On Mon, Jun 26, 2017 at 02:14:19PM +0000, [email protected] wrote: > > From: Job Snijders [mailto:[email protected]] > > Sent: Thursday, June 22, 2017 10:47 PM > > [...] > > > the place where the low local preference is set > > should move closer to the initiator of the gshut. Instead of setting > > the low LP on Adj-RIB-Out to IBGP neighbors, the low LP should be set > > during application of the local policy on the relevant Adj-RIB-In. > > Current version of the draft changes the LOCAL_PREF on the Adj-RIB-Out > and not on the Loc_RIB.
Yes, that should change. > This has a technical benefit as otherwise, the router may (locally) > select a backup route which it is not allowed to advertise, which > would trigger the sending of a withdraw of the original route. i.e. > not a g-shut. Sure, but the reverse is true too. It may select a path that it is not allowed to advertise and with the gshut community select something else. This is not a strong argument. > This may be considered as a corner case, but I don't see why we would choose > not cover it. > I suppose that one can also see some operational drawbacks: > a) seems less intuitive. > b) traffic received from external interfaces on this specific g-shut > router (the egress in the AS) are forwarded on the "nominal"/g-shut > path, rather than on the backup path. Yes, and avoiding the nominal path (using a backup path) has great benefit that the operator can monitor whether convergence is finished, which can be used in the decision making process when to proceed with the maintenance. Operational expectation is that when one initiates a process to drain traffic from a node or a link, that traffic is actually, visibly drained away from a link. > IMO: > - "a" is not a big concern as the related configuration is > pre-configured once for all on the router. We are not discussing the > configuration applied at maintenance time. > - "b" has no impact on the customer loss of connectivity as this > traffic may be locally rerouted in no time (up to zero packet loss) by > the router which needs to update its FIB "in place". i.e. the > destination IP prefix is never removed from the FIB. Only the outgoing > interface is changed, and during this change, both outgoing interfaces > are valid (both the old and the new). This assumes that all parties involved can actually locally reroute without packetloss. One cannot know this. Also, what of the case where a single ASN is composed of a single router (or a network is operated without the concept of IBGP as defined by IETF). > So although some may see a tradeoff, I'd rather favor the generality > of the mechanism. Specifically as not covering the corner cases may > surprise the operator. Also, as it currently stands operators, are implementing it on Loc-RIB. Another argument in favor of adjustment on Loc-RIB rather then "On Adj-RIB-Out but only for IBGP sessions", is that it is much easier to explain to people: "When you attach the GRACEFUL_SHUTDOWN, everyone is expected to lower LOCAL_PREF as low as possible" (and simply forgo explaining the particular conditionals of the current draft). Kind regards, Job _______________________________________________ GROW mailing list [email protected] https://www.ietf.org/mailman/listinfo/grow
