Hello,
commercial BGP implementations (Juniper, Nokia, Cisco) usually
implements silent saturation based on your point (2) in such cases,
Quagga does this too (see route_value_adjust function [1]; which handles
these overflows). It's not limited to locpref, also other attibutes can
be modified by addition/subtraction.
I suggest to follow this practice also in Bird code, as this behavior is
commonly expected here.
Length of relevant attributes are defined in RFC and I don't expect any
move from 32b to 64b integers here - as this will break compability
between speakers.
- Daniel
[1]
https://github.com/Quagga/quagga/blob/88d6516676cbcefb6ecdc1828cf59ba3a6e5fe7b/bgpd/bgp_routemap.c#L148
On 12/1/20 5:51 PM, Ondrej Zajicek wrote:
There are at least three reasonable behaviors for fixed-range
arithmetics:
1) silent overflow (current behavior)
2) silent saturation (as you suggested)
3) explicit (logged) error
Not really sure which is better. (1) is likely least astonishment (for
fixed-range), (2) is most useful when overflows are intentional, (3) is
most useful when overflows are unintentional.
I have minor preference for (3), but no strong preference either way to
change anything. Also note that in cases when fixed-range attributes have
lower range than 32bits (i.e. 16bit preference and 24bit ospf_metrics),
we generate explicit error on overflow on assignment.
Or perhaps we should just move to arbitrary-range integers .. many new
RFCs already use 64bit attributes anyways.
