Restructered pre-import
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Liz Cray
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Old Pages/Old Wiki/Babel.md
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Old Pages/Old Wiki/Babel.md
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Available in most Linux distributions (including Arch, Debian, OpenWRT).
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# Features
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Distance vector routing protocol:
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- Direction in which a packet should be forwarded.
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- Interface to which a protocol should be sent
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- Direction == address of next hop and exit interface
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- Distance from destination
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- Cost of reaching destination is computed using various metrics
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<!-- -->
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- Designed for both wireless (in ad-hoc mode) and wired network routing.
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- Designed with mobile nodes in mind.
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- Can route both IPv4 and IPv6 simultaneously and transparently. Doesn't
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care which layer 3 protocols are running on top of it.
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- Converges rapidly.
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- Triggered updates.
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- Explicit requests for routing information rather than continual
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broadcasting.
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<!-- -->
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- Uses link quality metrics.
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- Metric: packet loss, interference (optional) and RTT (optional).
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- History sensitive to avoid route flapping.
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<!-- -->
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- Does not optimize route tables immediately, more concerned with
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stability than slim tables. Premature optimization is the root of all
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coders' anguish, and all that.
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- This is used to cure route starvation.
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- Used to choose feasibility of a particular route.
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- Every route carries a sequence number that never decreases and is
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propagated unchanged through the network.
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- Only the route's source can ever increment that number.
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- If the sequence number is more recent that the feasibility distance
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maintained by the receiving node, or if it's equally recent but the
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metric is smaller, then that particular route will be selected.
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- Routes become feasible again after the sequence number is incremented.
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- Ideal for embedded systems due to the properties inherent of DVRPs.
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<!-- -->
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- Most routing loops are avoided, remaining routing loops are transient,
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disappear in time proportional to the diameter of the loops.
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- Routers take note of loops and ensure that they do not recur.
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<!-- -->
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- Highly mobile nodes may elect to use shorter time constants, to
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reflect their changing environment more accurately.
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<!-- -->
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- Nodes periodically broadcast HELLO packets. Nodes also respond to
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HELLO broadcasts from neighboring nodes with I HEARD YOU packets.
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These are used to calculate link costs.
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- Periodically, every node B broadcasts a routing update D(B).
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Every neighboring node A checks to see if B is its next hop. If so,
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` NH(A) = B`
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` D(A) = C(A, B) + D(B)`
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otherwise,
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` if (C(A, B) + D(B)) < D(A)`
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` the received route is a better one`
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` NH(A) = B`
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` D(A) = C(A, B) + D(B)`
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For any node A:
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` estimated distance to node S = D(A)`
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` next hop router to node S = NH(A)`
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Initially, D(S) == 0, D(A) == infinity, NH(A) == UNDEFINED
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If a route has to be retracted for any rason, babeld flags that route as
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UNREACHABLE for a few minutes. Even if the route comes back it won't be
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used until that timer is up. This is usually the worst case propagation
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time for the route to a particular node C.
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Every Babel router gets a unique ID, a string of 8 octets.
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- Transmitted over UDP.
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- Sent with a unicast source address to a multicast address (usually).
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- Known neighbors get both multicast and unicast (directed to a
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particular node).
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# Usage
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How to use babeld: Put the NIC into ad-hoc mode:
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` iwconfig wlan0 mode ad-hoc channel X essid "mesh"`
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` ifconfig wlan0 up`
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All nodes need to have unique IP addresses. IPv4 at least, IPv6 if you
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have it.
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` ifconfig wlan0 192.168.13.37/32`
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`` ifconfig wlan0 `generate-ipv6-address -r`/128 ``
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Start babeld:
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` babeld wlan0`
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If there are multiple network interfaces:
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` babeld wlan0 eth1 eth2 ppp0 ...`
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If a specific network gateway router exists, set it:
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` route add default gw 1.2.3.4 dev eth1`
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These are often set on a per-node basis. For example, babeld is running
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on a laptop with both wireless and wired interfaces.
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Then redistribute routes through the mesh:
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` babeld -C 'redistribute metric 128' eth1`
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It is possible to redistribute the routes associated only with a
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particular network interface:
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` babeld -C 'redistribute if eth2 metric 128' eth1`
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Other babeld options:
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` -h `<sec>`: interval in seconds between HELLO broadcasts over wireless.`
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` Default: 4 sec.`
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` -H `<sec>`: as -h, only for wired interfaces.`
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babeld is not designed for security. An attacker that is link-local can
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inject packets, just like ARP. Local firewalls, if applicable, should be
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configured to allow Babel packets. Default: 6697/UDP
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# Accessories
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## AHCPD
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AHCP can also be used to configure routing when using babeld:
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` `[`http://www.pps.jussieu.fr/~jch/software/ahcp/`](http://www.pps.jussieu.fr/~jch/software/ahcp/)
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Arch Linux package downloaded, compiled, and ready to install.
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Automagically configures IPv6 and IPv4/IPv6 networks when babeld is
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used. Implements router discovery. Replaces DHCP. Configures IPv?
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addresses, DNS, NTP. Does not configure default routes, that's babeld's
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job.
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Setting up an authoritative AHCP server:
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` Configure /etc/ahcpd.conf appropriately.`
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` ahcpd -c /etc/ahcpd.conf -D wlan0`
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Does not need to run as root, only needs to be able to write a pidfile
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and the lease database. If the server can sync its clock using NTP, it
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will. If it can't it will only give short leases and be careful with
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releasing them. Multiple servers can run on the same mesh so long as
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they work different IPv4 netblocks.
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Other options:
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` -t `<sec>` - time in second that leases are offered for.`
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` -L /path/to/log - Specify a logfile. By default, /var/log/ahcpd.log`
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kill -USR1 to print server status to logfile. kill -USR2 checks for
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interface status changes, then reopens logfile.
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Running an AHCP client:
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` ahcpd wlan0`
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Designed for mesh networks. Doesn't set default gateway, netmask, or
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on-link prefixes for IPv6.
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## WebGUI
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haxwithaxe doesn't know how this works yet but it looks really cool.
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[babelweb](http://babelweb.wifi.pps.univ-paris-diderot.fr:8080)
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git clone git://git.wifi.pps.univ-paris-diderot.fr/babelweb.git
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