how is the most important specifications of know if a Router can receive a full bgp table

[gbcbooksmj]

Hi all

i search google for a long time , most people would say "Memory and CPU" would be the most important specification of if a Router can store full bgp table .

but , i think CEF/FIB size it also a important specification . 

a full BGP tables will consume a lot of Router memory, even a double copy will aggravate it situation , and a high bandwidth throughput will raise CPU utilization .  but think about it , if your Router will only have 256K CEF/FIB , 4GB ram . 10% CPu utilization before BGP session established, and connected to two ISPs , two copy of full BGP routes tables , each table including more than 40K routes , do you still think your router can deal with this situation  ? 

in this scenario , if you have enable CEF feature on your Router , there would be at less 1.4K Route can not be insert into CEF/FIB . and definitely , the prefix of routes that did not insert into CEF/FIB would cause a big traffic forwarding problem. 

i dont know if this is right in Cisco products , but it did exist on Huawei products 

[Georg Pauwen]

Hello,

good point actually. The current full BGP table consists of 670K routes, which some of the Cisco routers cannot handle. Depending on your platform, RIB/FIB partition might be available. That said, you would really only need the full table if your AS is a transit AS. And if you are, your hardware is likely to be sufficient to handle the RIB/FIB size.

Are you dealing with a specific issue, or is this a general inquiry ?

[gbcbooksmj]

i am not dealing with a case , but i want to know how to choose a router the could satisfiy a specific requirement , especially balance between the full BGP routes and price .

[Masoud Pourshabanian]

Hello, 

Everything is depending on the router platform. Different routers use different design to store the FIB table so how much memory you need is also depending on the platform. 

For example, one router may need 1G of memory to handle the full BGP table but another 4 or even 8G. You need to check Cisco website for suggested memory for handling full bgp routes.

Just for example, Cisco 7600 and 6500 use TCAM to store the FIB table. The default size is 512k but can be extended. Please see the link below.

http://www.cisco.com/c/en/us/support/docs/switches/catalyst-6500-series-switches/116132-problem-catalyst6500-00.html

In ASR series, FIB resides in a chip in processor and also in DRAM so more memory is required to keep the full BGP table and depending on the processor, the routes they can handle vary. 

http://www.cisco.com/c/en/us/support/docs/routers/asr-1000-series-aggregation-services-routers/116777-technote-product-00.html

The 512k FIB exhaustion was popular but the newer routers which can handle full BGP routes are able to reside more routes in FIB.

Masoud

[gbcbooksmj]

so for ASR router , FIB can be extended too by upgrading their DRAM ?

for the further question ,  what knid of design platform does C3825 belong to,FIB in TCAM  or FIB resides in DRAM  

[gbcbooksmj]

how can i check FIB size ? 

[Masoud Pourshabanian]

The link I gave you was just an example.
Cisco ASR comes in many flavors. Some comes with ESP and some with RP and some with both.

I am giving you one example.
Cisco ASR-1001-x with 8 Gig memory supports 1M prefixes. It has intergraded ESP and RP.
The main component of ESP is QFP. QFD uses an atached memory and DRAM for FIB. If ESP does not have enough dedicated DRAM, It uses IRAM. If still miss, it uses RP for look up which is slow.

http://www.cisco.com/c/en/us/support/docs/routers/asr-1000-series-aggregation-services-routers/116777-technote-product-00.html
"In addition to the physical memory, there is also memory attached to the Quantum Flow Processor (QFP) ASIC that is used in order to forward data structures, which includes data such as Forwarding Information Base (FIB) and QoS policies"

With the following command you can see how much of DRAM has been dedicated to QFD.
show platform hardware qfp active infrastructure exmem statistics

ASR-1002-x#show platform hardware qfp active infrastructure exmem statistics
QFP exmem statistics

Type: Name: DRAM, QFP: 0
Total: 1073741824 ----->>> (1G)
InUse: 198994944
Free: 874746880
Lowest free water mark: 874746880
Type: Name: IRAM, QFP: 0
Total: 134217728
InUse: 8257536
Free: 125960192
Lowest free water mark: 125960192

For finding an ASR router to support FULL BGP routes, check the link below. The one supports 1000000 IPV4 should be fine. Check the memory options. You need to have 8G of memory.

http://www.cisco.com/c/en/us/products/collateral/routers/asr-1000-series-aggregation-services-routers/data_sheet_c78-441072.html

When it says, it supports 1000000 routes, It means its FIB has capacity to store these routes.

As far as I know, TCAM is used for ACL and QOS in newer version of routers.

[gbcbooksmj]

i check ASR Series Link you gave out, it said ASR also design the 4th generation of TCAM , are you sure that FIB of ASR Series Router resides in a chip in processor and in DRAM  ?

[gbcbooksmj]

any reply  ?