nanog mailing list archives
Re: Gigabit Linux Routers
From: Florian Weimer <fweimer () bfk de>
Date: Thu, 18 Dec 2008 13:07:03 +0100
* Eugeniu Patrascu:
Do you know if it's possible to switch of the route cache? Based on my past experience, it was a major source of routing performance dependency on traffic patterns (it's basically flow-based forwarding).I don't understand your question.
Flow-based routing does not deal well with certain traffic patterns (high HTTP or DNS load, or DoS attacks).
In kernel, when you compile it, you have two options: - hash based route algorithm - lc-trie based route algorithm From what I've read on the internet about the latter algorithm, it's supposed to be faster regarding route lookups with large routing tables (like a global routing table).
In the past, Linux used flow routing. First, an ordinary hash table (the dst cache, also called route cache) is looked up using the destination address of the packet (and a few other bits). In case of a hit, the information is used. In case of a miss, a FIB lookup (using the hash algorithm or LC-trie) is performed, and the result is stored in the cache and used. If there are more flows than cache entries, the work to update the cache (and expire old records from it) is wasted. But under more benign conditions, the cache is a win.
In that configuration you'll split available bandwidth on the NIC and also have less throughput because server NICs are not optimized for "same interface switching".
If this is a problem, I can use multiple trunk ports or multiple routers. -- Florian Weimer <fweimer () bfk de> BFK edv-consulting GmbH http://www.bfk.de/ Kriegsstraße 100 tel: +49-721-96201-1 D-76133 Karlsruhe fax: +49-721-96201-99
Current thread:
- Re: Gigabit Linux Routers, (continued)
- Re: Gigabit Linux Routers David Coulson (Dec 17)
- Re: Gigabit Linux Routers Jeroen Wunnink (Dec 18)
- Re: Gigabit Linux Routers Marshall Eubanks (Dec 18)
- Re: Gigabit Linux Routers Alex Thurlow (Dec 17)
- Re: Gigabit Linux Routers Eugeniu Patrascu (Dec 17)
- Re: Gigabit Linux Routers Florian Weimer (Dec 17)
- Re: Gigabit Linux Routers Alex Thurlow (Dec 17)
- Re: Gigabit Linux Routers Florian Weimer (Dec 18)
- Re: Gigabit Linux Routers Eugeniu Patrascu (Dec 17)
- Re: Gigabit Linux Routers Florian Weimer (Dec 18)
- Re: Gigabit Linux Routers Chris (Dec 17)
- Re: Gigabit Linux Routers Adrian Chadd (Dec 17)
- Advice requested for OpenBSD vs. Linux/OpenBGP vs. Quagga router deployment. Marc Runkel (Dec 17)
- Re: Advice requested for OpenBSD vs. Linux/OpenBGP vs. Quagga router deployment. Adrian Chadd (Dec 17)
- Re: Advice requested for OpenBSD vs. Linux/OpenBGP vs. Quagga router deployment. Scott Francis (Dec 17)
- Re: Advice requested for OpenBSD vs. Linux/OpenBGP vs. Quagga router deployment. Beat Vontobel (Dec 18)
- Re: Advice requested for OpenBSD vs. Linux/OpenBGP vs. Quagga router deployment. Tim Durack (Dec 18)
- Re: Advice requested for OpenBSD vs. Linux/OpenBGP vs. Quagga router deployment. Naveen Nathan (Dec 20)