6 ms·

But how does the NIC know that, 11 hops away, there is a layer 2 device, which cannot communicate with the NIC(switches do not typically have the ability to com

But how does the NIC know that, 11 hops away, there is a layer 2 device, which cannot communicate with the NIC(switches do not typically have the ability to communicate directly with the devices generating the packets), that only supports a 1500 byte frame? Now you need Path MTU discovery, which as the article indicates, has its own set of issues. (Overhead from trial and error, ICMP being blocked due to security concerns, etc...)

wbl 7y ago
If you block ICMP you deserve what you get. Don't do this. (Edit: don't block ICMP)
- oarsinsync 7y ago
  So now you're trying to communicate from your home machine to some random host on the internet (website, VPS, streaming service), and you're configured for MTU 9000, the remote service is also configured for MTU 9000, but some transit provider in the middle is not, and they've disabled ICMP for $reasons. They blocked ICMP, do you deserve what you get?
  - wbl 7y ago
    Transit providers should push packets and generally do. With PMTU failures it's usually clueless network admins on firewalls nearer endpoints. And no, you don't and I wish the admin responsible could feel your pain.
    - oarsinsync 7y ago
      > Transit providers should Agreed > and generally do Agreed. Now if you can make it 'will always just push packets', we'll be golden. Unfortunately, there are enough ATM/MPLS/SONET/etc networks being run by people who no longer understand what they're doing, that we're never going to get there. To make matters more entertaining, IPv6 depends on icmp6 even more.
willis936 7y ago
Why should it need to? Ethernet is designed to have non-deterministic paths (except in cases of automotive, industrial, and time sensitive networks). If you get to a hop that doesn’t support jumbo frames then break it into smaller frames and send them individually. The higher layers don’t care if the data comes in one frame or ten.
- deleted 7y ago
  [deleted]

wbl 7y ago

If you block ICMP you deserve what you get. Don't do this. (Edit: don't block ICMP)

oarsinsync 7y ago
So now you're trying to communicate from your home machine to some random host on the internet (website, VPS, streaming service), and you're configured for MTU 9000, the remote service is also configured for MTU 9000, but some transit provider in the middle is not, and they've disabled ICMP for $reasons. They blocked ICMP, do you deserve what you get?
- wbl 7y ago
  Transit providers should push packets and generally do. With PMTU failures it's usually clueless network admins on firewalls nearer endpoints. And no, you don't and I wish the admin responsible could feel your pain.
  - oarsinsync 7y ago
    > Transit providers should Agreed > and generally do Agreed. Now if you can make it 'will always just push packets', we'll be golden. Unfortunately, there are enough ATM/MPLS/SONET/etc networks being run by people who no longer understand what they're doing, that we're never going to get there. To make matters more entertaining, IPv6 depends on icmp6 even more.

willis936 7y ago

Why should it need to? Ethernet is designed to have non-deterministic paths (except in cases of automotive, industrial, and time sensitive networks). If you get to a hop that doesn’t support jumbo frames then break it into smaller frames and send them individually. The higher layers don’t care if the data comes in one frame or ten.

deleted 7y ago
[deleted]