Hello all,

We are receiving BGP routes from a number of IX peers over bilateral peering sessions, routes from the IX route servers, a full table from a transit provider and a default route from the colo provider.

What we are looking to do, is advertise a default route to our downstream peers. If we set Default Originate to always or if-installed it will readvertise our colo provider's default route. We've confirmed this by completing a traceroute.

Do we need to aggregate all routes received from our peers and then advertise 0.0.0.0/0 to our downstreams? If so, what's the easiest way to achieve this?

Currently running 7.12 on x86.

Thanks in advance for your help!

If the plan is to advertise only the default route downstream, you can stick with setting the default-originate to always. It doesn't re-advertise your colo provider's default route and gateway (unless you're using iBGP... in which case you should turn on next-hop-self for your downstream peers) but advertises a default route that's all your own. Once traffic arrives at your router, it will follow standard routing rules to decide where the traffic goes. If the colo provider's connection goes down, the default route to your downstreams will remain but your router will blackhole anything it doesn't have a route for once it arrives.

Routeros 7 Filter syntax

https://help.mikrotik.com/docs/display/ ... nd+Filters

If the plan is to advertise only the default route downstream, you can stick with setting the default-originate to always. It doesn't re-advertise your colo provider's default route and gateway (unless you're using iBGP... in which case you should turn on next-hop-self for your downstream peers) but advertises a default route that's all your own. Once traffic arrives at your router, it will follow standard routing rules to decide where the traffic goes. If the colo provider's connection goes down, the default route to your downstreams will remain but your router will blackhole anything it doesn't have a route for once it arrives.

I've got a pair of CCR2004 routers on their way, will play around with it when they arrive. We peer with Google on an IX and when we set default-originate to Always then traceroute to 8.8.8.8 it was routing out via our primary transit peer.

Routeros 7 Filter syntax
https://help.mikrotik.com/docs/display/ ... nd+Filters

How does this help achieve what I'm trying to do? We already have an advanced ruleset configured due to the number of peers and upstream providers we interconnect with.

Which gateway is used to forward packets from the client is not determined by the default route you are originating to the client but by the routing table on your router.