Re: QS: FIB and RIB: what is the difference

Hi Sayed,

You have already answered your question.
The traffic destined or originated by the router is always process
switched, which means it must be routed via RIB and it usually affects
CPU performance.
That's why we should configure features like CPP (Control Plane
Policy), disable ip unreachables, drop fragmented traffic or packets
with IP options used.

If you would like to see traffic going thru the router you must first
disable CEF globally (no ip cef) or per interface (no ip route-cache
cef).

HTH,

-- 
Piotr Matusiak
CCIE #19860 (R&S, SEC)
2009/9/25 Syed Khalid Ali <khalid_khursheed_at_hotmail.com>:
> Narbik,
>
> Thank you for this comprehensive reply.
>
> One more thing I noticed during the debugs, that for every reply message,
> router it telling me that it is routing via RIB. Why not FIB if corresponding
> network entry is already maintained/populated/cached via FIB.
>
> I am thinking, it is for the reason that traffic toward or locally generated
> by the router is always process switched???
>
> Thanks
> Khalid
>
>
>> Date: Fri, 25 Sep 2009 10:30:47 -0700
>> Subject: Re: QS: FIB and RIB: what is the difference
>> From: narbikk_at_gmail.com
>> To: tvarriale_at_flamboyaninc.com
>> CC: ccielab_at_groupstudy.com
>>
>> When you look at RIB and FIB you have to think of the 2 major and most
>> important components of routing:
>>
>>
>>
>>    - Control Plane
>>    - Data Plane
>>
>>  The control plane takes care of the routing information exchange, and in
>> MPLS environment, label exchange between adjacent devices.
>>
>> What do we have and see in the control plane? Routing protocols, exchange
> of
>> routing information, RIB (Routing Information Table) and once again in an
>> MPLS environment you will also see a Label Exchange Protocol such as LDP.
>>
>>
>>
>> So therefore control plane builds a routing table or RIB based on the
>> routing protocols.
>>
>> The control plane builds/populates 2 forwarding tables: a FIB (Which is
>> built from the information in the RIB) and in MPLS networks an LFIB (Label
>> Forwarding Information Base). These (FIB and LFIB) exist and work in the
>> Data plane.
>>
>>
>>
>> The data Plane is simply a forwarding engine that is* independent* of the
>> routing protocol or Label exchange protocol type; this Plane forwards
>> packets to the appropriate interface based on the info found in the FIB or
>> LFIB.
>>
>>
>>
>> So the way I envision it:
>>
>>
>>
>> You use a routing protocol to advertise routes upstream  and if any of the
>> upstream routers need to connect to the advertised networks, they connect
>> downstream toward the destination.
>>
>>
>>
>> Now this is a very brief and *basic* explanation of the RIB, FIB and LFIB.
>>
>>
>>
>> Now weather they are hardware based or software based I think is irrelevant
>> when you look at different platforms.
>>
>>
>> On Fri, Sep 25, 2009 at 9:24 AM, Tony Varriale
>> <tvarriale_at_flamboyaninc.com>wrote:
>>
>> > That's making a poor assumption that the device you are speaking about is
>> > hardware based.
>> >
>> > More than half of people won't come in contact with those devices (with
> the
>> > exception of a 6500).
>> >
>> > tv
>> >
>> > -----Original Message-----
>> > From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
>> > Anthony Sequeira
>> > Sent: Friday, September 25, 2009 10:13 AM
>> > To: Syed Khalid Ali
>> > Cc: ccielab_at_groupstudy.com
>> > Subject: Re: QS: FIB and RIB: what is the difference
>> >
>> > The Routing Information Base is the copy of the routing table stored
>> > in software on the Cisco device.
>> >
>> > The Forwarding Information Base is the copy of the routing table
>> > stored in hardware on the Cisco device.
>> >
>> > Thanks to Cisco Express Forwarding (CEF) and its use of the FIB,
>> > performance for Cisco routers is much improved.
>> >
>> > Warmest Regards,
>> >
>> > Anthony J. Sequeira, CCIE #15626
>> > http://www.INE.com <http://www.ine.com/>
>> >
>> > Test your Core Knowledge today!
>> > Q: What protocol supports load-balancing with first-hop redundancy?
>> > A: gateway load balancing protocol
>> > More Info:
>> >
>> >
>>
> http://www.cisco.com/en/US/docs/ios/12_2t/12_2t15/feature/guide/ft_glbp.html
>> >
>> >
>> > On Sep 25, 2009, at 10:47 AM, Syed Khalid Ali wrote:
>> >
>> > > dear group,
>> > >
>> > > I just started to prepare for R&S track. While going through the "ip
>> > > packet
>> > > debug command" these two terms just popped up.
>> > > What is the difference between these two?
>> > >
>> > > Thanks
>> > > Khalid
>> > >
>> > >
>> > >
>> > > _________________________________________________________________
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>> >
>> >
>> >
>> >
>> >
>>
>>
>> --
>> Narbik Kocharians
>> CCSI#30832, CCIE# 12410 (R&S, SP, Security)
>> www.MicronicsTraining.com
>> Sr. Technical Instructor
>>
>>
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