Prioritising default routes
mludvig at logix.net.nz
Fri Feb 28 03:49:29 CET 2014
Short version: Can I assign different priorities (metrics?) to the same
route inserted by Bird into different routing tables?
I've got a main office router with these uplinks:
- 1x SDSL with BGP, receives national routes
- 1x ADSL with OSPF Cisco modem that advertises default route
- 2x OpenVPN tunnel to our Datacentre (one over each physical
connection) with OSPF that's primarily for internal nets.
The SDSL and Datacentre are with the same ISP and I can propagate our
DMZ subnets over BGP from either location.
Then I've got two routing tables - one for internal LAN and one for DMZ
which has different rules.
In normal circumstances the LAN traffic goes out over ADSL unless there
is a better route learnt from BGP in which case it'd go out over SDSL.
The DMZ traffic (public IPs) always goes out over SDSL, and the DMZ
routing table has a static default rule in that sense.
Now if SDSL goes down - as it did yesterday after a fibre cut down the
- all LAN traffic goes out over ADSL, that's good
- DMZ subnet advertised from DC router over BGP and incoming traffic
arrives over the OpenVPN tunnel (which still works over ADSL).
- all DMZ egress is blocked though until I replace the default route in
DMZ routing table to go via the tunnel to datacentre and from there to
If ADSL goes down...
- LAN traffic is restricted to BGP learned routes (national traffic)
until I add a static default route via SDSL
- DMZ is fine
What I want is an automatic fail over for both LAN and DMZ if any one of
the links fails.
My idea is to advertise a default route over all the uplinks and for the
LAN routing table use them in this order of preference:
1. ADSL (OSPF), 2. SDSL (BGP), 3. one of the tunnels (unlikely if both
physical links are down)
For DMZ routing table do this order:
1. SDSL (BGP), 2. tunnel over ADSL (OSPF), 3. plain ADSL (OSPF)
I know I can manage different routing tables from Bird but how do I
assign different priorities (metrics?) for the same route going into
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