nanog mailing list archives
Re: IPv6 day and tunnels
From: Jimmy Hess <mysidia () gmail com>
Date: Tue, 5 Jun 2012 12:15:26 -0500
On 6/5/12, Owen DeLong <owen () delong com> wrote: [snip]
But that's a whole lot more packets than working PMTU-D to get there and you're also waiting for all those round trips, not just the 4 timeouts. The round trips add up if you're dealing with a 100ms+ RTT. 22 RTTs at 100ms is 2.2 seconds. That's a long time to go without first data packet
I'm only suggesting probing to discover the MTU between neighboring endpoints directly connected to the same subnet -- Layer 2 interconnect. PTMU doesn't work, because devices know the MTU of _their link_, but not necessarily the MTU of every intervening bridge or L2 tunnel, Not for IP end-end-to-end MTU discovery. The "too big packet" forwarded is just discarded by the L2 bridge, there's no ICMP packet that can result from that, the L2 bridge might not even have an IP address to source one from, so the PMTU method which relies on ICMP alone cannot possibly work. The router after discovering the local MTU constraints to its neighbors would then be responsible for sending TooBig messages as needed or passing on the MTU constraint. You've got an issue if there are 100ms between two peers on your LAN. You're right, you don't need to probe for possible MTUs below 1280. -- -JH
Current thread:
- RE: IPv6 day and tunnels, (continued)
- RE: IPv6 day and tunnels Templin, Fred L (Jun 05)
- Re: IPv6 day and tunnels Masataka Ohta (Jun 05)
- Re: IPv6 day and tunnels Owen DeLong (Jun 04)
- Re: IPv6 day and tunnels Jimmy Hess (Jun 04)
- Re: IPv6 day and tunnels Owen DeLong (Jun 04)
- Re: IPv6 day and tunnels Joe Maimon (Jun 05)
- Re: IPv6 day and tunnels Owen DeLong (Jun 05)
- RE: IPv6 day and tunnels Templin, Fred L (Jun 05)
- Re: IPv6 day and tunnels Mark Andrews (Jun 05)
- RE: IPv6 day and tunnels Templin, Fred L (Jun 05)
- Re: IPv6 day and tunnels Jimmy Hess (Jun 05)
- Re: IPv6 day and tunnels Owen DeLong (Jun 05)
- Re: IPv6 day and tunnels Jimmy Hess (Jun 05)
- Re: IPv6 day and tunnels Owen DeLong (Jun 05)
- Re: IPv6 day and tunnels valdis . kletnieks (Jun 06)
- Re: IPv6 day and tunnels Joe Maimon (Jun 06)
- RE: IPv6 day and tunnels Templin, Fred L (Jun 06)
- Re: IPv6 day and tunnels Owen DeLong (Jun 04)
- Re: IPv6 day and tunnels Joe Maimon (Jun 04)
- RE: IPv6 day and tunnels Templin, Fred L (Jun 04)
- Re: IPv6 day and tunnels Owen DeLong (Jun 04)