nanog mailing list archives
Re: Layer 2 vs. Layer 3 to TOR
From: Malte von dem Hagen <mvh () hosteurope de>
Date: Thu, 12 Nov 2009 22:08:57 +0100
Hej, Am 12.11.2009 21:04 Uhr schrieb Raj Singh:
We are actually looking at going Layer 3 all the way to the top of rack and make each rack its own /24.
what a waste of IPs and unnecessary loss of flexibility!
This provides us flexibility when doing maintenance (spanning-tree).
If you use a simple setup for aggregation, you do not need xSTP. Even including redundancy, RTG (big C: flex-link) will be sufficient. Spanning the L2 over more than one rack is dirty when you do L3 on the TORs, because you need to build a Virtual Chassis or VPLS tunnels (not sure if EX4200 does that as of today).
Also, troubleshooting during outages is much easier by using common tools like ping and trace routes.
Oh, c'mon. Yes, Layer 2 is a wild jungle compared to clean routing, but tracing isn't that magic there. You have LLDP, mac-address-tables, arp-tables...
I want to make sure this is something other people are doing out there and want to know if anyone ran into any issues with this setup.
From the design POV, it is a clean and nice concept to do L3 on the TOR-switches, but in real life, it's not working very well. Everytime I played with such, with every vendor I've seen, there is just always the same conclusion: Let routers route and let switches switch. Switches which are supposed to do routing never scale, provide almost always immature implementations of common L3 features and run into capacity problems just too fast (too small tables for firewall roules, route entries, no full IPv6 capabilities, sometimes expensive licenses needed for stuff like IS-IS...). I understand the wish to keep broadcast domains small and network paths deterministic and clean, but the switches you can buy today for not-too-much-money aren't ready yet. So my hint is: Look at model #4 from the mentioned NANOG presentation. My 2 Euro-Cents, .m
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Current thread:
- Layer 2 vs. Layer 3 to TOR Raj Singh (Nov 12)
- RE: Layer 2 vs. Layer 3 to TOR Paul Stewart (Nov 12)
- RE: Layer 2 vs. Layer 3 to TOR Raj Singh (Nov 12)
- Re: Layer 2 vs. Layer 3 to TOR Malte von dem Hagen (Nov 12)
- RE: Layer 2 vs. Layer 3 to TOR George Bonser (Nov 12)
- Re: Layer 2 vs. Layer 3 to TOR David Coulson (Nov 12)
- RE: Layer 2 vs. Layer 3 to TOR Raj Singh (Nov 12)
- RE: Layer 2 vs. Layer 3 to TOR Paul Stewart (Nov 12)
- Re: Layer 2 vs. Layer 3 to TOR Steve Feldman (Nov 12)
- Re: Layer 2 vs. Layer 3 to TOR Seth Mattinen (Nov 12)
- Re: Layer 2 vs. Layer 3 to TOR Brandon Ewing (Nov 12)
- RE: Layer 2 vs. Layer 3 to TOR Bulger, Tim (Nov 12)
- Re: Layer 2 vs. Layer 3 to TOR Brandon Galbraith (Nov 12)
- Re: Layer 2 vs. Layer 3 to TOR Nick Hilliard (Nov 12)
- Re: Layer 2 vs. Layer 3 to TOR Kinkie (Nov 18)
- Re: Layer 2 vs. Layer 3 to TOR Eugeniu Patrascu (Nov 18)
- Re: Layer 2 vs. Layer 3 to TOR Seth Mattinen (Nov 12)