Solved

Relation between Cisco CEF and Controle/Data/Forwarding Plane

Posted on 2014-04-02
16
1,041 Views
Last Modified: 2014-04-16
If I understand Cisco CEF relies on IOS Software (Routing and Adjacency table) then it copies the Routing table to ASIC  FIB and Adjacency table to ASIC Adjacency table ( I cannot remember how it is called )…
 Well, this is CEF , but I have encountered the terms Controle/Data/Forwarding plane….I would like to know if there is any relevance between those planes and the CEF…
 
Any help will be very much appreciated.
0
Comment
Question by:jskfan
  • 7
  • 5
  • 4
16 Comments
 
LVL 7

Accepted Solution

by:
unfragmented earned 222 total points
ID: 39972343
Think of the CEF and its constructs including the FIB and the adjacency table as the data or forwarding plane.  The data or forwarding is all about moving "normal" packets as fast as possible, with as little "handling" as possible.  Most high end products do this "in hardware" with ASICS.

However, the data plane can't build its tables on its own.  It relies on the intelligence of the control plane to analyze/discover/decide how the device should process the traffic.  The control plane then programs the data plane (the FIB and AdjTab) with a template of how it should handle that type of packet in the future.  The control plane will also update and remove the templates as required.  Analyze/discover/decide are based on our familiar protocols like ARP, BGP, OSPF etc.  This requires more complex processing, and a more flexible processor, and hence packets that require control plane involvement before being forwarded are said to be in the "slow path".

There is also a third plane referred to as the "management" plane.  In old devices, this was very much part of the control plane.  There has been a movement to separate this plane as much as possible.  This function is about "managing" the device, eg handles incoming telnet/ssh sessions, snmp requests/traps, syslog, config management etc.  These are things that ideally should not impact, nor be impacted by a busy control plane or data plane.

Thats a pretty rough explanation of it.  There would be plenty of good blogs about this topic if you have the time to do some googling.
0
 

Author Comment

by:jskfan
ID: 39972793
if I understand your comment :
Data plane and forwarding plane are the same ? If so do they use those terms interchangeably?

controle plane sounds like the software part that builds the routing table and adjacency table before it hands out to ASIC HARDWARE  that will feed it to FIB  and Adjacency table (the one in ASIC)
0
 
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 278 total points
ID: 39973874
"Forwarding plane" is just another term for "data plane"
0
 
LVL 7

Assisted Solution

by:unfragmented
unfragmented earned 222 total points
ID: 39973877
as donjohnston said, the data/forwarding plane terms are interchangeable.  Control plane - yes i think you have the right idea.
0
 

Author Comment

by:jskfan
ID: 39977711
OK…

In IOS Software side, it has:

- Routing Table
- Adjacency Table
- Topology Table

Which of them maps to Control plane and which maps to Forwarding plane ?

in Hardware side (ASIC), it has :
FIB
Adjacency Table
Which of the Routing /Adjacency/Topology gets copied to ASIC (FIB) and which gets copied to ASIC (Adjacency Table) ??

Thanks
0
 
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 278 total points
ID: 39977726
- Routing Table
- Adjacency Table
- Topology Table

Which of them maps to Control plane and which maps to Forwarding plane ?

Those are all Control Plane.

The forwarding plane is for data (hence, data plane).

Anything that has to do with building routing tables, spanning-tree, ARP caches, etc., is Control Plane. Any traffic that is going through the router is Data Plane traffic.
0
 

Author Comment

by:jskfan
ID: 39978102
Is the ASIC part (FIB table and adjacency table) considered as Data plane?

IOS software part (routing/Adjacency/topology tables( considered as Control plane ?
0
 
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 278 total points
ID: 39978124
If it has to do with how to move traffic (routing table, MAC address tables, adjacency tables, topology tables), it's control plane.

If it has to do with actually moving packets between interfaces (transporting a packet from interface G0/1 to interface G3/4), then it's data plane.
0
IT, Stop Being Called Into Every Meeting

Highfive is so simple that setting up every meeting room takes just minutes and every employee will be able to start or join a call from any room with ease. Never be called into a meeting just to get it started again. This is how video conferencing should work!

 

Author Comment

by:jskfan
ID: 39978942
donjohnson:

I guess you dod not get my point.

how does ASIC (FIB table and Adjacency table) get updated.??

