Routing table size in Cisco Routers

[prashanma]

Hi Team,

What is the routing table size in Cisco ISR 4331 ? I couldn't find any document regarding routing table size in the routers

Thnx

[Georg Pauwen]

Hello,

there is no hard limit on the amount of routes, it depends on the amount of DRAM. The 4331 has 4GB of DRAM by default, the entire BGP routing table would require roughly 1GB of DRAM, and that are, as of today, 761787 prefixes. So with these routers, the routing table size should never be a problem.

[prashanma]

Thank you for reply.

What is the connection between DRAM and Routing table(IPv4 and IPv6 routing) ?

[Joseph W. Doherty]

"What is the connection between DRAM and Routing table(IPv4 and IPv6 routing) ? "

More RAM allows for a larger route table (along with other data, such as IGP data).

IPv6, with an IP address 4 times the size of an IP4 address, may take another 12 bytes per route entry. (I recall Cisco Catalyst specifications note those devices can handle only half as many IPv6 addresses. Don't know if that has any direct bearing on a router doing IPv6.)

BTW, Georg mentions having enough RAM, to contain a large route table, that the route table's size would never be a problem. Well, on smaller routers, it's possible processing/maintaining huge route tables might overtax the capacity of the router in other ways.

[Georg Pauwen]

--> BTW, Georg mentions having enough RAM, to contain a large route table, that the route table's size would never be a problem. Well, on smaller routers, it's possible processing/maintaining huge route tables might overtax the capacity of the router in other ways.

I was specifically referring the ISR4Ks, which have 4GB of default memory, and that alone should usually be enough for any routing table. Unless of course there are loads of other processes using up capacity...

[Joseph W. Doherty]

Georg, my apologies!

You wrote: ". . . the routing table size should never be a problem."

Which I incorrectly paraphrased as ". . . the route table's size would never be a problem."

Big difference between "should" and "would".

Not withstanding the above, I only intended to caution the OP that huge route tables on a 4K ISR possibly might cause other issues due to their huge size.

[Georg Pauwen]

Joseph, OP,

on a side note, out of curiosity I tried to find out what equipment the real big companies use. I would think the biggest one must be Google. It turns out that even Google depends heavily on ISPs, and they don't own their own Internet core routers. I came across the story linked below, and it seems, like with almost anything, the best equipment and the most Gigabits cannot save you from the number one cause of error: human error !

https://arstechnica.com/information-technology/2018/11/major-bgp-mishap-takes-down-google-as-traffic-improperly-travels-to-china/

[Joseph W. Doherty]

Yup, some of the most "interesting" errors were due to some "manual" change.

My last employer had some large Internet core routers, such as Cisco CRS-3, etc.

[gajownik]

Hey,

I think you will find "Scalability Tests" chapter useful:

https://www.cisco.com/c/en/us/products/collateral/routers/4000-series-integrated-services-routers-isr/white-paper-c11-734550.html#_Toc424889858

Dawid

[prashanma]

@gajownik Thank you for reply.

But above URL is "403 - Forbidden Page or Application"

[gajownik]

@prashanma oops, looks like this white paper is available only to Cisco Partners.

To make long story short, full BGP table is supported on ISR4331 with 8GB of DRAM.

[mandarkulkarni1]

Looks like everyone does not have access to accessibility test.