Swap route priority in different routing tables

[Ondrej Zajicek]

On Thu, Nov 26, 2020 at 12:59:13PM +0100, Gianguido wrote:
> Hi all,
> 
> I have two sites, two links in between, one is high bandwith/high latency
> (HB), the other is low bandwidth/low latency (LB), bird 1.6.8.
> I neet all traffic to flow on HB link except for real time, which in my case
> is RTP that goes through LB. To achieve this, I'm using PBR with two kernel
> routing tables: main should have HB route as preferred route, low_latency
> should have LB as preferred. Should any of the two fail, all traffic needs
> to be routed on the other link.
> 
> Problem is to properly populate the tables. Local interface states are not
> reliable in terms of actual link availability, and anyways I'm already using
> OSPF in the whole network setup.
> Currently in bird OSPF runs and populate the main table, then I have a
> dedicated pipe+kernel populating the low_latency one. Of course OSPF elects
> the preferred route based on link costs, so only that route gets into bird
> routing table, and it's the only one that can be eventually piped into
> low_latency table. This way, all traffic goes either HB or LB depending on
> OSPF link costs because the two routing tables are identical.
> 
> Is there a way to get both routes learnt through OSPF into bird table and
> then apply a filter to the pipe in order to swap the preference when
> propagating those routes into the low_latency table? Or any other suggestion
> to rework this in order to achieve the goal above?

Hi

Not really, OSPF does not work this way. You can use different routing
protocols (e.g. BGP with BFD for quick failover), or use two OSPF
instances with different 'instance id' and metrics.

-- 
Elen sila lumenn' omentielvo

Ondrej 'Santiago' Zajicek (email: santiago at crfreenet.org)
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"To err is human -- to blame it on a computer is even more so."