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Ask the Expert: Carrier Routing System (CRS) Hardware Architecture

Community Manager
Community Manager

With Vinay Kumar, Sudhir Kumar and Raj Pathak 


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Welcome to the Cisco Support Community Ask the Expert conversation. This is an opportunity to learn and ask questions about Cisco Carrier Routing System (CRS) single-chassis and multichassis router hardware design and architecture with Cisco experts Vinay Kumar, Sudhir Kumar, and Raj Pathak. 


CRS routers are modular and distributed core routers developed by Cisco that enable service providers to deliver data, voice, and video services over a scalable IP next-generation network infrastructure. Today, CRS is one of the most trusted devices in the core of the service provider network and a proven architecture that has delivered 10 times the capacity over a period of 10 years.  Our three experts will cover the difference between CRS single-chassis and multichassis routers. They will also answer your questions about how CRS routers work and help in easily scaling the networks and different components of the CRS routers. 


For more details about CRS multichassis, read the blog and tech talk video. 


Hyperlink blog:     


Vinay Kumar is an experienced support engineer with the High-Touch Technical Support Team, Bangalore, India. He has been supporting major service providers and large enterprise customers for routing, Multiprotocol Label Switching (MPLS), multicast, and Layer 2 VPN issues on all routing platforms. He has more than eight years of experience with service providers and has been in his current role from more than three years. Vinay has completed his CCIE routing and switching certification (CCIE no. 35210) and is a Cisco IOS XR Software specialist.


Sudhir Kumar is a customer support engineer in High-Touch Technical Services at Cisco specializing in service provider technologies and platforms. He serves as a support engineer for technical issues supporting Cisco IOS XR Software customers on Cisco CRS and Cisco XR 12000 Series Routers. Sudhir has more than eight years of experience in the IT industry and holds CCIE certification no. 35219 in routing and switching. 


Raj Pathak is a customer support engineer in High-Touch Technical Services at Cisco in Bangalore, India. He supports service provider customers for technical issues with Cisco IOS XR Software on Cisco CRS and Cisco XR 12000 Series Routers. He covers many technologies, including routing protocols, service provider, CRS, and Cisco IOS XR Software. He has more than seven years of experience in the IT industry and holds CCIE certification no. 38760 in routing and switching. 


Remember to use the rating system to let Vinay, Sudhir, and Raj know if you have received an adequate response.


Because of the volume expected during this event, our experts might not be able to answer every question. Remember that you can continue the conversation in the Service Providers community, subcommunity XR OS and Platforms shortly after the event. This event lasts through November 29, 2013. Visit this forum often to view responses to your questions and the questions of other Cisco Support Community members.

1 Accepted Solution

Accepted Solutions

Jackson Braddock

Hello gentlemen,

How many line card chassis can we connect with one fabric chassis?  Please advise.

Thank you.


View solution in original post

25 Replies 25


Hi Experts ,

I have couple of questions on CRS . first Can you please explain what is the difference between a CRS-3 and CRS-1 Router and what makes CRS different with other core routers availabl in market.



Hi  Deepak ,

CRS-3 provides much more bandwidth than CRS-1. for an example  CRS-1, 16 SLOT chassis provides a Bandwithd of 1.12 Tbps but a CRS-3 Chassis  provides Bandwithd of 4.48 Tbps. From the Archicteure point of view bioth CRS-1  and CRS-3
are same the difference in the Line cards and the Fabric Cards  used in two routers. A CRS-1 router will
use 40G Line and 40 Gig Fabric card  on the other hand CRs-3 uses 140gig Line card and 140gig Fabric  Card.

Coming on to the Second part of your question, CRS routers can be  easliy scaled from a single chassis to Massive Multichassis routers. Now think  that
you need to increase the capacity in the core of your netwrok for which  you need to add more routers and this definately going to require lot of  rerouting , topology changes and wiring, however
In case of CRS you can just  add line card chassis if you already have multichassis running or covert from  Single chassis router to multichassis and in this case
topology changes ,  routing changes and cabling required will be much  less.


Hi ,

Can we use both 40gig and 140 gig Line cards in same chassis.



Hi  Deepak ,

Its  not recommanded to use mix of 40gig and 140 gig cards. CRS-MSc-B card is  compatiable with 140 G Fabric cards, However  CRS-MSC-140G card is only compatible with 140g Fabric cards and they can't be  used with 40 Gig cards. Mix of 40gig and 140 gig  cards can  be used temporarily during migration.



Charles Patrick

Hi ,

Its good to see experts on CRS ..

Can you please help me to understand what exactly midplane design in CRS system ?


Hi Charles ,

Line cards ( CRS-MSC, CRS-FP etc ) have their associated PLIM ( Physical Layer Interface modules ) which provides the physical interfaces. Desgin of CRS router is such that PLIM's are inserted in the front of chassis and MSC's are inserted from rear. MSC's connects to the PLIM's over the midpane this is reason CRS is known to have Mid plane design.

This Mid plane is not a field replaceable unit and is also responsible for providing the control plane interconnections, distributing power and providing connectivity between Line cards and Switch fabric.

