On Tuesday 05 April 2016 12:22:06 Prasant J wrote: > Hi, > > I'm using busybox version 1.23.1 (yocto jethro release). > > When DHCP server is not available I see my linux system getting IPv4LL > (Link local) address (169.254....). We may have many linux sytsems > running together. > > > My queries: > - Who assigns a link local address to the system? (ifup/udhcpc/... any > other tool)
Not quite sure about busy box-situation.. I've experimented with this link- local addresses. Usually, dhcpcd assigns them if/when no dhcp server is present. dhcpcd has an option (from-memory: -L) to disable this. With -L, if no dhcp server is present, no address at all will be assigned. > - Does udhcpc/ifup ensures each system is assigned a unique link local > address when multiple systems may be present? There it gets really interesting. A bit of background: This link-local addressing mechanism is -when used intentionally- usually part of a so-called 'bonjour' (Apple-name..), avahi (one of the linux implementations), mdns (more generic name) network. Yep: many names for the same thing. 'It' is a standard developed by Apple, with free implementations on Linux. The goal is to provide no-configuration networking to a cluster of computers all connected to a local network. The 169.254.X.X IP range is 'free' for this. IP address assignment works roughly as follows: When a node becomes active on such a network, it 'proclaims' its intention to use a 'wisely' choosen IP address by sending network packets to the 169.254.X.X network. If another node on the network already 'owns' that address, and receives such proclamation packets, the already-owner responds, effectively complaining that the newcomer is attempting to steal its address. The newcomer must respond with a re-try of proclamation with a different address. This is not race-free/bomb-proof, so the mechanism does allow a node to run-time re-assign its own address. NB: the 'wisely' in previous section usually entails that a node becoming active attempts to re-use the address that 'worked' the last time.. NB2: Yes a run-time re-assignment is a desaster for already-established TCP sockets, but: so is a network with an ghost of your IP address :-) The mdns protocol 'stuff' provides a whole load of other nice facilities. How much of that is active depends on how much of the zeroconf 'stack' you have installed and -hem, hem- configured... :-) A fully active stack would allow a cluster of zeroconf computers to form a network of peers with no dedicated 'servers' that can assing IP addresses, resolve names and find and access services (think: printer, ftp/nfs server, www-server) on the nodes of the cluster. That dhcpcd (or brother/sister app..) supports assigning a zeroconf address is the first step of a long and -for me at least- interesting road. I hardly ever *use* this mechanism on Linux, but it was a nice thing to study/learn about... NB: there is an O'Reilly book about 'zeroconf networking'.. > > > Any inputs will be of help to me. > > Regards, Pj > _______________________________________________ > busybox mailing list > busybox@busybox.net > http://lists.busybox.net/mailman/listinfo/busybox
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