Routing
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Bonding works with routing and shapers together. (See Chapter 10 for details of shapers.)
The basic principle is that you have two or more routes that are identical (same target IP prefix) and have the
same localpref, so that there is nothing to decide between them. As described above this normally means one
of the routes is picked.
However, where the two (or more) routes are the same type of interface, and there are shapers applied to those
routes, then a decisions is made on a per packet basis as to which interface to used. The shapers are used to
decide which link is least far ahead. This means that traffic is sent down each link at the speed of that link.
To make this work to the best effect, set the tx speed of the shapers on the links to match the actual link speed.
E.g. for broadband lines, set the speed to match the uplink from the FB6000.
8.6. Route overrides
The conventional routing logic described so far operates very much like any conventional router, with the
addition of some handling for bonding and duplicate subnets.
However the FB6000 also allows the possibility of route overrides which control routing in more more detail.
This feature is part of session tracking functionality, and so applies on a per-session basis (contrasting with the
per-packet basis for the conventional routing). For details on sessions, and session-tracking, refer to Chapter 7.
When establishing a session it is possible to scan an ordered list of rules which can consider not only the target
IP but also source IP, protocol, ports, and interfaces being used. The result is (typically) to set a routing target
IP for the session (and possibly a routing table to jump between tables).
Note
The destination IP in the packet header is not modified - rather, an 'overriding' routing target IP address
is stored in the session-table entry.
This is done for each direction on the session and remembered. This new target IP is then used on a per packet
basis in the same way as above instead of the destination IP address of the packet. This is the same as
set-
gateway
in the normal session tracking logic. However, routing overrides are applied at the end of checking
rule-sets and applied both ways, allowing, in effect, a set-reverse-gateway.
Tip
Because the route-override just sets a new target routing IP and does not allow you to set a specific
tunnel or such, you may want to have a dummy single IP address routed down a tunnel, and then use
route-override rules to tell specific sessions to use that IP as the gateway. Future software releases
may provide a means to specify a tunnel as a routing gateway more directly.
Note
Route override logic was originally devised to allow routing for use with tunneling protocols, but they
are usually better handled with much less configuration using routing tables. As such this feature is
rarely useful, and probably not the configuration setting you are looking for (waves hand in front of
your face).
