Subject: RE: Route cache performance under stress

From: "CIT/Paul" <[email-masked]>
Date: Mon, 9 Jun 2003 01:27:48 -0400

Ahah Jamal!! Yes I have tried.. It does absoutely nothing for the
constant randomness of packets.
It increases the overall distribution of the hash in the cache but it
does nothing for the addition of new packets..
Try fowarding packets generated by juno-z.101f.c and it adds EVERY
packet to the route cache.. Every one. And at 30,000 pps
It destroys the cache because every single packet coming in is NOT in
the route cache because it's random ips. Nothing you can do
About that except make the cache and everthing related to it wicked
faster, OR remove the per packet additions to the cache (I'm not
Even sure why this is necessary anyway.. Who would want to add every
single src/dst flow to a cache? That's what conntrack does and we all
Know how much you despise that heheheh)
And yes, you can die with 10mbps......Try putting in some netfilter
rules and try putting some basic traffic on it and then hit it with
10mbps of juno-z and see what happens to your cpu.  Granted if there is
a linux router doing ABSOUTELY NOTHING you might be able to hit 50kpps
of juno with dual p3 cpus w/ 512k cache each and tricked out settings
for the hash and route cache but you will also drop some packets along
the way..Still this is not  acceptable yet :>  
Point me at some decent cost linux hardware assist platforms.. IMHO the
only thing that needs hardware assist is the darn route cache (in its
entierty)
BTW, Juno-z can send 12,000 packets per second or more and it's still
10mbps :>

If anyone has any ideas please feel free to e-amil me direct :>

Paul [email-masked] http://www.httpd.net

-----Original Message-----
From: Jamal Hadi [mailto:[email-masked]] 
Sent: Sunday, June 08, 2003 11:16 PM
To: CIT/Paul
Cc: 'Simon Kirby'; 'Florian Weimer'; [email-masked];
[email-masked]
Subject: RE: Route cache performance under stress

On Sun, 8 Jun 2003, CIT/Paul wrote:

> The problem with the route cache as it stands is that it adds every 
> new packet that isn't in the route cache to the cache, say you have A 
> denial of service attack going on, OR you just have millions of hosts 
> going through the router (if you were an ISP).  Anything with seeminly

> Random source ips (something like juno-z.101f.c will generate worst 
> case scenario for forwarding packets) will cause the cache to 
> constantly Add new entries at pretty much the rate of the attack.. 
> This can stifle just about any linux router with a measly 10 
> megabits/second of traffic unless

foo have you tried the latest patches posted recently?
get the latest kernel 2.5.x and try it out.
BTW, i dont think it is true you can die with 10mbps. I was reading some
emails where someone said it was a few 100 pps that will kill the linux
sytem (theory mixed with nonsense;->)

> The router is tuned up to a large degree (NAPI, certain nics, route 
> cache timings, etc.) and even then it can still be destroyed no matter

> what The cpu is with less than 100,000 packets per second and in mosts

> cases less than 30k..

btw thats waay above 10Mbps.

> That's why it's just no acceptable for companies using
> it as a replacement for say a cisco 7200 VXR series (npe300,400 nsf-1,
> etc.) which can do 300K+ packet per second of routing (and yes it can
> even route juno-z.101f.c at 300kpps, I have tested it).   Linux has no
> problem doing 300kpps from a single source to a single destination 
> provided you have NAPI or ITR or something limiting the interrupts.. 
> The overhead is the route cache and the related systems that use it 
> and also netfilter is very slow :/  One of these days they will fix 
> it..... If anyone has any ideas or needs a test-bed to try out code on

> or would like me to test some of their code I would be happy to test 
> it on our development platforms (single and dual processor with intel 
> e1000 82545/6 and above, also e100 and tulip).
>

I think Robert has some numbers with the new patches with similar setups
as you. Why dont you compare how much the cost of a CISCO npex devices
with Linux PCs with e1000s as well while you are at it ?;-> I am sure
there are people who will like to sell you linux devices at half the
cisco prices doing Millions of PPS via hardware assists. Support these
linux supporting companies instead ;->

The more i think about it the more i think CEF is a lame escape from
route caches. What we need is multi-tries at the slow path and perhaps a
binary tree on hash collisions buckets of the dst cache (instead of a
linked list). You can avoid the packet drive cache generation event by
being a little creative if it gets overwhelming. Fix zebra to resolve
each BGP nexthop fully every periodic time.

In any case who said forwarding by itself was sexy anymore?

cheers,
jamal

> Thanks for your time
>
> P.S. to answer your iteration question.. It does not seem to be such 
> overhead on the cpu even if the route-cache is 600,000 in size.. I 
> have tested this and while there is a definite increase in cpu it 
> comes nothing close to the code that has to add every new arriving 
> packet to the list.  IMHO the best way to do this would be like CEF w/

> adjacency lists and not have it add every new packet that comes along
>
> Paul [email-masked] http://www.httpd.net
>
>
> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On 
> Behalf Of Simon Kirby
> Sent: Sunday, June 08, 2003 7:49 PM
> To: Florian Weimer
> Cc: [email-masked]; [email-masked]
> Subject: Re: Route cache performance under stress
>
>
> On Sun, Jun 08, 2003 at 03:10:25PM +0200, Florian Weimer wrote:
>
> > Further parameters which could be tweaked is the kind of adjacency 
> > information (where to store the L2 information, whether to include 
> > the
>
> > prefix length in the adjacency record etc.).
>
> What is the problem with the current approach?  Does the overhead come

> from having to iterate through the hashes for each prefix?
>
> Simon-
>
> [        Simon Kirby        ][        Network Operations        ]
> [     [email-masked]     ][   NetNation Communications Inc.  ]
> [  Opinions expressed are not necessarily those of my employer. ]
>
>
>
>