> > Also, you've put these in rejected: > > Lower the default MRAI timer for iBGP peers to 0 > Lower the default MRAI timer for EBGP peers to zero > > There is work, including some interesting academic work, that suggests 0 > is a bad value for MRAI. /Some/ MRAI is advisable to damp down BGP's > incredible and ever-increasing (exponentially) propensity to send messages > as MRAI approaches 0. That work, which was quite old, suggested the best > value was likely under 5s for Internet use - i.e. for eBGP. > > A quick summary and links to the primary works are in: > > https://tools.ietf.org/html/draft-jakma-mrai-02 > > No MRAI is likely ungood, from what's been described (empirically and > theoretically). However, the current 30s in Quagga is certainly way, way > too high, we'd surely all agree. > > We /should/ lower that dramatically - just not to 0. I'd be happy to have > the eBGP MRAI set to 5s, and the iBGP one to 1s. Note that some increase in > messaging and hence CPU is unavoidable, but the convergence benefits should > make it worth it for most.
FWIW IOS has used 0 for iBGP and 5 for eBGP since ~2004. We (cisco at the time) never had any complaints when we changed to these values (they were both 30s before). The only reason we didn't do 0 for eBGP was because dampening was still used a fair amount back then (not so much now). With the MRAIs set to 0 you can get some bursts of path hunting but they tend to be short lived because bgp ends up converging so fast (sub-second is typical). Given the lack of complaints when the iBGP timer was changed to 0, I don't think increased path hunting is much of a concern. Path hunting is worse as meshiness increases and an iBGP core tends to be more meshy and eBGP connections. I think we could use 0 for both without any path hunting issues. On the off chance that your peer is using dampening you could increase the MRAI for that one peer. Daniel
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