PoC: use ip route to read IPv6 routes instead of /proc

[grawity]

Note: This is a proof-of-concept only, handling just IPv6 routes at the moment (although it would be almost exactly same code for IPv4 too), and only tested on Arch (iproute2 v5.13, python v3.9). The intent is to check whether this approach would be suitable for scapy.

The legacy /proc/net interface has several disadvantages:

1. It is very slow, taking about 2-3 ms per route (about 60 times slower than netlink).
2. It doesn't support filtering by table, making it even slower and potentially confusing scapy when it sees multiple routes for the same destination.
3. It does not include many parameters that Linux routes have (such as routing table IDs or multiple nexthops).

For example, my system has ~60 routes in the 'main' table and ~120K routes in the 'inet' table. It is useless for scapy to scan routes from non-default tables because it does not process policy rules anyway; it would be better if it only looked at the 'main' table.

With netlink it is possible to request a filtered dump (even though getting the complete dump is already reasonably fast), but /proc/net does not even have an indication of which table a route belongs to.)

Of course, it would be much better to use a native Python netlink module instead of shelling out to ip (especially considering that the -json option only became available last year), but I honestly don't know which one to use, and even the current approach shows quite an improvement:

• /proc (all tables): 115690 routes in 304.03 seconds
• iproute2 (all tables): 115651 routes in 5.26 seconds
• iproute2 (main table): 32 routes in 0.08 seconds

(The small differences in route count come mostly from BGP announcements and withdrawals happening between dumps.)

Ref: #2133

[codecov]

Codecov Report

Merging #3275 (4373e44) into master (6eef12d) will not change coverage.
The diff coverage is n/a.

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[guedou]

Thanks for this PR! That is a really interesting approach. I think that is something that we should also do for IPv4.

Following on your idea, it will be awesome to be able to load specific tables using something like:

conf.route.routes = []
conf.route.resync(table="mytable")

A last thing: could you add some unit tests by mocking the output of ip route -json?