Operator here. We have limitations around 128 to avoid some vendor bugs. I suspect we could remove them but people with mental histories of pain always worry about that change.
Sent from my iStarship > On Sep 16, 2019, at 12:42 PM, Jeffrey Haas <[email protected]> wrote: > > Speaking as a vendor: > > >> On Sep 16, 2019, at 11:18 AM, David Farmer <[email protected]> wrote: >>> On Mon, Sep 16, 2019 at 8:25 AM Job Snijders <[email protected]> wrote: >>> Can we articulate what problem is solved by limiting the AS_PATH length? >> >> I'm aware of a Netflow tool that crashes when it receives BGP paths that are >> excessively long. Furthermore, excessively long paths will use more memory >> which could cause stability issues in some situations. > > There are a number of bugs in implementations over the life of BGP related to > path length. In particular, overflows either in the number of ASes in the > segment (max 255), where a second segment needs to be created; overflows in > the length of the path attribute and needing to switch the size of the length > field (the extended bit). > > This is the primary reason we've tended to see strong pushes for filter > length - attempts to avoid exercising such bugs. Ideally, implementations > should have been upgraded to avoid them by this point. > > I am not optimistic. :-) > > With regard to memory use, it's not a real problem for implementations and is > generally noise in the real world vs. the total number of paths in your > router. > >> >> Having a sanity limit on path length isn't a bad idea. Personally, I think >> 20 a little on the short side, but 40 or 50 seems like a reasonable limit. >> Anything beyond that is most definitely excessive, and I'm not sure you >> would even want to use such a path if it were real. > > Quoting a coworker: constants are almost always wrong. :-) > > -- Jeff > > _______________________________________________ > GROW mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/grow _______________________________________________ GROW mailing list [email protected] https://www.ietf.org/mailman/listinfo/grow
