[j-nsp] iBGP convergence time

[Ian MacKinnon]

Well we are running M40 and seeing very slow BGP convergence times, that
this thread seems to describe well.

We first noticed this after we upgraded to 8.0

A fix would be nice :-)



Richard A Steenbergen wrote:
> On Fri, Feb 02, 2007 at 04:13:27AM -0500, Richard A Steenbergen wrote:
>> You know I haven't had any free time to run real tests or anything, but I 
>> noticed a significant increase in BGP convergence time when upgrading from 
>> JUNOS 7.2/7.3 (and I think some 7.4) to 7.6. When you make a policy 
>> change, the routes take several minutes (from 2 to 7) to install. If you 
>> do a show route you can see the new routes sitting in + and the old routes 
>> sitting in - for minutes, RPD is spinning its heels at 100% cpu, and the 
>> packets continue to forward over the old path while it is processing.
> 
> Ok so, after about a dozen people contacted me privately to confirm that 
> they were seeing similar issues that hadn't been fully acknowledged, I ran 
> off and did a little testing to replicate the issue. The one thing I can 
> definitely confirm right now is that it only appears to affect M160 (or at 
> least, not M5-M40).
> 
> On an RE-2.0 on a single switch board platform, performance is about what 
> you would expect from a 7+ year old routing engine running modern code on 
> a modern routing table. It syncs a full table inbound (from empty) on an 
> otherwise unused RE-2.0 in just under 7 minutes, and it processes a switch 
> of best path and installed routes on a full table is just barely under 2 
> minutes (policy-statement with then local-preference only, no other 
> processing). However, on an M160 the switch of best path which leads to 
> installing new routes in the HW takes between 8-15 minutes in my tests. I 
> haven't yet had time to go through every version one at a time to find 
> exactly where there starts, but the behavior is definitely evident.
> 
> The following is based on absolutely nothing except my random guess as to 
> what is happening, so someone please let me know if I'm warm or cold. It 
> seems that the easiest way to replicate the state of new route showing up 
> as "+" and the old route showing up as "-" is to intentionally break 
> connectivity between the RE and PFE (easy with an m40 :P). My guess is 
> that this is a kind of transactional FIB installation system, where the RE 
> doesn't update its RIB to reflect that the new route has been installed 
> until the switch board processes it and confirms it (and allowing it to 
> retry the install if necessary), to prevent Customer Enragement Feature 
> with Juniper's move towards distributed forwarding tables on the Gibson 
> architecture. Whatever is going on with the M160 on RE-2.0 however, it is 
> significantly slower. Maybe this just wasn't sufficiently regression 
> tested on the M160 platform, or maybe it is just a natural effect of 
> having 4 switch boards which all need to be updated, but it is very 
> noticable. The offical Juniper line seems to be "just upgrade your REs", 
> but it would be nice if we had an alternate option.
> 
> So, two things. The most obvious question is, is there a way to turn this 
> behavior off or revert it to the previous behavior (if infact my guess as 
> to the cause is correct :P)? The next question is, I noticed in the 
> release notes for 8.2 that there is a new option to support indirect 
> next-hops which may significantly reduce the number of FIB updates. My 
> take on this feature is that you are changing from installing BGP route -> 
> physical next-hop to BGP route -> BGP next-hop and BGP next-hop -> 
> physical next-hop, so that when you make a routing change to the BGP 
> nexthop you only have to update the 1 entry instead of the potentially 
> thousands of entries for the BGP route itself (which I kinda thought 
> Juniper had done since forever :P). Am I correct in that interpretation, 
> or is there something else going on there?
> 

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