On Wed, Aug 13, 2014 at 10:27:01AM +0100, Alex Bligh wrote:
Ondrej,
On 13 Aug 2014, at 10:03, Ondrej Zajicek <santiago@crfreenet.org> wrote:
In short, the default values depends in this direction:
EBGP|IBGP -> direct|multihop -> gateway direct|recursive
Changing former would change the default value for later, but not otherwise.
Not sure I understand that.
The session is IBGP. It is not multihop (by which I mean it's on the same subnet), but AFAICT bird thinks it is.
Generally, by 'direct BGP session' or 'multihop BGP session' i mean the mode of operation of that BGP sesssion; i.e., whether it is expected to be on the same subnet, not whether it is really on the same subnet. The mode of operation cannot be reliably detected from the network topology, because the topology could change during the operation. E.g.: You have BGP neighbor 192.168.1.10 and two interfaces: eth0 with 192.168.1.1/24 and eth1 with 192.168.2.1/24. If the BGP session is in direct mode, it always uses eth0, packets are sent with TTL 1 and the session automatically shutdowns when eth0 is disabled. If the BGP session is in multihop mode, it reaches 192.168.1.10 based on IGP routes, which is probably a direct route through eth0, but could be rerouted by IGP (without dropout of the BGP session) through indirect hop over eth1 when eth0 is disabled.
How do I change it to a 'direct' (as opposed to multihop) session?
Use 'direct' option: <tag>direct</tag> Specify that the neighbor is directly connected. The IP address of the neighbor must be from a directly reachable IP range (i.e. associated with one of your router's interfaces), otherwise the BGP session wouldn't start but it would wait for such interface to appear. The alternative is the <cf/multihop/ option. Default: enabled for eBGP. I
think you are saying it's defaulting to a multihop configuration (and thus 'gateway' defaults to 'recursive'), as opposed to it detecting a multihop session.
Also, you cannot (it would seem) change to 'gateway direct' as you get the error.
At the very least I think there is a documentation error as it says 'gateway direct' is the default.
It only says that 'gateway direct' is the default for 'direct' sessions, which is true. -- Elen sila lumenn' omentielvo Ondrej 'Santiago' Zajicek (email: santiago@crfreenet.org) OpenPGP encrypted e-mails preferred (KeyID 0x11DEADC3, wwwkeys.pgp.net) "To err is human -- to blame it on a computer is even more so."