[Firehol-support] better understanding link-balancer and PBR
spike at drba.org
Thu Dec 8 17:23:16 GMT 2016
On Wed, Dec 7, 2016 at 11:16 AM Tsaousis, Costa <costa at tsaousis.gr> wrote:
> So, link-balancer copies the static routes, to provide a seamless
> experience for your static routes. You only need to care about the default
> gateway in policy based routing. All static routes just work.
ah, I get it now, thank you for your patience and clear explanation.
maybe I didn't ask this clearly, lemme try again. I'm wondering if when the
> kernel chooses the default nexthop route in main that triggers another pass
> of the rules or not. Does that make more sense?
> no. policy based routing (ip rules) is applied prior to the routing
> decision. The routing decision is the routing table itself. So a packet is
> to be forwarded, then the policy rules are consulted to decide the routing
> table (this is called policy based routing), then a lookup is made on the
> routing table to decide where to send the packet to.
> hm... I don't know how the routing cache works exactly. I know however,
> that in all cases I have encountered so far, my problem was only the
> iptables connection tracker, especially when NAT is involved or CONNMARK is
> I had to to run conntrack to delete all the rules of the failed gateway,
> to prevent long timeouts.
you mentioned this thing about CONNMARK and FW, could you elaborate on
that? I was just considering what's gonna happen to the connections who
have already been established and MASQUERADED to go out of a certain
link/with a certain ip.
> The whole idea is to keep policy based routing as stable as possible. So,
> link-balancer will never change policy based rules based on the state of
> the gateways. The only change when gateways change state are the default
> gateway of one or more routing tables. It does this optimally. For example,
> if you had PPPoE connections, when a PPPoE link goes down, only the default
> gateway of the tables this gateway is used, is affected (the kernel removes
> the default gateway automatically by itself). So, link-balancer just
> restores a gateway on these tables. Nothing more.
got it, thank you
> The ping-pong is a logical problem. You are using servers on the internet
> to test the gateways. Just make sure these servers are only accessed via
> the same gateway, independently of the state of the gateways. If you
> achieve this, there will no ping-pong. This is also why the RAS of your
> ISPs are probably a better choice. If you have multiple ISPs, you will most
> probably not be able to ping the RAS of ISP A via ISP B.
Thanks for this, you were right, once I setup the static route from the
other thread to solve the problem of no initial routes that also addressed
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