Ühel kenal päeval (reede 17 detsember 2004 20:37) kirjutas Martin A. Brown: > Hello Hasso and Andrea, > > We've gotten a little far afield from Neil Horman's initial question > about why there are primary and secondary IPs, and I can't address your > concern Andrea about the (route cache?) 500ms latency between the time > that an address is added (or removed) from an interface and the time that > the address is actually used. Even so, the Linux routing code allows the > kernel to suggest an IP with the "src" keyword. I know. > : > Why change the primary address? What is wrong with simply changing > : > the route to use the other source IP? > : > : There is no support for it in most of user space software. > : None of the routing protocols suites support it etc. > > Though some software provides support for explicit configuration of > source address for initiated sockets, you can use INADDR_ANY and let the > kernel perform source address selection for you. Well, that's the point - we want to have full control over this selection process without doing fancy things in user space. > Linux select an IP based on the routing table. [0] Example: > > # ip route show 192.168.90.0/24 > 192.168.90.0/24 dev eth0 scope link src 192.168.90.250 > # ip route change 192.168.88.0/24 dev eth0 scope link src $SECONDARY > > If you want to be fancy about it, you can have a higher preference > routing table (make sure there's an entry in /etc/iproute2/rt_tables for > $SECONDARY_TABLE). Then you can add and remove tables in this routing > table instead of changing the route in the main routing table. > > # ip rule add prio table $SECONDARY_TABLE > # ip route add table $SECONDARY_TABLE $DESTNET dev $REALDEV src > $SECONDARY All these tricks don't help if you are using dynamic routing. -- Hasso Tepper Elion Enterprises Ltd. WAN administrator - : send the line "unsubscribe linux-net" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