So logicall we have this type of connectivity.

PLIM----Midplane----LIne Card ( MSC )

Advatnage of this design is that if you have to replace the MSC card you do not need to unplug the cables from the PLIM.


Vinay, Sudhir, Raj

steve carell

Hello Cisco Experts,

Can you please explain What is the difference between CRS MSC , MSC-B and FP Cards ?


Hi Steve,

The MSC-B (Multi Service Card Rev B) is a cost reduced version of the existing CRS-MSC(=) linecard which provides L3 functions for the CRS-1router. 

CRS-MSC-B(=) will support ALL features that are supported on the existing CRS-MSC(=).  No new software features have been added.  There are NO new CLI, MIB or XML, all existing CLI, MIB and XML on MSC will continue to be supported on MSC-B. 

CRS-MSC-B(=) will NOT be supported with IOS XR release 3.5.x or earlier, but, it will be able to co-exist with CRS-MSC so long as IOS XR Software is R3.6 and above.  CRS-MSC-B(=) is supported with release 3.6.0 (and upwards).

Also please note CRS MSC is end of sale now.

I hope this helps.



Hi Steve ,

To add to the Sudhir's Explanation MSC cards provide better performance than FP cards. Also for some Features FP cards need licence however for MSC cards you dont need that.



jameel noori

Hello Experts,

I have one question regd drops for unrecognized upper-level protocol which i see on one of the bundle ether interface on CRS. can you please tell me the theory behind this and the troubleshooting procedure for that?

RP/0/RP0/CPU0:CRS#sh int bundle-ether 111 | i drops

     4078622818 packets input, 3905568847386 bytes, 0 total input drops

     1232 drops for unrecognized upper-level protocol              ----------->>>

     3837543455 packets output, 798508449473 bytes, 0 total output drops

RP/0/RP0/CPU0:CRS#sh int bundle-ether 111 | i drops

     4079432040 packets input, 3906315130169 bytes, 0 total input drops

     1278 drops for unrecognized upper-level protocol   -------------->>>

     3838309170 packets output, 798664965405 bytes, 0 total output drops



Hello Jameel,

"Drops for unrecognized upper-level protocol" means that we've received packets of a type that you haven't configured and therefore don't have a handler for in the interface protocol handling chain.

That may be (and most likely is) expected and purely cosmetic.


- other side (switch) has CDP configured but you don't have CDP configured on this end

- someone on the Ethernet is sending IS-IS hellos but you don't have IS-IS configured on this end

- someone on the Ethernet is sending IPv6 neigbor discovery packets but you don't have IPv6 configured on this end

It may be worth checking:

- do these packets increment periodically (i.e. one packet every 30 sec or so)?

- are there any obvious features (CDP is a good candidate) that you haven't configured but the far-end (switch, or if it's a crosslink, then

the connected peer) has?

Otherwise capture & decode the packets, and perhaps reviewing the config will already give the answer .




Hi All

I was upgrading my router and after reload My standby RP didnt come up in IOs-XR run state. When I consoled in the RP i observed that RP is reserting with the following errors.

Initializing DDR SDRAM...found 4096 MB

Initializing ECC on bank 0

Initializing ECC on bank 1

Initializing ECC on bank 2

Initializing ECC on bank 3

Turning off data cache, using DDR for first time

Initializing NVRAM...

Testing a portion of DDR SDRAM ...done

Reading ID EEPROMs ...

Initializing SQUID ...

Initializing PCI ...

PCI0 device[1]: Vendor ID 0x10ee

PCI0 device[1]: Device ID 0x300e

PCI1 device[1]: Device ID 0xac55

PCI1 device[1]: Vendor ID 0x104c

PCI1 device[2]: Device ID 0x680

PCI1 device[2]: Vendor ID 0x1095

PCI1 device[3]: Device ID 0x5618

PCI1 device[3]: Vendor ID 0x14e4

PCI1 device[4]: Device ID 0x5618

PCI1 device[4]: Vendor ID 0x14e4

Configuring MPPs ...

Configuring PCMCIA slots ...

System Bootstrap, Version 1.54(20091016:214209) [CRS-1 ROMMON],

Copyright (c) 1994-2009 by Cisco Systems, Inc.

Board type is 0x100006 (1048582)

Switch 0 initialized

Switch 1 initialized

Backplane FE port Up... Enabling

Enabling watchdog

G4(7457-SMP-MV64360 Rev 4) platform with 4096 MB of main memory


Initializing DDR SDRAM...found 4096 M



Hi Eric ,

Please try doing the following. In case this doesnt resolve your issue I would recommend you to open a TAC case for further investigation as it may be a Hardware problem as well.

Connect to RP console.

- Enter rommon by hitting Ctrl+c until you get the rommon prompt.

- Enter these commands to disable the watchdog timeout and reboot:




- When the RP is running IOS XR, format the bootflash:

format bootflash:

- Reload the RP:


- Hit Ctrl+c until you get the rommon prompt.





Vinay, Raj , Sudhir


What version are you upgrading from and too ? Please ensure you follow the specific version upgrade process and have any required SMU's, etc. The CRS upgrade guides are located here:



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