From: Pavel Bykov (slidersv@gmail.com)
Date: Tue Jan 20 2009 - 08:07:14 ARST
Also:
Rack1R4(config-if)#ip load-sharing ?
per-destination Deterministic distribution
per-packet Random distribution
Where did you get that information? Aren't you confusing CEF with
Etherchannel?
On Tue, Jan 20, 2009 at 9:21 AM, joshua atterbury <joshuaatterbury@gmail.com
> wrote:
> Take care to remember that cef uses the source ip and destination ip for
> the hashing process, To view the route that cef would take for a particular
> Src/Dst group use the following command
>
> show ip cef exact-route SRC DST
>
> Cheers
> Josh
>
> On Tue, Jan 20, 2009 at 5:12 PM, Pavel Bykov <slidersv@gmail.com> wrote:
>
>> Well, router chooses not source interface, but output interface. When the
>> packet came into interface, it can either drop it ( e.g. based on uRPF) or
>> process it.
>> In any case, output interface selection on not per-packet basis
>> (per-packet
>> is round-robin) is usually done per hash. I.E. you input something in, and
>> the output is hash.
>>
>> This is really a CEF thing, which you should read in to if you're
>> interested.
>> For example:
>>
>> OSPF finds out that there are 3 equal paths to a destination network
>> 150.1.146.0, so this is programmed into CEF. Output interfaces are Serial
>> 0/1, 0/2 and 0/3
>> CEF has 16 table entries, which CEF fills in the following fasion:
>> 00: Serial 0/1
>> 01: Serial 0/2
>> 02: Serial 0/3
>> 03: Serial 0/1
>> 04: Serial 0/2
>> 05: Serial 0/3
>> 06: Serial 0/1
>> 07: Serial 0/2
>> 08: Serial 0/3
>> 09: Serial 0/1
>> 10: Serial 0/2
>> 11: Serial 0/3
>> 12: Serial 0/1
>> 13: Serial 0/2
>> 14: Serial 0/3
>> 15: Serial 0/1
>>
>>
>> The packet comes into a router (through any interface, no uRPF).
>> Destination
>> is 150.1.146.56. Hash is run (I'm don't exactly know the algorithm). Hash
>> outptut is always 4 bits, therefore output will be from 00 to 15, and it
>> will correspond to CEF table entry. Let's say for 150.1.146.56 hash
>> outputs
>> 09.
>> 09 is looked up, and it corresponds to output interface Serial 0/1, so
>> packet is sent out using interface Serial 0/1.
>>
>> Next packet is let's say destined to 150.1.146.182. Hash for that
>> destination is 03. Output interface is Serial 0/1... again! So no load
>> balancing this time.
>> So you can see that load balancing really depends on quality of hash
>> algorithm.
>>
>>
>> On Tue, Jan 20, 2009 at 6:47 AM, Sidda6 <sidda6@gmail.com> wrote:
>>
>> > From your explanation I understood my scenario is by default using
>> > per-destination load balancing. So, how does router determines source
>> > interface for the packet here ( with per-destination ) .. does it pick
>> > randomly any one of two interfaces or is there there any specific
>> > criteria. ( Is there anything ARP cache plays role here with respect
>> > to picking up of source interface of packet)
>> >
>> > On Mon, Jan 19, 2009 at 3:30 PM, Pavel Bykov <slidersv@gmail.com>
>> wrote:
>> > > Default max-paths is 4 for all except BGP, (which is 1) so command is
>> not
>> > > needed.
>> > > If IP route outputs two destinations, the load balancing is taking
>> place.
>> > > Usually, CEF will do per destination load balancing.
>> > > Setting on the interface defines the method and can be per packet
>> > (depends
>> > > on platform)
>> > >
>> > > for information about CEF tables, use:
>> > >
>> > > "show ip cef 155.1.146.0 internal"
>> > >
>> > > So, to be exact and answer your questions:
>> > > 1. Depends on the method, per packet or per destination. Packets are
>> load
>> > > balanced
>> > > 2. Not required.
>> > >
>> > > On Mon, Jan 19, 2009 at 8:24 AM, Sidda6 <sidda6@gmail.com> wrote:
>> > >>
>> > >> I have route to 155.1.146.6 from my route table: route table looks
>> like
>> > >> this->
>> > >>
>> > >> R5# show ip route
>> > >> O IA 155.1.146.0 [110/65] via 150.1.0.4, 00:01:26, Serial0/0/0
>> > >> [110/65] via 150.1.0.1, 00:01:26, Serial0/0/0
>> > >>
>> > >> R5#show ip route 155.1.146.6
>> > >> Routing entry for 155.1.146.0/24
>> > >> Known via "ospf 1", distance 110, metric 65, type inter area
>> > >> Last update from 150.1.0.4 on Serial0/0/0, 00:04:06 ago
>> > >> Routing Descriptor Blocks:
>> > >> 150.1.0.4, from 160.1.4.4, 00:04:06 ago, via Serial0/0/0
>> > >> Route metric is 65, traffic share count is 1
>> > >> * 150.1.0.1, from 160.1.1.1, 00:04:06 ago, via Serial0/0/1
>> > >> Route metric is 65, traffic share count is 1
>> > >>
>> > >> 1. what happens with OSPF path selection to destination network when
>> > >> we have multiple equal costs...which path it selects in my case? if
>> it
>> > >> selected Serial0/0/1.. why it did not picked even Serial0/0/0 has
>> > >> equal cost.
>> > >> 2. Do i need to use max-paths command to load maximum-paths to
>> > >> loadbalance between two interfaces?
>> > >>
>> > >> Regards,
>> > >> Sidda
>> > >>
>> > >>
>> > >> Blogs and organic groups at http://www.ccie.net
>> > >>
>> > >>
>> _______________________________________________________________________
>> > >> Subscription information may be found at:
>> > >> http://www.groupstudy.com/list/CCIELab.html
>> > >>
>> > >>
>> > >>
>> > >>
>> > >>
>> > >>
>> > >>
>> > >
>> > >
>> > >
>> > > --
>> > > Pavel Bykov
>> > > ----------------
>> > > Don't forget to help stopping the braindumps, use of which reduces
>> value
>> > of
>> > > your certifications. Sign the petition at
>> http://www.stopbraindumps.com/
>> > >
>> >
>>
>>
>>
>> --
>> Pavel Bykov
>> ----------------
>> Don't forget to help stopping the braindumps, use of which reduces value
>> of
>> your certifications. Sign the petition at http://www.stopbraindumps.com/
>>
>>
>> Blogs and organic groups at http://www.ccie.net
>>
>> _______________________________________________________________________
>> Subscription information may be found at:
>> http://www.groupstudy.com/list/CCIELab.html
>>
>>
>>
>>
>>
>>
>>
>>
>
-- Pavel Bykov ---------------- Don't forget to help stopping the braindumps, use of which reduces value of your certifications. Sign the petition at http://www.stopbraindumps.com/Blogs and organic groups at http://www.ccie.net
This archive was generated by hypermail 2.1.4 : Sun Mar 01 2009 - 09:43:39 ARST