[c-nsp] Sizing a router for full feed (once and for all)

[Marko Milivojevic]

Once and for all, huh? :-)

I will take example of one of the routers I'm operating. It has a mix of two 
full BGP feeds + customer and our own routes.

Each BGP prefix is using 115 bytes on average (with some communities). 
Multiply that by number of prefixes received and full views, and you get the 
amount that BGP alone would consume. Based on this information, routing and 
CEF tables are built (more memory used). Exact calculation is very much 
topology-based (you may have 4 full views and use less memory than with only 
two feeds in some cases). But, the key point is, if your 
router/switch/whatever can't have the full BGP table multiplied by, say, 2.5 
(routing and CEF tables), you shouldn't really try it.

Marko.

P.S. It's really not that simple.

Joost greene wrote:
> Hello,
> 
> I always see people asking if their routers can handle BGP and alot of times
> the answer isnt just memory, sometimes TCAM limitation (3750 for e.g.) maybe
> other cases, what i want to have is some sort of check list for this, my
> case is a :
> 
> 
> 
> IOS (tm) 3700 Software (C3745-JK9O3S-M), Version 12.3(9), RELEASE SOFTWARE
> (fc2)
> System image file is "flash:c3745-jk9o3s-mz.123-9.bin"
> 
> cisco 3745 (R7000) processor (revision 2.0) with 250880K/11264K bytes of
> memory.
> R7000 CPU at 350MHz, Implementation 39, Rev 3.3, 256KB L2, 2048KB L3 Cache
> 2 FastEthernet/IEEE 802.3 interface(s)
> 8 Serial network interface(s)
> DRAM configuration is 64 bits wide with parity disabled.
> 151K bytes of non-volatile configuration memory.
> 125184K bytes of ATA System CompactFlash (Read/Write)
> 125184K bytes of ATA Slot0 CompactFlash (Read/Write)
> 
> 
> I want to know if it can handle two full tabes and more than that how do i
> do this math next time ?
> 
> Thanks
> Joost
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