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Memory / router required for full BGP table, Dual ISPs

I am working to implement Dual ISPs (10Mb connections) into a single router. We are currently running on a 2800 series router with minimum RAM and static routes.

At this point, we are looking to purchase a single router to terminate both connections. (Budget is a concern).

What router is recommended? My thoughts are (3925 / 3945 or ISR1001)? Is there a better fit?

How much RAM will be required to support BGP from both providers?

Thanks in advance for you input.

8 REPLIES

Re:Memory / router required for full BGP table, Dual ISPs

Hello,
My first thought is why do you need full BGP routing tables from both ISPs? Typically a default route is sufficient. If you need full routing tables, you would need to look at a much beefier router as you would be looking at somewhere over a million RIB entries between the two ISPs.

If you just take default routes with 10Mb connections, you only need minimal specs for that. The 2800 or an ISR1921 or similar should be sufficient. If you are doing any NAT, firewalling, or QoS on that router, I would bump that up to the ISR2900 series.

Regards,
Mike

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Re: Memory / router required for full BGP table, Dual ISPs

Mike Williams,

I have a doubt, I am very new to BGP infact.

What I know is when we have Dual ISPs then we will use BGP, it is fine,  but is that necessary to have full routing table.

Is my need of using BGP when i have Dual ISPs serve with the default route imported each from them?

How do I tweak my default routes to reach out to the best paths.

Regards
Thanveer
"Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."

Regards Thanveer "Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."

Memory / router required for full BGP table, Dual ISPs

Hi Thanveer,

If you want to ensure your packets take the most efficient path, then you must get a full BGP route table from each ISP. If you don't need to ensure the best path for every packet, or you can do BGP load sharing with the two ISPs. You could also combine this with communities from each ISP for some better efficiency. In my experience, most times a default route with BGP load sharing is perfecty acceptable, but your particular needs may vary.

Regards,
Mike

Memory / router required for full BGP table, Dual ISPs

Thanks Mike, Five Stars,  I didn't understand Communities part, can you please elaborate.

Regards
Thanveer
"Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."

Regards Thanveer "Everybody is genius. But if you judge a fish by its ability to climb a tree, it will live its whole life believing that it is a stupid."
Hall of Fame Super Gold

Memory / router required for full BGP table, Dual ISPs

What router is recommended? My thoughts are (3925 / 3945 or ISR1001)? Is there a better fit?

What is your bandwidth?  10 Mbps?

Super Bronze

Re: Memory / router required for full BGP table, Dual ISPs

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Posting

For dual 10 Mbps links, a 1941 or 2901 would be about the minimum, excluding considerations for processing dual full Internet BGP tables.

You might be fine just using defaults to both providers.  If you want optimal performance, if platform supports PfR use that.  It seems to have much less impact to the device and outbound routing is even "better" than having Internet route tables.

New Member

Memory / router required for full BGP table, Dual ISPs

Here is BGP memory usage for one full-view:

460129 network entries using 66258576 bytes of memory

460129 path entries using 23926708 bytes of memory

234141/89989 BGP path/bestpath attribute entries using 30906612 bytes of memory

67426 BGP AS-PATH entries using 3035068 bytes of memory

129 BGP community entries using 4204 bytes of memory

5 BGP extended community entries using 152 bytes of memory

0 BGP route-map cache entries using 0 bytes of memory

0 BGP filter-list cache entries using 0 bytes of memory

BGP using 124131320 total bytes of memory

BGP activity 529587/69458 prefixes, 569577/109448 paths, scan interval 60 secs

New Member

Memory / router required for full BGP table, Dual ISPs

Since you have budge concerns .. You can better design without using BGP.. use default routes instead.. I would suggest for 2911 instead of 1941 since it has three Ethernet ports..

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