Issue with unsigned integer LOCAL_PREF

[Alexandre Corso]

Hello, 

I have the same opinion. Silent saturation (with log). The goal is to have the same behavior on all BGP implementation.

Alexandre

> On Dec 2, 2020, at 6:45 PM, Daniel Suchy <danny at danysek.cz> wrote:
> 
> 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.