Memory requirement for full BGP table

[Ahmed Shahzad]

Hi,

I have read that the minimum memory requirement for full BGP routing table is 512MB. I have a router with 512MB memory, but the show memory command on that router show the memory left for processor is 367MB. Also the free memory is app. 53.8MB, which is 14.7% of total memory.

Would 367MB be sufficient for full BGP routing table?

Thanks and Regards,
Ahmed Shahzad.

[Leo Laohoo]

It ain't just the memory you have to look at it's also the CPU of your router.  What router do you have?

[Ahmed Shahzad]

It is Cisco 3845. Please see the show version:

uviprrt007#sh ver
Cisco IOS Software, 3800 Software (C3845-SPSERVICESK9-M), Version 12.4(24)T2, RE                                                                              LEASE SOFTWARE (fc2)
Technical Support: http://www.cisco.com/techsupport
Copyright (c) 1986-2009 by Cisco Systems, Inc.
Compiled Mon 19-Oct-09 21:47 by prod_rel_team

ROM: System Bootstrap, Version 12.4(13r)T11, RELEASE SOFTWARE (fc1)

uviprrt007 uptime is 2 weeks, 5 days, 1 hour, 8 minutes
System returned to ROM by Reload Command
System restarted at 10:02:41 AEST Wed Mar 24 2010
System image file is "flash:c3845-spservicesk9-mz.124-24.T2.bin"

........

Cisco 3845 (revision 1.0) with 487423K/36864K bytes of memory.
Processor board ID FHK1403F0KY
2 Gigabit Ethernet interfaces
DRAM configuration is 64 bits wide with parity enabled.
479K bytes of NVRAM.
126976K bytes of ATA System CompactFlash (Read/Write)

Configuration register is 0x2102

[Reza Sharifi]

Hi Ahmad,

You have to look in to not just the memory but also the processing power of the device. With the amount of routes on the internet today BGP scanner process will use lots of CPU while scanning a full routing table (I think over 300,000 routes)  The 3800 series is a single core processor with maximum amount of memory of 1Gig.  The 3945 is a better choice, as it comes with dual core processor with a default memory of 1Gig and can be upgraded to 4Gig. Also look at the 7200 and ASRs.

HTH

Reza

[Ahmed Shahzad]

Hi,

Thank you for your reply.

I agree about your concern. Actually I do not have choice to select the router model. I have read some document on net that minimum requirement is 512MB.

So question is what is the minimum memory requirement with Cisco 3845 router for full BGP routing table?

Thanks and Regards,
Ahmed Shahzad.

[Reza Sharifi]

Ahmed,

You need a minumum of 512MB DRAM.

HTH

Reza

[Ahmed Shahzad]

Hi,

Thank you for your quick reply.

Now come to my initial question:

I have a Cisco 3845 router with 512MB memory, but the show memory command on  that router show the memory left for processor is 367MB. Also the free  memory is app. 53.8MB, which is 14.7% of total memory. So rest of memory which is app. 91MB is used by IOS and Running Config.

Would 367MB  be sufficient for full BGP routing table? Will I face any performance issue with 53.8MB free momory only?

Thanks and Regards,
Ahmed Shahzad.

[Giuseppe Larosa]

Hello Ahmed,

>> Will I face any performance issue with 53.8MB free momory only?

you cannot put 300,000 BGP routes into 53.8 MB of RAM so your system is already using  too much memory, 512 MB is the requirement for a dedicated device.

example:

sh bgp sum | inc total
BGP using 75697852 total bytes of memory

this is taken from a C7600 receving  two iBGP full tables

I would say it is not enough, also you need to consider that CEF uses roughly 1KB for each prefix, so your system hasn't enough memory and cpu power to do this job

Hope to help

Giuseppe

[Ahmed Shahzad]

Hi,

Thank you for your response.

Currently I am running two eBGP connection with two different ISPs (10MB link each), and there is an output:

Router#sh bgp all summary | in total
BGP using 70517720 total bytes of memory

I am sorry not to communicating clearly. 53.8MB memory is free after these two eBGP connections, and other IOS stuff.

CPU utilization is given below:

Router#sh processes cpu
CPU utilization for five seconds: 3%/0%; one minute: 3%; five minutes: 3%
PID Runtime(ms)     Invoked      uSecs   5Sec   1Min   5Min TTY Process

Now my question is that would 53.8MB memory would be fine, or it might  affect the service at some point of time. Please note that currently there is not much traffic except BGP updates, and we are expecting full utilization of both link in future.

Thanks and Regards,
Ahmed Shahzad.

[Leo Laohoo]

As what Giuseppe's post said, 5.8 MB just ain't enough plus the CPU of the 3845 can't cope for a long duration.