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I personally think that Path MTU Discovery is one of the major obstacle of IPv6. It is quite unstable to me. My home WiFi router has v6-ready certification but

I personally think that Path MTU Discovery is one of the major obstacle of IPv6. It is quite unstable to me. My home WiFi router has v6-ready certification but cannot properly tell my Windows PC which MTU size should be chosen. I have to manually lower down MTU size but it keep reverting. Directly PPPoE from my PC is better but there's still some website I have to set my MTU size to 1280 to reach.

zAy0LfpBZLC8mAC 12y ago
Are you sure the problem is the uplink MTU of your DSL(?)? That's the only thing where your router would be responsible for telling your PC about the bottleneck (if it receives a packet from your PC that doesn't fit through the link, it should send an "ICMP6 packet too big" to the PC), and if you get any working TCP6 connections at all, that most likely is working just fine. If you get stuck connections with some websites, the problem most likely is with that website: Their server sends you a big-ish packet, the router at the provider's end of your DSL drops the packet and sends an "ICMP6 packet too big" back to the server, but some incompetent admin configured their firewall to drop ICMP6, so their server never learns that its packets are too big, and just keeps resending the big packet until it times out.
- simoncion 12y ago
  It really bothers me that some network admins choose to drop all ICMP traffic. I wish that the Shields UP! crowd had sent the message that ICMP is a very important part of IP signalling; rather than sending the message that eeeevil hackers might discover your network and Hax your Gibsons, so you'd better drop everything you can on the floor to throw them off of your trail.
  - ghshephard 12y ago
    With IPv6, admins learn within a week or two that they have to allow ICMPv6, or their networks don't work. With IPv4 you could (sort of) get by without ICMP, with IPv6 it's mandatory.

zAy0LfpBZLC8mAC 12y ago

Are you sure the problem is the uplink MTU of your DSL(?)? That's the only thing where your router would be responsible for telling your PC about the bottleneck (if it receives a packet from your PC that doesn't fit through the link, it should send an "ICMP6 packet too big" to the PC), and if you get any working TCP6 connections at all, that most likely is working just fine. If you get stuck connections with some websites, the problem most likely is with that website: Their server sends you a big-ish packet, the router at the provider's end of your DSL drops the packet and sends an "ICMP6 packet too big" back to the server, but some incompetent admin configured their firewall to drop ICMP6, so their server never learns that its packets are too big, and just keeps resending the big packet until it times out.

simoncion 12y ago
It really bothers me that some network admins choose to drop all ICMP traffic. I wish that the Shields UP! crowd had sent the message that ICMP is a very important part of IP signalling; rather than sending the message that eeeevil hackers might discover your network and Hax your Gibsons, so you'd better drop everything you can on the floor to throw them off of your trail.
- ghshephard 12y ago
  With IPv6, admins learn within a week or two that they have to allow ICMPv6, or their networks don't work. With IPv4 you could (sort of) get by without ICMP, with IPv6 it's mandatory.