BGP and memory consumption

[Antonio_1_2]

Hello,

If anyone can help me with this please:

Generaly speaking, one router R is connected to 2 different ISPs via BGP and receive full BGP table

1) How much memory this router R needs? Does it need to store 2 BGP tables ( 2 x 300.000 routes) plus routing table?

If this is case then this should be approximately 600MB, is this correct?

2) What if router has 4 BGP uplinks on which it receives full BGP table? Does this mean that it should receive and store 4 full

BGP tables and needs 1,2 GB DRAM?

3) what if this is the scenario:

IPS1---eBGP--R1---iBGP--R_CENTRAL----iBGP----R2---eBGP ---ISP2

R_CENTRAL has 2 IBGP peer sessions with R1 and R2 which have eBGP sessions with ISP1 and 2 respectively.

Also R_CENTRAL is route reflector for R1 and R2. R1 and R2 receives full BGP table  from ISP1 and 2.

Will R_CENTRAL receive 2 full BGP tables or just 1 BGP table (since R1 and R2 will send only send its best routes after a while)?

Is it correct that R_CENTRAL will need only 300MB DRAM?

4) aproximately if one router receives full routing table from BGP peer which is cca 300.000 routes then it needs aproximately 300MB DRAM.

This include BGP as well as RIB table. Is this statement correct?

Thanks

A. 

[ajay chauhan]

The amount of memory required to store BGP routes depends on many factors, such as the router, the number of alternate paths available, route dampening, community, the number of maximum paths configured, BGP attributes, and VPN configurations. Without knowledge of these parameters it is difficult to calculate the amount of memory required to store a certain number of BGP routes. Cisco typically recommends a minimum of 512 MB of RAM in the router to store a complete global BGP routing table from one BGP peer. However, it is important to understand ways to reduce memory consumption and achieve optimal routing without the need to receive the complete Internet routing table. Refer to

http://www.cisco.com/en/US/tech/tk365/technologies_tech_note09186a0080094a83.shtml

[Antonio_1_2]

Hi Ajay,

Questions in my previous post were relating to default BGP configuration toward Internet (to ISPs): No soft-reconfiguration, no multipaths, no route dumpening.

BGP session is for Internet uplink (there is no VPN but there is standard BGP attributes). Also I need full Internet routing table, so I cannot filter it.

It is not so important the know correct number regarding RAM consumption in MBs, but more qualitative approximation.

a) The main question is if router R is connected to 3 different ISPs via eBGP: Does router R store two 3 BGP tables, then form from its BGP table (which consists of received  3 x 300.000 = 900.000 routes) the RIB table (formed from best routes from BGP table which would have 300.000 routes).

b)  Other question would be the scenario with router R that is connected via iBGP to two diffrenet border routers which are further connected to 2 diffrent ISPs via eBGP. (R is route reflector)

ISP1---eBGP--R_border1---iBGP-----R----iBGP----R_border2---eBGP ---ISP2

So will router R have (after some period) only BGP table with cca 300.000 routes (because border_routers exchanged each other BGP tables via route reflector and after all advertises to R only the best routes)  or will it have BGP table that consists of full intenet table form R_border1 and R_boder2 (that should be 300.000 routes from R_border1 + 300.000 routes from R_border2)?

c) Also How router model relates to memory consumption? Shouldn't router have the same BGP and RIB tables no mether wheter 7600 , GSR or 2900 series is involved? And if they have the same tables hence they should allocate the simmilar amount of memory in RAM,

Regards,

A.

[ajay chauhan]

Here will be diffrence consider like this.

It would be somewhere around 370000 Network Entries which i can see on my router as of now.

When you run full BGP Resources are comsumed by -

# show ip bgp sum

374398 network entries using 49420536 bytes of memory

374398 path entries using 19468696 bytes of memory

62737/62406 BGP path/bestpath attribute entries using 10539816 bytes of memory

56722 BGP AS-PATH entries using 2097412 bytes of memory 374398 network entries using 49420536 bytes of memory
374398 path entries using 19468696 bytes of memory
62737/62406 BGP path/bestpath attribute entries using 10539816 bytes of memory
56722 BGP AS-PATH entries using 2097412 bytes of memory

BGP using 81440248 total bytes of memory    >>> If I convert in MB =77.66747

This is the router running full BGP with ISP with I GB RAM.

When you peer with multiple then hardly matter network entries but path will be doubled based on peering. CEF and other factors will also comsume RAM .

I would also recommond to go for 1 GB RAM.

In second example yes that will get routes from two peer so basically number of path will get changed would be double .

keeping 1 GB on each router would be safe enough.

Thanks

Ajay