Therefore changing my windows MTU or even HE MTU will have no effect on the what MTU the streaming server uses, so that is were MSS comes in play..?
The MSS option is only sent on TCP SYN packets. Each end of the connection knows the MTU of the link it is directly attached to. The default MSS is computed by subtracting the size of IP and TCP headers from that MTU, so in the case of IPv6 the default MSS is computed by subtracting 60 from the MTU,
Each end of the connection will consider both the MTU of the directly attached interface and the MSS reported by the other end of the connection to decide how large packets to send. It will use the one which results in the smaller packets. Except from cases where some asymmetric routing is going on, both ends of the connection will start with the same size of packets.
ICMP packets are only needed if a hop somewhere in between has a smaller MTU. The first and last hop of the route are automatically covered by the MSS. However though the default MSS is computed from the MTU, there is nothing preventing you from using a smaller MSS. If you have a 1500 byte MTU there is no major performance penalty from reducing the MSS to 1220. An MSS value of 1220 should eliminate MTU problems from all TCP connections.
Reducing the MTU is one way to drive the MSS down, but then that applies to other packets as well, and you may be better off reducing the MSS instead. This is particular important if the link where you would reduce the MTU carries packets where neither sender nor receiver of that packet is directly attached to the link with the lowered MTU. Also remember that the MTU setting for a link is not necessarily the same at both ends, one end doesn't know what the other end has set as MTU for that link.
A reasonable behaviour is to use the configured MTU as limit for outgoing packets on that link but still accept incoming packets on that link, which exceed the configured MTU. Another not completely unreasonable reaction is to send a packet too big ICMP message if a packet is received exceeding the MTU of the link on which it is received. Silently dropping a packet because it exceeds the configured MTU of the link on which it is received is not reasonable, but I wouldn't trust that no system would do so.
Reducing the MSS does not have the same potential to introduce new problems, so I consider that a better solution. If you have that option reduce the MSS first and keep the MTU.
I would only reduce the MTU if reducing MSS is not an option.
I assume when PMTU is working, my computer would cache the info somewhere for that partiular host, is this correct? and if so how can i see this w/o sniffing packets?
Yeah, there need to be a cache for this. It is somehow tied to routing information, but I don't know how to see it without looking at the network packets. And it differs between operating systems anyway.
