add action=accept chain=tw-out prefix=38.121.0.0/20 set-bgp-prepend=4
add action=accept chain=tw-out prefix=38.121.16.0/20 set-bgp-prepend=4
add action=accept chain=tw-out
add action=accept chain=tw-in

I’ve tried both ‘accept’ and ‘passthrough’. I’ve disabled and reenabled the peers. 80% of the traffic prefers the TWTelecom route even when I prepend=1, 2, 3, or 4. TWTelecom says they are not seeing the Prepend. Cogent said the same when I tested another ip block we BGP with them.

Any ideas on what to try?

2

Disable the filter the enable it

3

We have tried disabling and enabling the filters, it doesn’t help, prepend still not working.

4

Hi Brian,

I just looked over your filters and they do indeed look correct.

The other thing we have had work is moving the policy order.

I often will paste in a bunch of filter rules that work perfectly on another router, then have to move them around enable/disable them in winbox to get them working.