I thought Control plane updates FIB Table and Data plane updates Adjacency table.

**just a note: ASIC does not have Topology table (not mentioned in any Docs).
0
 
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 278 total points
ID: 39978967
I don't know if that's documented or even if it's published information. The ASICs are proprietary so I doubt that information on how they are updated is available.
0
 

Author Comment

by:jskfan
ID: 39978976
http://blog.ine.com/2011/06/15/control-plane-vs-data-plane/

As explained in the link above, I guess Control/Data planes have nothing to do with ASIC (FIB and Adjacency tables)…

Control and Data plane if I understand they are just "Description" of packets.
Control plane= Router originating the packets or router to which the packets are destined to.
Data plane = Router or Routers through which the packets transit ( Excluding the source and destination).
0
 
LVL 50

Assisted Solution

by:Don Johnston
Don Johnston earned 278 total points
ID: 39978991
Correct. The ASICs are just a high performance means of storing, organizing and searching for the information required to forward packets.

The information that eventually gets into the ASICs comes from the various tables that routers have been using for years.

Those tables are created by information that is classified as "control plane" traffic. Basically things like ARP, routing protocols, etc.

How the information gets from the routing tables, etc. to the ASIC is anyone's guess.  I would guess that methodology is not available to the public.
0
 
LVL 7

Assisted Solution

by:unfragmented
unfragmented earned 222 total points
ID: 39979297
Note that donjohnston said earlier that "Routing Table, Adjacency Table and Topology Table" are considered control plane.

I was originally going to contradict donjohnston regarding the Adjacency table but then realized there is some ambiguity here.

If you are talking OSPF adjacency table...It helps the router with path selection, its run in software, it involves packets that are for the router itself....definitely control plane.  

If you're talking CEF adjacency table... it contains prefix to MAC and egress interface mappings.  It caches and avoids ARP.  Its job is egress and layer2 rewrite for EVERY packet.  Easily defined in hardware (ie can be performed by ASIC)....definitely data plane IMO.

**just a note: ASIC does not have Topology table (not mentioned in any Docs).

Too non-specific a statement.  The CEF ASIC does not have a topology table.  

It has a CEF FIB and CEF adjacency table.  Why?  because CEF only cares about getting it out the right interface, with the right MAC address.  It blindly trusts what ARP and the routing table have told it, therefore does not need to know topology info.
0
 

Author Comment

by:jskfan
ID: 39981290
Per IPExpert video, in MPLS world
FIB is built from RIB and L2 to L3 Mapping( I am not sure though where L2 to L3 mapping comes from)
LIB is built from RIB and Label Exchange protocols (LDP,TDP,BGP)
LFIB is Built from RIB,LIB,FIB as well as L2 to L3 Mapping
FIB and LFIB are called CEF, and both share the same database
0
 
LVL 7

Assisted Solution

by:unfragmented
unfragmented earned 222 total points
ID: 39985707
L2 to L3 mapping is a generic term for what ARP does.
0
 

Author Closing Comment

by:jskfan
ID: 40003545
Thank you Guys!
0

Featured Post

Threat Intelligence Starter Resources

Integrating threat intelligence can be challenging, and not all companies are ready. These resources can help you build awareness and prepare for defense.

Join & Write a Comment

Suggested Solutions

Title # Comments Views Activity
NSD FAIL 2 25
cisco switch stacking 6 35
Can't access router via web browser 21 52
iPad Won't Connect 16 42
We've been using the Cisco/Linksys RV042 for years as: - an internet Gateway - a site-to-site VPN device - a leased line site-to-site subnet-to-subnet interface (And, here I'm assuming that any RV0xx behaves the same way as an RV042.  So that's …
Problem Description:   Couple of months ago we upgraded the ADSL line at our branch office from Home to Business line. The purpose of transforming the service to have static public IP’s. We were in need for public IP’s to publish our web resour…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…
After creating this article (http://www.experts-exchange.com/articles/23699/Setup-Mikrotik-routers-with-OSPF.html), I decided to make a video (no audio) to show you how to configure the routers and run some trace routes and pings between the 7 sites…

743 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question

Need Help in Real-Time?

Connect with top rated Experts

13 Experts available now in Live!

Get 1:1 Help Now